The authors have no acknowledgements or financial disclosures.

Ensure that each patient is reviewed for suitability for the research study, and appropriate patients must be consented for participation in the study according to local IRB procedures.
1. Patient Selection for SEEG and Research
<ol>
	<li>Patient Selection for SEEG 
	Note: Epilepsy patients must be clinically assessed by a multidisciplinary team consisting of epileptologists, neuropsychologists and neurosurgeons.
	<ol>
		<li>Ensure that the patient has medically refractory focal epilepsy, defined as failure to respond to at least 2 adequate trials of anti-epileptic medications.</li>
		<li>Ensure that non-invasive techniques have failed to localize the epileptogenic foci.</li>
		<li>Confirm with multidisciplinary team that patient is not suitable for investigation only with subdural grid electrodes.</li>
		<li>Confirm with multidisciplinary team that there is clinical suspicion of a deep seizure onset zone.</li>
	</ol>
	</li>
	<li>Patient selection for research task
	<ol>
		<li>Ensure that subject is between the ages of 13 and 65 years.</li>
		<li>Obtain consent or assent (together with parental consent if below the age of 18 years) from the patient.</li>
		<li>Ensure that subjects are able to attend to the task and cooperate with the testing.</li>
	</ol>
	</li>
</ol>
2. Preparation and Implantation Technique
<ol>
	<li>Perform a volumetric T2 and contrast enhanced volumetric T1 MRI preoperatively and transfer the images to the stereotactic navigation software, according to manufacturer&#8217;s protocol.
	<ol>
		<li>Plan the depth electrode targets based on the MRI and clinical suspicion of seizure foci. 
		Note: The examples provided are based on the BrainLab navigation software and are thus specific to this system. However, any stereotactic navigation software can be used to plan depth electrode trajectories and placement.</li>
		<li>Define the anatomical region of interest as the target point within the &#8220;Stereotactic Planning&#8221; function in the stereotactic navigation software.</li>
		<li>For example, use dACC as the target of interest. To define its trajectory, press &#8220;New Trajectory,&#8221; then press &#8220;target&#8221; and click on the dACC. Center the target in the middle of dACC by examining dACC in all 3 planes (axial, coronal and sagittal) and clicking on the middle of dACC in each plane.
		<ol>
			<li>Define the entry point on the scalp within the &#8220;Stereotactic Planning&#8221; function in the stereotactic navigation software.</li>
		</ol>
		</li>
		<li>For example, choose a point on the scalp that appears to be the shortest path to the dACC. Press &#8220;entry&#8221; and choose the point on the scalp to make the entry point.</li>
		<li>Click and drag the &#8220;target&#8221; and &#8220;entry&#8221; points to modify the defined trajectory to avoid cortical and subcortical vascular structures as well as any potential eloquent cerebral regions.</li>
		<li>Repeat for all planned depth electrode targets (Figure 1).</li>
		<li>Admit the patient on the morning of the surgery, bring to the operating room, and induce under general anesthesia26,27.</li>
		<li>Attach a Cosman-Roberts-Wells (CRW) stereotactic headframe to the patient&#8217;s head with skull screws.</li>
		<li>Obtain a volumetric CT with the headframe in place.</li>
		<li>Load the volumetric CT and MRI images into the stereotactic navigation software via the &#8220;Load and Import&#8221; function.</li>
		<li>Click on the &#8220;Localization&#8221; function within the stereotactic navigation software.</li>
		<li>Localize the CRW headframe by clicking on all of the images defined by the stereotactic navigation software as containing the headframe and then pushing the &#8220;Assign localizer&#8221; button.</li>
		<li>Click on the &#8220;AC/PC Localization&#8221; function within the stereotactic navigation software.</li>
		<li>Identify the anterior and posterior commissures based on their anatomical location.</li>
		<li>Designate the anterior and posterior commissures via the &#8220;Set AC/PC system&#8221; function within the stereotactic navigation software.</li>
		<li>Click on the &#8220;Image Fusion&#8221; function within the stereotactic navigation software.</li>
		<li>Merge the CT images with the MRI images in the stereotactic navigation software28,29. Click on the paired volumetric CT and MRI images underneath the &#8220;Fusion&#8221; tab and then click &#8220;Auto Fusion&#8221;. 
		Note: This places the MRI within the stereotactic frame coordinates.</li>
		<li>Click on the &#8220;Stereotactic Planning&#8221; function within the stereotactic navigation software and confirm the planned trajectories from steps 2.1.2 - 2.1.6.</li>
		<li>Choose the volumetric CT as the stereotactic reference under the &#8220;Stereotactic Functions&#8221; tab.</li>
		<li>Click the &#8220;print&#8221; icon in the vertical column of icons to print the final stereotactic coordinates for each depth electrode trajectory 30,31.</li>
	</ol>
	</li>
	<li>Implantation technique
	<ol>
		<li>Return the patient to the operating room following the CT scan.</li>
		<li>Prepare and drape the surgical field using routine sterile methods32,33.</li>
		<li>Ensure that a fluoroscope is in the operating room and draped along with the rest of the surgical field.</li>
		<li>Using the printed stereotactic coordinates from step 2.1.20, set the coordinates for the first depth electrode on the headframe. 
		Note: The stereotactic coordinates are given in 3 planes: lateral (x), vertical (y) and anterior-posterior (z). For example, the printed coordinates for a target in the right dACC are +48.2 mm A-P, 6.6 mm Lateral and +2.2 mm Vertical. The headframe is then set to those coordinates accordingly.</li>
		<li>Extend the guideblock down to the skin and mark the location of the burr hole on the scalp with a marking pen. Fix the guideblock in place based on the stereotactic coordinates and as such, no landmarks are necessary to mark the incision.</li>
		<li>Inject 2 - 3 ml&#160;of 0.5% bupivicaine in a 1:100,000 dilution of epinephrine into the marked incision.</li>
		<li>Make a nick in the scalp with a scalpel down to the skull into the marked incision.</li>
		<li>Cauterize the dermis and deep tissue using monopolar cautery directed with a coated obturator in order to minimize any bleeding from vessels in the skin or subcutaneous tissue.</li>
		<li>Drill a burr hole using a 2.1 mm twist drill bit in the middle of the incision.</li>
		<li>Open the dura with a rigid obturator probe. Screw an anchor bolt into the skull. Place a pre-measured stylet probe through the anchor bolt to make a track for the electrode.</li>
		<li>Carefully advance the electrode to the pre-calculated depth. Tighten the anchor bolt cap down to secure the electrode.</li>
		<li>Repeat this process for all of the depth electrodes.</li>
		<li>Place the fluoroscope underneath and surrounding the patient&#8217;s head in both AP and lateral planes to obtain fluoroscopic images to ensure adequate placement trajectories of all electrodes.</li>
		<li>Connect the electrodes to the clinical EEG system to verify appropriate impedances.</li>
		<li>Wake the patient from anesthesia and transport to the recovery room, and subsequently to the EMU.</li>
		<li>In the EMU, monitor the patient via closed circuit monitoring for clinical seizures and via ECoG for electrographic evidence of seizures.</li>
	</ol>
	</li>
</ol>
3. Behavioral Task and Data Acquisition
<ol>
	<li>Behavioral task
	<ol>
		<li>Open behavioral software on computer devoted solely to running the behavioral software. 
