Pupil Size as a Window on Neural Substrates of Cognition

Spatiotemporal processing of real faces is modified by visual sensing

Live human faces, when engaged as visual stimuli, recruit unique and extensive patterns of neural activity. However, the underlying neural mechanisms that underly these live face-to-face processes are not known. We hypothesized that the neural correlates for live face processes are modulated by both spatial and temporal features of the live faces as well as visual sensing parameters. Hemodynamic signals detected by functional near infrared spectroscopy (fNIRS) were acquired concurrently with co-activated electroencephalographic (EEG) and eye-tracking signals during interactive gaze at a live human face or gaze at a human-like robot face. Regression of the fNIRS signals with two eye-gaze variables, fixation duration and dwell time, revealed separate regions of neural correlates, right supramarginal gyrus (lateral visual stream) and right inferior parietal sulcus (dorsal visual stream), respectively. These two areas served as the regions of interest for the EEG analysis. Standardized low-resolution brain electromagnetic tomography (sLORETA) was applied to determine theta (4 - 7 Hz) and alpha (8-13 Hz) oscillatory activity in these regions. Variations in oscillatory patterns corresponding to the neural correlates of the visual sensing parameters suggest an increase in spatial binding for the dorsal relative to the lateral regions of interest during live face-to-face visual stimulation.

Does pseudoneglect influence pupillary light or dark response?

Pupillary light response (PLR) is modulated by the allocation of spatial attention. Larger pupil constrictions for bright stimuli presented on the left side are considered indicative of pseudoneglect, a subtle attentional bias observed in neurotypical populations. This study aimed to replicate this effect using the split-screen method-a newly introduced measure of spatial attentional bias-while accounting for factors such as contraction anisocoria by recording from both pupils. Additionally, we introduced conditions with and without competing stimuli (a black patch on the opposite side to the original white patch that is supposed to elicit pupil contraction) to investigate the role of visual competition in PLR modulation and explored the pupillary dark response (PDR) to assess whether attentional biases affect pupil dilation. Contrary to our hypothesis, we did not observe a significant pseudoneglect effect, as pupil constriction was not consistently greater for left-sided stimuli. We found clear evidence for contraction anisocoria, whereby ipsilateral stimuli produce stronger constrictions than contralateral stimuli, thus highlighting the need to account for this physiological effect in future studies. Regarding PDR, we did not find significant attentional modulation or evidence of dilation anisocoria as pupil dilation amplitudes were similar across both hemifields. These findings suggest that although the split-screen method may reveal physiological asymmetries like anisocoria, its sensitivity to attentional biases in neurotypical populations still requires further investigation.

Subcortical nuclei of the human ascending arousal system encode anticipated reward but do not predict subsequent memory

Subcortical nuclei of the ascending arousal system (AAS) play an important role in regulating brain and cognition. However, functional MRI (fMRI) of these nuclei in humans involves unique challenges due to their size and location deep within the brain. Here, we used ultra-high-field MRI and other methodological advances to investigate the activity of 6 subcortical nuclei during reward anticipation and memory encoding: the locus coeruleus (LC), basal forebrain, median and dorsal raphe nuclei, substantia nigra, and ventral tegmental area. Participants performed a monetary incentive delay task, which successfully induced a state of reward anticipation, and a 24-h delayed surprise memory test. Region-of-interest analyses revealed that activity in all subcortical nuclei increased in anticipation of potential rewards as opposed to neutral outcomes. In contrast, activity in none of the nuclei predicted memory performance 24 h later. These findings provide new insights into the cognitive functions that are supported by the human AAS.

Emotional conflict affects microsaccade dynamics in the emotional face-word Stroop task

Achieving optimal performance requires effectively resolving emotional conflict arising from the interference of task-irrelevant, emotionally salient stimuli. While microsaccade behavior has been linked to various cognitive and emotional processes, whether emotional conflict affects microsaccade responses remains to be determined. Additionally, pupil dilation is known to be modulated by emotional conflict signals, and both microsaccades and pupil dilation are arguably mediated by the superior colliculus (SC). However, the relationship between microsaccades and pupil dilation remains poorly understood. In this study, we investigated the effects of emotional conflict on microsaccade rates and metrics by presenting an emotional face-word stimulus in the face-word Stroop task. Larger microsaccade amplitudes (or higher peak velocities) were observed in the incongruent condition compared to the congruent condition, while microsaccade rates were similar between the two conditions. Additionally, microsaccade amplitudes were larger in incongruent trials following congruent trials than in those following incongruent trials. Furthermore, interindividual correlations between differences in microsaccade responses and State-Trait Anxiety Inventory scores were observed. Finally, trials with higher microsaccade rates were associated with larger pupil dilation. These results demonstrate the modulation of microsaccade metrics by emotional conflict, implicating the SC in integrating signals from the locus coeruleus network to coordinate these responses.

Adrenergic Modulation of Cortical Gain and Sensory Processing in the Mouse Visual Cortex

Background/Objectives: Sensory perception is influenced by internal neuronal variability and external noise. Neuromodulators such as norepinephrine (NE) regulate this variability by modulating excitation-inhibition balance, oscillatory dynamics, and interlaminar connectivity. While NE is known to modulate cortical gain, it remains unclear how it shapes sensory processing under noisy conditions. This study investigates how adrenergic modulation affects signal-to-noise processing and perceptual decision-making in the primary visual cortex (V1) of mice exposed to varying levels of visual noise. Methods: We performed in vivo local field potential (LFP) recordings from layers 2/3 and 4 of V1 in sedated mice to assess the impact of visual noise and systemic administration of atomoxetine, a NE reuptake inhibitor, on cortical signal processing. In a separate group of freely moving mice, we used a two-alternative forced-choice to evaluate the behavioral effects of systemic and intracortical adrenergic manipulations on visual discrimination. Results: Moderate visual noise enhanced cortical signal processing and visual choices, consistent with stochastic resonance. High noise levels impaired both. Systemic atomoxetine administration flattened the cortical signal-to-noise ratio function, suggesting disrupted gain control. Behaviorally, clonidine impaired accuracy at moderate noise levels, while atomoxetine reduced discrimination performance and increased response variability. Intracortical NE infusions produced similar effects. Conclusions: Our findings demonstrate that NE regulates the balance between signal amplification and noise suppression in a noise- and context-dependent manner. These results extend existing models of neuromodulatory function by linking interlaminar communication and cortical variability to perceptual decision-making.

Pupil and Eye Blink Response Abnormalities During Emotional Conflict Processing in Late-Life Depression

IntroductionThis study aims to investigate the locus coeruleus-norepinephrine system (LC-NE) function in late-life depression (LLD) patients by examining task-evoked pupil dilation in the emotional face-word Stroop task, given the recently established coupling between task-evoked pupil dilation and LC-NE activation.Materials and MethodsUsing video-based eye-tracking and principal component analysis, we explored task-evoked pupil responses and eye blinks in LLD patients (N = 25) and older healthy controls (CTRL) (N = 29) to determine whether there were alterations in pupil responses and eye blinks in LLD compared to CTRL.ResultsLLD patients exhibited significantly different pupil and eye-blink behavior compared to CTRL, with dampened task-evoked pupil dilation associated with emotional congruency and valence processing mediated by the sympathetic system compared to CTRL. Eye-blink rates associated with emotional valence were also altered in LLD compared to CTRL Moreover, Geriatric Depression Scale-15 scores in LLD correlated with emotional congruency effects revealed by task-evoked pupil dilation.ConclusionThe findings demonstrate that LLD patients display altered pupil behavior compared to CTRL. These altered responses correlated with the severity of depressive symptoms, indicating their potential as objective biomarkers for use in large at-risk populations for LLD.

