CENTER FOR RESEARCH IN
COGNITION & NEUROSCIENCES/ConnexConnex

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Humans operate in a dynamic and uncertain world; sudden changes in an object’s position require rapid changes in motor control. Previous research in humans has shown that on-going visually-guided actions can be altered at latencies that approach minimal afferent and efferent conduction delays. The contribution of such a fast visuomotor system to overall motor control has long been recognized, but fundamental questions remain about the underlying neural substrates, and about the comparative contribution of cortical versus subcortical pathways.
My talk will focus on what we term the “express visuomotor response”, which are brief bursts of muscle recruitment that appear on upper-limb muscles in humans in less than 100 ms, and in less than 65 ms in non-human primates. Such remarkably short latencies limit the opportunity for extensive cortical processing, leading to the hypothesis that express visuomotor responses arise via tecto-reticulo-spinal signalling through the superior colliculus. Ongoing neurophysiological experiments establish that visually-related reaching signals arise within ~50 ms in the movement related layers of the superior colliculus, preceding express visuomotor responses, but within ~70 ms in premotor and motor cortex, following express visuomotor responses. These findings resonate with recent results showing that express visuomotor responses persist in Parkinson’s Disease, despite degradation of signals related to voluntary reaching. In the final part of my talk, I will discuss recent results showing that express visuomotor responses persist even for visual targets flashed during a high-velocity saccadic eye movement, even though such peri-saccadic targets are often not subjectively perceived. Overall, our findings suggest that a subcortical tecto-reticulo-spinal circuit, which itself can be primed by cortical inputs, distributes the earliest visuomotor response that can be shared across multiple body effectors. Activation of this circuit can be selectively spared in the context of neurodegeneration, and can also be teased apart from those circuits leading to subjective perception of visual event in the world.