Analysis of Electrocorticographic Signals

The objectives of this research are to understand how the brain can keep information in mind ("working memory"), and use this information to guide behavior. The two experiments that fall under this study will collect brain signals from epilepsy patients who are having surgery as part of their treatment. More specifically, these signals will be studied from the time while the patient is performing two cognitive tasks.The endpoints are publication of the results from each of the proposed experiments in peer-reviewed journals.

There are 2 separate experiments proposed, both of which use repeated-measures designs.

1: Electrocorticography (ECoG) study of visual working memory. Each trial from the behavioral task will start by presenting subjects with two visual images, one each from two of these three categories: faces, words, and outdoor scenes. They will then be cued as to which one they'll be tested on with a recognition probe, and after the first probe the cuing-probing process is repeated. Patients selected for this study will have depth electrodes implanted in the left medial temporal lobe and/or grids covering left occipital, temporal, and/or parietal cortex, and suitability of a patient's data for the final dataset will require that a minimum of one stimulus category can be decoded from them. (The precise minimum number of trials required cannot be calculated a priori, because this requires knowing the signal-to-noise ratio in a dataset, a property that is highly variable in electrocorticography data.)

2. Electrocorticography of spatial selective attention. Each trial from the behavioral task will start by presenting subjects with a white "+" on a screen, with each arm pointing to a potential target location. During each 92-trial block of trials, only two 180-degree opposing locations will ever be cued, with one arm of the "+" turning yellow and the opposing one turning blue, to indicate with 75% validity the location at which an oriented Gabor patch will appear (5 degrees from fixation; cue color mapping counterbalanced), requiring a speeded "R/L" tilt judgment. Orthogonal to cue-color configuration, half of the trials in each block will begin with presentation of an "x" that will rotate by 45 degrees with an unpredictable lag (.5 sec +/- .3). On these trials, the cue-to-target interval (i.e., from rotation to "+" to color-cue onset) will be 750 msec. On trials that begin with the onset of a "+", cue-to-target interval will vary unpredictably between 650, 750, and 850 msec. Decomposition of alpha-band oscillations (brain waves cycling at roughly 10 times per second) into components associated with each location will be derived by filtering the whole-scalp signal with weights from the inverted encoding model trained to encode the four critical locations.

Eligibility Criteria:
Inclusion Criteria:

* Participants with implanted electrode arrays who are willing to participate and able to cooperate and follow research instructions will be recruited.
* Must be able to read
* Must be able to name objects
* Must be able to articulate thoughts with spoken language

Exclusion Criteria:

* post-operative pain requiring narcotics
* repeated seizures clouding consciousness
* IQ of 85 and below
* post-operative subdural bleeding
* cerebral pathology affecting the cortical regions from which recordings are made
* women who are pregnant, or who think they may be pregnant