The representation of voluntary and reflexive fast eye movements in the macaque lateral intraparietal area (LIP)

The macaque lateral intraparietal area (LIP) is known for its role in visually guided saccades as well as in higher cognitive functions. However, its contribution to more basic visuomotor processes remains unclear. Here, we investigated whether neural activity in area LIP is also related to involuntary reflexive eye movements, specifically the fast phases of optokinetic nystagmus (OKN). To address this question, we compared spiking activity and local field potentials (LFPs) in area LIP of two male macaque monkeys during visually guided saccades and during kinematically similar OKN fast phases. Neurons exhibiting robust perisaccadic activation during voluntary saccades showed markedly reduced or no activity around the time of OKN fast phases and were not modulated by fast-phase amplitude or frequency. Using a Generalized Linear Model, we found that during OKN slow phases, area LIP reliably encoded gaze position and the direction of visual motion driving the reflexive eye movement. LFP analyses further revealed that beta-band power differed between voluntary saccades and OKN fast phases, whereas theta-band phase coherence increased following both types of fast eye movements, suggesting distinct local processing but shared post-movement network coordination. Our results reinforce the view of area LIP as a key area for integrating sensory and cognitive signals relevant for goal-directed action rather than a generic oculomotor controller.