Flexible sensitivity to inputs during skilled tongue movements

Abstract

A hallmark of complex goal-directed movement sequences is the ability to rapidly switch motor programs by integrating incoming sensations with action context1,2, yet the underlying neural implementation remains elusive. Here, we demonstrate a network mechanism for flexibly adjusting the sensitivity of ongoing motor execution to external inputs in different sensorimotor contexts. We trained mice to make sequences of licks directed at a moving target. In a random subset of trials, they made "backtracking" licks by abruptly switching motor programs based on tactile feedback. We divided sessions into alternating cued blocks of trials; sensory-driven backtracking was required during one block-type, but not in the other. Targeted optogenetic stimulation of tongue/jaw somatosensory cortical inputs to the tongue premotor (anterolateral motor, or ALM) cortex that were precisely timed to arrive near the motor switching point reliably induced licking movements resembling those in backtracking trials. This effect was more readily induced during blocks with sensory-driven backtracking and was accompanied by larger optically-evoked deviations in neural activity. Population activity patterns could be separated along a latent axis that discriminated between block-types. On single trials, the location of population activity along this axis correlated with the impact of optogenetic stimulation and influenced the speed of sensory-driven motor switching. Our findings provide causal evidence for how external inputs are integrated with internal context signals to achieve flexible motor control.