		Note: The instructions provided are based on MonkeyLogic, a MATLAB toolbox designed for the presentation and execution of temporally precise psychophysical tasks34,35 and are thus specific to that behavioral software platform. This program is run on Matlab version 2010a and requires the &#8220;Data Acquisition Toolbox.&#8221; However, any behavioral software platform capable of presenting visual stimuli and recording electrophysiological data could be used.</li>
		<li>Set the conditions file designed to run the MSIT task to include all four trial types of equal frequency. 
		Note: The MSIT task consists of presenting the subject with a cue of three numbers between 0 and 3, where two of the numbers, the &#8216;distractors&#8217;, are the same and one number, the &#8216;target&#8217;, is different.
		<ol>
			<li>Instruct the subject to identify the &#8216;target&#8217; by pressing the corresponding button on a button box. If &#8216;1&#8217; is the target, the left button is the correct choice. If &#8216;2&#8217;, the middle button, and if &#8216;3&#8217;, the right button. &#8216;0&#8217; does not correspond to a possible button (Figure 2).</li>
		</ol>
		</li>
		<li>Press the &#8220;Set conditions&#8221; button and choose the desired conditions file set in the prior step. 
		Note: There are two types of cognitive interference that induce conflict during the decision making process. Flanker interference trials occur when the distractors are possible (1, 2, or 3, rather than 0) button choices (e.g., 121), while spatial interference trials occur when the target number&#8217;s spatial location differs from the response location (e.g., 200, in which the middle button is the correct response, despite the fact that the target number is in the left position). There are four trial types based on the presence or absence of these two interference types.</li>
		<li>Test the behavioral display monitor by clicking &#8220;Test&#8221; in the display box. The display monitor should show the test visual stimulus for 2 - 3 sec.</li>
		<li>Connect the subject interface device (button box) to the analog inputs on the data acquisition board on the computer devoted to recording the electrophysiological data via three standard BNC cables.</li>
		<li>Connect the button box to a power source.</li>
		<li>Connect the data acquisition board to the 512-channel neural signal processor via a ribbon cable split into 9 ribbons. 8 of the ribbons are connected to ports 0 -&#160;7 on the digital I/O portion of the data acquisition board while the 9th ribbon is connected to port 0 on the digital PFI portion of the data acquisition board. 
		Note: The ribbons send 8-bit digital markers (ports 0 - 7, digital I/O) and a strobe pulse (port 0, digital PFI), to the neural signal processor.</li>
		<li>Set the desired sampling rate in the neural signal processor software.
		<ol>
			<li>In this example, set the desired sampling rate to 50,000 samples per second, alias and down-sample online to 1,000 samples per second. Adjust the sample rate to fit the specific goals of the task. Sub-millisecond precision timing requires an extremely high sampling rate.</li>
		</ol>
		</li>
		<li>Connect the amplifier to the neural signal processor via fiber optic cable.</li>
		<li>Connect the neural signal processor to the data streamer and the optical PCI card in the neural data acquisition computer via fiber optic cable.</li>
	</ol>
	</li>
	<li>Data acquisition
	<ol>
		<li>Use the research rig for EMU electrophysiology containing a 512-channel neural signal processor for processing and filtering digitized, pre-amplified electrical signals from the depth electrodes. 
		Note: While there are 512 channels for processing, in practice, there are never more than 15 - 20 electrodes placed for clinical purposes. Therefore, we recommend recording from as many electrodes as feasible as data size and spatial resolution is never an issue.</li>
		<li>Transport the rig to the patient&#8217;s room, place the behavioral monitor in front of the patient on a portable table and connect to the behavioral control computer running the behavioral software using a standard DVI cable.</li>
		<li>Place the recording rig behind or to the side of the patient&#8217;s bed in order to remain as unobtrusive as possible.</li>
		<li>Connect the research system to the splitter box that separates the research recording from the clinical system.</li>
		<li>Control recording parameters&#160;using the neural signal processor software34,35. 
		Note: This system enables sub-millisecond control over behavioral events34,35. Synchronization between neural and behavioral data can be accomplished with either analog pulses coding for task events or digital markers. Both signals can be sent from either the digital or analog outputs on the data acquisition board to the analog or digital inputs on the neural signal processor.</li>
		<li>Hand the patient the subject interface device (button box) and give task instructions.</li>
		<li>Click &#8220;Run&#8221; to run the task.</li>
		<li>Allow the patient to complete 2 blocks of 150 trials each.</li>
	</ol>
	</li>
</ol>
4. Data Analysis
<ol>
	<li>Open software package that allows for visualization of electrophysiological data. 
	Note: The instructions provided below are specific to Matlab version 2010a but any software that allows for visualization and manipulation of electrophysiological data can be used.</li>
	<li>Open .edf file containing raw electrophysiological data from the trial session.</li>
	<li>Visualize SEEG signal from the session to ensure there is no visible artifact such as epileptiform discharges or movement artifact (Figure 3A).</li>
	<li>Overlay the timing pulses from the behavioral task onto the raw LFP trace (Figure 3B) to illustrate how analog pulses can delineate trial structure.</li>
	<li>Using the timing pulses, align the SEEG trace to cue presentation for each trial (Figure 3C).</li>
	<li>Remove outliers (&#62;4 standard deviations) and artifact traces (Figure 3D).</li>
	<li>Save all aligned trials in a matrix for further analyses (20 trials shown stacked in Figure 3E).</li>
	<li>Average LFP activity across trials to reduce effect of noise, artifact, or EEG activity not related to the presented stimuli, and to increase the signal of interest (Figure 3F).</li>
	<li>Create the raw, trial-averaged spectrogram using multi-tapered spectral analysis36-38. 
	Note: Time-frequency analysis can be used in order to investigate the specific spectro-temporal dynamics across single or multiple trials. This method enables the investigation of neuronal oscillations at different frequencies over time.</li>
	<li>Pad the signal from each trial with zeroes to the next largest power of 2 to avoid edge effects.</li>
	<li>Apply a 800 ms sliding window with 5 leading tapers and a time-bandwidth product of 9 every 10 ms through the duration of the signal to create the spectrogram (Figure 4A).</li>
	<li>Multiply the log of the spectrogram by 10 and normalize to display higher frequency information. 
	Note: Spectrograms can be normalized by a theoretical frequency distribution (i.e., each frequency value raised to the negative 2nd power)(Figure 4B), the mean spectrum of some baseline activity (Figure 4C), or by dividing by the mean and subtracting the standard deviation of the values in each frequency band (Figure 4D). This procedure allows for the examination of specific frequency bands in both raw and normalized forms over time for changes specific to the task. For example, high gamma band activation (70 - 150 Hz), which is shown in Figure 3E, is thought to reflect local excitatory activity of the local neuronal population surrounding the electrode39,40.</li>
</ol>

