The Neural Correlates of Self-Regulatory Fatigability During Inhibitory Control of Eye Blinking

Engagement of mental effort in response to mental fatigue: A psychophysiological analysis

Acute mental fatigue, characterized by a transient decline in cognitive efficiency during or following prolonged cognitive tasks, can be managed through adaptive effort deployment. In response to mental fatigue, individuals can employ two main behavioral patterns: engaging a compensatory effort to limit performance decrements, or disengaging effort, leading to performance deterioration. This study investigated the behavioral pattern used by participants in mental fatigue conditions. Fifty participants underwent a sequential-task protocol with counterbalanced sessions who took place in two separate sessions: a 30-min incongruent Stroop task (fatiguing session) or a 30-min documentary viewing task (control session), followed by a time-to-exhaustion (TTE) handgrip task at 13 % of maximal voluntary contraction. Psychophysiological measures included the preejection period, heart rate variability, blood pressure, and respiration. Behavioral results showed deteriorated TTE handgrip performance after the Stroop task compared to after the documentary viewing task. During the Stroop task participants were more conservative and prioritized accuracy over speed. Self-reported fatigue was greater after the Stroop task. Psychophysiological data revealed a gradual decrease in sympathetic activity over time in both tasks, with the Stroop task showing a more pronounced decrease. Taken together, these findings suggest a disengagement of effort for a large proportion of participants (49 %) that could be partly attributed to a habituation to the demands of the Stroop task. This study illustrates the interplay of behavioral patterns of effort investment in the context of mental fatigue and underscores the role of disengagement as a dominant response to this phenomenon among healthy participants.

Neuroimaging the emotional modulation of urge inhibition in Tourette Syndrome

Tourette Syndrome (TS) is a neuropsychiatric condition characterized by tics that are typically preceded by uncomfortable urges that build until the tic is performed. Both tics and their associated urges are commonly exacerbated during states of heightened emotion. However, the neural substrates that are responsible for the development of urges have not been fully elucidated, particularly with regards to the influence of emotion. In this study, we investigate the brain areas associated with the development of urges and their modulation by emotion in patients with TS. Moreover, we explore the influence of obsessive-compulsive symptoms (OCS) which are commonly comorbid in TS. Forty patients with TS and 20 healthy controls completed an emotional blink suppression paradigm while undergoing functional magnetic resonance imaging. For the paradigm, participants completed alternating blocks of blink inhibition and free blinking while viewing pictures of angry and neutral facial expressions. Compared to controls, patients exhibited greater activity in the superior temporal gyrus and midcingulate during the inhibition of urges. Within the patient group, tic severity was associated with activity in the superior frontal gyrus during the angry inhibition contrast as compared to neutral; greater premonitory urge severity was associated with greater activity in the hippocampus, middle temporal gyrus and in the subcortex; blink inhibition ability was negatively associated with activity in the thalamus and insula. There were no significant associations with OCS severity for the emotion-related contrasts. The observed activated regions may represent a network that produces urges in patients, or alternatively, could represent compensatory cortical activity needed to keep urges and tics under control during emotional situations. Additionally, our findings suggest that OCS in the context of TS is similar to traditional obsessive-compulsive disorder and is neurobiologically dissociable from tics.

The urge to blink in Tourette syndrome

Functional neuroimaging studies have attempted to explore brain activity that occurs with tic occurrence in subjects with Tourette syndrome (TS). However, they are limited by the difficulty of disambiguating brain activity required to perform a tic, or activity caused by the tic, from brain activity that generates a tic. Inhibiting ticcing following the urge to tic is important to patients' experience of tics and we hypothesize that inhibition of a compelling motor response to a natural urge will differ in TS subjects compared to controls. This study examines the urge to blink, which shares many similarities to premonitory urges to tic. Previous neuroimaging studies with the same hypothesis have used a one-size-fits-all approach to extract brain signal putatively linked to the urge to blink. We aimed to create a subject-specific and blink-timing-specific pathophysiological model, derived from out-of-scanner blink suppression trials, to eventually better interpret blink suppression fMRI data. Eye closure and continuously self-reported discomfort were reported during five blink suppression trials in 30 adult volunteers, 15 with a chronic tic disorder. For each subject, data from four of the trials were used with an empirical mathematical model to predict discomfort from eye closure observed during the remaining trial. The blink timing model of discomfort during blink suppression predicted observed discomfort much better than previously applied models. Combining this approach with observed eye closure during fMRI blink suppression trials should therefore extract brain signal more tightly linked to the urge to blink. The simple mean of time-discomfort curves from each subject's other trials also outperformed older models. The TS group blinked more than twice as often during the blink suppression block, and reported higher baseline discomfort, smaller excursion from baseline to peak discomfort during the blink suppression block, and slower return of discomfort to baseline during the recovery block.

Neural activation and connectivity during cued eye blinks in Chronic Tic Disorders

Objective

The pathophysiology of Chronic Tic Disorders (CTDs), including Tourette Syndrome, remains poorly understood. The goal of this study was to compare neural activity and connectivity during a voluntary movement (VM) paradigm that involved cued eye blinks among children with and without CTDs. Using the precise temporal resolution of electroencephalography (EEG), we used the timing and location of cortical source resolved spectral power activation and connectivity to map component processes such as visual attention, cue detection, blink regulation and response monitoring. We hypothesized that neural activation and connectivity during the cued eye blink paradigm would be significantly different in regions typically associated with effortful control of eye blinks, such as frontal, premotor, parietal, and occipital cortices between children with and without CTD.

Method

Participants were 40 children (23 with CTD, 17 age-matched Healthy Control [HC]), between the ages of 8–12 (mean age = 9.5) years old. All participants underwent phenotypic assessment including diagnostic interviews, behavior rating scales and 128-channel EEG recording. Upon presentation of a cue every 3 s, children were instructed to make an exaggerated blink.

Results

Behaviorally, the groups did not differ in blink number, latency, or ERP amplitude. Within source resolved clusters located in left dorsolateral prefrontal cortex, posterior cingulate, and supplemental motor area, children with CTD exhibited higher gamma band spectral power relative to controls. In addition, significant diagnostic group differences in theta, alpha, and beta band power in inferior parietal cortex emerged. Spectral power differences were significantly associated with clinical characteristics such as tic severity and premonitory urge strength. After calculating dipole density for 76 anatomical regions, the CTD and HC groups had 70% overlap of top regions with the highest dipole density, suggesting that similar cortical networks were used across groups to carry out the VM. The CTD group exhibited significant information flow increase and dysregulation relative to the HC group, particularly from occipital to frontal regions.

Conclusion

Children with CTD exhibit abnormally high levels of neural activation and dysregulated connectivity among networks used for regulation and effortful control of voluntary eye blinks.

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First cortical source level EEG study on brain activity and connectivity in CTD.

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Children with CTD exhibit aberrant levels of neural activation and connectivity.

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Neural activation was significantly associated with tic severity and premonitory urge.