A preparatory cranial potential for saccadic eye movements in macaque monkeys

Response preparation is accomplished by gradual accumulation in neural activity until a threshold is reached. In humans, such a preparatory signal, referred to as the lateralized readiness potential, can be observed in the EEG over sensorimotor cortical areas before execution of a voluntary movement. Although well-described for manual movements, less is known about preparatory EEG potentials for saccadic eye movements in humans and nonhuman primates. Hence, we describe a lateralized readiness potential over the frontolateral cortex in macaque monkeys. Homologous to humans, we observed lateralized electrical potentials ramping before the execution of both rewarded and non-rewarded contralateral saccades. This potential parallels the neural spiking of saccadic movement neurons in the frontal eye field, suggesting that it may offer a non-invasive correlate of intracortical spiking activity. However, unlike neural spiking in the frontal eye field, polarization in frontolateral channels did not distinguish between saccade generation and inhibition. These findings provide new insights into non-invasive electrophysiological signatures of saccadic preparation in nonhuman primates, highlighting the potential of EEG measures to bridge invasive neural recordings and non-invasive studies of eye movement control in humans.