Delay-related cerebral activity and motor preparation.

Flexible goal-oriented behavior requires the ability to carry information across temporal delays. This ability is associated with sustained neural firing. In cognitive terms, this ability has often been associated with the maintenance of sensory material online, as during short-term memory tasks, or with the retention of a motor code, as during movement preparation tasks. The general issue addressed in this paper is whether short-term storage of sensory information and preparation of motor responses rely on different anatomical substrates. We used functional magnetic resonance imaging (fMRI) to measure sustained and time-varying delay-related cerebral activity evoked during performance of a delay non-match to sample (DNMS) task, where task contingencies rather than explicit instructions ensured that either sensory or motor representations were used to cross the delay period on each trial. This approach allowed us to distinguish sensory from motor characteristics of delay-related activity evoked by task contingencies, rather than differences in the control of short-term storage driven by verbal instructions. Holding sensory material online evoked both sustained and time-varying delay-related activity in prefrontal regions, whereas movement preparation evoked delay-related responses in precentral areas. Intraparietal cortex was sensitive to the presence of memoranda, but indifferent to the type of information that was retained in memory. Our findings indicate that short-term storage of sensory information and preparation of motor responses rely on partially segregated cerebral circuits. In the frontal lobe, these circuits are organized along a rostro-caudal dimension, corresponding to the sensory or motor nature of the stored material.