PhD defence P. (Peipei) Zhai

Below is a brief summary of the dissertation:

This dissertation investigates how the cerebellar cortex and its downstream pathways control bilateral whisker movements and represent motor signals. By combining anatomical, physiological, optogenetic, and genetic approaches, it uncovers how distinct cerebellar regions contribute to symmetric and asymmetric whisker control and how neural activity patterns encode movement features.

Chapter 1 provides an overview of cerebellar and downstream circuitry in whisker control. Chapter 2 reveals that asymmetric whisker movements are associated with climbing fiber activity in medial Crus2 Purkinje cells (PCs), while symmetric movements involve medial Crus1 and lateral Crus2, likely reflecting differences in projection targets. Chapter 3 shows that optogenetic excitation of PCs in different cerebellar regions induces distinct whisker patterns, with medial PML producing the earliest and longest rhythmic whisking. PC activity preferentially encodes velocity rather than position, suggesting that medial PML may form a more direct pathway to premotor or motor neurons. Chapter 4 demonstrates that multiple premotor nuclei can drive specific bilateral whisker movements, with patterns that overlap those induced by PCs, implying shared decoding mechanisms. Chapter 5 identifies an 8 Hz resonant frequency in PCs as critical for generating rhythmic whisking.

Overall, the findings show that motor representations are widely distributed throughout the cerebellar cortex. PC climbing fiber signals relate to symmetry control, while simple spike activity encodes velocity, with both dependent on PC location.