Recording Cortical and Subcortical Neuronal Activity Using Electrode Systems

Protocol

All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human welfare and have been reviewed by the local institutional review board.

1. Experimental Paradigm Design and Patient's Consent

NOTE: Design an experimental paradigm or select an existing experimental paradigm to target a cognitive/emotional aspect of interest.

1. Select patients who will undergo DBS treatment. Ask if the patient meets the study's inclusion criteria. If yes, obtain signed informed consent from the patient and/or ethical commission (if applicable) to carry out a post-operative recording and application of the respective cognitive paradigm.
   NOTE: Post-operative recording takes place the following day after an initial DBS surgery is carried out for DBS electrode implantation (together with their corresponding externalization from the head by means of special cables) and before a second surgery is carried out for permanent implantation of DBS electrodes and stimulators.
   1. In the Flanker task (Example 1), obtain signed informed consent from a patient with a movement disorder (e.g., Huntington's or Parkinson's disease) to carry out a post-operative recording. The goal of the Flanker experiment is to test the patient's ability to adapt to error behavior and to determine how such adaptation is reflected in brain oscillatory activity at the cortical and subcortical levels.
      ​NOTE: The choice of a patient is dictated by the cognitive mechanism to be addressed and the patient's disorder. In the DBS-DOC case example (Example 2), a female DOC patient who suffered from a head injury at the age of 38 was selected. Because of the patient's condition limiting informed consent, DBS treatment and experimental participation were approved solely by the local ethics commission. The main goal of the DOC postoperative recording was to determine whether brain function in relation to cognitive-emotional processing was still intact in a patient with such a severe disorder of consciousness.
2. Choose between the type of stimulus to be presented (auditory, visual). Identify the order of stimulus presentation (block or mixed design). Select the duration of the stimulus, inter-stimulus interval (ISI), and the number of trials.
   1. As one practical example, perform the Flanker task (Example 1, Figure 1A), to examine the ability to adapt behavior in response to the commitment of response errors. This task consists of visual stimuli (flanked arrowheads vertically arranged).
   2. Flank the target stimulus (arrowhead in the center) by two adjacent arrows (above and below the target) pointing in the same (compatible) or opposite (incompatible) direction. Additionally, consider stop trials (circle in the center).
   3. Present the target to the left or right, and ask the participant to press a response button with their left or right thumb. In the stop trials, instruct the participants not to respond. Present flankers 200 msec before the target. Display the target for 300 msec and set the response stimulus interval to 2,000 msec (elapsed time is indicated by a cue tone). Present a total of four blocks of 120 stimuli each in this task. Present compatible (60%), incompatible (20%), and stop-trial (20%) stimuli randomly.
      NOTE: This stimulus interval value was chosen to avoid a large number of missed trials when considering motor-disabled patients. Flankers and targets were switched off simultaneously, and patients were instructed to respond as quickly as possible.
      NOTE: In the DBS-DOC case example (Example 2, Figure 1B), the experimental paradigm consisted of neutral non-addressing and familiar-addressing speech stimuli26 in a block design. The stimulus duration was set to 4 sec (with a randomized 4 5 sec inter-stimulus interval). A total of 80 trials per condition were considered in this paradigm (Figure 1B).
3. Envision the patient's physical constraints and needs in a post-operative setting recording. Specifically, determine if the patient is able to make use of the computer keyboard by considering the presence of excessive chorea movements (Huntington's disease) or tremors (Parkinson's disease).
   1. Make sure the patient can see the monitor (as the local anesthetic or the stereotactic head frame applied during DBS surgery may have caused swelling in the face and around the eyes) and sit comfortably during the duration of the whole experiment. Do not perform the experiment if the patient fails to meet these conditions.

