Heterogeneous effects of cognitive arousal on the contrast response in human visual cortex.

While animal studies have found that arousal states modulate visual responses, direct evidence for effects of arousal on human vision remains limited. Here, we used fMRI to examine effects of cognitive arousal on the gain of contrast response functions (CRFs) in human visual cortex. To measure CRFs, we measured BOLD responses in early visual cortex (V1-V3) while participants (n=20, 14 females and 6 males) viewed stimuli that parametrically varied in contrast. To induce different cognitive arousal states, participants solved auditory arithmetic problems categorized as either Easy (low arousal) or Hard (high arousal). We found surprising diversity in the modulatory effects across individuals: some individuals exhibited enhanced neural response with increased arousal, whereas others exhibited the opposite effect - a decrease in response with increased arousal. The pattern of overall BOLD modulation showed within-individual stability and was correlated with the degree of arousal-driven change in pupil size. Individuals who exhibited larger increases in pupil size with the arousal manipulation tended to show greater arousal-related decreases in visuocortical responses. We speculate that the polarity of the modulatory effect by cognitive arousal may relate to individual differences in cognitive effort expended in the high-difficulty condition, with individuals reaching different points on an underlying non-monotonic function.Significance Statement While animal work suggests that arousal state has a profound impact on visual processing, the effects on human vision remain less understood. Here we assessed the influence of cognitive arousal on the neural gain of visual responses in humans to better characterize the mechanisms by which arousal affects vision. Minimal modulation was observed at the group level, but closer examination revealed substantial variability in modulation across individuals, with some showing enhancement and others exhibiting a decrease in neural modulation of visual responses with high arousal. Changes in pupil size correlated with neural modulation, suggesting a non-linear inverted-U relationship between cognitive arousal and visual processing. These results provide evidence of arousal's differential impact on vision across individuals.