![]() Along this line, the transient pupil dilation response has been observed around the occurrence of perceptual alternation (Einhäuser et al., 2008 Grenzebach et al., 2021 Hupé et al., 2009 Sato et al., 2020). ![]() In other words, if the changes in the tonic arousal level through the LC-NE system involves intrinsic perceptual alternation, the baseline pupil-like arousal should reflect a dynamic neural network change with an intrinsic perceptual shift in bistable perception. Since the connectivity among brain functions is correlated with pupil size via a role in the modulation of neural gain in the LC (Shine et al., 2016), the dynamics of the internal brain state through is expected to reflect the frequency of perceptual alternation. Although relative-phase distributions for perceptual alternations have certain stochastic dynamics approximated to gamma distributions (Logothetis et al., 1996), the relationship between temporal dynamics of tonic NE level change and internal neural network stochastics as a perceptual alternation is still poorly understood. Pharmacologically elevating the tonic NE level in humans increases the intrinsic behavioral variability in perceptual alternations (Pfeffer et al., 2018). Based on the correlation between the changes in pupil size and LC-mediated NE release, several previous studies have reported that the baseline pupil size correlates to various aspects of cognitive and behavioral performance (Aminihajibashi et al., 2020 Eldar et al., 2013 McGinley et al., 2015 Schneider et al., 2016). Furthermore, changes in neuromodulators of the NE level in the brain (i.e., fluctuation of tonic LC activity) are cross-correlated with fluctuation of baseline pupil size as evidenced from animal studies (Aston-Jones & Cohen, 2005 Rajkowski et al., 1993 Reimer et al., 2016). It is well known that the tonic LC activity is related to cognitive task performance in an inverted U-shaped manner (Aston-Jones & Bloom, 1981). The fluctuations in the tonic activity occur in a longer range of timescales than the phasic activity. Corresponding to this, the LC neuron activities are classified into tonic and phasic patterns, which have different timescales of neuron firing. The noradrenergic projection throughout the central nervous system suppresses neurons in most cases, whereas it exceptionally functions to accentuate a novel stimulus (Zerbi et al., 2019). Pupillary changes are thought to reflect changes in neural activity via the LC-NE system, which has been shown to be involved in a broad range of cognitive processes.Ī dynamic neural network change accompanied by a cognitive shift is reconciled by the discharge of noradrenergic LC neurons in a manner of both inhibition or excitement (Bouret & Sara, 2005). The neurons project to a major part of the brain, the so-called locus coeruleus norepinephrine system (LC-NE system). Norepinephrine (NE) is used as a neurotransmitter of noradrenergic neurons released from the locus coeruleus (LC). The sympathetic and parasympathetic divisions of the ANS are controlled by the acetylcholine and noradrenergic system. Pupillary changes function as an adjustment of light entering the eyes mediated by the autonomic nervous system (ANS) (Beatty & Lucero-Wagoner, 2000 Goldwater, 1972 Granholm & Steinhauer, 2004 Irene et al., 1993 Samuels & Szabadi, 2008). ![]() The overall results suggest that variability of baseline pupil size reflects the stochastic dynamics of arousal fluctuation in the brain related to bistable perception. Furthermore, a cross-correlation analysis indicates that baseline pupil size predicted perceptual alternation at least 35 s before the behavioral response and that the overall correspondence between pupil size and perceptual alternation was maintained over a sustained time window of 45 s at minimum. The results showed that the baseline pupil size monotonically increased with an increasing number of perceptual alternations and its occurrence probability. Baseline pupil size was defined as the mean pupil diameter over a period of 1 s prior to the task requirement (i.e., before the observation period for counting the perceptual alternations in Experiment 1 and reporting whether participants experienced the perceptual alternations in Experiment 2). Here, we found that baseline pupil size, an index of temporal fluctuation of arousal level over a longer range of timescales than that for the transient pupil changes, relates to the frequency of perceptual alternation in auditory bistability. Transient pupil dilation as a consequence of the reconciliation with the neural network in bistable perception has been reported to precede the reported perceptual alternation. A dynamic neural network change, accompanied by cognitive shifts such as internal perceptual alternation in bistable stimuli, is reconciled by the discharge of noradrenergic locus coeruleus neurons.
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