Thesis Format

Monograph

Responding when time is of the essence: An analysis of signal timing in the macaque superior colliculus during reflexive visually guided reaching

Amirhossein Asadian, The University of Western OntarioFollow

Degree

Master of Science

Program

Neuroscience

Supervisor

Corneil, Brian D.

Abstract

The superior colliculus (SC) is a subcortical structure well known for contributing to saccades and reflexive orienting. SC neurons in primates are also active during arm movements, including those involving voluntary reaching. What is not known is whether SC neurons could contribute to reflexive visually guided reaches. A marker for such reaches is the express visuomotor response (EVR), which is generated on upper limb muscles in monkeys within 65 milliseconds. Here, we recorded the activity of SC neurons while two monkeys performed a task known to produce EVRs. When accounting for efferent delays, our results show that the SC neurons respond early enough to initiate EVRs. Our results show a potential role for the SC in initiating reflexive visually guided reaches and lay the groundwork for performing a comparative analysis of signal timing across cortical and subcortical areas when time is of the essence.

Summary for Lay Audience

Visually guided reaching is a critical aspect of primate behaviour, crucial for interacting with their surroundings. Many studies have explored the role of cortical areas in voluntary, visually directed reaching. Equally important, our brain possesses a remarkable capacity to rapidly transform visual inputs into actions. For instance, recent research has shown that humans can initiate muscle movements toward a target in less than 100 milliseconds after seeing it. We refer to this rapid reaction as “express visuomotor response.” A recent study from our lab shows that these responses can occur even earlier (~65 ms after stimulus onset) in monkeys. This raises questions about whether the cortical areas involved in deliberative reaches can process information quickly enough to produce express visuomotor responses. An alternative hypothesis is that these responses are generated by a subcortical pathway, involving the midbrain superior colliculus. Here, we test this hypothesis directly by recording from the superior colliculus.

We recorded data from the superior colliculus of two macaque monkeys reaching in a task where they had to reach for a moving target. Our findings show that visually related information in this task arrives within ~50 ms into different layers of the superior colliculus, which is early enough to generate express visuomotor responses. Our results set the stage for comparative analysis of signal timing in this task across cortical and subcortical areas, aiming to better understand visual-to-motor transformations when time is of the essence.

Recommended Citation

Asadian, Amirhossein, "Responding when time is of the essence: An analysis of signal timing in the macaque superior colliculus during reflexive visually guided reaching" (2024). Electronic Thesis and Dissertation Repository. 10293.
https://ir.lib.uwo.ca/etd/10293