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J Neurophysiol 97: 604-617, 2007. First published November 1, 2006; doi:10.1152/jn.00379.2006
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Interstitial Nucleus of Cajal Encodes Three-Dimensional Head Orientations in Fick-Like Coordinates

¹York Centre for Vision Research, Canadian Institutes of Health Research Group for Action and Perception, Departments of Psychology, Biology and Kinesiology and Health Sciences, York University, Toronto, Ontario, Canada; and ²Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri

Submitted 10 April 2006; accepted in final form 30 October 2006

Two central, related questions in motor control are 1) how the brain represents movement directions of various effectors like the eyes and head and 2) how it constrains their redundant degrees of freedom. The interstitial nucleus of Cajal (INC) integrates velocity commands from the gaze control system into position signals for three-dimensional eye and head posture. It has been shown that the right INC encodes clockwise (CW)-up and CW-down eye and head components, whereas the left INC encodes counterclockwise (CCW)-up and CCW-down components, similar to the sensitivity directions of the vertical semicircular canals. For the eyes, these canal-like coordinates align with Listing’s plane (a behavioral strategy limiting torsion about the gaze axis). By analogy, we predicted that the INC also encodes head orientation in canal-like coordinates, but instead, aligned with the coordinate axes for the Fick strategy (which constrains head torsion). Unilateral stimulation (50 µA, 300 Hz, 200 ms) evoked CW head rotations from the right INC and CCW rotations from the left INC, with variable vertical components. The observed axes of head rotation were consistent with a canal-like coordinate system. Moreover, as predicted, these axes remained fixed in the head, rotating with initial head orientation like the horizontal and torsional axes of a Fick coordinate system. This suggests that the head is ordinarily constrained to zero torsion in Fick coordinates by equally activating CW/CCW populations of neurons in the right/left INC. These data support a simple mechanism for controlling head orientation through the alignment of brain stem neural coordinates with natural behavioral constraints.

This article has been cited by other articles:

				F. Farshadmanesh, E. M. Klier, P. Chang, H. Wang, and J. D. Crawford Three-Dimensional Eye-Head Coordination After Injection of Muscimol Into the Interstitial Nucleus of Cajal (INC) J Neurophysiol, March 1, 2007; 97(3): 2322 - 2338. [Abstract] [Full Text] [PDF]