The authors have no conflict of interest to disclose.

In this paper SEEG was used to investigate the activity of local neuronal populations within the dACC during a decision-making task in humans. Previous work has investigated the activity of individual neurons in the dACC using intraoperative microelectode recordings 14 and demonstrated that dACC activity is modulated by previous activity. Microelectrode studies enable the investigation of the spiking activity of individual neurons. SEEG measures LFPs, which are related to the summated synaptic potentials acros...

Epilepsy, a common neurological disorder characterized by multiple recurrent seizures over time, accounts for 1% of the worldwide burden of diseases 1. Anti-epileptic medications fail to control seizures in 20 - 30% of patients 2,3. In these medically intractable patients, epilepsy surgery is often indicated 4,5. The decision to proceed with surgery requires locating the seizure focus, a prerequisite to formulating a surgical plan. Initially, non-invasive techniques are used to lateralize and localize the seizure focus. Electroencephalography (EEG), for example, measures cortical electrical activity recorded from electrodes placed on the scalp and can often provide sufficient information about the location of the seizure focus. In addition, magnetic resonance imaging (MRI) can demonstrate discrete lesions, such as hippocampal sclerosis, the classic pathology seen in the most common form of medically intractable epilepsy, mesial temporal lobe epilepsy (MTLE).
Frequently, however, the noninvasive workup is unable to identify a seizure focus. In these cases, invasive electrocorticography (ECoG) with intracerebral electrodes is required to localize the focus and guide further surgical treatment 6. ECoG is a neurophysiological technique used to measure electrical activity using electrodes placed in direct contact with the brain. Grids or strips of surface (subdural) electrodes are placed over the surface of the brain, a process that requires a craniotomy (removal of a bone flap) and large opening of the dura. These surface electrodes can be placed over the putative area(s) of seizure onset. The distal ends of the electrodes are tunneled through small openings in the skin and connected to the recording equipment in the epilepsy monitoring unit (EMU). In the EMU, the patient is monitored for clinical seizure activity through continuous video and ECoG recordings. This technique is useful for collecting long-term (days to weeks) recordings of ictal and interictal electrical discharges over relatively large areas of the cortical surface. While these intracranial recordings are invaluable clinically for investigating seizure foci and propagation, they also provide us with the opportunity to investigate cognitive function and neurophysiology in humans undergoing specifically designed behavioral tasks.
ECoG using subdural grid electrodes has been used to investigate various aspects of cortical function, including sensory and language processing. As one of many examples, Bouchard et al demonstrated the temporal coordination of the oral musculature in the formation of syllables for spoken language in the ventral sensorimotor cortex, a region identified as the human speech sensorimotor cortex 7. Furthermore, ECoG with subdural grid placement has also been utilized to study the mechanisms by which humans are able to attend to a particular voice within a crowd: the so-called &#8216;cocktail party effect&#8217; 8,9. ECoG recordings demonstrated that there are two distinct neuronal bands that dynamically track speech streams, both low frequency phase and high-gamma amplitude fluctuations, and that there are distinct processing sites - one &#8216;modulation&#8217; site that tracks both speakers, and one &#8216;selection&#8217; site that tracks the attended talker 5.
Another emerging application of ECoG with subdural electrode placement is the potential for use with Brain Computer Interfaces (BCIs), which &#8220;decode&#8221; neuronal activity in order to drive an external output. This technology has the potential of allowing patients with severe brain or spinal cord injuries to communicate with the world and manipulate prostheses 10,11.
While subdural grid placement has contributed greatly to our understanding of superficial cortical areas and is useful in identifying cortical epileptogenic foci, this technique does require a craniotomy and its attendant risks, and is generally limited to studying the outer surface of the brain. Stereotactic electroencephalography (SEEG) is a technique that enables the assessment of deep epileptogenic foci12. With a long history of use in France and Italy, it is also increasingly being used in the US 13. SEEG involves the placement of multiple electrodes (typically 10 - 16) deep within the substance of the brain through small (few mm) twist drill burr holes. Advantages of SEEG over subdural grid placement include its less invasive nature, the ease of examining bilateral hemispheres when required, and the ability to generate three-dimensional maps of seizure propagation. Furthermore, these electrodes enable the identification of deep epileptogenic foci that were previously difficult to identify with surface electrodes. This procedure also provides the opportunity to investigate the neurophysiology and function of deep cortical structures, such as the limbic system, the mesoparietal cortex, the mesotemporal cortex, and the orbitofrontal cortex, all of which were previously difficult to directly investigate in humans.
This paper demonstrates how SEEG can be utilized to investigate cognitive function in the dorsal anterior cingulate cortex (dACC). The dACC is a widely investigated brain region, but it is also one of the most poorly understood. Considered a significant region for human cognition, it is likely that the dACC is central to the dynamic neural processing of decisions in the context of continuously changing demands imposed by the environment 14. Studies in both primates 15,16 and humans 17 suggest that the dACC integrates potential risks and rewards of a given action, especially in situations of multiple simultaneous conflicting demands18-21, and modulates these decisions in the context of previous actions and their outcomes 14,22,23.
The Multi-Source Interference Task (MSIT), a Stroop-like behavioral task, is frequently used to investigate conflict processing in the dACC. The MSIT task activates the dACC by recruiting neurons involved in multiple domains of processing regulated by the dACC 24,25. This task specifically activates the dACC by testing features of decision-making, target detection, novelty detection, error detection, response selection, and stimulus/response competition. In addition, the MSIT task introduces multiple dimensions of cognitive interference, which are utilized in this study to investigate dACC neural responses to simultaneous conflicting stimuli using SEEG.

