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The Journal of Neurophysiology Vol. 84 No. 5 November 2000, pp. 2582-2594
Copyright ©2000 by the American Physiological Society
Center for Neurobiology and Behavior, Columbia University; and the New York State Psychiatric Institute, New York, New York 10032
Chakrabarty, Samit and
John H. Martin.
Postnatal Development of the Motor Representation in Primary
Motor Cortex. J. Neurophysiol. 84: 2582-2594, 2000. The purpose of this study was to examine when the
muscles and joints of the forelimb become represented in primary motor
cortex (M1) during postnatal life and how local representation patterns change. We examined these questions in cats that were anesthetized (45-90 days, n = 14; adults, n = 3)
and awake (n = 4; 52-86 days). We used intracortical
microstimulation (45 ms duration train, 330 Hz, 0.2-ms balanced
biphasic pulses, with a leading cathodic pulse; up to 100 µA). In
young animals (less than day 70), we also used stimulus
trains and pulses that could produce greater temporal summation (up to
200-ms train duration, down to 143-Hz stimulus frequency, up to 0.8-ms
pulse width). Anesthetized animals were areflexic, and muscle tone was
similar to that of the awake cats (i.e., relaxed, not weight or load
bearing, with minimal resistance to passive stretch). We monitored the
kinematic effects of microstimulation and changes in electromyographic
(EMG) activity in forelimb muscles. There was an age-dependent
reduction in the number of sites where microstimulation did not produce
a motor effect (i.e., ineffective sites), from 95% in animals younger than 60 days to 33% between 81 and 90 days. In adults, 24% of sites
were ineffective. Median current thresholds for evoking movements
dropped from 79 µA in animals younger than day 60 to 38 and 28 µA in day 81-90 animals and adults, respectively.
There was a proximal-to-distal development of the somatotopic
organization of the motor map. Stimulation at the majority of sites in
animals younger than day 71 produced shoulder and elbow
movement. Wrist sites were first present by day 71, and
digit sites by day 81. Sites at which multiple responses
were evoked, between 1.0 and 1.5 times threshold, were present after
day 71, and increased with age. A higher percentage of
distal joints were co-represented with other joints, rather than being
represented alone. We found that effective sites initially were
scattered and new sites representing proximal and distal joints filled
in the gaps between effective sites. During most of the period
examined, development of the caudal M1 subregion lagged that of the
rostral subregion (percent of effective sites; threshold currents),
although these differences were minimal or absent in adults. Our
results show that the M1 motor representation is absent at day
45 and, during the subsequent month, the motor map is constructed
by progressively representing more distal forelimb joints.
This article has been cited by other articles:
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  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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K. M. Friel and J. H. Martin Bilateral Activity-Dependent Interactions in the Developing Corticospinal System J. Neurosci., October 10, 2007; 27(41): 11083 - 11090. [Abstract] [Full Text] [PDF]
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 K. M. Friel, T. Drew, and J. H. Martin Differential Activity-Dependent Development of Corticospinal Control of Movement and Final Limb Position During Visually Guided Locomotion J Neurophysiol, May 1, 2007; 97(5): 3396 - 3406. [Abstract] [Full Text] [PDF]
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S. Chakrabarty and J. H. Martin Motor But Not Sensory Representation in Motor Cortex Depends on Postsynaptic Activity During Development and in Maturity J Neurophysiol, November 1, 2005; 94(5): 3192 - 3198. [Abstract] [Full Text] [PDF]
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 M.-H. Monfils, E. J. Plautz, and J. A. Kleim In Search of the Motor Engram: Motor Map Plasticity as a Mechanism for Encoding Motor Experience Neuroscientist, October 1, 2005; 11(5): 471 - 483. [Abstract] [PDF]
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J. H. Martin, D. Engber, and Z. Meng Effect of Forelimb Use on Postnatal Development of the Forelimb Motor Representation in Primary Motor Cortex of the Cat J Neurophysiol, May 1, 2005; 93(5): 2822 - 2831. [Abstract] [Full Text] [PDF]
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J. H. Martin The Corticospinal System: From Development to Motor Control Neuroscientist, April 1, 2005; 11(2): 161 - 173. [Abstract] [PDF]
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J. H. Martin, M. Choy, S. Pullman, and Z. Meng Corticospinal System Development Depends on Motor Experience J. Neurosci., March 3, 2004; 24(9): 2122 - 2132. [Abstract] [Full Text] [PDF]
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Z. Meng, Q. Li, and J. H. Martin The Transition from Development to Motor Control Function in the Corticospinal System J. Neurosci., January 21, 2004; 24(3): 605 - 614. [Abstract] [Full Text] [PDF]
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Z. Meng and J. H. Martin Postnatal Development of Corticospinal Postsynaptic Action J Neurophysiol, August 1, 2003; 90(2): 683 - 692. [Abstract] [Full Text] [PDF]
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 S. Grossberg and A. Seitz Laminar Development of Receptive Fields, Maps and Columns in Visual Cortex: The Coordinating Role of the Subplate Cereb Cortex, August 1, 2003; 13(8): 852 - 863. [Abstract] [Full Text] [PDF]
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