Time-Place Learning, Circadian Rhythms, and Memory

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Animals tend to associate time of day with places: dogs greet us at our door minutes before our usual arrival time from work; children ask to watch television at the time of their favourite show. My research program seeks to understand how animals, including humans, learn about spatiotemporal regularities and the role of temporal (specifically, circadian) information in learning and memory. To understand how animals learn about events that vary predictably in space and time, I use a paradigm known as Time-Place Learning (TPL). In rats, TPL is demonstrated when rats learn to go to one location in morning sessions and a different location in afternoon sessions for a food reward or to avoid an aversive stimulus. I have also successfully modified this task for use in children. I intend to accomplish three primary goals with this proposed work. First, to understand how oscillators entrained by light, food, and cognitive tasks interact to provide reliable circadian information that can be used in TPL and learning and memory more generally. Second, to characterize similarities and differences between appetitive (used mostly in rats) and aversive (used mostly in mice) versions of TPL tasks. To take advantage of the neuropsychological techniques in both mice and rats, it is imperative that we better understand the similarities and differences between these species and tasks. Third, to use TPL as a method to study the development of children's sense of time of day, separate from verbal ability. The experiments described in this proposal will allow the development of a comprehensive framework outlining the role of circadian information in learning and memory. I hypothesize that temporal information is so important in learning and memory that redundancies have been built into the system so that accurate circadian information is always available. For example, if animals learn that light information is unreliable, they will use constant meal times to keep track of time day. The adverse effects of circadian rhythm disruption on memory are noted in shift workers and those experiencing jet lag. Knowledge of how various oscillators interact and whether the presence of additional oscillators may attenuate the deleterious effects of a disrupted circadian rhythm will be valuable in assisting those with circadian rhythm disruptions. While considerable research has examined animal's use of time of day information, research with humans on this topic is lacking. This is largely due to confounds with vocabulary ability. The study of daily TPL in humans allows an innovative method to study time of day understanding that is independent of temporal vocabulary.