This research was supported by the University of Texas at Austin Moody College of Communication Grant Preparation Award and the University of Texas at Austin Office of the Vice President of Research Special Research Grant.

All methods described here have been approved by the Institutional Review Board (IRB) for Human Research at the University of Texas at Austin.
1. Stimuli Characteristics
<ol>
	<li>Create object stimuli using open source images available through the Bank of Standardized Stimuli (BOSS). This database consists of standardized images used throughout visual cognitive experiments.&#160; Download four images (e.g., ball02, book01a, brick, button03) with a high rate of identification (above 75%)20,21.&#160;&#160;</li>
	<li>Create motion stimuli using a modified version of the DotDemo script, which is available through the open source Psychtoolbox-3 set of functions operated via MATLAB, as well as the movie function available in MATLAB (see the Supplementary File).
	<ol>
		<li>Configure the dot field parameters according to the size of the presentation screen and viewing distance.&#160;&#160;</li>
		<li>Enter 3600 for the number of movie frames.&#160;</li>
		<li>Enter 80 (in cm) for monitor width.</li>
		<li>Enter dot speed at 5&#176;/s.</li>
		<li>Enter a dot limited lifetime fraction of 0.05.</li>
		<li>Enter 200 for the number of dots.</li>
		<li>Enter the minimum radius of the field annulus as 1&#176; and the maximum as 15&#176;.&#160;&#160;</li>
		<li>Enter 0.2&#176; for the width of each dot.</li>
		<li>Enter 0.35&#176; for the radius of the fixation point.</li>
		<li>Specify that white dots are used on a black background.</li>
		<li>Export the movie in .avi format.</li>
	</ol>
	</li>
</ol>
2. Visual Paradigm Design
<ol>
	<li>Create paradigms via stimulus-presentation software. Generate fixation crosses with Courier New size 18 font, bold, and centered on the presentation screen.</li>
	<li>Design the visual object paradigm without temporal jitter (i.e., consistent ISI values) by creating a black fixation cross on a white background presented for 500 ms, followed by one of four objects presented in randomized order: ball, book, brick, or button.&#160;&#160;
	<ol>
		<li>Present each object for 600 ms (Figure 1A).&#160; Show all objects 75 times, for a total of 300 trials and a paradigm duration of 5.5 min.&#160;&#160;</li>
	</ol>
	</li>
	<li>Design the visual object paradigm with temporal jitter to consist of the same black fixation cross on a white background, shown for a period of 500 or 1,000 ms and followed by one of the four objects, lasting for 600 or 1000 ms (Figure 1B).&#160;&#160;
	<ol>
		<li>Create four trials using stimulus-presentation software: a fixation cross with a duration of 500 ms, followed by an object for 600 ms; a fixation cross with a duration of 500 ms, followed by an object for 1,000 ms; a fixation cross with a duration of 1,000 ms, followed by an object for 600 ms; and a fixation cross with a duration of 1,000 ms followed by an object for 1,000 ms.&#160;&#160;
		<ol>
			<li>Randomize these trials. Present each trial 19 times, culminating in 304 trials and resulting in a viewing time of approximately 7.85 minutes.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Create the visual motion paradigm without temporal jitter by generating a white fixation cross centered on a black background, lasting for 500 ms, followed by the visual motion movie, which is truncated to present for approximately 1,000 ms (Figure 2A).&#160;
	<ol>
		<li>Repeat this sequence a total of 300 times, for a viewing duration of approximately 7.5 min.&#160;&#160;</li>
	</ol>
	</li>
	<li>Create the visual motion paradigm with temporal jitter using the same fixation cross, lasting for intervals of 500, 750, or 1,000 ms.&#160;&#160;
	<ol>
		<li>After each fixation cross, present the visual motion movie with a duration of approximately 600 or 1,000 ms (Figure 2B).&#160;&#160;</li>
		<li>Create six trials: A fixation cross with a duration of 500 ms, followed by a movie for 600 ms, a fixation cross with a duration of 750 ms, followed by a movie for 600 ms, a fixation cross with a duration of 1,000 ms, followed by a movie for 600 ms, a fixation cross with a duration of 500 ms followed by a movie for 1000 ms, a fixation cross with a duration of 750 ms followed by a movie for 1,000 ms and a fixation cross with a duration of 1,000 ms followed by a movie for 1,000 ms.&#160;&#160;
		<ol>
			<li>Randomize these trials, with each shown 50 times.&#160; Present a total of 300 trials, for a viewing period of approximately 7.75 min.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
3. Participant Consent, Case History, and Vision Screening
<ol>
	<li>Greet the participant on arrival. Obtain informed consent by presenting the participant with a consent for participation in research form. Explain the consent form to the participant and answer any questions that arise.</li>
	<li>Have the participant fill out a case history form that includes information on native language, handedness, hearing status, vision status, and other diagnoses the participant may have (e.g., psychological and neurological). Exclude participants who report hearing loss and/or neurological diagnoses, such as traumatic brain injury.&#160; Include all other participants.</li>
	<li>Escort the participant out of the lab to complete a vision screening using a Snellen chart to determine visual acuity. Have the participant stand 20 feet away from the chart and begin by covering his or her left eye to determine right eye visual acuity, and then switch eyes to determine left eye visual acuity. Calculate visual acuity based on the smallest line of text that the participant can repeat at least one more than half of the total number of letters.&#160; 
	NOTE: For example, if the participant repeats 5 of the 8 letters on the 20/20 line, visual acuity is calculated as 20/20 in that eye.</li>
	<li>Escort the participant into the EEG recording room. Have the participant sit in the designated chair in the center of a double-walled magnetic-shielded soundproof booth.&#160;&#160;</li>
</ol>
4. EEG Preparation
<ol>
	<li>Measure the head circumference of the participant in centimeters and select the appropriate EEG net size. Measure and mark the midpoint of the scalp (midway between nasion/inion and right and left mastoids) for the placement of the reference electrode.</li>
	<li>Prepare a solution of warm water (1 L) mixed with baby shampoo (5 mL) and potassium chloride (11 g/10 cc), which increases the electrical conductance between the electrodes and scalp, leading to lower voltage impedances and an increased signal-to-noise ratio.</li>
