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The Journal of Neuroscience, October 10, 2007, 27(41):11083-11090; doi:10.1523/JNEUROSCI.2814-07.2007

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Behavioral/Systems/Cognitive
Bilateral Activity-Dependent Interactions in the Developing Corticospinal System

Kathleen M. Friel^1,3 and John H. Martin^1,2,3

Departments of ¹Neuroscience and ²Neurological Surgery and Psychiatry, Columbia University, New York, New York 10032, and ³New York State Psychiatric Institute, New York, New York 10032

Correspondence should be addressed to Dr. John H. Martin, Department of Neuroscience, Columbia University, 1051 Riverside Drive, New York, NY 10032. Email: jm17{at}columbia.edu

Activity-dependent competition between the corticospinal (CS) systems in each hemisphere drives postnatal development of motor skills and stable CS tract connections with contralateral spinal motor circuits. Unilateral restriction of motor cortex (M1) activity during an early postnatal critical period impairs contralateral visually guided movements later in development and in maturity. Silenced M1 develops aberrant connections with the contralateral spinal cord whereas the initially active M1, in the other hemisphere, develops bilateral connections. In this study, we determined whether the aberrant pattern of CS tract terminations and motor impairments produced by early postnatal M1 activity restriction could be abrogated by reducing activity-dependent synaptic competition from the initially active M1 later in development. We first inactivated M1 unilaterally between postnatal weeks 5–7. We next inactivated M1 on the other side from weeks 7–11 (alternate inactivation), to reduce the competitive advantage that this side may have over the initially inactivated side. Alternate inactivation redirected aberrant contralateral CS tract terminations from the initially silenced M1 to their normal spinal territories and reduced the density of aberrant ipsilateral terminations from the initially active side. Normal movement endpoint control during visually guided locomotion was fully restored. This reorganization of CS terminals reveals an unsuspected late plasticity after the critical period for establishing the pattern of CS terminations in the spinal cord. Our findings show that robust bilateral interactions between the developing CS systems on each side are important for achieving balance between contralateral and ipsilateral CS tract connections and visuomotor control.

Key words: voluntary movement; locomotion; visual guidance; spinal cord; motor cortex; activity dependence; cerebral palsy

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Received June 20, 2007; revised July 25, 2007; accepted Aug. 28, 2007.

Correspondence should be addressed to Dr. John H. Martin, Department of Neuroscience, Columbia University, 1051 Riverside Drive, New York, NY 10032. Email: jm17{at}columbia.edu

This article has been cited by other articles:

				I. Salimi, K. M. Friel, and J. H. Martin Pyramidal Tract Stimulation Restores Normal Corticospinal Tract Connections and Visuomotor Skill after Early Postnatal Motor Cortex Activity Blockade J. Neurosci., July 16, 2008; 28(29): 7426 - 7434. [Abstract] [Full Text] [PDF]

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