Robert Wurtz – April 12, 2013
Robert H. Wurtz Laboratory of Sensorimotor Research, National Eye Institute, NIH : « Contribution of a corollary discharge circuit to the perception of visual space ».
Friday, April 12, 2013 at 11:30 am
Our ability to perceive a stable visual world in spite of displacements of the visual scene several times per second by our saccadic eye movements is one of the major achievements of our visual system. The brain mechanisms underlying this marvel have been hypothesized at least since the time of Descartes in the 17th century and von Helmholtz in the 19th century to depend upon an internal copy in the brain of the same signals that control eye movements. Such an internal copy, referred to as a corollary discharge or an efference copy, has recently been identified in a neuronal circuit in the monkey brain extending from the saccadic eye movement centers in the brain stem to the prefrontal cortex. While this corollary discharge has been shown to be critical for guiding sequential saccades, it has yet to be shown to contribute to the stable perception of object location across saccades that is critical for our stable perception. Using a behavioral test of perceived visual location developed in human psychophysical experiments, we have attempted to measure the effect of interrupting the corollary discharge circuit on a monkey’s perception of visual location. We have found that inactivation of a relay in the circuit to frontal cortex results in a change in the monkey’s perceived visual location that is consistent with a decrease in the strength of the corollary discharge that should follow inactivation. This provides evidence that that the corollary discharge signal does indeed provide the critical internal information that is used to determine visual location. Furthermore, if this visual localization of objects after the saccade is anticipated before the saccade, as the recordings from frontal and parietal cortex neurons suggest, this localization mechanism might contribute to our continuity of visual perception across saccades. The combination of the human psychophysical observations on visual localization and attention and the emerging knowledge of the corollary discharge brings us closer to understanding the brain mechanisms underlying our stable visual perception.
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