	<li>Place the EEG net in the solution. Allow the net to soak in the solution for 5 min before placing on the participant&#8217;s scalp.</li>
	<li>Turn on the stimulus-presentation computer and the EEG acquisition computer.</li>
	<li>Place a towel or other absorbent material around the participant&#8217;s neck to prevent the solution from dripping onto his or her clothes.&#160;</li>
	<li>Connect the EEG net to the amplifier. Instruct the participant to close his or her eyes when putting on the EEG net to prevent the solution from dripping into his or her eyes.</li>
	<li>Firmly grip the EEG net with both hands and spread into place onto the participant&#8217;s head. Ensure that the net is placed symmetrically on the scalp head, with the reference electrode at the scalp midline point that was measured. Tighten the chin and ocular net lines to ensure a secure connection between the scalp and electrodes. Ask the participant if he or she is comfortable and if anything needs to be adjusted.</li>
	<li>Check for the proper electrode impedance values, with an average target of 10 k&#937;.</li>
	<li>To reduce impedance values following the placement of the electrode net, use a 1 mL pipette to apply the potassium chloride solution onto the scalp/electrodes that have a high impedance. Continue this process until adequate impedances values across the electrodes are achieved.&#160;</li>
</ol>
5. EEG Recording
<ol>
	<li>Instruct the participant to focus on the visual stimuli that will appear on the monitor. The viewing distance is approximately 65 inches.</li>
	<li>Use a pseudorandom number generator to determine the order of presentation for the four visual paradigms.&#160;</li>
	<li>Begin the visual tasks and EEG recording.</li>
	<li>Monitor the EEG recording as necessary. If ongoing EEG shows high myogenic or 60 Hz activity, pause the experiment to recheck electrode-scalp connectivity.</li>
	<li>Repeat steps 5.3 and 5.4 for the visual object paradigm, the visual object with the temporal jitter paradigm, the visual motion paradigm, and the visual motion with temporal jitter paradigm.</li>
	<li>At the conclusion of the experiment, instruct the participant to close his or her eyes in order to prevent the solution from entering his or her eyes when removing the net. Begin by loosening the chin and ocular net lines, then remove the net by gently pulling the chin strap up and over the participant&#8217;s head, making sure to pull slowly to ensure the net will not get tangled in the participant&#8217;s hair.&#160;</li>
	<li>Disconnect the EEG net from the amplifier. Begin the disinfection process by placing the EEG cap in and out of a bucket filled with water and rinsing under a faucet. Then, create the disinfectant solution by adding approximately 2 l of water to the disinfectant bucket and mixing 15 ml of disinfectant with the water.&#160;</li>
	<li>Immerse the sensor end of the net in the disinfectant. Set a timer for 10 min; for the first 2 min, continuously plunge the net up and down. Leave the net soaking for the remainder of the 10 min.</li>
	<li>Remove EEG net from disinfectant solution. Place the EEG net in and out of the electrode bucket filled with water and under running water to rinse. Repeat four times.&#160; Allow the net to air dry.&#160;</li>
</ol>
6. EEG Analyses
<ol>
	<li>Export EEG files for analyses in MATLAB via the EEGLAB toolbox using a 1 Hz high-pass filter, segmentation around each trial (or event) of 100 ms pre-stimulus and 500 ms post-stimulus periods.&#160;&#160;</li>
	<li>Import data using the EEGLAB toolbox.&#160;&#160;
	<ol>
		<li>Choose the File option from the drop-down menu and click on Import data.&#160; Select using EEGLAB Functions and plugins from the menu.&#160; Next click on the appropriate export file format.</li>
	</ol>
	</li>
	<li>Re-assign channel locations based on the type of electrode montage used by choosing Edit from the drop-down menu and selecting Channel locations.&#160; Click on Look up locs and select the ellipses to locate the path of the electrode montage file of interest.&#160;</li>
	<li>Assign pre- and post-stimulus times to the epoch start and end times. Enter a value of -0.1 s in the Start time box.&#160;</li>
	<li>Baseline-correct data according to the pre-stimulus interval.</li>
	<li>Identify and remove bad channels using probability at a Z-score threshold of 2.5.&#160;
	<ol>
		<li>Verify successful identification and removal of bad channels by plotting all electrodes.&#160;Manually remove channels with mean voltage amplitudes outside of the range of +/- 30 &#181;V.</li>
	</ol>
	</li>
	<li>Perform artifact rejection by entering values of -100 &#181;V and +100 &#181;V. 
	NOTE: This method is effective in the removal of ocular activity recorded at ocular electrodes (126, 127). However, it may be necessary to manually remove trials with artifact occurring at small-voltage amplitude (i.e., within the +/- 100 &#181;V range) for certain participants.&#160;
	<ol>
		<li>Take note of channels that were bad for entire segments (i.e., with voltages outside of the +/-100 &#181;V range) and highlighted in red. Manually remove these bad channels if they constitute 60% or more of the rejected trials. Repeat this step as many times as necessary.&#160;</li>
		<li>Follow artifact removal steps as previously described. Ensure that a minimum of 100 sweeps are accepted. Remove trials marked for rejection.</li>
	</ol>
	</li>
	<li>Plot channel 75 (equivalent to Oz), or the channel(s) of interest, to categorize morphological patterns. Prior to plotting this channel, make sure to perform pre-stimulus baseline correction.&#160;&#160;</li>
	<li>Choose pattern A if CVEP morphology is characterized by a large positive peak at approximately 100-115 ms (P1), followed by a negative peak at approximately 140-180 ms (N1) and a positive peak at approximately 165-240 ms (P2).&#160;&#160;</li>
	<li>Choose pattern B if CVEP morphology is characterized by a large positive peak at approximately 100-115 ms (P1), followed by a negative peak at approximately 140-180 ms (N1a), a positive peak at approximately 180-240 ms (P2a), then a negative peak at approximately 230-280 ms (N1b) and positive peak at approximately 260-350 ms (P2b).&#160; &#160;&#160;</li>
	<li>Append individual datasets together according to the morphological pattern visually observed to create a group average. Name and save the newly merged dataset file.&#160;&#160;</li>
	<li>View appended files as an average by plotting the channel(s) of interest.</li>
</ol>

