Time, Internal Clocks and Movement

Tile ability of all animal to process temporal information has adaptive significance across different temporal ranges. The ability to encode and utilize temporal information allows an animal to predict and anticipate events. However, the lime scales var3.' widely. The predictable event might be based on information that changes over relatively long periods such as a year or a day. or over periods comprising much shorter durations, events that change within a few minutes or milliseconds. Are there a single set of neural mechanisms thai are essential for representing temporal information over these different scales? Despite the facl thai numerous neural sln~clures have been linked to successfid performance on a varieD' of timing tasks, this question has received relalively little allen!ion. In this chapler, we will focus on the role of the cerebellum in a varie .ty of timing tasks. We will review the hypothesis that the cerebellum can be conceptualized as a relatively task-independent tinting mechanism. An important feature of this hypothesis is that the range of the cerebellar tinting s.vslem is assumed to be relatively reslriclcd. Specifically, we assume thai the cerebellum is capable of representing temporal information ranging from a few milliseconds to an upper bound of a few seconds. What remains unclear is whether the cerebellum is involved on tasks spanning longer durations. Cognitive processes such as attention and memor3.' become clearly imporlant here. and indeed, may dominate performance for longer inlervals. The animal literature points !o noncerebellar stn~ctures as playing a crilical role in these tasks and we will provide a brief review of this work. Finally. we will present the preliminary resulls from two experimenls designed to directly test the hypothesis that the cerebeilum's temporal capabilities are limilcd Io rclalivcly shorl durations. 1. Studies with patients with cerebellar lesions Ivry and Keele (1989) assessed the performance of a variety of neurological patients and age-matched control subjects on two tasks that were designed to