The ability to accurately determine when to perform actions is a fundamental function of the nervous system and vital to shaping behavioral responses that achieve there intended outcome. Fixed-interval reinforcement schedules require animals to respond following a specified interval duration in order to obtain a reward. When reinforcement trials are interleaved with non-rewarded, or probe, trials during training, animals develop peak press distributions in these omission trials around the reinforced time. This peak press distribution under omission conditions indicates animals can correctly start and stop responding in a manner according to when the reward outcome would be expected. The cortex and striatum have been canonically implicated in action timing and behavioral models have proposed the idea that action behavioral states during motor timing performance could play a role in the pacing of action with respect to time. In this dissertation, I describe a sensorimotor feedback mechanism in which modal cortical activation by action-derived sensory cues is utilized to shape response dynamics in a self-paced fixed-interval timing task. Acute deprivation of the action-cued sensory modality, but not other action-based senses, is sufficient to disrupt timing dynamics in trained animals. Staining for immediate early gene protein expression in animals that performed the motor timing task revealed active populations in a modal cortical region related to pressing. Using an activity-dependent labeling system that exploits the cFos promoter, action-triggered optical activation of these populations via channelrhodopsin, partially rescues the key features of learned action timing behavior under sensory deprivation. Finally, using a viral activity-dependent labeling strategy in combination with the retrograde adeno-associated virus serotype, I demonstrate a role of layer V, striatal-projecting populations in task performance also under a sensory deprived state. These data point toward a feedback component of motor timing control in which modal cortices and the basal ganglia transduce self-generated sensory cues to assist in performing complex motor timing patterns.

The overbite clam (Potamocorbula amurensis) is a major invasive species in the San Francisco Estuary, California, and has been implicated in the decline of pelagic productivity and native fish species. Little is known of its impact on Suisun Marsh, a large brackish tidal region of the estuary. We looked at the abundance and spatial distribution of clams in the marsh, including examining the influence of water quality, using long-term (1988–2015) otter trawl surveys. Temporal trends indicated that overbite clam abundance has been increasing, but adult clams were spatially restricted to a single large slough (Suisun). Clams were absent from most interior channels, limiting their overall effect on the marsh aquatic ecosystem. Abiotic variables, particularly salinity, proved important predictors of overbite clam abundance, although the variables examined alone could not explain overbite clam distributions. We propose that connectivity, detritus loads, and/or predation pressure may work in conjunction with abiotic variables to cause poor survival rates for recruits in interior marsh sites, keeping the distribution limited. Overall results are encouraging for restoration projects in brackish tidal marshes that need to deal with overbite clams.