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The authors have nothing to disclose.

The goal of this methodological report was to evaluate the feasibility in recording differential CVEP morphology by using visual object and motion stimuli specifically designed to separately stimulate ventral and dorsal streams in passive viewing tasks6,7,8, both with and without variation of ISIs (jitter)19. Conditions were not designed to be directly compared, rather, observations were made as to whethe...

Electroencephalography (EEG) is a tool that offers an inexpensive and non-invasive approach to the study of cortical processing, especially when compared to cortical assessment methods such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and diffusion tensor imaging (DTI)1. EEG also provides high temporal resolution, which is not possible to attain when using measures such as fMRI, PET, or DTI2. High temporal resolution is critical when examining central temporal function in order to obtain millisecond-precision of neurophysiologic mechanisms related to the processing of specific input or events.&#160; In the central visual system, cortical visual evoked potentials (CVEPs) are a popular approach in studying time-locked neural processes in the cerebral cortex.&#160; CVEP responses are recorded and averaged over a number of event trials, resulting in peak components (e.g., P1, N1, P2) arising at specific millisecond intervals. The timing and amplitude of these peak neural responses can provide information concerning cortical processing speed and maturation, as well as deficits in cortical function3,4,5.&#160;&#160;
CVEPs are specific to the type of visual input presented to the viewer. Using certain stimuli in a CVEP paradigm, it is possible to observe the function of distinct visual networks such as the ventral stream, involved in processing form and color, or parvocellular and magnocellular input6,7,8, and the dorsal stream, which largely processes motion or magnocellular input9,10. CVEPs generated by these networks have been useful not only in better understanding typical neurophysiologic mechanisms underlying behavior but also in the targeted treatment of atypical behaviors in clinical populations. For example, delayed CVEP components in both dorsal and ventral networks have been reported in children with dyslexia, which suggests that visual function in both these networks should be targeted when designing an intervention plan11.&#160; Thus, CVEPs recorded via EEG offer a powerful clinical tool through which to assess both typical and atypical visual processes.&#160;
In a recent study, high-density EEG was used to measure the apparent motion-onset CVEPs in typically developing children, with the goal of examining variable CVEP responses and related visual cortical generators across development. Participants passively viewed apparent motion stimuli12,13,14,15, which consisted of both shape&#160;change and motion,&#160;designed to simultaneously stimulate dorsal and ventral streams. It was found that approximately half of the children responded with a CVEP waveform shape, or morphology, consisting of three peaks (P1-N1-P2, pattern A).&#160; This morphology is a classic CVEP response observed throughout the literature. In contrast, the other half of the children presented with a morphological pattern comprised of five peaks (P1-N1a-P2a-N1b-P2b, pattern B). To our knowledge, the robust occurrence and comparison of these morphological patterns have not previously been discussed in CVEP literature in either child or adult populations, although variable morphology has been noted in both apparent-motion and motion-onset CVEPs14,16. Furthermore, these morphological differences would not have been apparent in research using other cortical functional assessment methods, such as fMRI or PET, due to the low temporal resolution of these measures.
To determine the cortical generators of each peak in CVEP patterns A and B, source localization analyses were performed, which is a statistical approach used to estimate the most likely cortical regions involved in the CVEP response12,13. For each peak, regardless of the morphological pattern, primary and higher-order visual cortices were identified as sources of the CVEP signal.&#160; Thus, it appears that the main difference underlying CVEP morphology elicited by apparent motion is that those with pattern B activate visual cortical regions additional times during processing. Because these types of patterns have not been previously identified in the literature, the purpose of the additional visual processing in those with CVEP pattern B remains unclear.&#160; Therefore, the next aim in this line of research is to gain a better understanding of the cause of the differential CVEP morphology and whether such patterns may relate to visual behavior in both typical and clinical populations.&#160;
The first step in understanding why some individuals might demonstrate one CVEP morphology versus another is to determine whether these responses are intrinsic or extrinsic in nature.&#160; In other words, if an individual demonstrates one pattern in response to a visual stimulus, will they respond with a similar pattern to all stimuli?&#160; Or is this response stimulus-dependent, specific to the visual network or networks activated?
To answer this question, two passive visual paradigms were designed, intended to separately activate specific visual networks. The stimulus presented in the initial study was designed to stimulate both dorsal and ventral streams simultaneously; thus, it was unknown if one or both networks were involved in generating specific waveform morphology. In the current methodological approach, the paradigm designed to stimulate the ventral stream is composed of highly identifiable objects in basic shapes of squares and circles, eliciting object-onset CVEPs. The paradigm designed to stimulate the dorsal stream consists of visual motion via a radial field of coherent central dot motion dots at a fixed speed toward a fixation point, eliciting motion-onset CVEPs.&#160;
A second question that arose as a result of the initial study was whether differential VEP morphology could be due to participant anticipation of upcoming stimuli13. For instance, research has shown that top-down cortical oscillatory activity occurring prior to a target stimulus may predict subsequent CVEP and behavioral responses to some degree17,18,19. The apparent motion paradigm in the first study employed non-randomized frames of a radial star and circle with consistent inter-stimulus intervals (ISIs) of 600 ms. This design may have encouraged the expectation and prediction of the upcoming stimulus, with resulting oscillatory activity affecting subsequent CVEP morphology12,13,19.&#160;&#160;
To address this issue, the visual object and motion paradigms in the current protocol are designed with both consistent ISIs of the same temporal value and randomized ISIs with different temporal values (i.e., jitter).&#160; Using this approach, it may be possible to determine how temporal variation can affect VEP morphology within distinct visual networks. Altogether, the aim of the described protocol is to determine if the visual object and motion stimuli would be sensitive to variations in CVEP morphology and whether the temporal variation of stimuli presentation would affect characteristics of the CVEP response, including peak latency, amplitude, and morphology. For the purpose of the current paper, the goal is to determine the feasibility of the methodological approach. It is hypothesized that both visual objects and motion may elicit variable morphology (i.e., patterns A and B will be observed across subjects in response to both stimuli) and that temporal variation would affect object-onset and motion-onset CVEP components.&#160;