<table><tbody><tr><td>Trigger I/O cable</td><td>Natus Medical Inc.</td><td>5029</td><td>PS2 to BNC cable</td></tr><tr><td>BNC cables for analog pulses</td><td></td><td></td><td>Can be ordered from most electronics stores.</td></tr><tr><td>Power strip with surge protection and battery backup</td><td>Tripp Lite</td><td>SMART500RT1U UPC</td><td>Power source and backup</td></tr><tr><td>National instruments multifunctional daq data acquisition box NI PCIe-6382 DAQ cards</td><td>National Instruments</td><td>PCIe-6382 w/ BNC 2090A</td><td>PCI cards for behavioral control interface</td></tr><tr><td>Custom made button box - human interface device</td><td></td><td></td><td>Any human interface device with three buttons may be used. Alternatively, 3 keyboard buttons may be used.</td></tr><tr><td>Xltek 128 channel clinical intracranial EEG monitoring system EMU128FS</td><td>Natus Medical Inc.</td><td>002047c</td><td>Clinical recording system</td></tr><tr><td>Subject monitor and associated cables for visual stimulus presentation</td><td>Dell</td><td>U2212HMc</td><td>Most Monitors are adequate here.</td></tr><tr><td>Personal comptuer running behavioral software with DAQ cards installed</td><td>Superlogics</td><td>SL-2U-PD-Q87SLQ-BA</td><td>Computer for recording neural data</td></tr><tr><td>Mains cable for monitor</td><td></td><td></td><td>Usually comes with the monitor, can be purchased at any electronics store.</td></tr><tr><td>Monkey Logic software which runs on Matlab 2010A</td><td></td><td></td><td>Free from MonkeyLogic website</td></tr><tr><td>MATLAB 2010a software with data acquisition toolbox</td><td>Mathworks</td><td></td><td>Matlab software</td></tr><tr><td>sEEG electrodes AD TECH or PMT</td><td>AD TECH</td><td>2102-##-101</td><td>Platinum tip, diameter (0.89 mm, 1 mm, 1.1 mm), uninsulated length 2.3 mm; The ## in the catalog number indicates the number of contacts on the electrode (08, 10, 12, or 16)</td></tr><tr><td>Cabrio connectors</td><td>PMT</td><td>2125-##-01</td><td>The ## in the catalog number indicates the number of contacts on the electrode (08, 10, 12, or 16)</td></tr><tr><td>Tucker Davis Technologies Amplifier</td><td>Tucker Davs Technologies</td><td>PZ5</td><td>preamplifier for neural data</td></tr><tr><td>Tucker Davis Technologies processor</td><td>Tucker Davs Technologies</td><td>RZ2</td><td>Neural signal processor for neural data</td></tr><tr><td>TuckerDavis Technologies data streamer</td><td>Tucker Davs Technologies</td><td>RS4</td><td>Data streamer and storage</td></tr><tr><td>Fiber optics cables to connect TDT systems</td><td>Tucker Davs Technologies</td><td>F05</td><td>Fiber optic cables for connecting Tucker Davis Technologies&#039; prodcuts.</td></tr><tr><td>ribbon cable and snap serial connector for digital markers</td><td></td><td></td><td>Can be ordered from ost electronics stores.</td></tr><tr><td>personal computer fro running TDT RPvdsEx and OpenEx software</td><td>Superlogics</td><td>SL-2U-PD-Q87SLQ-BA</td><td>computer for behavioral control</td></tr><tr><td>middle atlantics server cabinet with casters</td><td>Middle Atlantic Products</td><td>PTRK-21</td><td>Server case to house all of the research items</td></tr><tr><td>Tucker Davis Technologies splitter box to split clinical and research recrodings</td><td>Tucker Davs Technologies</td><td></td><td>This splitter box is a semi-custom device. Researchers should consult the attending neurologists about splitting the research and clinical recordings in a way that doesn&#039;t interfere with clinical care.</td></tr><tr><td>Researcher monitor with requisite cables</td><td>Dell</td><td>U2212HMc</td><td>Most Monitors are adequate here.</td></tr><tr><td>button box power source - 5 volts, 2 amperes</td><td></td><td></td><td>Can be purchased at any electronics store.</td></tr><tr><td>TDT optical interface PCI card</td><td>Tucker Davs Technologies</td><td>P05</td><td></td></tr></tbody></table>

investigating the function of deep cortical and subcortical structures using stereotactic electroencephalography: lessons from the anterior cingulate cortex

Stereotactic Electroencephalography (SEEG) is a technique used to localize seizure foci in patients with medically intractable epilepsy. This procedure involves the chronic placement of multiple depth electrodes into regions of the brain typically inaccessible via subdural grid electrode placement. SEEG thus provides a unique opportunity to investigate brain function. In this paper we demonstrate how SEEG can be used to investigate the role of the dorsal anterior cingulate cortex (dACC) in cognitive control. We include a description of the SEEG procedure, demonstrating the surgical placement of the electrodes. We describe the components and process required to record local field potential (LFP) data from consenting subjects while they are engaged in a behavioral task. In the example provided, subjects play a cognitive interference task, and we demonstrate how signals are recorded and analyzed from electrodes in the dorsal anterior cingulate cortex, an area intimately involved in decision-making. We conclude with further suggestions of ways in which this method can be used for investigating human cognitive processes.

