Cerebellar, hippocampal, and striatal time cells

- Striatal 'time cells' are described.
- Hippocampal 'time cells' are described.
- Cerebellar 'time cells' are described.
- Integration of these different types of 'time cells' is provided.

The ability to decipher where one needs to be and when it is most beneficial to be there are fundamental to the success of an organism. Humans along with other animals are able to extract duration and temporal order from external as well as internal stimuli, though lacking a dedicated sensory organ for time. A plethora of studies have focused on dorsal striatal and cerebellar networks as primary timing circuits with medium spiny neurons and Purkinje cells acting as the core temporal integrators within these circuits, respectively. However, recent findings have also made a strong case for the inclusion of the hippocampus with the discovery of hippocampal 'time cells'. The denoted cells are pyramidal cells within the hippocampal CA1 area that exhibit increased firing rates in relation to elapsing durations, independent of the space and distance traveled. Previous behavioral work had implicated the role of the hippocampus in temporal processing, but only as of late has this work been substantiated with direct electrophysiological evidence. We describe the most recent evidence supporting the identification of 'time cells' in the subcortical structures of the striatum, hippocampus, and cerebellum and indicate how these different timing systems might be integrated into a common percept for time.