Movement preparation and motor intention.
This paper addresses the functional anatomy of movement representation. We have used associative visuomotor tasks with instructed delays to elicit motor preparatory activity. We regard such activity, when independent from transient stimulus-locked responses, as a likely candidate for the neural basis of movement representation (M. Jeannerod, The Cognitive Neuroscience of Action. Blackwell, Oxford, 1997). In a first event-related fMRI experiment, we found that preparing to move according to arbitrary visuomotor associations relies not only on parietofrontal circuitry, but also on portions of the posterior superior temporal sulcus. In a separate behavioral experiment, we discarded the hypothesis that such activities were confounded by working memory processes. In a second imaging experiment, we have further defined the relative contributions of these parietal, premotor, and temporal areas to the preparatory process and their involvement in motor representations. We conclude that posterior parietal cortex is interested in evaluating the potential motor significance of sensory stimuli, irrespectively of the likelihood of providing a response ("motor intention"). Conversely, preparatory activity in frontal premotor regions appears to be a function of the probability of a subsequent movement. Finally, on the basis of the present and published data, we suggest that posterior temporal cortex might be involved in the extraction of contextual and intentional cues during goal-oriented behavior.