Local circuit in the motor cortex

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Takeshi Kaneko, Ryong-Ho Cho

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To study cortical motor control, we morphologically and electrophysiologically classified pyramidal neurons of the motor cortex into several types, and examined intra- or juxta-columnar connections of the pyramidal neurons to corticospinal neurons. Of 108 intracellularly labeled pyramidal neurons, 27 neurons were selected for morphological analysis by successful staining of their axonal arborizations and sufficient retrograde labeling of corticospinal neurons. Many varicosities of local axon collaterals of each pyramidal neuron were closely apposed to the dendrites of corticospinal neurons, suggesting the convergent projections of layer II-VI pyramidal neurons to corticospinal neurons. In particular, the axons of a layer IV star-pyramidal neuron showing phasic responses made 2- to 3-fold more contacts to the dendrites of corticospinal neurons than those of a pyramidal neuron in the other layers. The present results suggest that thalamic inputs are conveyed to corticospinal neurons preferentially via layer IV star-pyramidal neurons with phasic response properties.

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