STRENGTHENING OF HORIZONTAL CORTICAL CONNECTIONS FOLLOWING SKILL LEARNING

Learning a new motor skill requires an alteration in the spatiotempora l pattern of muscle activation. Motor areas of cerebral neocortex are thought to be involved in this type of learning, possibly by functiona l reorganization of cortical connections. Here we show that skill lear ning is accompanied by changes in the strength of connections within a dult rat primary motor cortex (M1). Rats were trained for three or fiv e days in a skilled reaching task with one forelimb, after which slice s of motor cortex were examined to determine the effect of training on the strength of horizontal intracortical connections in layer II/III. The amplitude of field potentials in the forelimb region contralatera l to the trained limb was significantly increased relative to the oppo site 'untrained' hemisphere. No differences were seen in the hindlimb region. Moreover, the amount of long-term potentiation (LTP) that coul d be induced in trained M1 was less than in controls, suggesting that the effect of training was at least partly due to LTP-like mechanisms. These data represent the first direct evidence that plasticity of int racortical connections is associated with learning a new motor skill.