2. Set-up for Postoperative Subcortical (local field potentials or LFPs) and Surface (EEG) Recordings

1. Set up the EEG equipment (see Materials in the supplementary files) in the room where the experiment will be conducted. Connect the recording computer to the EEG system. Start the EEG recording software (see "materials" in the supplementary files).
2. Click "File" and then "New workspace" to define the workspace in the EEG recording software by specifying: a sampling frequency of 5 kHz, a low cut-off (DC) and high cut-off frequency (1,000 Hz), EEG channels according to the international 10/20 system (at least: fronto-central (Fz), centro-central (Cz), fronto-polar reference (Fpz) and ground (mastoid) and depending on the paradigm furthermore parieto-central (Pz), occipito-central (Oz), temporal (T3/T4), fronto-medial (F3/F4), fronto-lateral (F7/F8) ) (Figure 2D) and LFP channels (LFPL 0, LFPL1, LFPL2, LFPL3 (left hemisphere, Figure 2C); LFPR0, LFPR1, LFPR2 and LFPR3 (right hemisphere)). Click "Monitor" to verify that the specified channels are now set up for recording.
   NOTE: The workspace should be prepared beforehand to minimize experiment time and oversee unexpected changes in the recording's configuration. This will ensure the highest temporal resolution, correct filter settings, adequate sampling rate, and proper selection of channels of interest.
3. Set up the stimulus computer by connecting the parallel port to the EEG system. Start the stimulus software. Click "run" to check the paradigm's functionality on the computer's monitor (visual stimuli) and/or speakers (auditory stimuli, sound cues). Make sure markers (triggers) from the stimulus computer are read into the recording system during the presentation of stimuli and the subject's response by checking their appearance on the EEG recording software.
   NOTE: Triggers from stimulus devices must have a duration of at least 200 µsec to be detected by the EEG system (with the 5 kHz sampling rate). Since triggers are markers of event-related events or evoked-related activity that occur at a specified period of time, their function is crucial for posterior data analysis. In the DBS-DOC case example (Example 2), the experimental paradigm (Figure 1B) consisted of auditory stimuli (familiar and unfamiliar voices), so triggers were set up at the beginning and end of each stimulus presented. In the case of the Flanker task (Figure 1A), triggers were set up at the instant when 1) the flankers and target stimuli appeared, 2) the patient responded, and 3) a cue tone was heard to inform the patient that the response-time had elapsed.
4. Mark the vertex of the patient's head as the midpoint between the nasion and inion using a skin marker pen and following the advice of an experienced neurologist or EEG specialist. Additionally, mark chosen EEG electrode positions using the 10-20 system. Attach EEG surface electrodes to the scalp by first cleaning each selected location with an isopropyl alcohol pad and then using an abrasive paste.
   NOTE: Such actions are constrained by the placement of bandages on the head of the DBS patient. However, an experienced neurologist should be able to define an appropriate (approximate) location for each electrode/channel. To ensure proper contact, move hair out of the way (if applicable). Due to their ease of placement, self-adhesive electrodes secured by surgical tape might be used.
5. Connect externalized DBS electrodes to a percutaneous extension. Connect the percutaneous extension to the external cable connector. Connect each electrode provided by the external cable connector to the EEG control box according to the EEG recording set-up. Connect EEG scalp electrodes to the EEG control box by first plugging ground and reference.
6. Attach EMG electrodes (reference and active electrodes) at specified muscles by first cleaning the area with an isopropyl alcohol pad. Then, connect the EMG electrodes to the EEG control box.
   NOTE: This step is optional and mainly conducted when motor tasks are considered in the paradigm or when monitoring the activity of muscles is required, as in the case of patients with motor disorders.
7. Click "Monitor" to visualize data. Make sure EEG and EMG signals displayed on the monitor are artifact-free by detecting the presence of jittering and superimposed high-frequency components. Check guidelines about types of artifacts and other factors related to recording electroencephalographic signals35 and/or request technical advice from an experienced neurologist or neuroscientist until you become familiar with the type of disturbances present in such physiological recordings.
   NOTE: This step is important to ensure high-quality signals for off-line data analysis.

3. Recording of Post-operative Subcortical (LFPs) and Surface (EEG) Brain Activity

1. Provide instructions to the patient. Make sure the patient is comfortable and instruct him/her to stop the experiment at any time of discomfort.
2. Click "run" on the stimulus software so that the patient is able to see the paradigm on the monitor and/or listen to the cue tones and sounds. Perform a training session with the patient until he/she is comfortable with the task. Start simultaneous recording of subcortical (LFP) and cortical (EEG) brain activity while the patient performs the experimental task.
   NOTE: In the case of the DBS-DOC case example (Example 2) the paradigm consisted of auditory stimuli in a block design as described in (Figure 1B). In the case of the Flanker task (Figure 1A), visual stimuli corresponding to three conditions (compatible (60%), incompatible (20%) and stop-trial (20%)) were presented randomly within each block (mixed design), each block consisted of 120 stimuli and the paradigm consisted of a total of four blocks. After the task has been finalized, data is stored on the hard disk of the recording computer for later offline screening and quantitative analysis.

النتائج

Figure 1: Sample Experimental Paradigms. (A) (Example 1) Flanker task: target stimulus (arrowhead in the center) is flanked by two adjacent arrows (above and below target) either pointing in the same (compatible) or opposite (incompatible) direction, stop trials (circle in the center) were also considered. When the target is pointed to the left or right, a participant has to press a response butt...

Materials

Name	Company	Catalog Number	Comments
BrainAmp Amplifier	Brain Products GmbH, Gilching Germany		Quantity: 2
BrainVision Recorder Software	Brain Products GmbH, Gilching Germany		1 License
BrainVision Analyzer Software	Brain Products GmbH, Gilching Germany		1 License
Fiber Optic cables and USB connectors	Brain Products GmbH, Gilching Germany		These come with the above listed equipment
Electrode Input box (64 channels)	Brain Products GmbH, Gilching Germany		Quantity: 1
EEG gel	Natus Inc		Quantity: 1
Isopropyl alcohol	Schülke & Mayr GmbH, Germany		Quantity: 1
Skin preparation gel	Weaver and Co, USA		Quantity: 1
MATLAB	Math-Works, Natick, Massachusetts, USA		1 License
FieldTrip toolbox	http://www.fieldtriptoolbox.org/		Open Source
INOMED MER system	INOMED Corp., Emmendingen, Germany		Quantity: 1
Macroelectrodes (model 3387 quadripolar DBS lead)	Medtronic Inc., Minneapolis, MN, USA		Quantity: 2
Sterile percutaneous extension wires (model 3550-05)	Medtronic Inc., Minneapolis, MN, USA		Quantity: 2
Twist lock cable (model 3550-03)	Medtronic Inc., Minneapolis, MN, USA		Quantity: 2
custom made connectors to DIN 428092 touch proof connectors			Quantity: 2
Vercise Lead kit DB -2201	Boston Scientific		Quantity: 2
Contact extenion kit NM-3138	Boston Scientific		Quantity: 2
O.R. cabel & extension SC-4100 A	Boston Scientific		Quantity: 2
connector to touch proof	Twente Medical Systems International B.V.		Quantity: 2
CT scanner Modell PQ2000 (Postoperative CT scans)	Philips Healthcare GmbH Hamburg		Quantity: 1
Presentation Software (Flanker Task)	Neurobehavioral systems Inc.		1 License