<table><tbody><tr><td>E-Prime 2.0</td><td>Psychology Software Tools, Inc</td><td></td><td>Used in data acquisition</td></tr><tr><td>Net Amps 400</td><td>Electrical Geodesics, Inc</td><td></td><td>Used in data acquisition</td></tr><tr><td>Net Station Acquisition V5.2.0.2</td><td>Electrical Geodesics, Inc</td><td></td><td>Used in data acqusition</td></tr><tr><td>iMac (27 inch)</td><td>Apple</td><td></td><td>Used in data acquisition</td></tr><tr><td>Optiplex 7020 Computer</td><td>Dell</td><td></td><td>Stimulus computer</td></tr><tr><td>HydroCel GSN EEG net</td><td>Electrical Geodesics, Inc</td><td></td><td>Used in data acqusition</td></tr><tr><td>1 mL pipette</td><td>Electrical Geodesics, Inc</td><td></td><td>Used to lower impedances</td></tr><tr><td>Johnson&#039;s Baby Shampoo</td><td>Johnson &amp;amp; Johnson</td><td></td><td>Used in impedance solution</td></tr><tr><td>Potassium Chloride (dry)</td><td>Electrical Geodesics, Inc</td><td></td><td>Used in impedance solution</td></tr><tr><td>Control III Disinfectant Germicide</td><td>Control III</td><td></td><td>Used in disinfectant solution</td></tr><tr><td>32 inch LCD monitor&amp;nbsp;</td><td>Vizio</td><td></td><td>Used to present stimuli</td></tr><tr><td>Matlab (R2016b)</td><td>MathWorks</td><td></td><td>Used in data analysis</td></tr><tr><td>EEGlab v14.1.2</td><td>Swartz Center for Computational Neuroscience, University of California, San Diego</td><td>https://sccn.ucsd.edu/eeglab/index.php</td><td>Used in data analysis</td></tr><tr><td>BOSS Database</td><td>Bank of Standardized Stimuli</td><td>https://sites.google.com/site/bosstimuli/</td><td>Used in generation of visual object stimuli&amp;nbsp;</td></tr><tr><td>Psychtoolbox-3</td><td>Psychophysics Toolbox Version 3 (PTB-3)</td><td>http://psychtoolbox.org/</td><td>Used in generation of visual motion stimuli</td></tr></tbody></table>