Once a patient is selected for SEEG electrode placement, he/she undergoes a volumetric T2 and T1 contrast enhanced MRI. SEEG electrode trajectories are then planned using stereotactic navigation of the volumetric MRI sequences (Figure 1). This technique allows for the collection of local field potentials from structures deep within the cortex such as dorsal anterior cingulate cortex (light orange trajectory, Figure 1) that would not be possible with typical surface electrode placement. P...

Watch this Scientific Journal Video about Investigating the Function of Deep Cortical and Subcortical Structures Using Stereotactic Electroencephalography: Lessons from the Anterior Cingulate Cortex a

Investigating the Function of Deep Cortical and Subcortical Structures Using Stereotactic Electroencephalography: Lessons from the Anterior Cingulate Cortex

Stereotactic Electroencephalography (SEEG) is an operative technique used in epilepsy surgery to help localize seizure foci. It also affords a unique opportunity to investigate brain function. Here we describe how SEEG can be used to investigate cognitive processes in human subjects.

Stereotactic Electroencephalography (SEEG) is a technique used to localize seizure foci in patients with medically intractable epilepsy. This procedure ...

investigating-function-deep-cortical-subcortical-structures-using

Research

JoVE Journal

Neuroscience

12.3K Views.  Columbia University Medical Center, New York Presbyterian Hospital.  Stereotactische Electroencephalography (SEEG) is een operatietechniek gebruikt bij epilepsie chirurgie te helpen lokaliseren beslag brandpunten. Het biedt ook een unieke gelegenheid om de hersenfunctie te onderzoeken. Hier beschrijven we hoe SEEG kunnen worden gebruikt om cognitieve processen bij mensen te onderzoeken. 

Video: Investigating the Function of Deep Cortical and Subcortical Structures Using Stereotactic Electroencephalography: Lessons from the Anterior Cingulate Cortex

Performing Behavioral Tasks in Subjects with Intracranial Electrodes

Patients having stereo-electroencephalography (SEEG) electrode, subdural grid or depth electrode implants have a multitude of electrodes implanted in different areas of their brain for the localization of their seizure focus and eloquent areas. After implantation, the patient must remain in the hospital until the pathological area of brain is found and possibly resected. During this time, these patients offer a unique opportunity to the research community because any number of behavioral paradigms can be performed to uncover the neural correlates that guide behavior. Here we present a method for recording brain activity from intracranial implants as subjects perform a behavioral task designed to assess decision-making and reward encoding. All electrophysiological data from the intracranial electrodes are recorded during the behavioral task, allowing for the examination of the many brain areas involved in a single function at time scales relevant to behavior. Moreover, and unlike animal studies, human patients can learn a wide variety of behavioral tasks quickly, allowing for the ability to perform more than one task in the same subject or for performing controls. Despite the many advantages of this technique for understanding human brain function, there are also methodological limitations that we discuss, including environmental factors, analgesic effects, time constraints and recordings from diseased tissue. This method may be easily implemented by any institution that performs intracranial assessments; providing the opportunity to directly examine human brain function during behavior.

Patients implanted with intracranial electrodes provide a unique opportunity to record neurological data from multiple areas of the brain while the patient performs behavioral tasks. Here, we present a method of recording from implanted patients that can be reproducible at other institutions with access to this patient population.

Patients having stereo-electroencephalography (SEEG) electrode, subdural grid or depth electrode implants have a multitude of electrodes implanted in ...

Behavior

Combined Invasive Subcortical and Non-invasive Surface Neurophysiological Recordings for the Assessment of Cognitive and Emotional Functions in Humans

In spite of the success in applying non-invasive electroencephalography (EEG), magneto-encephalography (MEG) and functional magnetic resonance imaging (fMRI) for extracting crucial information about the mechanism of the human brain, such methods remain insufficient to provide information about physiological processes reflecting cognitive and emotional functions at the subcortical level. In this respect, modern invasive clinical approaches in humans, such as deep brain stimulation (DBS), offer a tremendous possibility to record subcortical brain activity, namely local field potentials (LFPs) representing coherent activity of neural assemblies from localized basal ganglia or thalamic regions. Notwithstanding the fact that invasive approaches in humans are applied only after medical indication and thus recorded data correspond to altered brain circuits, valuable insight can be gained regarding the presence of intact brain functions in relation to brain oscillatory activity and the pathophysiology of disorders in response to experimental cognitive paradigms. In this direction, a growing number of DBS studies in patients with Parkinson&#39;s disease (PD) target not only motor functions but also higher level processes such as emotions, decision-making, attention, memory and sensory perception. Recent clinical trials also emphasize the role of DBS as an alternative treatment in neuropsychiatric disorders ranging from obsessive compulsive disorder (OCD) to chronic disorders of consciousness (DOC). Consequently, we focus on the use of combined invasive (LFP) and non-invasive (EEG) human brain recordings in assessing the role of cortical-subcortical structures in cognitive and emotional processing trough experimental paradigms (e.g. speech stimuli with emotional connotation or paradigms of cognitive control such as the Flanker task), for patients undergoing DBS treatment.

The present protocol aims at assessing cognitive-emotional functions in the basal ganglia by simultaneous neurophysiological recording of local field potentials and non-invasive brain cortical activity (EEG). The procedure is exemplified by the use of paradigms involving speech stimuli with emotional connotation or the Flanker task involving cognitive control.

In spite of the success in applying non-invasive electroencephalography (EEG), magneto-encephalography (MEG) and functional magnetic resonance imaging ...

