Kari Hoffman

Enhanced neuronal coherence in the temporal lobe following eye movements

Saccadic eye movements (SEMs) strongly influence visual perception in primates. During visual exploration of the environment (‘active vision’) SEMs produce suppression during saccades and enhancement upon fixation, in early visual areas. The influence of eye movements on neural population dynamics is less well understood, and its influence in higher-order visual areas is unclear. For example, the superior temporal sulcus (uSTS), is critical for perception of faces, objects, and biological motion, and shows frequency-dependent coherence during processing of these visual stimulus categories. Whether visually-evoked responses are modulated by SEMs is unknown. In this study, we examined how SEMs modulate local field potentials (LFPs) in the uSTS of macaque monkeys during a free viewing task with static face and non-face object stimuli. Stimulus-driven eye movements lead to short latency (40 ms) LFP activity mediated by phase concentration (i.e. inter-trial coherence) in uSTS. This response was distinct from the image-evoked response. Furthermore, near-coincident image onsets and fixation onsets – like those that occur in active vision – led to an enhanced image-evoked response through greater phase concentration in the alpha (8-14 Hz), beta (14-30 Hz), and gamma (30-60 Hz) bands. These same frequency bands show spike-phase modulation of single-unit activity. Together, these results demonstrate enhanced neuronal coherence in STS following eye movements, revealing a plausible neural basis for the enhancement of visual processing in active vision.