stimulus-specific cortical visual evoked potential morphological patterns

This paper presents a methodology for the recording and analysis of cortical visual evoked potentials (CVEPs) in response to various visual stimuli using 128-channel high-density electroencephalography (EEG). The specific aim of the described stimuli and analyses is to examine whether it is feasible to replicate previously reported CVEP morphological patterns elicited by an apparent motion stimulus, designed to simultaneously stimulate both ventral and dorsal central visual networks, using object and motion stimuli designed to separately stimulate ventral and dorsal visual cortical networks.&#160; Four visual paradigms are presented: 1. Randomized visual objects with consistent temporal presentation. 2. Randomized visual objects with inconsistent temporal presentation (or jitter).&#160; 3. Visual motion via a radial field of coherent central dot motion without jitter.&#160; 4. Visual motion via a radial field of coherent central dot motion with jitter.&#160; These four paradigms are presented in a pseudo-randomized order for each participant.&#160; Jitter is introduced in order to view how possible anticipatory-related effects may affect the morphology of the object-onset and motion-onset CVEP response.&#160; EEG data analyses are described in detail, including steps of data exportation from and importation to signal processing platforms, bad channel identification&#160;and removal, artifact rejection, averaging, and categorization of average CVEP morphological pattern type based upon latency ranges of component peaks. Representative data show that the methodological approach is indeed sensitive in eliciting differential object-onset and motion-onset CVEP morphological patterns and may, therefore, be useful in addressing the larger research aim. Given the high temporal resolution of EEG and the possible application of high-density EEG in source localization analyses, this protocol is ideal for the investigation of distinct CVEP morphological patterns and the underlying neural mechanisms which generate these differential responses.&#160; &#160; &#160;&#160;

Figure 3 and Figure 4 show the representative object-onset and motion-onset CVEP results of five participants, aged 19-24 years, who passively viewed each visual paradigm. This design allowed observation of CVEP responses elicited by visual objects (with and without jitter) and visual motion (with and without jitter) both within and across subjects according to each condition.&#160; Participant CVEPs were grouped according to the morphological pattern elicited b...

Watch this Scientific Journal Video about Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns at JoVE.com

Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns

In this paper, we present a protocol to investigate differential cortical visual evoked potential morphological patterns through stimulation of ventral and dorsal networks using high-density EEG. Visual object and motion stimulus paradigms, with and without temporal jitter, are described. Visual evoked potential morphological analyses are also outlined.&#160;&#160;

This paper presents a methodology for the recording and analysis of cortical visual evoked potentials (CVEPs) in response to various visual stimuli using ...

stimulus-specific-cortical-visual-evoked-potential-morphological

Research

JoVE Journal

Neuroscience

5.9K Views.  The University of Texas at Austin. In this paper, we present a protocol to investigate differential cortical visual evoked potential morphological patterns through stimulation of ventral and dorsal networks using high-density EEG. Visual object and motion stimulus paradigms, with and without temporal jitter, are described. Visual evoked potential morphological analyses are also outlined.  

Video: Stimulus-specific Cortical Visual Evoked Potential Morphological Patterns

Topographical Estimation of Visual Population Receptive Fields by fMRI

Visual cortex is retinotopically organized so that neighboring populations of cells map to neighboring parts of the visual field. Functional magnetic resonance imaging allows us to estimate voxel-based population receptive fields (pRF), i.e., the part of the visual field that activates the cells within each voxel. Prior, direct, pRF estimation methods1 suffer from certain limitations: 1) the pRF model is chosen a-priori and may not fully capture the actual pRF shape, and 2) pRF centers are prone to mislocalization near the border of the stimulus space. Here a new topographical pRF estimation method2 is proposed that largely circumvents these limitations. A linear model is used to predict the Blood Oxygen Level-Dependent (BOLD) signal by convolving the linear response of the pRF to the visual stimulus with the canonical hemodynamic response function. PRF topography is represented as a weight vector whose components represent the strength of the aggregate response of voxel neurons to stimuli presented at different visual field locations. The resulting linear equations can be solved for the pRF weight vector using ridge regression3, yielding the pRF topography. A pRF model that is matched to the estimated topography can then be chosen post-hoc, thereby improving the estimates of pRF parameters such as pRF-center location, pRF orientation, size, etc. Having the pRF topography available also allows the visual verification of pRF parameter estimates allowing the extraction of various pRF properties without having to make a-priori assumptions about the pRF structure. This approach promises to be particularly useful for investigating the pRF organization of patients with disorders of the visual system.

It is important to obtain unbiased estimates of visual population receptive fields (pRFs) by functional magnetic resonance imaging. We use mild regularization constraints to estimate pRF topography without a-priori assumptions about pRF shape, allowing us to choose specific pRF models post-hoc. This is particularly advantageous in subjects with visual-pathway lesions.

Visual cortex is retinotopically organized so that neighboring populations of cells map to neighboring parts of the visual field. Functional magnetic ...