Neural mechanisms of resource allocation in working memory

To mitigate capacity limits of working memory, people allocate resources according to an item's relevance. However, the neural mechanisms supporting such a critical operation remain unknown. Here, we developed computational neuroimaging methods to decode and demix neural responses associated with multiple items in working memory with different priorities. In striate and extrastriate cortex, the gain of neural responses tracked the priority of memoranda. We decoded higher-priority memoranda with smaller error and lower uncertainty. Moreover, these neural differences predicted behavioral differences in memory prioritization between and within participants. Trial-wise variability in the magnitude of delay activity in the frontal cortex predicted differences in decoded precision between low- and high-priority items in visual cortex. These results support a model in which feedback signals broadcast from frontal cortex sculpt the gain of memory representations in the visual cortex according to behavioral relevance, thus identifying a neural mechanism for resource allocation.

Effort drives saccade selection

What determines where to move the eyes? We recently showed that pupil size, a well-established marker of effort, also reflects the effort associated with making a saccade ('saccade costs'). Here, we demonstrate saccade costs to critically drive saccade selection: when choosing between any two saccade directions, the least costly direction was consistently preferred. Strikingly, this principle even held during search in natural scenes in two additional experiments. When increasing cognitive demand experimentally through an auditory counting task, participants made fewer saccades and especially cut costly directions. This suggests that the eye-movement system and other cognitive operations consume similar resources that are flexibly allocated among each other as cognitive demand changes. Together, we argue that eye-movement behavior is tuned to adaptively minimize saccade-inherent effort.

Pupillometry: A Simple and Automatic Way to Explore Implicit Cognitive Processing

Pupil size is a non-invasive and highly sensitive technique used to measure changes in pupil diameter. It not only responds to light but also reflects inner cognitive processes (e.g., attention and emotion perception). Recently, it has been introduced to the traditional cognitive neuroscience field as a useful tool to objectively and sensitively capture the current cognitive state and its temporal dynamics. Importantly, this index is automatic and requires no explicit reports, thus it could be used to investigate the rarely explored realm of implicit cognitive processing. Here, we describe a comprehensive protocol that records pupil responses during the passive viewing of emotional biological motion (BM). Our results reliably reveal the multi-level implicit processing mechanism of BM emotion, as indicated by the fine-grained emotion processing in intact BM and the rapid but rather coarse emotion processing in local BM. Moreover, the emotion modulation effects observed in intact BM are indicative of individual autistic tendencies. We believe this protocol could be adapted to unveil the automatic processing of emotions and other attributes in social signals and further assist the early detection of social-cognitive disorders (e.g., autism). Key features • Pupil measurements could automatically and objectively reflect current cognitive states, which is useful for unfolding the implicit cognitive processes and related time courses. • It requires no explicit reports; thus, with modifications, this procedure could be utilized in a wide range of populations (e.g., infants, patients) and even animals. • Autistic traits strongly correlate with observed emotion-related pupil responses, revealing the potential application of pupil measurements in the detection of social cognitive deficits. • This protocol has been found to reveal the multi-level emotion processing of biological motion, which is further validated by a test-retest replication.

Main Sequence of Human Luminance-evoked Pupil Dynamics

Pupil responses are commonly used to provide insight into visual perception, autonomic control, cognition, and various brain disorders. However, making inferences from pupil data can be complicated by nonlinearities in pupil dynamics and variability within and across individuals, which challenge the assumptions of linearity or group-level homogeneity required for common analysis methods. In this study, we evaluated luminance evoked pupil dynamics in young healthy adults (n = 10, M:F = 5:5, age 19-25 years) by identifying nonlinearities, variability, and conserved relationships across individuals to improve the ability to make inferences from pupil data. We found a nonlinear relationship between final pupil diameter and luminance, linearized by considering the logarithm of luminance. Peak diameter change and peak velocity were nonlinear functions of log-luminance for constriction but not dilation responses. Across participants, curve fit parameters characterizing pupil responses as a function of luminance were highly variable, yet there was an across-participant linear correlation between overall pupil size and pupil gain (i.e., diameter change per unit log-luminance change). In terms of within-participant trial-by-trial variability, participants showed greater variability in final pupil size compared with constriction peak diameter change as a function of log-luminance. Despite the variability in stimulus-response metrics within and across participants, we found that all participants showed a highly stereotyped "main sequence" relationship between peak diameter change and peak velocity (independent of luminance). The main sequence relationship can be used to inform models of the neural control of pupil dynamics and as an empirical analysis tool to evaluate variability and abnormalities in pupil behavior.

Enhanced neural speech tracking through noise indicates stochastic resonance in humans

Neural activity in auditory cortex tracks the amplitude-onset envelope of continuous speech, but recent work counterintuitively suggests that neural tracking increases when speech is masked by background noise, despite reduced speech intelligibility. Noise-related amplification could indicate that stochastic resonance - the response facilitation through noise - supports neural speech tracking, but a comprehensive account is lacking. In five human electroencephalography experiments, the current study demonstrates a generalized enhancement of neural speech tracking due to minimal background noise. Results show that (1) neural speech tracking is enhanced for speech masked by background noise at very high signal-to-noise ratios (~30 dB SNR) where speech is highly intelligible; (2) this enhancement is independent of attention; (3) it generalizes across different stationary background maskers, but is strongest for 12-talker babble; and (4) it is present for headphone and free-field listening, suggesting that the neural-tracking enhancement generalizes to real-life listening. The work paints a clear picture that minimal background noise enhances the neural representation of the speech onset-envelope, suggesting that stochastic resonance contributes to neural speech tracking. The work further highlights non-linearities of neural tracking induced by background noise that make its use as a biological marker for speech processing challenging.

Attachment is in the eye of the beholder: a pupillometry study on emotion processing

Early attachment relationships exert lasting effects on psychophysical health across the lifespan. Limited behavioral evidence suggests that these effects stem from how individuals perceive, interpret, and respond to their environment. This study investigated whether adults' attachment representations modulate autonomic responses to happy and sad facial expressions, evidenced by changes in pupil size. We utilized a sample of healthy adults (N = 100; 68% females, 18-35 years, prevalently White European). In an eye-tracking experiment, we assessed pupil dilation to happy and sad facial expressions (n = 152 trials). Dismissing and preoccupied attachment orientations were assessed as continuous dimensions via self-report. Linear mixed models revealed that individuals with higher scores on dismissing orientations exhibited a significant increase in pupil dilation in response to sad and not happy expressions. No significant effects were observed for preoccupied orientations, age, or sex. These findings suggest that individuals with increased scores on dismissing attachment show heightened arousal to negative emotions.

Classification of Hearing Status Based on Pupil Measures During Sentence Perception

PURPOSE

Speech understanding in noise can be effortful, especially for people with hearing impairment. To compensate for reduced acuity, hearing-impaired (HI) listeners may be allocating listening effort differently than normal-hearing (NH) peers. We expected that this might influence measures derived from the pupil dilation response. To investigate this in more detail, we assessed the sensitivity of pupil measures to hearing-related changes in effort allocation. We used a machine learning-based classification framework capable of combining and ranking measures to examine hearing-related, stimulus-related (signal-to-noise ratio [SNR]), and task response-related changes in pupil measures.

METHOD

Pupil data from 32 NH (40-70 years old, M = 51.3 years, six males) and 32 HI (31-76 years old, M = 59 years, 13 males) listeners were recorded during an adaptive speech reception threshold test. Peak pupil dilation (PPD), mean pupil dilation (MPD), principal pupil components (rotated principal components [RPCs]), and baseline pupil size (BPS) were calculated. As a precondition for ranking pupil measures, the ability to classify hearing status (NH/HI), SNR (high/low), and task response (correct/incorrect) above random prediction level was assessed. This precondition was met when classifying hearing status in subsets of data with varying SNR and task response, SNR in the NH group, and task response in the HI group.

