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

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.