Loss of the innate cortical engram for action patterns used in skilled reaching and the development of behavioral compensation following motor cortexlesions in the rat

Damage to the motor cortex of the rat (Rattus norvegicus) impairs skilled m ovements used in reaching For Food with the contralateral forepaw. Neverthe less, there is substantial recovery in success over a two-week postsurgical period. The profile of behavioral recovery is believed to reflect the even tual normalization of behavior, but this idea has not been explicitly exami ned. The present experiments examined postsurgical reaching success and rea ching movements as a function of (1) lesion type, (2) lesion size, (3) lesi on location, (4) depletion of forebrain noradrenaline, and (4) presurgical and postsurgical experience. The results show that at least two separate pr ocesses contribute to recovery in postsurgical performance. The early posts urgical period was characterized by extreme difficulties in making reaching movements. The experiments suggest that this initial impairment was due to the loss of the innate cortical engram that supports the action patterns u sed for skilled movements. Subsequent recovery in reaching success was not due to the reacquisition of normal movements, but was due rather to the use of compensatory movements. The results are discussed in relation to the id ea that true recovery from motor cortex injury will require that damaged ne urons and their connections be rescued or replaced. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.