RESULTS

A combination of pupil measures was necessary to classify the dependent factors. Hearing status, SNR, and task response were predicted primarily by the established measures-PPD (maximum effort), RPC2 (speech processing), and BPS (task anticipation)-and by the novel measures RPC1 (listening) and RPC3 (response preparation) in tasks involving SNR as an outcome or sometimes difficulty criterion.

CONCLUSIONS

A machine learning-based classification framework can assess sensitivity of, and rank the importance of, pupil measures in relation to three effort modulators (factors) during speech perception in noise. This indicates that the effects of these factors on the pupil measures allow for reasonable classification performance. Moreover, the varying contributions of each measure to the classification models suggest they are not equally affected by these factors. Thus, this study enhances our understanding of pupil responses and their sensitivity to relevant factors.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.28225199.

The Interplay of Spontaneous Pupil-Size Fluctuations and EEG Power in Near-Threshold Detection

Detection of near-threshold stimuli depends on the properties of the stimulus and the state of the observer. In visual detection tasks, improved accuracy is associated with larger prestimulus pupil size. However, it is still unclear whether this association is due to optical effects (more light entering the eye), correlations with arousal, correlations with cortical excitability (as reflected in alpha power), or a mix of these. To better understand this, we investigated the relative contributions of pupil size and power in the alpha, beta, and theta frequency bands on near-threshold detection. We found that larger prestimulus pupil size is associated with improved accuracy and more stimulus-present responses, and these effects were not mediated by spectral power in the EEG. Pupil size was also positively correlated with power in the beta and alpha bands. Taken together, our results show an independent effect of pupil size on detection performance that is not driven by cortical excitability but may be driven by optical effects, physiological arousal, or a mix of both.

Separating cognitive and motor processes in the behaving mouse

The cognitive processes supporting complex animal behavior are closely associated with movements responsible for critical processes, such as facial expressions or the active sampling of our environments. These movements are strongly related to neural activity across much of the brain and are often highly correlated with ongoing cognitive processes. A fundamental issue for understanding the neural signatures of cognition and movements is whether cognitive processes are separable from related movements or if they are driven by common neural mechanisms. Here we demonstrate how the separability of cognitive and motor processes can be assessed and, when separable, how the neural dynamics associated with each component can be isolated. We designed a behavioral task in mice that involves multiple cognitive processes, and we show that dynamics commonly taken to support cognitive processes are strongly contaminated by movements. When cognitive and motor components are isolated using a novel approach for subspace decomposition, we find that they exhibit distinct dynamical trajectories and are encoded by largely separate populations of cells. Accurately isolating dynamics associated with particular cognitive and motor processes will be essential for developing conceptual and computational models of neural circuit function.

The pupillary respiratory-phase response: pupil size is smallest around inhalation onset and largest during exhalation

Respiration shapes brain activity and synchronizes sensory and exploratory motor actions, with some evidence suggesting that it also affects pupil size. However, evidence for a coupling between respiration and pupil size remains scarce and inconclusive, hindered by small sample sizes and limited controls. Given the importance of pupil size in visual perception and as a reflection of brain state, understanding its relationship with respiration is essential. In five experiments using a pre-registered protocol, we systematically investigated how respiratory phase affects pupil size across different conditions. In Experiment 1 (n = 50), we examined nasal and oral breathing at rest under dim lighting with nearby fixation points, then replicated these results under identical conditions in Experiment 2 (n = 53). Experiment 3 (n = 112) extended this to active visual tasks, while Experiment 4 (n = 57) extended this to controlled breathing at different paces under ambient lighting with distant fixation. Finally, in Experiment 5 (n = 34), individuals with isolated congenital anosmia (born without olfactory bulbs) were used as a lesion-type model during visual-auditory tasks to assess whether the respiratory-pupil link depends on olfactory bulb-driven oscillations. Across all conditions - free and controlled breathing; different tasks, lighting and fixation distances; and with and without olfactory bulbs - we consistently found that pupil size is smallest around inhalation onset and largest during exhalation. We term this effect the pupillary respiratory-phase response, the fourth known mechanism influencing pupil size, alongside the pupillary light, near fixation and psychosensory responses. KEY POINTS: The influence of respiration on pupil size dynamics has long been debated. In this study, we systematically investigated how pupil size changes across the breathing cycle through a series of five experiments, while varying tasks, lighting, fixation distance and brain region involvement. We show that pupil size is smallest around inhalation onset and largest during exhalation, with pupil dilatation occurring through most of inhalation and the early phase of exhalation, and pupil constriction occurring primarily during the latter part of exhalation. This pattern was consistent across all experimental conditions, demonstrating that it is robust and likely controlled by brainstem circuits. We term this effect the pupillary respiratory-phase response, the fourth known mechanism influencing pupil size.

Pupil size reveals arousal level fluctuations in human sleep

Recent animal research has revealed the intricate dynamics of arousal levels that are important for maintaining proper sleep resilience and memory consolidation. In humans, changes in arousal level are believed to be a determining characteristic of healthy and pathological sleep but tracking arousal level fluctuations has been methodologically challenging. Here we measured pupil size, an established indicator of arousal levels, by safely taping the right eye open during overnight sleep and tested whether pupil size affects cortical response to auditory stimulation. We show that pupil size dynamics change as a function of important sleep events across different temporal scales. In particular, our results show pupil size to be inversely related to the occurrence of sleep spindle clusters, a marker of sleep resilience. Additionally, we found pupil size prior to auditory stimulation to influence the evoked response, most notably in delta power, a marker of several restorative and regenerative functions of sleep. Recording pupil size dynamics provides insights into the interplay between arousal levels and sleep oscillations.

Probing locus coeruleus functional network in healthy aging and its association with Alzheimer's disease biomarkers using pupillometry

BACKGROUND

Alzheimer's disease (AD) is the leading cause of dementia, and the early detection of the disease-associated changes allows early interventions. The locus coeruleus (LC) has been reported to be the first brain region to develop tau pathology in AD. However, the functional brain network of the LC in both healthy aging and AD pathology is largely unknown due to technical difficulties associated with the small size of the LC. In this study, we used the measurement of spontaneous pupil constriction/dilation as a surrogate for LC activity to study LC brain network changes during healthy aging.

METHODS

Thirty-seven healthy younger and thirty-nine healthy older adults were included from the Emory Healthy Brain Study and underwent resting-state functional MRI while simultaneously tracking pupil diameter. The measurements of pupil diameter dynamics were used as reference signals in brain connectivity analysis. The connectivity of the identified networks was then compared between younger and older participants. Correlations of the identified regions with neuropsychological assessments and cerebrospinal fluid (CSF) biomarkers were also evaluated.

RESULTS

A brain network of 20 clusters associated with pupil diameter dynamics was identified, including the LC as well as brain regions functionally connected to the LC. The pupil diameter network was found to positively correlate with the salience network and negatively correlate with the central executive network. Functional connectivity decreased within the pupil diameter network with healthy aging. The pupil diameter connectivity was associated with memory, executive, and visuospatial functioning. CSF total tau closely correlated with pupil diameter network.

CONCLUSIONS

Pupil diameter dynamics provide valuable insights into LC-related processes. While they are not solely influenced by LC activity, spontaneous pupil constrictor/dilatory activity shows promise as a non-invasive approach to probe the LC network and warrants further studies to evaluate its value as an early biomarker of AD.