Intracortical Inhibition Within the Primary Motor Cortex Can Be Modulated by Changing the Focus of Attention

It is well recognized that an external focus (EF) compared with an internal focus (IF) of attention improves motor learning and performance. Studies have indicated benefits in accuracy, balance, force production, jumping performance, movement speed, oxygen consumption, and fatiguing task. Although behavioral outcomes of using an EF strategy are well explored, the underlying neural mechanisms remain unknown. A recent TMS study compared the activity of the primary motor cortex (M1) between an EF and an IF. More precisely, this study showed that, when adopting an EF, the activity of intracortical inhibitory circuits is enhanced.
On the behavioral level, the present protocol tests the influence of attentional foci on the time to task failure (TTF) when performing submaximal contractions of the first dorsal interosseous (FDI). Additionally, the current paper describes two TMS protocols to assess the influence of attentional conditions on the activity of cortical inhibitory circuits within the M1. Thus, the present article describes how to use single-pulse TMS at intensities below the motor threshold (subTMS) and paired-pulse TMS, inducing short-interval intracortical inhibition (SICI) when applied to the M1. As these methods are assumed to reflect the responsiveness of GABAergic inhibitory neurons, without being affected by spinal reflex circuitries, they are well suited to measuring the activity of intracortical inhibitory circuits within the M1.
The results show that directing attention externally improves motor performance, as participants were able to prolong the time to task failure. Moreover, the results were accompanied by a larger subTMS-induced electromyography suppression and SICI when adopting an EF compared to an IF. As the level of cortical inhibition within the M1 was previously demonstrated to influence motor performance, the enhanced inhibition with an EF might contribute to the better movement efficiency observed in the behavioral task, indicated by a prolonged TTF with an EF.

Using two different transcranial magnetic stimulation (TMS) protocols, this manuscript describes how to measure and compare cortical inhibition within the primary motor cortex when adopting different attentional foci.

It is well recognized that an external focus (EF) compared with an internal focus (IF) of attention improves motor learning and performance. Studies have ...

Recording Human Electrocorticographic (ECoG) Signals for Neuroscientific Research and Real-time Functional Cortical Mapping

Neuroimaging studies of human cognitive, sensory, and motor processes are usually based on noninvasive techniques such as electroencephalography (EEG), magnetoencephalography or functional magnetic-resonance imaging. These techniques have either inherently low temporal or low spatial resolution, and suffer from low signal-to-noise ratio and/or poor high-frequency sensitivity. Thus, they are suboptimal for exploring the short-lived spatio-temporal dynamics of many of the underlying brain processes. In contrast, the invasive technique of electrocorticography (ECoG) provides brain signals that have an exceptionally high signal-to-noise ratio, less susceptibility to artifacts than EEG, and a high spatial and temporal resolution (i.e., &lt;1 cm/&lt;1 millisecond, respectively). ECoG involves measurement of electrical brain signals using electrodes that are implanted subdurally on the surface of the brain. Recent studies have shown that ECoG amplitudes in certain frequency bands carry substantial information about task-related activity, such as motor execution and planning1, auditory processing2 and visual-spatial attention3. Most of this information is captured in the high gamma range (around 70-110 Hz). Thus, gamma activity has been proposed as a robust and general indicator of local cortical function1-5. ECoG can also reveal functional connectivity and resolve finer task-related spatial-temporal dynamics, thereby advancing our understanding of large-scale cortical processes. It has especially proven useful for advancing brain-computer interfacing (BCI) technology for decoding a user's intentions to enhance or improve communication6 and control7. Nevertheless, human ECoG data are often hard to obtain because of the risks and limitations of the invasive procedures involved, and the need to record within the constraints of clinical settings. Still, clinical monitoring to localize epileptic foci offers a unique and valuable opportunity to collect human ECoG data. We describe our methods for collecting recording ECoG, and demonstrate how to use these signals for important real-time applications such as clinical mapping and brain-computer interfacing. Our example uses the BCI2000 software platform8,9 and the SIGFRIED10 method, an application for real-time mapping of brain functions. This procedure yields information that clinicians can subsequently use to guide the complex and laborious process of functional mapping by electrical stimulation.
Prerequisites and Planning:
Patients with drug-resistant partial epilepsy may be candidates for resective surgery of an epileptic focus to minimize the frequency of seizures. Prior to resection, the patients undergo monitoring using subdural electrodes for two purposes: first, to localize the epileptic focus, and second, to identify nearby critical brain areas (i.e., eloquent cortex) where resection could result in long-term functional deficits. To implant electrodes, a craniotomy is performed to open the skull. Then, electrode grids and/or strips are placed on the cortex, usually beneath the dura. A typical grid has a set of 8 x 8 platinum-iridium electrodes of 4 mm diameter (2.3 mm exposed surface) embedded in silicon with an inter-electrode distance of 1cm. A strip typically contains 4 or 6 such electrodes in a single line. The locations for these grids/strips are planned by a team of neurologists and neurosurgeons, and are based on previous EEG monitoring, on a structural MRI of the patient's brain, and on relevant factors of the patient's history. Continuous recording over a period of 5-12 days serves to localize epileptic foci, and electrical stimulation via the implanted electrodes allows clinicians to map eloquent cortex. At the end of the monitoring period, explantation of the electrodes and therapeutic resection are performed together in one procedure.
In addition to its primary clinical purpose, invasive monitoring also provides a unique opportunity to acquire human ECoG data for neuroscientific research. The decision to include a prospective patient in the research is based on the planned location of their electrodes, on the patient's performance scores on neuropsychological assessments, and on their informed consent, which is predicated on their understanding that participation in research is optional and is not related to their treatment. As with all research involving human subjects, the research protocol must be approved by the hospital's institutional review board. The decision to perform individual experimental tasks is made day-by-day, and is contingent on the patient's endurance and willingness to participate. Some or all of the experiments may be prevented by problems with the clinical state of the patient, such as post-operative facial swelling, temporary aphasia, frequent seizures, post-ictal fatigue and confusion, and more general pain or discomfort.
At the Epilepsy Monitoring Unit at Albany Medical Center in Albany, New York, clinical monitoring is implemented around the clock using a 192-channel Nihon-Kohden Neurofax monitoring system. Research recordings are made in collaboration with the Wadsworth Center of the New York State Department of Health in Albany. Signals from the ECoG electrodes are fed simultaneously to the research and the clinical systems via splitter connectors. To ensure that the clinical and research systems do not interfere with each other, the two systems typically use separate grounds. In fact, an epidural strip of electrodes is sometimes implanted to provide a ground for the clinical system. Whether research or clinical recording system, the grounding electrode is chosen to be distant from the predicted epileptic focus and from cortical areas of interest for the research. Our research system consists of eight synchronized 16-channel g.USBamp amplifier/digitizer units (g.tec, Graz, Austria). These were chosen because they are safety-rated and FDA-approved for invasive recordings, they have a very low noise-floor in the high-frequency range in which the signals of interest are found, and they come with an SDK that allows them to be integrated with custom-written research software. In order to capture the high-gamma signal accurately, we acquire signals at 1200Hz sampling rate-considerably higher than that of the typical EEG experiment or that of many clinical monitoring systems. A built-in low-pass filter automatically prevents aliasing of signals higher than the digitizer can capture. The patient's eye gaze is tracked using a monitor with a built-in Tobii T-60 eye-tracking system (Tobii Tech., Stockholm, Sweden). Additional accessories such as joystick, bluetooth Wiimote (Nintendo Co.), data-glove (5th Dimension Technologies), keyboard, microphone, headphones, or video camera are connected depending on the requirements of the particular experiment.
Data collection, stimulus presentation, synchronization with the different input/output accessories, and real-time analysis and visualization are accomplished using our BCI2000 software8,9. BCI2000 is a freely available general-purpose software system for real-time biosignal data acquisition, processing and feedback. It includes an array of pre-built modules that can be flexibly configured for many different purposes, and that can be extended by researchers' own code in C++, MATLAB or Python. BCI2000 consists of four modules that communicate with each other via a network-capable protocol: a Source module that handles the acquisition of brain signals from one of 19 different hardware systems from different manufacturers; a Signal Processing module that extracts relevant ECoG features and translates them into output signals; an Application module that delivers stimuli and feedback to the subject; and the Operator module that provides a graphical interface to the investigator.
A number of different experiments may be conducted with any given patient. The priority of experiments will be determined by the location of the particular patient's electrodes. However, we usually begin our experimentation using the SIGFRIED (SIGnal modeling For Realtime Identification and Event Detection) mapping method, which detects and displays significant task-related activity in real time. The resulting functional map allows us to further tailor subsequent experimental protocols and may also prove as a useful starting point for traditional mapping by electrocortical stimulation (ECS).
Although ECS mapping remains the gold standard for predicting the clinical outcome of resection, the process of ECS mapping is time consuming and also has other problems, such as after-discharges or seizures. Thus, a passive functional mapping technique may prove valuable in providing an initial estimate of the locus of eloquent cortex, which may then be confirmed and refined by ECS. The results from our passive SIGFRIED mapping technique have been shown to exhibit substantial concurrence with the results derived using ECS mapping10.
The protocol described in this paper establishes a general methodology for gathering human ECoG data, before proceeding to illustrate how experiments can be initiated using the BCI2000 software platform. Finally, as a specific example, we describe how to perform passive functional mapping using the BCI2000-based SIGFRIED system.

