Chakrabarty S, Friel K M, Martin J H
Department of Neuroscience, Columbia University, New York, NY, USA.
J Neurophysiol. 2009 Mar;101(3):1283-93. doi: 10.1152/jn.91026.2008. Epub 2008 Dec 17.
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.
出生后第5至7周期间，运动皮层（M1）的活动对于皮质脊髓束（CST）的正常发育和视觉引导运动至关重要。在此期间，通过皮质内注入蝇蕈醇使M1单侧可逆性失活，会永久性损害CST终末正常背腹分布的发育以及视觉引导的运动技能。如果在M1失活后，从第7周开始至第11周使对侧最初活跃的M1失活（称为交替失活），这些损害就会消除。后期是M1运动表征正常发育的时期。本研究的目的是确定交替失活对最初失活的M1运动表征的影响。在左侧M1注入蝇蕈醇结束后1至2个月，我们使用皮质内微刺激来绘制左侧M1的图谱。我们比较了单侧失活组和交替失活组的表征。交替失活将单侧失活产生的稀疏近端M1运动表征转变为完整且高分辨率的近端 - 远端表征。到第11周时运动图谱恢复，这与我们目前和先前的研究表明交替失活恢复CST脊髓连接的年龄相同。因此，M1运动图谱的发育可塑性与CST脊髓终末的可塑性密切平行。交替失活重建CST连接和运动图谱后，运动技能恢复还需要额外3周时间。由于运动图谱恢复先于行为恢复，我们的研究结果表明，该表征对于恢复运动技能是必要的，但需要额外的时间或经验来学习利用恢复的CST连接和运动图谱。