Violation of auditory regularities is reflected in pupil dynamics

The brain builds and maintains internal models and uses them to make predictions. When predictions are violated, the current model can either be updated or replaced by a new model. The latter is accompanied by pupil dilation responses (PDRs) related to locus coeruleus activity/norepinephrine release (LC-NE). Following earlier research, we investigated PDRs associated with transitions between regular and random patterns of tones in auditory sequences. We presented these sequences to participants and instructed them to find gaps (to maintain attention). Transitions from regular to random patterns induced PDRs, suggesting that an internal model attuned to the regular pattern is reset. Transitions from one regular pattern to another regular pattern also induced PDRs, suggesting that they also led to a model reset. In contrast, transitions from random patterns to regular patterns did not induce PDRs, suggesting a gradual update of model parameters. We modelled these findings, using pupil response functions to show how ongoing PDRs and pupil event rates were sensitive to the trial-by-trial changes in the information content of the auditory sequences. Expanding on previous research, we suggest that PDRs-as biomarkers for LC-NE activation-may indicate the extent of prediction violations.

Effects of Noise and Reward on Pupil Size and Electroencephalographic Speech Tracking in a Word-Detection Task

Speech is hard to understand when there is background noise. Speech intelligibility and listening effort both affect our ability to understand speech, but the relative contribution of these factors is hard to disentangle. Previous studies suggest that speech intelligibility could be assessed with EEG speech tracking and listening effort via pupil size. However, these measures may be confounded, because poor intelligibility may require a larger effort. To address this, we developed a novel word-detection paradigm that allows for a rapid behavioural assessment of speech processing. In this paradigm, words appear on the screen during continuous speech, similar to closed captioning. In two listening experiments with a total of 51 participants, we manipulated intelligibility by changing signal-to-noise ratios (SNRs) and modulated effort by varying monetary reward. Increasing SNR improved detection performance along with EEG speech tracking. Additionally, we find that pupil size increases with increased SNR. Surprisingly, when we modulated both reward and SNR, we found that reward modulated only pupil size, whereas SNR modulated only EEG speech tracking. We interpret this as the effects of arousal and listening effort on pupil size and of intelligibility on EEG speech tracking. The experimental paradigm developed here may be beneficial when assessing hearing devices in terms of speech intelligibility and listening effort.

Using pupillometry to predict outcome in cognitive behavioral therapy for negative symptoms of schizophrenia

BACKGROUND

Clinical trials of cognitive-behavioral therapy (CBT) for negative symptoms of schizophrenia have provided mixed results, perhaps because some patients are more likely to benefit than others. Patients likely to benefit may be those with greater pre-treatment motivation. To better examine the effects of motivation on treatment outcome, more objective measures of motivation are needed. Pupillary responses provide an objective biomarker of cognitive effort and motivation, with greater dilation associated with greater effort and motivation.

AIMS

The current study examined whether pre-treatment baseline pupil dilation predicted motivation and pleasure (MAP) negative symptom reduction in an open clinical trial of CBT for individuals with schizophrenia.

METHODS

Pupil dilation was recorded during the digit-span task at low (3 digits), moderate (6 digits) and high (9 digits) loads in participants with schizophrenia or schizoaffective disorder (N = 31) with persistent negative symptoms prior to delivery of mobile-assisted CBT for negative symptoms (mCBTn).

RESULTS

Greater pre-treatment pupil dilation during low, but not moderate or high, loads of the digit-span task significantly predicted greater reduction in MAP negative symptoms. However, while MAP negative symptoms improved throughout treatment, pupil dilation did not significantly change throughout treatment for any digit-span loads.

IMPLICATIONS

Pupil dilation may provide a much-needed prognostic biomarker of patients most likely to benefit from CBT for MAP symptoms, but did not change with change in MAP symptoms.

Three Hundred Hertz Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) Impacts Pupil Size Non-Linearly as a Function of Intensity

Transcutaneous auricular vagus nerve stimulation (taVNS) is a neuromodulatory technique that may have numerous potential health and human performance benefits. However, optimal stimulation parameters for maximizing taVNS efficacy are unknown. Progress is impeded by disagreement on the identification of a biomarker that reliably indexes activation of neuromodulatory systems targeted by taVNS, including the locus coeruleus-norepinephrine (LC-NE) system. Pupil size varies with LC-NE activity and is one potential taVNS biomarker that has shown inconsistent sensitivity to taVNS in prior studies. The present study examined the relationship between pupil size and taVNS using stimulation parameters that have shown promising behavioral effects in prior studies but have received comparatively little attention. Participants received trains of 50 μs taVNS pulses delivered continuously below perceptual threshold at 300 Hz to the left external acoustic meatus (EAM) while pupil size was recorded during a pupillary light reflex task. Analysis of pupil size using generalized additive mixed modeling (GAMM) revealed a non-linear relationship between taVNS intensity and pupil diameter. Active taVNS increased pupil size during stimulation for participants who received taVNS between 2 and approximately 4.8 mA, but not for participants who received higher-intensity taVNS (up to 8.1 mA). In addition, taVNS effects persisted in subsequent blocks, mitigating decreases in pupil size over the course of the task. These findings suggest 300 Hz taVNS activates the LC-NE system when applied to the EAM, but its effects may be counteracted at higher intensities.

Phase synchrony between prefrontal noradrenergic and cholinergic signals indexes inhibitory control

Inhibitory control is a critical executive function that allows animals to suppress their impulsive behavior in order to achieve certain goals or avoid punishment. We investigated norepinephrine (NE) and acetylcholine (ACh) dynamics and population neuronal activity in the prefrontal cortex (PFC) during inhibitory control. Using fluorescent sensors to measure extracellular levels of NE and ACh, we simultaneously recorded prefrontal NE and ACh dynamics in mice performing inhibitory control tasks. The prefrontal NE and ACh signals exhibited strong coherence at 0.4-0.8 Hz. Although inhibition of locus coeruleus (LC) neurons projecting to the PFC impaired inhibitory control, inhibiting LC neurons projecting to the basal forebrain (BF) caused a more profound impairment, despite an approximately 30% overlap between LC neurons projecting to the PFC and BF, as revealed by our tracing studies. The inhibition of LC neurons projecting to the BF did not diminish the difference in prefrontal NE/ACh signals between successful and failed trials; instead, it abolished the difference in NE-ACh phase synchrony between successful and failed trials, indicating that NE-ACh phase synchrony is a task-relevant neuromodulatory feature. Chemogenetic inhibition of cholinergic neurons that project to the LC region did not impair inhibitory control, nor did it abolish the difference in NE-ACh phase synchrony between successful or failed trials, further confirming the relevance of NE-ACh phase synchrony to inhibitory control. To understand the possible effect of NE-ACh synchrony on prefrontal population activity, we employed Neuropixels to record from the PFC during inhibitory control. The inhibition of LC neurons projecting to the BF not only reduced the number of prefrontal neurons encoding inhibitory control, but also disrupted population firing patterns representing inhibitory control, as revealed by a demixed principal component (dPCA) analysis. Taken together, these findings suggest that the LC modulates inhibitory control through its collective effect with cholinergic systems on population activity in the prefrontal cortex. Our results further indicate that NE-ACh phase synchrony is a critical neuromodulatory feature with important implications for cognitive control.

Disrupted microsaccade responses in late-life depression

Late-life depression (LLD) is a psychiatric disorder in older adults, characterized by high prevalence and significant mortality rates. Thus, it is imperative to develop objective and cost-effective methods for detecting LLD. Individuals with depression often exhibit disrupted levels of arousal, and microsaccades, as a type of fixational eye movement that can be measured non-invasively, are known to be modulated by arousal. This makes microsaccades a promising candidate as biomarkers for LLD. In this study, we used a high-resolution, video-based eye-tracker to examine microsaccade behavior in a visual fixation task between LLD patients and age-matched healthy controls (CTRL). Our goal was to determine whether microsaccade responses are disrupted in LLD compared to CTRL. LLD patients exhibited significantly higher microsaccade peak velocities and larger amplitudes compared to CTRL. Although microsaccade rates were lower in LLD than in CTRL, these differences were not statistically significant. Additionally, while both groups displayed microsaccadic inhibition and rebound in response to changes in background luminance, this modulation was significantly blunted in LLD patients, suggesting dysfunction in the neural circuits responsible for microsaccade generation. Together, these findings, for the first time, demonstrate significant alterations in microsaccade behavior in LLD patients compared to CTRL, highlighting the potential of these disrupted responses as behavioral biomarkers for identifying individuals at risk for LLD.

