Abstract
SummaryThe neural circuits underlying goal-directed sensorimotor transformations in the mammalian brain are incompletely understood. Here, we compared the role of primary tongue-jaw motor cortex (tjM1) and primary whisker sensory cortex (wS1) in head-restrained mice trained to lick a reward spout in response to whisker deflection. Two-photon microscopy combined with microprisms allowed imaging of neuronal network activity across cortical layers in transgenic mice expressing a genetically encoded calcium indicator. Early-phase activity in wS1 encoded the whisker sensory stimulus and was necessary for detection of whisker stimuli. Activity in tjM1 encoded licking direction during task execution and was necessary for contralateral licking. Pre-stimulus activity in tjM1, but not wS1, was predictive of lick direction and contributed causally to small preparatory jaw movements. Our data reveal a shift in coding scheme from wS1 to tjM1, consistent with the hypothesis that these areas represent cortical start and end points for this goal-directed sensorimotor transformation.
Highlights
Animals can learn to transform sensory input into motor output in order to obtain rewards
Identification of Tongue-Jaw Primary Motor Cortex Licking requires jaw and tongue muscles to be orchestrated in a reliable and precise way under the control of brain stem nuclei, which act as central pattern generators (Travers et al, 1997)
In a transgenic mouse line expressing channelrhodopsin-2 in excitatory cortical neurons (Arenkiel et al, 2007), different locations of the dorsal cortex were focally stimulated using a blue laser while facial movements were filmed with a high-speed camera to track C2 whisker movement and jaw opening (Figures 1A and S1A; STAR Methods)
Summary
Animals can learn to transform sensory input into motor output in order to obtain rewards. Different areas of neocortex are specialized for distinct functions, with some being more important for sensory processing and others being more involved in controlling movement. An essential step toward mechanistic understanding of goal-directed sensorimotor transformations is to identify where and how relevant sensory and motor information is represented within cortex during task performance. Causal contributions of neuronal activity within primary sensory cortices have been ascribed in various goal-directed sensorimotor transformations (Jaramillo and Zador, 2011; Resulaj et al, 2018). Neuronal activity in wS1 has been shown to be involved in whisker-based decision-making tasks (Guo et al, 2014; Miyashita and Feldman, 2013; Sachidhanandam et al, 2013; Yang et al, 2016), providing a well-defined starting point for cortical processing of whisker-related information
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