Darlington, T. R. | Search bioRxiv

bioRxiv2019

Mechanisms that allow cortical preparatory activity without inappropriate movement

We reveal a novel mechanism that explains how preparatory activity can evolve in motor-related cortical areas without prematurely inducing movement. The smooth eye movement region of the frontal eye fields (FEFSEM) is a critical node in the neural circuit controlling smooth pursuit eye movement. Preparatory activity evolves in FEFSEM during fixation in parallel with an objective measure of visual-motor gain. We propose that the use of FEFSEM output as a gain signal allows for preparation to progress in the pursuit system without causing movement. We also show that preparatory modulation of firing rate in FEFSEM progresses in a way that predicts movement, providing evidence against the \"movement-null\" space hypothesis of how preparatory activity can progress without movement. Finally, there is partial reorganization of FEFSEM population activity between preparation and movement. We propose that this reorganization allows for a directionally non-specific component of preparatory visual-motor gain enhancement in the pursuit system.

neuroscience↗

bioRxiv2019

The neural basis for response latency in a sensory-motor behavior

We seek a neural circuit explanation for sensory-motor reaction times. We have found evidence that two of three possible mechanisms could contribute to reaction times in smooth pursuit eye movements. In the smooth eye movement region of the frontal eye fields (FEFSEM), an area that causally affects the initiation of smooth pursuit eye movement, neural and behavioral latencies have significant trial-by-trial correlations that can account for 40% to 100% of the variation in behavioral latency. The amplitude of preparatory activity, which represents the motor systems expectations for target motion, shows negative trial-by-trial correlations with behavioral latency and could contribute to the neural computation of reaction time. In contrast, the traditional \"ramp-to-threshold\" model is contradicted by the responses of many, but not all FEFSEM neurons. As evidence of neural processing that determines reaction time, the local field potential in FEFSEM includes a brief wave in the 5-15 Hz frequency range that precedes pursuit initiation and whose phase is correlated with the latency of pursuit in individual trials. We suggest that the latency of the incoming visual motion signals combines with the state of preparatory activity to determine the latency of the transient response that drives eye movement.

neuroscience↗