Cortical networks for visual reaching: intrinsic frontal lobe connectivity.

The anatomical substrates of reaching to visual targets were studied in monkeys (Macaca nemestrina) by combining behavioural neurophysiology and neuroanatomy. An instructed-delay reaching task was used to characterize the arm-related regions of the dorsolateral frontal cortex. This task revealed gradients of signal-, set- movement- and position-related activity along the rostrocaudal extent of the frontal lobe. The frontal mesial projections to these physiologically defined gradients were studied through anatomical methods based on the retrograde transport of distinguishable tracers. The tangential distribution of the cells of origin of these projections displayed a gradient-like arrangement similar to that defined physiologically in their terminal territory. These mesial projections to the dorsolateral frontal cortex may therefore be considered part of a cortical network wherein connections make only a limited contribution to the integration of different sources of information for the control of reaching movements. Further combination of such information must occur within each given cortical region by intrinsic local connections.