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The Journal of Neuroscience, October 22, 2003, 23(29):9611-9619
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Behavioral/Systems/Cognitive
Firing Properties of Spinal Interneurons during Voluntary Movement. II. Interactions between Spinal Neurons
Yifat Prut2 and
Steve I. Perlmutter1
1Department of Physiology and Biophysics and the Washington National Primate Research Center, University of Washington, Seattle, Washington 98195, and 2The Hebrew University, Hadassah Medical School, Jerusalem 91120, Israel
The relationship between the activity of pairs of simultaneously recorded spinal interneurons (INs) in the cervical enlargement was studied in five monkeys performing voluntary wrist movements. The tendency for INs to exhibit similar response properties and synchronized firing was tested as a function of physical distance between the cells and their correlational linkages with forearm muscles. Nearby INs tended to have more similar torque and direction turning (signal correlation) and more similar response profiles (e.g., tonic vs phasic firing) than INs that were far apart. This suggests that nearby cells receive common synaptic input. In contrast, the trial-to-trial covariation of rate around the mean rate for all trials (noise correlation) was independent of the distance between the neurons. Furthermore, signal and noise correlation were independent, suggesting different underlying mechanisms. Surprisingly, spike-to-spike correlation between INs was relatively infrequent and weak, as measured by cross-correlation histograms. In contrast, single motor units (SMUs) in forearm muscles fired more synchronously, particularly for SMUs in single extensor muscles. Either common drive to INs is too weak to induce synchronized firing, or there is an active decorrelation mechanism within IN networks.
Key words: spinal cord; interneurons; primates; firing pattern; synchronization; motor control
Received March 31, 2003;
revised July 30, 2003;
accepted August 19, 2003.
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