Abstract
On a daily basis, we perform a variety of perceptual tasks that depend on the precise encoding of sensory information. Our performance on these tasks is modulated by the internal state of the brain with respect to ongoing fluctuations in arousal, motivation and effort. Several studies have shown that signals related to these processes are embedded in the population activity of cortical neurons. For example, recent work identified a pattern of neural activity (termed "slow drift") in macaque visual and prefrontal cortex that is correlated with: 1) performance on a range of behavioral tasks; and 2) metrics related to the action of the eyes e.g., pupil size, microsaccade rate and saccade velocity. This motivated us to ask if slow drift is present in subcortical regions that have been implicated in oculomotor control. To this end, we recorded from populations of neurons in the superior colliculus (SC) and prefrontal cortex (PFC) of two monkeys while they performed a memory-guided saccade task. Using dimensionality reduction, we identified a pattern of neural activity in the SC that was strongly correlated with slow drift in the PFC. Furthermore, we found that slow drift in the SC was associated with a constellation of eye metrics including pupil size, microsaccade rate and saccade velocity. These findings are important for at least two reasons. Firstly, they highlight the brain-wide nature of fluctuations in arousal and demonstrate their presence in subcortical regions linked to gaze control. Secondly, they support a growing body of research suggesting that the action of the eyes, both when they move and during periods of steady fixation, can provide a window to internal states of the brain.