Toward a functional future for the cognitive neuroscience of human aging

The cognitive neuroscience of human aging seeks to identify neural mechanisms behind the commonalities and individual differences in age-related behavioral changes. This goal has been pursued predominantly through structural or "task-free" resting-state functional neuroimaging. The former has elucidated the material foundations of behavioral decline, and the latter has provided key insight into how functional brain networks change with age. Crucially, however, neither is able to capture brain activity representing specific cognitive processes as they occur. In contrast, task-based functional imaging allows a direct probe into how aging affects real-time brain-behavior associations in any cognitive domain, from perception to higher-order cognition. Here, we outline why task-based functional neuroimaging must move center stage to better understand the neural bases of cognitive aging. In turn, we sketch a multi-modal, behavior-first research framework that is built upon cognitive experimentation and emphasizes the importance of theory and longitudinal design.

Pupil responds spontaneously to visuospatial regularity

Beyond the light reflex, the pupil responds to various high-level cognitive processes. Multiple statistical regularities of stimuli have been found to modulate the pupillary response. However, most studies have used auditory or visual temporal sequences as stimuli, and it is unknown whether the pupil size is modulated by statistical regularity in the spatial arrangement of stimuli. In three experiments, we created perceived regular and irregular stimuli, matching physical regularity, to investigate the effect of spatial regularity on pupillary responses during passive viewing. Experiments using orientation (Experiments 1 and 2) and size (Experiment 3) as stimuli consistently showed that perceived irregular stimuli elicited more pupil constriction than regular stimuli. Furthermore, this effect was independent of the luminance of the stimuli. In conclusion, our study revealed that the pupil responds spontaneously to perceived visuospatial regularity, extending the stimulus regularity that influences the pupillary response into the visuospatial domain.

Aperiodic Pupil Fluctuations at Rest Predict Orienting of Visual Attention

The aperiodic exponent of the power spectrum of signals in several neuroimaging modalities has been found to be related to the excitation/inhibition balance of the neural system. Leveraging the rich temporal dynamics of resting-state pupil fluctuations, the present study investigated the association between the aperiodic exponent of pupil fluctuations and the neural excitation/inhibition balance in attentional processing. In separate phases, we recorded participants' pupil size during resting state and assessed their attentional orienting using the Posner cueing tasks with different cue validities (i.e., 100% and 50%). We found significant correlations between the aperiodic exponent of resting pupil fluctuations and both the microsaccadic and behavioral cueing effects. Critically, this relationship was particularly evident in the 50% cue-validity condition rather than in the 100% cue-validity condition. The microsaccadic responses mediated the association between the aperiodic exponent and the behavioral response. Further analysis showed that the aperiodic exponent of pupil fluctuations predicted the self-rated hyperactivity/impulsivity trait across individuals, suggesting its potential as a marker of attentional deficits. These findings highlight the rich information contained in pupil fluctuations and provide a new approach to assessing the neural excitation/inhibition balance in attentional processing.

Pupil size correlates with heart rate, skin conductance, pulse wave amplitude, and respiration responses during emotional conflict and valence processing

Pupil size is a non-invasive index for autonomic arousal mediated by the locus coeruleus-norepinephrine (LC-NE) system. While pupil size and its derivative (velocity) are increasingly used as indicators of arousal, limited research has investigated the relationships between pupil size and other well-known autonomic responses. Here, we simultaneously recorded pupillometry, heart rate, skin conductance, pulse wave amplitude, and respiration signals during an emotional face-word Stroop task, in which task-evoked (phasic) pupil dilation correlates with LC-NE responsivity. We hypothesized that emotional conflict and valence would affect pupil and other autonomic responses, and trial-by-trial correlations between pupil and other autonomic responses would be observed during both tonic and phasic epochs. Larger pupil dilations, higher pupil size derivative, and lower heart rates were observed in the incongruent condition compared to the congruent condition. Additionally, following incongruent trials, the congruency effect was reduced, and arousal levels indexed by previous-trial pupil dilation were correlated with subsequent reaction times. Furthermore, linear mixed models revealed that larger pupil dilations correlated with higher heart rates, higher skin conductance responses, higher respiration amplitudes, and lower pulse wave amplitudes on a trial-by-trial basis. Similar effects were seen between positive and negative valence conditions. Moreover, tonic pupil size before stimulus presentation significantly correlated with all other tonic autonomic responses, whereas tonic pupil size derivative correlated with heart rates and skin conductance responses. These results demonstrate a trial-by-trial relationship between pupil dynamics and other autonomic responses, highlighting pupil size as an effective real-time index for autonomic arousal during emotional conflict and valence processing.

Self-face processing in relation to self-referential tasks in 24-month-old infants: A study through eye movements and pupillometry measures

The aim of the current study was to investigate visual scan patterns for the self-face in infants with the ability to recognize themselves with a photograph. 24-month-old infants (N = 32) were presented with faces including the self-face in the upright or inverted orientation. We also measured infants' ability to recognize oneself in a mirror and with a photograph. Results showed that only in trials with the self-face was pupil dilation greater in the upright orientation than in the inverted orientation, and that eye movements and pupil dilation were not associated with PSR tasks. Our findings suggest that the processing of the self-face was processed in a manner similar to that of others, with longer and more fixations on eyes and nose, but infants allocated more attentional resources to processing upright self-face. Self-face processing in infancy may be independent of the understanding of the self beyond the here and now.

Broadscale dampening of uncertainty adjustment in the aging brain

The ability to prioritize among input features according to relevance enables adaptive behaviors across the human lifespan. However, relevance often remains ambiguous, and such uncertainty increases demands for dynamic control. While both cognitive stability and flexibility decline during healthy ageing, it is unknown whether aging alters how uncertainty impacts perception and decision-making, and if so, via which neural mechanisms. Here, we assess uncertainty adjustment across the adult lifespan (N = 100; cross-sectional) via behavioral modeling and a theoretically informed set of EEG-, fMRI-, and pupil-based signatures. On the group level, older adults show a broad dampening of uncertainty adjustment relative to younger adults. At the individual level, older individuals whose modulation more closely resembled that of younger adults also exhibit better maintenance of cognitive control. Our results highlight neural mechanisms whose maintenance plausibly enables flexible task-set, perception, and decision computations across the adult lifespan.

Emotional and visual responses to trypophobic images with object, animal, or human body backgrounds: an eye-tracking study

Background

Trypophobia refers to the visual discomfort (e.g., disgust or anxiety) experienced by some people when viewing clusters of bumps or holes. The spectral profile framework suggests that the spectral components of clustered patterns induces trypophobia. In contrast, the cognitive framework speculates that cognitive appraisal of dangerous objects (e.g., ectoparasites) causes trypophobia. A background effect (e.g., more disgust toward trypophobic patterns on the skin than on a desk) seems to support the cognitive framework. However, there is no study providing objective evidence for that effect and verifying these frameworks at the same time. This study aims to address that limitation by psychometric and eye-tracking experiments.

Methods

We recruited 183 participants from colleges. Initially, participants finished a personality questionnaire. The cohort then completed an eye-tracking experiment which showed the trypophobic pattern of lotus seed on three categories of background images (objects, animals and human bodies). Finally, participants rated the image's disgust and arousal levels using a self-assessment rating scale. Meanwhile, we compared all images' luminosity and power spectra.

