Extracellular spike waveform analysis reveals cell type-specific changes in the superior colliculus of fragile X mice

Sensory processing deficits are common in neurodevelopmental disorders (NDDs); however, we lack a full understanding of the circuits impacted. The superior colliculus (SC) is a sensorimotor region that directs complex behaviours, which recent work suggests is adversely impacted in NDDs. However, our understanding of cellular diversity in the SC lags in comparison to other regions, limiting our ability to parse circuit changes in NDDs. A goal of neuroscience has been to elucidate the diversity of neurons in the brain. Analysis of action potential shape in extracellular recordings has revealed subpopulations in several regions, allowing for insights into subtype-specific function in the intact brain. Here, we utilized semi-automated clustering methods to classify neurons in the mouse SC based on features of extracellularly recorded waveforms to identify five putative cell types. Secondary analysis of firing statistics and visual tuning properties supported cluster segregation. Interestingly, the proportions of units assigned to each cluster differed in a mouse model of fragile X syndrome (Fmr1-/y). Furthermore, we observed changes in waveform properties and firing statistics between genotypes in a subtype-specific manner. Taken together, these data add to our understanding of neuronal diversity in the SC and alterations of visual circuit organization and function in NDDs.