Diversity in Whisking-Related Dynamics of Layer 5 Neurons in the Motor Cortex.

Rodents manipulate their vibrissae to actively interact with their environment. The vibrissa area of the primary motor cortex (vM1) is a central player in orchestrating the rhythmic whisker movement, known as "whisking," and previous in vivo electrophysiological studies have revealed the presence of neurons exhibiting activity modulation related to whisking within vM1. vM1 innervates premotoneurons regulating whisking in the reticular nucleus via corticofugal fibers originating exclusively from pyramidal tract (PT) neurons in Layer 5 (L5), while this layer also contains another pyramidal cell subclass, intratelencephalic (IT) neurons, whose axons remain confined within the telencephalon. However, the potential diversity among these morphological subtypes involved in whisking execution remains largely unexplored. Here, we demonstrate functional heterogeneity among both PT and IT neurons in the execution of whisker movement. Juxtacellular recording within L5 of vM1 in head-fixed, awake male mice during self-initiated whisking, followed by post hoc immunohistochemistry, revealed that firing activity in a substantial proportion of neurons was significantly correlated with parameters of whisker movement, such as whisking amplitude and midpoint. Among these, approximately half were activated during whisking, while the rest preferred nonwhisking periods, with these modulation patterns corresponding to their baseline firing properties at rest. Although both types of whisking-related neurons were present within PT and IT populations, whisking-related activation was relatively prevalent in PT neurons, whereas nonwhisking preference was more typical of IT cells. Our findings highlight the functional heterogeneity within morphologically defined neuronal subclasses, providing new insights into the intricate cortical mechanisms underlying various rhythmic movements.