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Abstract:
It is well established that the inferior temporal (IT) cortex of the macaque monkey contains cells that respond selectively to faces. How information about faces is represented and organized at the network level remains largely unknown. Here we simultaneously recorded local field potentials (LFPs) and spiking activity in the IT cortex of two monkeys fixating at realistic human, monkey faces and objects, to investigate the neural representation of these stimulus classes. Our previous results indicate that spike information recorded from single neurons clearly differentiates between these three classes of stimuli. Here we investigate whether LFPs also contain information about these three types of stimuli. From the visual evoked potentials (VEP), we reliably and automatically extracted (in 44/65 sites in monkey M1 and in 20/68 sites in monkey 20) different features that convey time or amplitude information about stimulus class. Specifically, we focused on the timing and amplitude of the so called “N70” (negative deflection after about 70 ms of stimulus presentation), “P100” (positive deflection at about 100 ms) and “N170” (positive deflection at about 170 ms) components of the VEP. We grouped the VEPs into three classes according to the stimulus: humans, monkeys and objects VEPs. We found in both monkeys that the onset time of the face VEPs was significantly faster compared to the object VEPs (ttests, P<0.01) for all three deflections. Moreover, the onset of these deflections was faster for the monkey face VEPs compared to the human face VEPs (ttests, P<0.05). By contrast, the amplitude of these deflections did not systematically vary between stimulus classes. These results suggest that timing information in the LFPs can be used to reliably discriminate between human and monkey face stimuli. Furthermore, activation evoked by monkey faces reaches IT cortex earlier than the one evoked by human faces. These findings suggest a privileged role for processing of own species faces in the macaque brain.
