Tactile responses in the granule cell layer of cerebellar folium Crus IIa of freely behaving rats

We recorded activity from the granule cell layer (GCL) of cerebellar folium Crus IIa as freely moving rats engaged in a variety of natural behaviors, including grooming, eating, and free tactile exploration. Multiunit respons es in the 1000- 4500 Hz range were found to be strongly correlated with tac tile stimulation of lip and whisker (perioral) regions. These responses occ urred regardless of whether the stimulus was externally or self-generated a nd during both active and passive touch. In contrast, perioral movements th at did not tactually stimulate this region of the face (e. g., chewing) pro duced no detectable increases in GCL activity. In addition, GCL responses w ere not correlated with movement extremes. When rats used their lips active ly for palpation and exploration, the tactile responses in the GCL were not detectably modulated by ongoing jaw movements. However, active palpation a nd exploratory behaviors did result in the largest and most continuous burs ts of GCL activity: responses were on average 10% larger and 50% longer dur ing palpation and exploration than during grooming or passive stimulation. Although activity levels differed between behaviors, the position and spati al extent of the peripheral receptive field was similar over all behaviors that resulted in tactile input. Overall, our data suggest that the 1000- 45 00 Hz multiunit responses in the Crus IIa GCL of awake rats are correlated with tactile input rather than with movement or any movement parameter and that these responses are likely to be of particular importance during the a cquisition of sensory information by perioral structures.