Recording Human Electrocorticographic ECoG Signals for Neuroscientific Research and Real-time Functional Cortical Mapping

We present a method for collecting electrocorticographic signals for research purposes from humans who are undergoing invasive epilepsy monitoring. We show how to use the BCI2000 software platform for data collection, signal processing and stimulus presentation. Specifically, we demonstrate SIGFRIED, a BCI2000-based tool for real-time functional brain mapping.

Neuroimaging studies of human cognitive, sensory, and motor processes are usually based on noninvasive techniques such as electroencephalography (EEG), ...

Mapping Cortical Dynamics Using Simultaneous MEG/EEG and Anatomically-constrained Minimum-norm Estimates: an Auditory Attention Example

Magneto- and electroencephalography (MEG/EEG) are neuroimaging techniques that provide a high temporal resolution particularly suitable to investigate the cortical networks involved in dynamical perceptual and cognitive tasks, such as attending to different sounds in a cocktail party. Many past studies have employed data recorded at the sensor level only, i.e., the magnetic fields or the electric potentials recorded outside and on the scalp, and have usually focused on activity that is time-locked to the stimulus presentation. This type of event-related field / potential analysis is particularly useful when there are only a small number of distinct dipolar patterns that can be isolated and identified in space and time. Alternatively, by utilizing anatomical information, these distinct field patterns can be localized as current sources on the cortex. However, for a more sustained response that may not be time-locked to a specific stimulus (e.g., in preparation for listening to one of the two simultaneously presented spoken digits based on the cued auditory feature) or may be distributed across multiple spatial locations unknown a priori, the recruitment of a distributed cortical network may not be adequately captured by using a limited number of focal sources.
Here, we describe a procedure that employs individual anatomical MRI data to establish a relationship between the sensor information and the dipole activation on the cortex through the use of minimum-norm estimates (MNE). This inverse imaging approach provides us a tool for distributed source analysis. For illustrative purposes, we will describe all procedures using FreeSurfer and MNE software, both freely available. We will summarize the MRI sequences and analysis steps required to produce a forward model that enables us to relate the expected field pattern caused by the dipoles distributed on the cortex onto the M/EEG sensors. Next, we will step through the necessary processes that facilitate us in denoising the sensor data from environmental and physiological contaminants. We will then outline the procedure for combining and mapping MEG/EEG sensor data onto the cortical space, thereby producing a family of time-series of cortical dipole activation on the brain surface (or "brain movies") related to each experimental condition. Finally, we will highlight a few statistical techniques that enable us to make scientific inference across a subject population (i.e., perform group-level analysis) based on a common cortical coordinate space.

We use magneto- and electroencephalography (MEG/EEG), combined with anatomical information captured by magnetic resonance imaging (MRI), to map the dynamics of the cortical network associated with auditory attention.

Magneto- and electroencephalography (MEG/EEG) are neuroimaging techniques that provide a high temporal resolution particularly suitable to investigate the ...

Analysis of Gene Expression Changes in the Rat Hippocampus After Deep Brain Stimulation of the Anterior Thalamic Nucleus

Deep brain stimulation (DBS) surgery, targeting various regions of the brain such as the basal ganglia, thalamus, and subthalamic regions, is an effective treatment for several movement disorders that have failed to respond to medication. Recent progress in the field of DBS surgery has begun to extend the application of this surgical technique to other conditions as diverse as morbid obesity, depression and obsessive compulsive disorder. Despite these expanding indications, little is known about the underlying physiological mechanisms that facilitate the beneficial effects of DBS surgery. One approach to this question is to perform gene expression analysis in neurons that receive the electrical stimulation. Previous studies have shown that neurogenesis in the rat dentate gyrus is elicited in DBS targeting of the anterior nucleus of the thalamus1. DBS surgery targeting the ATN is used widely for treatment refractory epilepsy. It is thus of much interest for us to explore the transcriptional changes induced by electrically stimulating the ATN. In this manuscript, we describe our methodologies for stereotactically-guided DBS surgery targeting the ATN in adult male Wistar rats. We also discuss the subsequent steps for tissue dissection, RNA isolation, cDNA preparation and quantitative RT-PCR for measuring gene expression changes. This method could be applied and modified for stimulating the basal ganglia and other regions of the brain commonly clinically targeted. The gene expression study described here assumes a candidate target gene approach for discovering molecular players that could be directing the mechanism for DBS.