Behavior

Infant Auditory Processing and Event-related Brain Oscillations

Rapid auditory processing and acoustic change detection abilities play a critical role in allowing human infants to efficiently process the fine spectral and temporal changes that are characteristic of human language. These abilities lay the foundation for effective language acquisition; allowing infants to hone in on the sounds of their native language. Invasive procedures in animals and scalp-recorded potentials from human adults suggest that simultaneous, rhythmic activity (oscillations) between and within brain regions are fundamental to sensory development; determining the resolution with which incoming stimuli are parsed. At this time, little is known about oscillatory dynamics in human infant development. However, animal neurophysiology and adult EEG data provide the basis for a strong hypothesis that rapid auditory processing in infants is mediated by oscillatory synchrony in discrete frequency bands. In order to investigate this, 128-channel, high-density EEG responses of 4-month old infants to frequency change in tone pairs, presented in two rate conditions (Rapid: 70 msec ISI and Control: 300 msec ISI) were examined. To determine the frequency band and magnitude of activity, auditory evoked response averages were first co-registered with age-appropriate brain templates. Next, the principal components of the response were identified and localized using a two-dipole model of brain activity. Single-trial analysis of oscillatory power showed a robust index of frequency change processing in bursts of Theta band (3 - 8 Hz) activity in both right and left auditory cortices, with left activation more prominent in the Rapid condition. These methods have produced data that are not only some of the first reported evoked oscillations analyses in infants, but are also, importantly, the product of a well-established method of recording and analyzing clean, meticulously collected, infant EEG and ERPs. In this article, we describe our method for infant EEG net application, recording, dynamic brain response analysis, and representative results.

High-density electroencephalography (dEEG) is being used increasingly to study brain development and plasticity in the early years of life. Here we present an application of sophisticated analysis techniques that builds on traditional EEG recording to understand the oscillatory dynamics of rapid auditory processing in the infant brain.

Rapid auditory processing and acoustic change detection abilities play a critical role in allowing human infants to efficiently process the fine spectral ...

Cross-Modal Multivariate Pattern Analysis

Multivariate pattern analysis (MVPA) is an increasingly popular method of analyzing functional magnetic resonance imaging (fMRI) data1-4. Typically, the method is used to identify a subject's perceptual experience from neural activity in certain regions of the brain. For instance, it has been employed to predict the orientation of visual gratings a subject perceives from activity in early visual cortices5 or, analogously, the content of speech from activity in early auditory cortices6.
Here, we present an extension of the classical MVPA paradigm, according to which perceptual stimuli are not predicted within, but across sensory systems. Specifically, the method we describe addresses the question of whether stimuli that evoke memory associations in modalities other than the one through which they are presented induce content-specific activity patterns in the sensory cortices of those other modalities. For instance, seeing a muted video clip of a glass vase shattering on the ground automatically triggers in most observers an auditory image of the associated sound; is the experience of this image in the "mind's ear" correlated with a specific neural activity pattern in early auditory cortices? Furthermore, is this activity pattern distinct from the pattern that could be observed if the subject were, instead, watching a video clip of a howling dog?
In two previous studies7,8, we were able to predict sound- and touch-implying video clips based on neural activity in early auditory and somatosensory cortices, respectively. Our results are in line with a neuroarchitectural framework proposed by Damasio9,10, according to which the experience of mental images that are based on memories - such as hearing the shattering sound of a vase in the "mind's ear" upon seeing the corresponding video clip - is supported by the re-construction of content-specific neural activity patterns in early sensory cortices.

Classical multivariate pattern analysis predicts sensory stimuli a subject perceives from neural activity in the corresponding cortices (e.g. visual stimuli from activity in visual cortex). Here, we apply pattern analysis cross-modally and show that sound- and touch-implying visual stimuli can be predicted from activity in auditory and somatosensory cortices, respectively.

Multivariate pattern analysis (MVPA) is an increasingly popular method of analyzing functional magnetic resonance imaging (fMRI) data1-4. Typically, the ...

Extracting Visual Evoked Potentials from EEG Data Recorded During fMRI-guided Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) is an effective method for establishing a causal link between a cortical area and cognitive/neurophysiological effects. Specifically, by creating a transient interference with the normal activity of a target region and measuring changes in an electrophysiological signal, we can establish a causal link between the stimulated brain area or network and the electrophysiological signal that we record. If target brain areas are functionally defined with prior fMRI scan, TMS could be used to link the fMRI activations with evoked potentials recorded. However, conducting such experiments presents significant technical challenges given the high amplitude artifacts introduced into the EEG signal by the magnetic pulse, and the difficulty to successfully target areas that were functionally defined by fMRI. Here we describe a methodology for combining these three common tools: TMS, EEG, and fMRI. We explain how to guide the stimulator&#39;s coil to the desired target area using anatomical or functional MRI data, how to record EEG during concurrent TMS, how to design an ERP study suitable for EEG-TMS combination and how to extract reliable ERP from the recorded data. We will provide representative results from a previously published study, in which fMRI-guided TMS was used concurrently with EEG to show that the face-selective N1 and the body-selective N1 component of the ERP are associated with distinct neural networks in extrastriate cortex. This method allows us to combine the high spatial resolution of fMRI with the high temporal resolution of TMS and EEG and therefore obtain a comprehensive understanding of the neural basis of various cognitive processes.

This paper describes a method for collecting and analyzing electroencephalography (EEG) data during concurrent transcranial magnetic stimulation (TMS) guided by activations revealed with functional magnetic resonance imaging (fMRI). A method for TMS artifact removal and extraction of event related potentials is described as well as considerations in paradigm design and experimental setup.

