REVIEW ARTICLE: Cortical control of eye and head movements: integration of movements and percepts

Authors


  • 1

    This review is focused on saccadic gaze shifts. For gaze shifts made by smooth pursuits and vergence, see recent reviews by Fukushima et al. (2004b) and Gamlin (2002).

  • 2

    Head contribution to gaze shifts refers to the head displacement between gaze shift onset and gaze shift offset, during which the VOR is inhibited (Roy & Cullen, 2002; Fuchs et al., 2005). The total head displacement additionally includes pre-gaze shift and post-gaze shift head movements that may occur before and after gaze shifts; the VOR remains in action.

  • 3

    In the superior colliculus, it is shown that the current insufficient to elicit saccadic eye movements could sometimes evoke head movements, suggesting the head pathway has a relatively lower activation threshold compared with that of the saccadic eye pathway (Pelisson et al., 2001; Corneil et al., 2002). In contrast, in the eye fields the activation threshold is in general higher for the head than the eyes (Tehovnik & Lee, 1993; Tu & Keating, 2000; Chen & Walton, 2005; Chen, 2006). It remains unclear whether a head-gating mechanism exists downstream from the eye fields.

Dr Lewis Longtang Chen, as above.
E-mail: lochen@utmb.edu

Abstract

The cortical control of eye movements is well known. It remains unclear, however, as to how the eye fields of the frontal lobes generate and coordinate eye and head movements. Here, we review the recent advances in electrical stimulation studies and evaluate relevant models. As electrical stimulation is conducted in head-unrestrained, behaving subjects with the evoked eye and head movements sometimes being indistinguishable from natural gaze shifts, a pertinent question becomes whether these movements are evoked by motor programs or sensory percepts. Recent stimulation studies in the visual cortex and the eye fields of the frontal lobes have begun to bring both possibilities to light. In addition, cognitive variables often interact with behavioral states that can affect movements evoked by stimulation. Identifying and controlling these variables are critical to our understanding of experimental results based on electrically evoked movements. This understanding is needed before one can draw inferences from such results to elucidate the neural mechanisms underlying natural and complex movements.

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