The mechanism underlying the therapeutic effects of Deep Brain Stimulation (DBS) surgery needs investigation. The methods presented in this manuscript describe an experimental approach to examine the cellular events triggered by DBS by analyzing the gene expression profile of candidate genes that can facilitate neurogenesis post DBS surgery.

Deep brain stimulation (DBS) surgery, targeting various regions of the brain such as the basal ganglia, thalamus, and subthalamic regions, is an effective ...

Combined Transcranial Magnetic Stimulation and Electroencephalography of the Dorsolateral Prefrontal Cortex

Transcranial magnetic stimulation (TMS) is a non-invasive method that produces neural excitation in the cortex by means of brief, time-varying magnetic field pulses. The initiation of cortical activation or its modulation depends on the background activation of the neurons of the cortical region activated, the characteristics of the coil, its position and its orientation with respect to the head. TMS combined with simultaneous electrocephalography (EEG) and neuronavigation (nTMS-EEG) allows for the assessment of cortico-cortical excitability and connectivity in almost all cortical areas in a reproducible manner. This advance makes nTMS-EEG a powerful tool that can accurately assess brain dynamics and neurophysiology in test-retest paradigms that are required for clinical trials. Limitations of this method include artifacts that cover the initial brain reactivity to stimulation. Thus, the process of removing artifacts may also extract valuable information. Moreover, the optimal parameters for dorsolateral prefrontal (DLPFC) stimulation are not fully known and current protocols utilize variations from the motor cortex (M1) stimulation paradigms. However, evolving nTMS-EEG designs hope to address these issues. The protocol presented here introduces some standard practices for assessing neurophysiological functioning from stimulation to the DLPFC that can be applied in patients with treatment resistant psychiatric disorders that receive treatment such as transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (rTMS), magnetic seizure therapy (MST) or electroconvulsive therapy (ECT).

The protocol presented here is for TMS-EEG studies utilizing intracortical excitability test-retest design paradigms. The intent of the protocol is to produce reliable and reproducible cortical excitability measures for assessing neurophysiological functioning related to therapeutic interventions in the treatment of neuropsychiatric diseases such as major depression.

Transcranial magnetic stimulation (TMS) is a non-invasive method that produces neural excitation in the cortex by means of brief, time-varying magnetic ...

A Visuospatial Planning Task Coupled with Eye-Tracker and Electroencephalogram Systems

The planning process, characterized by the capability to formulate an organized plan to reach a goal, is essential for human goal-directed behavior. Since planning is compromised in several neuropsychiatric disorders, the implementation of proper clinical and experimental tests to examine planning is critical. Due to the nature of the deployment of planning, in which several cognitive domains participate, the assessment of planning and the design of behavioral paradigms coupled with neuroimaging methods are current challenges in cognitive neuroscience. A planning task was evaluated in combination with an electroencephalogram (EEG) system and eye movement recordings in 27 healthy adult participants. Planning can be separated into two stages: a mental planning stage in which a sequence of steps is internally represented and an execution stage in which motor action is used to achieve a previously planned goal. Our protocol included a planning task and a control task. The planning task involved solving 36 maze trials, each representing a zoo map. The task had four periods: i) planning, where the subjects were instructed to plan a path to visit the locations of four animals according to a set of rules; ii) maintenance, where the subjects had to retain the planned path in their working memory; iii) execution, where the subjects used eye movements to trace the previously planned path as indicated by the eye-tracker system; and iv) response, where the subjects reported the order of the visited animals. The control task had a similar structure, but the cognitive planning component was removed by modifying the task goal. The spatial and temporal patterns of the EEG revealed that planning induces a gradual and lasting rise in frontal-midline theta activity (FM&#952;) over time. The source of this activity was identified within the prefrontal cortex by source analyses. Our results suggested that the experimental paradigm combining EEG and eye-tracker systems was optimal for evaluating cognitive planning.

The study of cognitive planning combining EEG and eye-tracking systems provides a multimodal approach to investigate the neural mechanisms that mediate cognitive control and goal-directed behavior in humans. Here, we describe a protocol for investigating the role of brain oscillations and eye movements in planning performance.

The planning process, characterized by the capability to formulate an organized plan to reach a goal, is essential for human goal-directed behavior. Since ...

Recording Cortical and Subcortical Neuronal Activity Using Electrode Systems

Source: Trenado, C., et al. <a href="https://app.jove.com/v/53466">Combined Invasive Subcortical and Non-invasive Surface Neurophysiological Recordings for the Assessment of Cognitive and Emotional Functions in Humans.</a> J. Vis. Exp. (2016).
This video demonstrates the process of recording cortical and subcortical neuronal activity using electroencephalography (EEG) and deep brain stimulation (DBS) electrodes during an attention-based visual stimulation test.

All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human ...

JoVE Encyclopedia of Experiments

Neurophysiology

Stimulation and Modulation Techniques

Monitoring the Brain Cortex with a Multi-Electrode Array in Response to Seizure-Inducing Agents

Source: Lu, H. C., et al. <a href="https://app.jove.com/v/53709">Direct-current stimulation and multi-electrode array recording of seizure-like activity in mice brain slice preparation.</a> J. Vis. Exp. (2016).
In this video, the effects of transcranial direct-current stimulation (tDCS) on brain slices containing the anterior cingulate cortex (ACC) and thalamus regions are investigated, using a multi-electrode array (MEA) to measure electric signals. By delivering electric pulses and infusing seizure-inducing drugs, the study investigates the ACC response to seizures.

All procedures involving animal samples have been reviewed and approved by the appropriate animal ethical review committee.
1. Preparing Experimental ...

Investigating the Function of Deep Cortical and Subcortical Structures Using Stereotactic Electroencephalography: Lessons from the Anterior Cingulate Cortex

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