Temporal Control Deficits in Murine Models of Huntington's Disease

Timing is a ubiquitous process that underlies a great variety of human activities and depends on highly conserved neuronal circuitry, the cortico-striatal loops. The peak interval (PI) task is an operant task that conditions subjects to initiate and terminate behavioral responses bracketing a fixed interval associated with reinforcement. Performance in this task depends on the efficacy of temporal control processes that coordinate interval encoding and decoding, instrumental response innitiation, cessation and maintenance, and motor control. Here, we used the PI procedure to characterize temporal control in zQ175 knockin (KI) and BAC HD transgenic (Tg) mice generated to model Huntington's Disease (HD), and contrast the result with previously published R6/2 Tg PI data. HD is a progressive neurodegenerative disorder that involves degeneration of the same neural circuits underlying temporal information processing and control of motor output. Our results indicate that temporal control is disrupted in R6/2 Tg and zQ175 KI mice but intact in BAC HD Tg mice. Trial-by-trial analysis of break-run patterns in response rates indicated that shifts in zQ175 KI response curves were driven by significant delays in response initiation and cessation. Similar temporal control deficits were previously reported in HD patients and R6/2 transgenic HD mice. These findings support the use of zQ175 mice in preclinical studies of HD-related cognitive deficits. They provide evidence of a strong homology between the human and rodent neural bases of temporal information processing, temporal response control, and their pathology in neurodegeneration.