Branching Thalamic Afferents Link Action and Perception

Recent observations of single axons and review of older literature show that axons afferent to the thalamus commonly branch, sending one branch to the thalamus and another to a motor or premotor center of the brain stem. That is, the messages that the thalamus relays to the cerebral cortex can be regarded as copies of motor instructions. This pattern of axonal branching is reviewed, particularly for the somatosensory and the visual pathways. The extent to which this anatomical evidence relates to views that link action to perception is explored. Most pathways going through the thalamus to the cortex are already involved in motor mechanisms. These motor links occur before and during activity in the parallel and hierarchical corticocortical circuitry that currently forms the focus of many studies of perceptual processing.