How does the limbic system assist motor learning? A limbic comparator hypothesis.

This paper offers a new hypothesis about how the limbic system might assist motor learning. It is proposed that interactions of limbic and sensorimotor-related systems are essential for learning what to do in a motor task (appropriate, relevant behavior) and how to do it best (motor skill). Limbic modulations of sensorimotor-related neural centers are envisaged to result from comparisons in various neural centers of converging inputs from the relevance-sensitive amygdala and from corollary, cortically-modulated recipients of amygdaloid information. Such comparisons of relatively 'raw' limbic inputs and their 'processed', corollary forms could be achieved in a side-loop manner resembling that in the cerebellum. This 'limbic comparator' hypothesis was prompted by studies of motor learning that show how monkeys develop skill only after gaining insight into appropriate, task-related behavior, and that inappropriate behavior during transition into the insightful state produces 'error' signals from the anterior cingulate cortex. Known sites of limbic projections that could serve corollary comparisons are examined with regard to their possible influence on motivation, appropriate, task-related behavior and motor skill. Anatomical and functional tests of convergence and comparison in sensorimotor-related neural centers are suggested in order to stimulate investigations of the limbic comparator hypothesis.