Multi-electrode recordings in human lateral occipital cortex

The lateral occipital complex (LOC) is a set of areas in human occipito-temporal cortex responding more to objects as opposed to non-object control stimuli, but the correspondence between LOC and the macaque inferotemporal areas is poorly understood. We had the unique opportunity to implant a 96-channel Utah array in human LOC, in a patient requiring surgery for epilepsy, at MNI coordinates -50 (mediolateral), -77 (anteroposterior), 6 (dorsoventral). An LOC localizing fMRI experiment performed after array extraction showed stronger activations during presentation of non-scrambled versus scrambled objects at the implantation site. Multi-unit (MUA) and local field potential (LFP) activity was recorded on four consecutive days, and the LOC localizer task was presented to the patient on three out of four days (day 1, 2 and 4). During the LOC localizer task, we presented images of stimuli, stimulus-outlines and scrambled controls for both, as in previous fMRI experiments, while monitoring the position of both eyes using an infrared tracker (Iscan). We found significant stimulus-induced gamma (25-150 Hz) responses (shapes compared to baseline) on all channels (n = 95) in all three sessions (permutation test, p <0.01). Moreover, 92 (day 1), 55 (day 2) and 79/96 (day 4) channels showed significant differences in gamma response between scrambled and non-scrambled objects. Receptive field testing showed significant gamma responses during ipsi- and contralateral stimulus presentation on virtually all channels (permutation test, p <0.01). We obtained qualitatively similar results when restricting the analysis to the high-gamma band (80-120 Hz). Furthermore, we measured significant MUA spiking responses during visual stimulation compared to baseline on 19 channels, and significant differences in MUA response between non-scrambled and scrambled stimuli on 9 channels (day 1). MUA latencies were around 175 msec, with a peak response at 200 msec. As a final test, we recorded neural activity during foveal presentation of disparity-defined convex or concave stimuli on a stereoscope during binocular eye movement control. We found an increase in gamma power on 92 channels (permutation test, p