Abstracts

Rationale: The ventral and lateral occipitotemporal cortex, known as the ‘ventral stream', activates in a category specific manner during visual object recognition. Studies of the ventral stream have focused predominantly on the specificity of neural responses to three major categories: faces, places, and common objects. The regional selectivity for each of these categories has been studied using fMRI, but data from electrophysiology is sparse due to the location. Methods: Thirteen patients diagnosed with temporal lobe epilepsy were scheduled for implantation of subdural electrodes (SDEs) for clinical localization of seizure focus sites. Subjects were presented images of faces and places during concurrent collection of electrocorticography (ECoG) from lingual, fusiform, inferior temporal, and parahippocampal gyrii. ECoG data were decomposed into seven frequency bands: delta (0-4Hz), theta (4-8), alpha (813), beta (13-30), low gamma (30-60), mid gamma (60-120) and high gamma (120-240). Percent change was calculated over prestimulus baseline. Results: In all SDEs, power increases in the gamma frequency bands were most strongly locked to task performance. Right hemisphere electrodes showed greater increases in gamma power during face naming tasks than place naming tasks, while left hemisphere SDEs had greater activation during place naming. Further, medial SDEs in the left hemisphere were more active for places while lateral SDEs were more active for faces. Conclusions: These results collaborate findings from similar fMRI studies. However, the temporal resolution and signal-to-noise ratio afforded by SDEs is greater than that of neuroimaging. This allows for validation of current models of lexical access and precise mapping of category specificity in naming.