Loss of the innate cortical engram for action patterns used in skilled reaching and the development of behavioral compensation following motor cortex lesions in the rat
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Abstract
Damage to the motor cortex of the rat (Rattus norvegicus) impairs skilled movements
used in reaching for food with the contralateral forepaw. Nevertheless, there is substantial
recovery in success over a two-week postsurgical period. The profile of behavioral
recovery is believed to reflect the eventual normalization of behavior, but this idea
has not been explicitly examined. The present experiments examined postsurgical reaching
success and reaching movements as a function of (1) lesion type, (2) lesion size,
(3) lesion location, (4) depletion of forebrain noradrenaline, and (4) presurgical
and postsurgical experience. The results show that at least two separate processes
contribute to recovery in postsurgical performance. The early postsurgical 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 used 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 idea that true recovery from motor cortex injury will require that damaged
neurons and their connections be rescued or replaced.