Results

Trypophobic images with the human body or animal backgrounds induced a higher level of disgust and arousal than those with the object backgrounds. Participants gazed faster and dwelled longer at the trypophobic patterns on human body images than on object or animal images. Furthermore, trypophobic images with human body or animal backgrounds induced more substantial pupil dilation than those upon object backgrounds. No significant difference was detected between the power of trypophobic images with human body backgrounds and objects backgrounds. As the trypophobic images with human body backgrounds induced significant emotional or visual responses compared to those with inanimate object backgrounds. Such inconsistent results imply that the differential emotional or visual responses to trypophobic images are probably not induced by the difference in power spectra. Finally, the disgust/arousal level toward trypophobic images did not correlate with personality traits.

Conclusion

These results supported the background effect of trypophobia, namely, trypophobic images with animal or human body backgrounds induce more severe disgust and cause more arousal than those with object backgrounds. Our results support the cognitive, but not spectral profile, framework of trypophobia.

Mobilizing effort to reduce lapses of sustained attention: examining the effects of content-free cues, feedback, and points

Three experiments with the psychomotor vigilance task examined whether presenting content-free cues, feedback, and points would reduce lapses of sustained attention. In all three experiments, behavioral lapses of attention (particularly slow reaction times) were reduced with the motivation manipulations compared with control conditions, but self-reports of off-task thinking (e.g., mind-wandering) were unaffected. Pupillary responses (preparatory and phasic) also tended to be larger with the different manipulations compared to control conditions. Collectively, the results are consistent with attentional effort models, suggesting that sustained attention was improved and lapses of attention reduced owing to participants in the motivation conditions mobilizing more attentional effort than participants in the control conditions. These results are consistent with recent research, which suggests that the locus coeruleus norepinephrine system is associated with the mobilization of effort.

Pupillometry as a biomarker of postural control: Deep-learning models reveal side-specific pupillary responses to increased intensity of balance tasks

Pupillometry has been used in the studies of postural control to assess cognitive load during dual tasks, but its response to increased balance task intensity has not been investigated. Furthermore, it is unknown whether side-specific changes in pupil diameter occur with more demanding balance tasks providing additional insights into postural control. The two aims of this study were to analyze differences in steady-state pupil diameter between balance tasks with increased intensity and to determine whether there are side-specific changes. Forty-eight healthy subjects performed parallel and left and right one-legged stances on a force plate with and without foam with right and left pupil diameters measured with a mobile infrared eye-tracker. Differences between balance tasks in parameters (average pupil diameter of each eye, average of both pupil diameters and the difference between the left and right pupil diameter) were analyzed using a two-way repeated measures analysis of variance, and deep learning neural network models were used to investigate how pupillometry predicted each balance task. The pupil diameter of the left eye, the average pupil diameter of both eyes and the difference in pupil diameters increased statistically significantly from simpler to more demanding balance tasks, with this being more pronounced for the left eye. The deep learning neural network models revealed side-specific changes in pupil diameter with more demanding balance tasks. This study confirms pupillary responses to increased intensity of balance task and indicates side-specific pupil responses that could be related to task-specific involvement of higher levels of postural control.

Individual differences in baseline eye movement indices: Examining the relationships between baseline pupil size, inhibitory control, and fixation stability

The relationship among baseline pupil size, fixation stability, and inhibitory control were examined in this study. Participants performed a baseline eye measure in which they were instructed to stare at a fixation dot on screen for 2 min. Following the baseline eye measure, participants completed an antisaccade task to measure inhibitory control ability. We found a correlation between baseline pupil size variability and inhibitory control, as well as between fixation stability and inhibitory control. We showed that participants with better inhibitory control exhibited larger variability in pupil size, and those with better fixation stability showed superior inhibitory control ability. Overall, our results indicate that there are significant correlations between inhibitory control and baseline pupil size, as well as between inhibitory control and fixation stability.

Age-related changes in pupil dynamics and task modulation across the healthy lifespan

The pupil is modulated by luminance, arousal, bottom-up sensory, and top-down cognitive signals, and has increasingly been used to assess these aspects of brain functioning in health and disease. However, changes in pupil dynamics across the lifespan have not been extensively examined, hindering our ability to fully utilize the pupil in probing these underlying neural processes in development and aging in healthy and clinical cohorts. Here, we examined pupil responses during the interleaved pro-/anti-saccade task (IPAST) in healthy participants across the lifespan (n = 567, 5-93 years of age). Based on the extracted measurements of pupil dynamics, we demonstrated age-related changes in pupil measures and task modulation. Moreover, we characterized the underlying factors and age-related effects in components of pupil responses that may be attributed to developmental and aging changes in the associated brain regions. Finally, correlations between factors of pupil dynamics and saccade behaviors revealed evidence of shared neural processes in the pupil and saccade control circuitries. Together, these results demonstrate changes in pupil dynamics as a result of development and aging, providing a baseline with which altered pupil responses due to neurological deficits at different ages can be studied.

Blink-induced changes in pupil dynamics are consistent and heritable

Pupil size and blink rates are heritable but the extent to which they interact with one another has not been properly investigated. Though changes in pupil size due to eye blinks have been reported, they are considered a pupillary artifact. In this study we used the HCP 7T fMRI dataset with resting state eye-tracking data obtained in monozygotic and dizygotic twins to assess their heritability and their interactions. For this purpose, we characterized the pupil dilation (positive peak) and constriction (negative peak) that followed blink events, which we describe as blink-induced pupillary response (BIPR). We show that the BIPR is highly consistent with a positive dilatory peak (D-peak) around 500ms and a negative constricting peak (C-peak) around 1s. These patterns were reproducible within- and between-subjects across two time points and differed by vigilance state (vigilant versus drowsy). By comparing BIPR between monozygotic and dizygotic twins we show that BIPR have a heritable component with significant additive genetic (A) and environmental (E) factors dominating the structural equation models, particularly in the time-domain for both D- and C-peaks (a2 between 42 and 49%) and shared effects (C) as observed in the amplitude domain for the C-peak. Blink duration, pupil size and blink rate were also found to be highly heritable (a2 up to 62% for pupil size). Our study provides evidence of that shared environmental and additive genetic factors influence BIPR and indicates that BIPR should not be treated as a coincidental artefact. Instead BIPR appears to be a component of a larger oculomotor system that we label here as Oculomotor Adaptive System, that is genetically determined.

Task-irrelevant stimuli reliably boost phasic pupil-linked arousal but do not affect decision formation

The arousal systems of the brainstem, specifically the locus coeruleus-noradrenaline system, respond "phasically" during decisions. These central arousal transients are accompanied by dilations of the pupil. Mechanistic attempts to understand the impact of phasic arousal on cognition would benefit from temporally precise experimental manipulations. Here, we evaluated a non-invasive candidate approach to manipulate arousal in humans: presenting task-irrelevant auditory stimuli at different latencies during the execution of a challenging task. Task-irrelevant auditory stimuli drive responses of brainstem nuclei involved in the control of pupil size, but it is unknown whether such sound-evoked responses mimic the central arousal transients evoked during cognitive computations. A large body of evidence has implicated central arousal transients in reducing bias during challenging perceptual decisions. We thus used challenging visual decisions as a testbed, combining them with task-irrelevant sounds of varying onset latency or duration. Across three experiments, the sounds consistently elicited well-controlled pupil responses that superimposed onto task-evoked responses. While we replicated a negative correlation between task-evoked pupil responses and bias, the task-irrelevant sounds had no behavioral effect. This dissociation suggests that cognitive task engagement and task-irrelevant sounds may recruit distinct neural systems contributing to the control of pupil size.