Transcranial Magnetic Stimulation (TMS) is an effective method for establishing a causal link between a cortical area and cognitive/neurophysiological ...

A Large Lateral Craniotomy Procedure for Mesoscale Wide-field Optical Imaging of Brain Activity

The craniotomy is a commonly performed procedure to expose the brain for in vivo experiments. In mouse research, most labs utilize a small craniotomy, typically 3 mm x 3 mm. This protocol introduces a method for creating a substantially larger 7 mm x 6 mm cranial window exposing most of a cerebral hemisphere over the mouse temporal and parietal cortices (e.g., bregma 2.5 - 4.5 mm, lateral 0 - 6 mm). To perform this surgery, the head must be tilted approximately 30&#176; and much of the temporal muscle must be retracted. Due to the large amount of bone removal, this procedure is intended only for acute experiments with the animal anesthetized throughout the surgery and experiment.
The main advantage of this innovative large lateral cranial window is to provide simultaneous access to both medial and lateral areas of the cortex. This large unilateral cranial window can be used to study the neural dynamics between cells, as well as between different cortical areas by combining multi-electrode electrophysiological recordings, imaging of neuronal activity (e.g., intrinsic or extrinsic imaging), and optogenetic stimulation. Additionally, this large craniotomy also exposes a large area of cortical blood vessels, allowing for direct manipulation of the lateral cortical vasculature.

This protocol presents a method for creating a large unilateral craniotomy over the temporal and parietal regions of the mouse cerebral cortex. This is especially useful for real time imaging over an expansive area of a cortical hemisphere.

The craniotomy is a commonly performed procedure to expose the brain for in vivo experiments. In mouse research, most labs utilize a small craniotomy, ...

Simultaneous Recording of Electroretinography and Visual Evoked Potentials in Anesthetized Rats

The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the electrical responses of the retina to light stimulation, while the VEP measures the corresponding functional integrity of the visual pathways from the retina to the primary visual cortex following the same light event. The ERG waveform can be broken down into components that reflect responses from different retinal neuronal and glial cell classes. The early components of the VEP waveform represent the integrity of the optic nerve and higher cortical centers. These recordings can be conducted in isolation or together, depending on the application. The methodology described in this paper allows simultaneous assessment of retinal and cortical visual evoked electrophysiology from both eyes and both hemispheres. This is a useful way to more comprehensively assess retinal function and the upstream effects that changes in retinal function can have on visual evoked cortical function.

This protocol describes simultaneous measurement of electroretinogram and visual evoked potentials in anesthetized rats.

The electroretinogram (ERG) and visual evoked potential (VEP) are commonly used to assess the integrity of the visual pathway. The ERG measures the ...

A Multimodal Imaging- and Stimulation-based Method of Evaluating Connectivity-related Brain Excitability in Patients with Epilepsy

Resting-state functional connectivity MRI (rs-fcMRI) is a technique that identifies connectivity between different brain regions based on correlations over time in the blood-oxygenation level dependent signal. rs-fcMRI has been applied extensively to identify abnormalities in brain connectivity in different neurologic and psychiatric diseases. However, the relationship among rs-fcMRI connectivity abnormalities, brain electrophysiology and disease state is unknown, in part because the causal significance of alterations in functional connectivity in disease pathophysiology has not been established. Transcranial Magnetic Stimulation (TMS) is a technique that uses electromagnetic induction to noninvasively produce focal changes in cortical activity. When combined with electroencephalography (EEG), TMS can be used to assess the brain's response to external perturbations. Here we provide a protocol for combining rs-fcMRI, TMS and EEG to assess the physiologic significance of alterations in functional connectivity in patients with neuropsychiatric disease. We provide representative results from a previously published study in which rs-fcMRI was used to identify regions with abnormal connectivity in patients with epilepsy due to a malformation of cortical development, periventricular nodular heterotopia (PNH). Stimulation in patients with epilepsy resulted in abnormal TMS-evoked EEG activity relative to stimulation of the same sites in matched healthy control patients, with an abnormal increase in the late component of the TMS-evoked potential, consistent with cortical hyperexcitability. This abnormality was specific to regions with abnormal resting-state functional connectivity. Electrical source analysis in a subject with previously recorded seizures demonstrated that the origin of the abnormal TMS-evoked activity co-localized with the seizure-onset zone, suggesting the presence of an epileptogenic circuit. These results demonstrate how rs-fcMRI, TMS and EEG can be utilized together to identify and understand the physiological significance of abnormal brain connectivity in human diseases.

Resting-state functional-connectivity MRI has identified abnormalities in patients with a wide range of neuropsychiatric disorders, including epilepsy due to malformations of cortical development. Transcranial Magnetic Stimulation in combination with EEG can demonstrate that patients with epilepsy have cortical hyperexcitability in regions with abnormal connectivity.

Resting-state functional connectivity MRI (rs-fcMRI) is a technique that identifies connectivity between different brain regions based on correlations ...

