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Activity-Dependent Plasticity Improves M1 Motor Representation and Corticospinal Tract Connectivity

¹Department of Neuroscience, ²Division of Brain Stimulation and Therapeutic Modulation of the Department of Psychiatry, and ³Departments of Neurological Surgery and Psychiatry, Columbia University, and New York State Psychiatric Institute, New York, New York

Submitted 13 September 2008; accepted in final form 15 December 2008

Abstract

Motor cortex (M1) activity between postnatal weeks 5 and 7 is essential for normal development of the corticospinal tract (CST) and visually guided movements. Unilateral reversible inactivation of M1, by intracortical muscimol infusion, during this period permanently impairs development of the normal dorsoventral distribution of CST terminations and visually guided motor skills. These impairments are abrogated if this M1 inactivation is followed by inactivation of the contralateral, initially active M1, from weeks 7 to 11 (termed alternate inactivation). This later period is when the M1 motor representation normally develops. The purpose of this study was to determine the effects of alternate inactivation on the motor representation of the initially inactivated M1. We used intracortical microstimulation to map the left M1 1 to 2 mo after the end of left M1 muscimol infusion. We compared representations in the unilateral inactivation and alternate inactivation groups. Alternate inactivation converted the sparse proximal M1 motor representation produced by unilateral inactivation to a complete and high-resolution proximal–distal representation. The motor map was restored by week 11, the same age that our present and prior studies demonstrated that alternate inactivation restored CST spinal connectivity. Thus M1 motor map developmental plasticity closely parallels plasticity of CST spinal terminations. After alternate inactivation reestablished CST connections and the motor map, an additional 3 wk was required for motor skill recovery. Since motor map recovery preceded behavioral recovery, our findings suggest that the representation is necessary for recovering motor skills, but additional time, or experience, is needed to learn to take advantage of the restored CST connections and motor map.

This article has been cited by other articles:

				S. Chakrabarty, B. Shulman, and J. H. Martin Activity-Dependent Codevelopment of the Corticospinal System and Target Interneurons in the Cervical Spinal Cord J. Neurosci., July 8, 2009; 29(27): 8816 - 8827. [Abstract] [Full Text] [PDF]

				M. Brus-Ramer, J. B. Carmel, and J. H. Martin Motor Cortex Bilateral Motor Representation Depends on Subcortical and Interhemispheric Interactions J. Neurosci., May 13, 2009; 29(19): 6196 - 6206. [Abstract] [Full Text] [PDF]