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This Article Full Text Full Text (PDF) All Versions of this Article: 102/4/2131    most recent 91319.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Capaday, C. Articles by Gingras, D. PubMed PubMed Citation Articles by Capaday, C. Articles by Gingras, D.

RESEARCH-ARTICLE

On the Nature of the Intrinsic Connectivity of the Cat Motor Cortex: Evidence for a Recurrent Neural Network Topology

¹Brain and Movement Laboratory, Dept. of Electrical Engineering, Division of Biomedical Engineering, Danish Technical University, Lyngby, Denmark; ²Cellular Neuroscience, Division of Neuroscience, School of Medicine, University of Birmingham, Vincent Drive, Edgbaston, Birmingham, United Kingdom; ³Neurophysique et Physiologie du Système Moteur, Paris, France; and ⁴Department of Electrical Engineering, Université de Sherbrooke, Sherbrooke, Quebec, Canada

Submitted 15 December 2008; accepted in final form 15 July 2009

ABSTRACT

The details and functional significance of the intrinsic horizontal connections between neurons in the motor cortex (MCx) remain to be clarified. To further elucidate the nature of this intracortical connectivity pattern, experiments were done on the MCx of three cats. The anterograde tracer biocytin was ejected iontophoretically in layers II, III, and V. Some 30–50 neurons within a radius of 250 µm were thus stained. The functional output of the motor cortical point at which biocytin was injected, and of the surrounding points, was identified by microstimulation and electromyographic recordings. The axonal arborizations of the stained neurons were traced under camera lucida. The axon collaterals were extensive, reaching distances of 7 mm from the injection site. More importantly, the axonal branches were studded all along their course with boutons. The vast majority of boutons formed synaptic contacts on the target cells as identified by electron microscopy. The majority of these boutons made asymmetric (type I, excitatory) synapses mainly on dendritic spines. The bouton density decreased approximately monotonically with distance from the center of the injection. Cluster analysis, lagged covariance analysis, and eigenvalue decomposition showed the bouton distribution map to be unimodal. Superposition of the synaptic bouton distribution map and the motor output map revealed that motor cortical neurons don't make point-to-point connections but rather bind together the representations of a variety of muscles within a large neighborhood. This recurrent-network type connectivity strongly supports the hypothesis that the MCx controls the musculature in an integrated manner.