Medicine

Topographical EEG Recordings of Visual Evoked Potentials in Mice using Multichannel Thin-film Electrodes

Visual evoked potentials (VEP) allow the characterization of visual function in preclinical mouse models. Various methods exist to measure VEPs in mice, from non-invasive EEG, subcutaneous single-electrodes, and ECoG to fully invasive intracortical multichannel visual cortex recordings. It can be useful to acquire a global, topographical EEG-level characterization of visual responses previous to local intracortical microelectrode measurements in acute experimental settings. For example, one use case is&#160;to assess global cross-modal changes in VEP topography in deafness models before studying its effects on a local intracortical level. Multichannel epicranial EEG is a robust method to acquire such an overview measure of cortical visual activity.&#160;Multichannel epicranial EEG provides comparable results through a standardized, consistent approach to, for example, identify cross-modal, pathological, or age-related changes in cortical visual function. The current study presents a method to obtain the topographical distribution of flash-evoked VEPs with a 32-channel thin-film EEG electrode array in anesthetized mice. Combined with analysis in the time and frequency domain, this approach allows fast characterization and screening of the topography and basic visual properties of mouse cortical visual function, which can be combined with various acute experimental settings.

The present protocol describes a simple procedure to acquire and analyze the topography of epicranial visual evoked potentials with 32-multichannel thin-film electrodes in the mouse.

Visual evoked potentials (VEP) allow the characterization of visual function in preclinical mouse models. Various methods exist to measure VEPs in mice, ...

Advancing Visual Cortex Mapping for Enhanced Evaluation of Vision Disorders

Functional Magnetic Resonance Imaging (fMRI) of the Visual Cortex with Wide-View Retinotopic Stimulation

High-resolution retinotopic blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) with a wide-view presentation can be used to functionally map the peripheral and central visual cortex. This method for measuring functional changes of the visual brain allows for functional mapping of the occipital lobe, stimulating &gt;100&#176; (&plusmn;50&#176;) or more of the visual field, compared to standard fMRI visual presentation setups which usually cover &lt;30&#176; of the visual field. A simple wide-view stimulation system for BOLD fMRI can be set up using common MR-compatible projectors by placing a large mirror or screen close to the subject's face and using only the posterior half of a standard head coil to provide a wide-viewing angle without obstructing their vision. The wide-view retinotopic fMRI map can then be imaged using various retinotopic stimulation paradigms, and the data can be analyzed to determine the functional activity of visual cortical regions corresponding to central and peripheral vision. This method provides a practical, easy-to-implement visual presentation system that can be used to evaluate changes in the peripheral and central visual cortex due to eye diseases such as glaucoma and the vision loss that may accompany them.

Author Spotlight: Insights into Visual Cortex Research Through Wide-View fMRI Mapping 

We have developed techniques for mapping the visual cortex function utilizing more of the visual field than is commonly used. This approach has the potential to enhance the evaluation of vision disorders and eye diseases.

High-resolution retinotopic blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) with a wide-view presentation can be ...

Integrating MEG and HD-EEG in Pediatric Epilepsy Localization

Electromagnetic Source Imaging in Presurgical Evaluation of Children with Drug-Resistant Epilepsy

For children with drug-resistant epilepsy (DRE), seizure freedom relies on the delineation and resection (or ablation/disconnection) of the epileptogenic zone (EZ) while preserving the eloquent brain areas. The development of a reliable and noninvasive localization method that provides clinically useful information for the localization of the EZ is, therefore, crucial to achieving successful surgical outcomes. Electric and magnetic source imaging (ESI and MSI) have been increasingly utilized in the presurgical evaluation of these patients showing promising findings in the delineation of epileptogenic as well as eloquent brain areas. Moreover, the combination of ESI and MSI into a single solution, namely electromagnetic source imaging (EMSI), performed on simultaneous high-density electroencephalography (HD-EEG) and magnetoencephalography (MEG) recordings has shown higher source localization accuracy than either modality alone. Despite these encouraging findings, such techniques are performed in only a few tertiary epilepsy centers, are rarely recorded simultaneously, and are underutilized in pediatric cohorts. This study illustrates the experimental setup for recording simultaneous MEG and HD-EEG data as well as the methodological framework for analyzing these data aiming to localize the irritative zone, the seizure onset zone, and eloquent brain areas in children with DRE. More specifically, the experimental setups are presented for (i) recording and localizing interictal and ictal epileptiform activity during sleep and (ii) recording visual-, motor-, auditory-, and somatosensory-evoked responses and mapping relevant eloquent brain areas (i.e., visual, motor, auditory, and somatosensory) during visuomotor task, as well as auditory and somatosensory stimulations. Detailed steps of the data analysis pipeline are further presented for performing EMSI as well as individual ESI and MSI using equivalent current dipole (ECD) and dynamic statistical parametric mapping (dSPM).

Author Spotlight: Advancing Pediatric Epilepsy Surgery in Children Through Novel Biomarkers and Enhanced Localization

Magnetoencephalography (MEG) and high-density electroencephalography (HD-EEG) are rarely recorded simultaneously, although they yield confirmatory and complementary information. Here, we illustrate the experimental setup for recording simultaneous MEG and HD-EEG and the methodology for analyzing these data aiming to localize epileptogenic and eloquent brain areas in children with drug-resistant epilepsy.

For children with drug-resistant epilepsy (DRE), seizure freedom relies on the delineation and resection (or ablation/disconnection) of the epileptogenic ...