The role of motor and environmental visual rhythms in structuring auditory cortical excitability

One of the ways we perceive our external world is through the process of active sensing in which biological sensors (e.g. fingers and eyes) sample the environment utilizing mostly rhythmic motor routines. Previous studies indicate that these motor sampling patterns modulate neuronal excitability in sensory brain regions by entraining brain rhythms, a process termed motor-initiated entrainment. Additionally, rhythms of the external environment, that are independent of internal motor commands, are also capable of entraining rhythmic brain activity. The goal of our study was twofold. First, we aimed to investigate the properties of motor-initiated entrainment in the auditory system using the most prominent motor sampling pattern in primates, eye movements. Second, we wanted to determine whether/how motor-initiated entrainment by eye movements interacts with visual environmental entrainment. By examining laminar profiles of neuronal ensemble activity in the primary auditory cortex of non-human primates, we found that while motor-initiated entrainment has a suppressive, visual environmental entrainment has an enhancive effect. We also found that the two processes are temporally coupled during free viewing, and their temporal relationship ensures that their effect on neuronal ensemble excitability is complementary rather than interfering. Taken together, our results provide strong evidence that motor and sensory systems continuously interact in orchestrating the brains rhythmic context for the optimal sampling of our multisensory environment.