We posted a new preprint on bioRxiv titled “Activity in primate visual cortex is minimally driven by spontaneous movements”. In this project, we investigated if spontaneous body movements modulate activity in early visual regions (V1, V2, V3/V3A) of macaque monkeys performing visual tasks and found that neuronal activity in these regions is not driven by movements.
Conventional neuroscience experiments in the past decades required subjects to be in an artificial environment that restricted body movements. However, most species from single-celled organisms like ciliates (see this recording captured by Charles Krebs for 2016 Nikon Small World in Motion competition), to the more complicated organisms like humans make sense of their environments by moving around with their bodies. This disconnect between natural behavior and artificial laboratory setup makes it difficult to understand any modulatory effect of spontaneous natural movements on the brain. With the advancement in machine learning and videography techniques, we are now able to record the spontaneous movements of animals as they perform laboratory tasks and relate these movements to neural activity recorded at fine timescales, teasing apart the contribution of movements from other task-related variables like visual stimuli. Indeed, using such techniques, recent studies reported brainwide neuromodulation due to spontaneous movements in rodents, including the visual cortex. The findings in rodents can have serious implications to neuroscience if this is generalisable across species. For example, neurophysiological investigations of the non-human primate visual system (dating back a few decades) laid the foundation for our understanding of the fundamental neural mechanisms underlying vision. Given that these studies used experimental setups that did not monitor body movements, should we now revisit decades of neurophysiological research on the primate visual system?
Inspired by the work in rodents, we recorded neural activity from early visual areas of macaque monkeys performing visual tasks, and used videography to monitor animal’s movements. We extracted the time-courses of these movements using singular value decomposition, using methodology established by Stringer, Pachitariu and colleagues. Despite being head-fixed, and seated in a primate chair, analysis of videography data showed that our monkeys moved a lot during the experiment, like adjusting their posture, scratching their hands, etc. Using multivariate linear regression methods established here, we quantified the variance explained by movements in the activity recorded by each unit. We found a significant modulation due to movements agreeing with the findings from rodents, and this was true in almost all recorded units. But this was true only during those epochs in a trial where the animals were not fixating at the center of the screen (inter-trial intervals). Strikingly, the modulation due to movements completely disappeared during the fixation epochs. Together, these results and subsequent analyses suggest that spontaneous movements minimally modulate activity in early visual cortex after factoring out the changes in retinal input caused by the movements. Check out the preprint for a detailed description of the methods, and results.
Update: Our abstract based on this work is now accepted for a talk at Cosyne 2023, which will be held at Montreal in early March.