Electrocorticography of category-selectivity in human ventral temporal cortex: spatial organization, responses to single images, and coupling with fMRI

Abstract

Both functional neuroimaging (fMRI) and electrocorticography (ECoG) research has revealed selective responses to faces, bodyparts, words and places, in human ventral temporal cortex (VTC). However, the precise spatial organization of ECoG selective responses in VTC, as well as the nature of the coupling between functional responses measured with ECoG and fMRI is poorly understood. To address these questions we measured category selectivity to faces, bodyparts, cars, and houses using ECoG and fMRI in six epileptic patients and precisely located ECoG and fMRI responses relative to each subject's cortical surface. Our data indicate a clear spatial organization of ECoG selectivity, where the mid-fusiform sulcus forms an anatomical boundary between regions showing preference to animate vs. inanimate categories. Specifically, ECoG broadband (30-160Hz) responses on the lateral fusiform gyrus and inferotemporal gyrus showed strong selectivity to faces, but responses in the mid fusiform gyrus, collateral suclus and parahippocampal gyrus showed a preference to houses and cars. Strikingly, an independent data set revealed that these preferential responses are reliable and are evident for individual images from these categories. We next compared the distributed pattern of ECoG selectivity with that measured with fMRI, finding significant correlations between the two measurements when the fMRI signal was extracted in the vicinity (3-5mm) of each electrode. The strength of this coupling varied with time and frequency band: early (100-350ms) ECoG responses across all frequency bands were positively coupled with fMRI, while later (>350ms) ECoG responses showed positive correlation with fMRI in the broadband range and negative correlation in low frequencies (4-12Hz). Our data thus reveal a clear spatial organization of ECoG category selectivity in VTC, which is evident even in responses to single images. Finally, the coupling between ECoG and fMRI selectivity in the human VTC depends on the timing and properties of neural response at different frequencies.

Meeting abstract presented at VSS 2013