NEURAL BASES OF INTERNAL TIMERS - A BRIEF OVERVIEW

Internal timers are thought to control information processing in situa tions in which accurate timing of durations is a key aspect of one's b ehavior. As concerns durations on the order of seconds or minutes, a s imple model of a temporal accumulator has been proposed. Considerable behavioral evidence suggests that internal pulses are accumulated from the beginning to the end of the period to be coded. The total accumul ated number of pulses determines the subject's temporal judgment, with a larger number leading to a longer subjective duration. The nature o f the pulses is still an open question, but diverse approaches (such a s pharmacological and neuropsychological studies, or brain imaging met hods) suggest that several cerebral structures subserve critical funct ions in timing brief durations. This set of structures includes fronto striatal loops, the lateral cerebellum, and the supplementary motor ar ea. The question of which particular step of temporal control is subse rved by each structure is currently being investigated.