Oxyopia Abstract

March 14, 2008
Friday, 4:00 PM
489 Minor Hall

Justin Ales, PhD
Post-Doctoral Researcher, Smith-Kettlewell Institute, San Francisco
Host: Stanley Klein

Title

Using the folding fingerprint of visual cortex to disambiguate EEG responses from human V1 and V2

Abstract

Primate neocortex contains many visual areas. Recent techniques such as functional magnetic resonance imaging (fMRI) have had wonderful success identifying many of these areas in the human brain, but have had difficulty revealing the temporal dynamics between visual areas. The electroencephalogram (EEG) provides information with high temporal precision, but has had limited success separating out the signals from individual neighboring cortical areas. Consequently, controversies exist over the temporal dynamics between cortical areas. In order to address this problem we developed a new method to identify the sources of the EEG. Each subjects unique cortical pattern of sulci and gyri along with a visual area's functional retinotopic layout provides a folding fingerprint that predicts specific EEG distributions for stimuli presented in different parts of the visual field. Using this folding fingerprint with a 96 or 192 location stimulus severely constrains the possible solution space making it relatively easy to extract the temporal response of multiple visual areas. The large number of stimuli also provides a means to validate the waveforms by comparing across identical stimuli presented in many different locations. This validation is an important feature not present in most EEG source identification procedures. Using this method our data reveals that both V1 and V2 waveforms have similar onset latencies, and temporal dynamics that can explain previous controversial findings regarding the response latencies of these areas in humans. Our method enables the previously unattainable separation of EEG responses from neighboring brain areas.

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