Attentional failures after sleep deprivation represent moments of cerebrospinal fluid flow

Sleep deprivation rapidly disrupts cognitive function, and in the long term contributes to neurological disease. Why sleep deprivation has such profound effects on cognition is not well understood. Here, we use simultaneous fast fMRI-EEG to test how sleep deprivation modulates cognitive, neural, and fluid dynamics in the human brain. We demonstrate that after sleep deprivation, sleep-like pulsatile cerebrospinal fluid (CSF) flow events intrude into the awake state. CSF flow is coupled to attentional function, with high flow during attentional impairment. Furthermore, CSF flow is tightly orchestrated in a series of brain-body changes including broadband neuronal shifts, pupil constriction, and altered systemic physiology, pointing to a coupled system of fluid dynamics and neuromodulatory state. The timing of these dynamics is consistent with a vascular mechanism regulated by neuromodulatory state, in which CSF begins to flow outward when attention fails, and flow reverses when attention recovers. The attentional costs of sleep deprivation may thus reflect an irrepressible need for neuronal rest periods and widespread pulsatile fluid flow.

Hearing Impairment: Reduced Pupil Dilation Response and Frontal Activation During Degraded Speech Perception

PURPOSE

A relevant aspect of listening is the effort required during speech processing, which can be assessed by pupillometry. Here, we assessed the pupil dilation response of normal-hearing (NH) and hard of hearing (HH) individuals during listening to clear sentences and masked or degraded sentences. We combined this assessment with functional magnetic resonance imaging (fMRI) to investigate the neural correlates of the pupil dilation response.

METHOD

Seventeen NH participants (Mage = 46 years) were compared to 17 HH participants (Mage = 45 years) who were individually matched in age and educational level. Participants repeated sentences that were presented clearly, that were distorted, or that were masked. The sentence intelligibility level of masked and distorted sentences was 50% correct. Silent baseline trials were presented as well. Performance measures, pupil dilation responses, and fMRI data were acquired.

RESULTS

HH individuals had overall poorer speech reception than the NH participants, but not for noise-vocoded speech. In addition, an interaction effect was observed with smaller pupil dilation responses in HH than in NH listeners for the degraded speech conditions. Hearing impairment was associated with higher activation across conditions in the left superior temporal gyrus, as compared to the silent baseline. However, the region of interest analysis indicated lower activation during degraded speech relative to clear speech in bilateral frontal regions and the insular cortex, for HH compared to NH listeners. Hearing impairment was also associated with a weaker relation between the pupil response and activation in the right inferior frontal gyrus. Overall, degraded speech evoked higher frontal activation than clear speech.

CONCLUSION

Brain areas associated with attentional and cognitive-control processes may be increasingly recruited when speech is degraded and are related to the pupil dilation response, but this relationship is weaker in HH listeners.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.27162135.

Pupillary response to cognitive control in depression-prone individuals

Revealing the pupillary correlates of depression-prone individuals is conducive to the early intervention and treatment of depression. This study recruited 31 depression-prone and 31 healthy individuals. They completed an emotional task-switching task combined with a go/no-go task, and task-evoked pupillary responses (TEPR) were recorded. Behavioral results showed no significant differences in behavioral performance in terms of cognitive flexibility and inhibition between the depression-prone group and the healthy control group. The pupillary results revealed that (1) the depression-prone group showed slightly lower TEPRs to positive stimuli than the healthy controls during cue presentation; (2) during target presentation, the depression-prone group did not show an effect of emotional valence on the pupillary response in the task-repeat trials; and (3) compared to the healthy controls, the depression-prone group showed significantly smaller TEPRs to negative no-go stimuli and had a longer latency of the second peak of pupil dilation in no-go trials. These results imply that depression-prone individuals may have slower neural responses in cognitive control tasks and emotion-specific weakened cognitive control than healthy individuals.

Dopamine and Norepinephrine Differentially Mediate the Exploration-Exploitation Tradeoff

Dopamine (DA) and norepinephrine (NE) have been repeatedly implicated in neuropsychiatric vulnerability, in part via their roles in mediating the decision-making processes. Although two neuromodulators share a synthesis pathway and are coactivated under states of arousal, they engage in distinct circuits and modulatory roles. However, the specific role of each neuromodulator in decision-making, in particular the exploration-exploitation tradeoff, remains unclear. Revealing how each neuromodulator contributes to exploration-exploitation tradeoff is important in guiding mechanistic hypotheses emerging from computational psychiatric approaches. To understand the differences and overlaps of the roles of these two catecholamine systems in regulating exploration, a direct comparison using the same dynamic decision-making task is needed. Here, we ran male and female mice in a restless two-armed bandit task, which encourages both exploration and exploitation. We systemically administered a nonselective DA antagonist (flupenthixol), a nonselective DA agonist (apomorphine), a NE beta-receptor antagonist (propranolol), and a NE beta-receptor agonist (isoproterenol) and examined changes in exploration within subjects across sessions. We found a bidirectional modulatory effect of dopamine on exploration. Increasing dopamine activity decreased exploration and decreasing dopamine activity increased exploration. The modulatory effect of beta-noradrenergic receptor activity on exploration was mediated by sex. Reinforcement learning model parameters suggested that dopamine modulation affected exploration via decision noise and norepinephrine modulation affected exploration via sensitivity to outcome. Together, these findings suggested that the mechanisms that govern the exploration-exploitation transition are sensitive to changes in both catecholamine functions and revealed differential roles for NE and DA in mediating exploration.

Neurophysiology of Effortful Listening: Decoupling Motivational Modulation from Task Demands

In demanding listening situations, a listener's motivational state may affect their cognitive investment. Here, we aim to delineate how domain-specific sensory processing, domain-general neural alpha power, and pupil size as a proxy for cognitive investment encode influences of motivational state under demanding listening. Participants (male and female) performed an auditory gap-detection task while the pupil size and the magnetoencephalogram were simultaneously recorded. Task demand and a listener's motivational state were orthogonally manipulated through changes in gap duration and monetary-reward prospect, respectively. Whereas task difficulty impaired performance, reward prospect enhanced it. The pupil size reliably indicated the modulatory impact of an individual's motivational state. At the neural level, the motivational state did not affect auditory sensory processing directly but impacted attentional postprocessing of an auditory event as reflected in the late evoked-response field and alpha-power change. Both pregap pupil dilation and higher parietal alpha power predicted better performance at the single-trial level. The current data support a framework wherein the motivational state acts as an attentional top-down neural means of postprocessing the auditory input in challenging listening situations.

Neurobehavioral meaning of pupil size

Pupil size is a widely used metric of brain state. It is one of the few signals originating from the brain that can be readily monitored with low-cost devices in basic science, clinical, and home settings. It is, therefore, important to investigate and generate well-defined theories related to specific interpretations of this metric. What exactly does it tell us about the brain? Pupils constrict in response to light and dilate during darkness, but the brain also controls pupil size irrespective of luminosity. Pupil size fluctuations resulting from ongoing "brain states" are used as a metric of arousal, but what is pupil-linked arousal and how should it be interpreted in neural, cognitive, and computational terms? Here, we discuss some recent findings related to these issues. We identify open questions and propose how to answer them through a combination of well-defined tasks, neurocomputational models, and neurophysiological probing of the interconnected loops of causes and consequences of pupil size.

No effects of cerebellar transcranial random noise stimulation on cerebellar brain inhibition, visuomotor learning, and pupil diameter

Cerebellar brain inhibition (CBI) is an inhibitory output from the cerebellum to the primary motor cortex, which is decreased in early motor learning. Transcranial random noise stimulation (tRNS) is a noninvasive brain stimulation to induce brain plastic changes; however, the effects of cerebellar tRNS on CBI and motor learning have not been investigated yet to our knowledge. In this study, whether cerebellar tRNS decreases CBI and improves motor learning was examined, and pupil diameter was measured to examine physiological changes due to the effect of tRNS on motor learning. Thirty-four healthy subjects were assigned to either the cerebellar tRNS group or the Sham group. The subjects performed visuomotor tracking task with ten trials each in the early and late learning stages while receiving the stimulus intervention. CBI and motor evoked potentials were measured before the learning task, after the early learning stage, and after the late learning stage, and pupil diameter was measured during the task. There was no change in CBI in both groups. No group differences in motor learning rates were observed at any learning stages. Pupil diameter was smaller in the late learning stage than in the early learning stage in both groups. The cerebellar tRNS was suggested not to induce changes in CBI and improvement in motor learning, and it did not affect pupil diameter.

