Last Friday (28/06/2019) I gave a seminar at the department of “Medicine and Surgery” at the University of Parma. I presented new data on the “sensory race” of visual information to subcortical structures such as the Superior Colliculus and the Brainstem. This work finally links the well-known behavioural effect of (micro)Saccadic Inhibition and its spatial counterpart with the activity in the Brainstem and in the Colliculus. It was great to be a guest in Parma and exchange new ideas with the various research groups working there. Attached below the abstract of my work.

Pausing the oculomotor system: on the race between subcortical visual bursts at the time of saccade generation

Antimo Buonocore^1,2, Ziad M. Hafed^1,2

Abstract

A hallmark of sensory processing is that inputs can be processed in parallel by diverse, functionally specialized circuits. In the visual system, the same visual input can quasi-simultaneously reach neurons concerned with visual analysis, gaze orienting, and even gaze-orienting inhibition. From a behavioral perspective, such a “sensory race” leads to a paradoxical scenario: within essentially the same time, the same visual input can reach a brain circuit serving rapid orient towards the appearing stimulus (e.g. superior colliculus) or another circuit potently inhibiting orienting towards it (e.g. brainstem premotor nuclei). Our long term goal is to study the mechanisms behind such “sensory races”, especially because they directly impact behavior. For example, even though conventional wisdom states that abrupt visual onsets trigger reflexive orienting, the reality is that they almost always first “interrupt” ongoing behavior. I will first demonstrate this fact through experiments showing that visual onsets inevitably lead to saccadic inhibition, except for a tiny fraction of strategically timed stimuli. For these, the opposite of inhibition occurs, with rapid and systematically modified saccades consistent with “capture” by the stimuli. Motived by a lack of neurophysiological explanations for these effects, I will describe our approach to study two main areas involved in the “sensory race” underlying them. In the superior colliculus, where spatial orienting is implemented, I will show that visually-induced spikes from stimulus onset can still occur during the execution of an ongoing eye movement, modifying the saccade vector in a predictable manner, as if to “capture” it. In the brainstem premotor nuclei, where movement inhibition takes place, I will show that the same stimulus can trigger a strong response, abruptly closing the gate and interrupting the onset of the eye movement. Therefore, we are uncovering a sensory race among subcortical areas with opposing roles, and we are revealing a highly mechanistic depiction of exactly what to expect in terms of either interruption or orienting. The outcome of the race ultimately dictates the spatio-temporal structure of the behavior. This demonstrates how parallel pathways, while being functionally optimized to serve behavior, often reveal interesting race conditions in which apparent “variability” in behavior (e.g. bigger saccades) are simply an emergent property of how the system is organized.

¹Werner Reichardt Centre for Integrative Neuroscience, Tübingen University, Tübingen, BW, 72076, Germany

²Hertie Institute for Clinical Brain Research, Tübingen University, Tübingen, BW, 72076, Germany