Evaluating phasic transcutaneous vagus nerve stimulation (taVNS) with pupil dilation: the importance of stimulation intensity and sensory perception

The efficacy of transcutaneous auricular vagus nerve stimulation (taVNS) as a non-invasive method to modulate physiological markers of noradrenergic activity of the Locus Coeruleus (LC), such as pupil dilation, is increasingly more discussed. However, taVNS studies show high heterogeneity of stimulation effects. Therefore, a taVNS setup was established here to test different frequencies (10 Hz and 25 Hz) and intensities (3 mA and 5 mA) during phasic stimulation (3 s) with time-synchronous recording of pupil dilation in younger adults. Specifically, phasic real taVNS and higher intensity led to increased pupil dilation, which is consistent with phasic invasive VNS studies in animals. The results also suggest that the influence of intensity on pupil dilation may be stronger than that of frequency. However, there was an attenuation of taVNS-induced pupil dilation when differences in perception of sensations were considered. Specifically, pupil dilation during phasic stimulation increased with perceived stimulation intensity. The extent to which the effect of taVNS induces pupil dilation and the involvement of sensory perception in the stimulation process are discussed here and require more extensive research. Additionally, it is crucial to strive for comparable stimulation sensations during systematic parameter testing in order to investigate possible effects of phasic taVNS on pupil dilation in more detail.

Pupil dilation responds to the intrinsic social characteristics of affective touch

Affective Touch is characterized by both emotional and arousing dimensions that rely on specific features of a gentle human caress. In this study, we investigated whether and how both the nature of the touching effector (Human hand vs. Artificial hand) and touch type (Dynamic vs. Static) influenced the participants' pupil dilation and their subjective experience during tactile stimulation. We observed that when participants received a dynamic touch, their pupil dilation increased more when the touch was produced by a human compared to an artificial hand. This discrimination was not present for static touch. Also, dynamic touch given by a human hand invoked a supralinear enhancement of pupil dilation indicating that the combination of these two features induced a stronger autonomic activation than the summed effects of each separately. Moreover, this specific type of touch was perceived as the most pleasant compared to all other tactile stimulations. Overall, our results suggest that pupil dilation could reflect the pleasant experience of human-to-human tactile interactions, supporting the notion that the autonomic nervous system is responsive to the emotional and hedonic aspects associated with Affective Touch as a part of a complex and holistic social experience, rather than solely reacting to its low-level sensory properties.

Semantic inhibition impairment in college students with depressive states as evidenced by EEG and pupillometry during the hayling task

In this study we tested whether depression is associated with impaired semantic inhibition, resulting in symptoms of rumination and anhedonia. For this purpose and using the Beck Depression Inventory II (BDI-II) college students with depressive states (DEP) and matched controls (CTL) performed a Hayling's task, while EEG and pupillometry measures were recorded. Participants were asked to complete sentential contexts with either a highly associated word (initiation) or a non-related word (inhibition), in response to randomly presented trial-by-trial cues. The DEP group, compared to the CTL group, showed lower performance, and reduced frontal negativity (N450) in inhibition trials. Source analyses revealed greater activation for inhibition trials than for initiation trials in bilateral orbitofrontal cortex for the CTL group, but the difference was reduced and more left lateralized for the DEP group. In addition, the DEP group showed more pupil size reactivity to inhibition trials than the CTL group, indicating higher cognitive effort during semantic inhibition. Finally, self-reported rumination and anhedonia correlated with N450 in inhibition trials, and rumination correlated with pupil dilation. Overall, this research contributes to understanding the neural underpinnings of impaired semantic inhibition in individuals with depression, with potential clinical applications.

Multi-level processing of emotions in life motion signals revealed through pupil responses

Perceiving emotions from the movements of other biological entities is critical for human survival and interpersonal interactions. Here, we report that emotional information conveyed by point-light biological motion (BM) triggered automatic physiological responses as reflected in pupil size. Specifically, happy BM evoked larger pupil size than neutral and sad BM, while sad BM induced a smaller pupil response than neutral BM. Moreover, this happy over sad pupil dilation effect is negatively correlated with individual autistic traits. Notably, emotional BM with only local motion features retained could also exert modulations on pupils. Compared with intact BM, both happy and sad local BM evoked stronger pupil responses than neutral local BM starting from an earlier time point, with no difference between the happy and sad conditions. These results revealed a fine-grained pupil-related emotional modulation induced by intact BM and a coarse but rapid modulation by local BM, demonstrating multi-level processing of emotions in life motion signals. Taken together, our findings shed new light on BM emotion processing, and highlight the potential of utilizing the emotion-modulated pupil response to facilitate the diagnosis of social cognitive disorders.

Cardiac-Sympathetic Contractility and Neural Alpha-Band Power: Cross-Modal Collaboration during Approach-Avoidance Conflict

As evidence mounts that the cardiac-sympathetic nervous system reacts to challenging cognitive settings, we ask if these responses are epiphenomenal companions or if there is evidence suggesting a more intertwined role of this system with cognitive function. Healthy male and female human participants performed an approach-avoidance paradigm, trading off monetary reward for painful electric shock, while we recorded simultaneous electroencephalographic and cardiac-sympathetic signals. Participants were reward sensitive but also experienced approach-avoidance "conflict" when the subjective appeal of the reward was near equivalent to the revulsion of the cost. Drift-diffusion model parameters suggested that participants managed conflict in part by integrating larger volumes of evidence into choices (wider decision boundaries). Late alpha-band (neural) dynamics were consistent with widening decision boundaries serving to combat reward sensitivity and spread attention more fairly to all dimensions of available information. Independently, wider boundaries were also associated with cardiac "contractility" (an index of sympathetically mediated positive inotropy). We also saw evidence of conflict-specific "collaboration" between the neural and cardiac-sympathetic signals. In states of high conflict, the alignment (i.e., product) of alpha dynamics and contractility were associated with a further widening of the boundary, independent of either signal's singular association. Cross-trial coherence analyses provided additional evidence that the autonomic systems controlling cardiac-sympathetics might influence the assessment of information streams during conflict by disrupting or overriding reward processing. We conclude that cardiac-sympathetic control might play a critical role, in collaboration with cognitive processes, during the approach-avoidance conflict in humans.

Shaping dynamical neural computations using spatiotemporal constraints

Dynamics play a critical role in computation. The principled evolution of states over time enables both biological and artificial networks to represent and integrate information to make decisions. In the past few decades, significant multidisciplinary progress has been made in bridging the gap between how we understand biological versus artificial computation, including how insights gained from one can translate to the other. Research has revealed that neurobiology is a key determinant of brain network architecture, which gives rise to spatiotemporally constrained patterns of activity that underlie computation. Here, we discuss how neural systems use dynamics for computation, and claim that the biological constraints that shape brain networks may be leveraged to improve the implementation of artificial neural networks. To formalize this discussion, we consider a natural artificial analog of the brain that has been used extensively to model neural computation: the recurrent neural network (RNN). In both the brain and the RNN, we emphasize the common computational substrate atop which dynamics occur-the connectivity between neurons-and we explore the unique computational advantages offered by biophysical constraints such as resource efficiency, spatial embedding, and neurodevelopment.