Spontaneous blink rates correlate with dopamine levels in the caudate nucleus of MPTP-treated monkeys

Altered pupil light and darkness reflex and eye-blink responses in late-life depression

BACKGROUND

Late-life depression (LLD) is a prevalent neuropsychiatric disorder in the older population. While LLD exhibits high mortality rates, depressive symptoms in older adults are often masked by physical health conditions. In younger adults, depression is associated with deficits in pupil light reflex and eye blink rate, suggesting the potential use of these responses as biomarkers for LLD.

METHODS

We conducted a study using video-based eye-tracking to investigate pupil and blink responses in LLD patients (n = 25), older (OLD) healthy controls (n = 29), and younger (YOUNG) healthy controls (n = 25). The aim was to determine whether there were alterations in pupil and blink responses in LLD compared to both OLD and YOUNG groups.

RESULTS

LLD patients displayed significantly higher blink rates and dampened pupil constriction responses compared to OLD and YOUNG controls. While tonic pupil size in YOUNG differed from that of OLD, LLD patients did not exhibit a significant difference compared to OLD and YOUNG controls. GDS-15 scores in older adults correlated with light and darkness reflex response variability and blink rates. PHQ-15 scores showed a correlation with blink rates, while MoCA scores correlated with tonic pupil sizes.

CONCLUSIONS

The findings demonstrate that LLD patients display altered pupil and blink behavior compared to OLD and YOUNG controls. These altered responses correlated differently with the severity of depressive, somatic, and cognitive symptoms, indicating their potential as objective biomarkers for LLD.

Blink-related arousal network surges are shaped by cortical vigilance states

The vigilance state and the excitability of cortical networks impose wide-range effects on brain dynamics that arousal surges could promptly modify. We previously reported an association between spontaneous eye-blinks and BOLD activation in the brain arousal ascending network (AAN) and in thalamic nuclei based on 3T MR resting state brain images. Here we aimed to replicate our analyses using 7T MR images in a larger cohort of participants collected from the Human Connectome Project (HCP), which also contained simultaneous eye-tracking recordings, and to assess the interaction between the blink-associated arousal surges and the vigilance states. For this purpose, we compared blink associated BOLD activity under a vigilant versus a drowsy state, a classification made based on the pupillary data obtained during the fMRI scans. We conducted two main analyses: i) Cross-correlation analysis between the BOLD signal and blink events (eye blink time-series were convolved with the canonical and also with the temporal derivative of the Hemodynamic Response Function, HRF) within preselected regions of interests (ROIs) (i.e., brainstem AAN, thalamic and cerebellar nuclei) together with an exploratory voxel-wise analyses to assess the whole-brain, and ii) blink-event analysis of the BOLD signals to reveal the signal changes onset to the blinks in the preselected ROIs. Consistent with our prior findings on 3T MRI, we showed significant positive cross correlations between BOLD peaks in brainstem and thalamic nuclei that preceded or were overlapping with blink moments and that sharply decreased post-blink. Whole brain analysis revealed blink-related activation that was strongest in cerebellum, insula, lateral geniculate nucleus (LGN) and visual cortex. Drowsiness impacted HRF BOLD (enhancing it), time-to-peak (delaying it) and post-blink BOLD activity (accentuating decreases). Responses in the drowsy state could be related to the differences in the excitability of cortical, subcortical and cerebellar tissue, such that cerebellar and thalamic regions involved in visual attention processing were more responsive for the vigilant state, but AAN ROIs, as well as cerebellar and thalamic ROIs connected to pre-motor, frontal, temporal and DMN regions were less responsive. Such qualitative and quantitative differences in the blink related BOLD signal changes could reflect delayed cortical processing and the ineffectiveness of arousal surges during states of drowsiness. Future studies that manipulate arousal are needed to corroborate a mechanistic interaction of arousal surges with vigilance states and cortical excitability.

Spontaneous blink-related beta power increase and theta phase reset in subthalamic nucleus of Parkinson patients during walking

OBJECTIVE

Both blinking and walking are altered in Parkinson's disease and both motor outputs have been shown to be linked in healthy subjects. Additionally, studies suggest an involvement of basal ganglia activity and striatal dopamine in blink generation. We investigated the role of the basal ganglia circuitry on spontaneous blinking and if this role is dependent on movement state and striatal dopamine.

METHODS

We analysed subthalamic nucleus (STN) activity in seven chronically implanted patients for deep brain stimulation (DBS) with respect to blinks and movement state (resting state and unperturbed walking). Neurophysiological recordings were combined with individual molecular brain imaging assessing the dopamine reuptake transporter (DAT) density for the left and right striatum separately.

RESULTS

We found a significantly higher blink rate during walking compared to resting. The blink rate during walking positively correlated with the DAT density of the left caudate nucleus. During walking only, spontaneous blinking was followed by an increase in the right STN beta power and a bilateral subthalamic phase reset in the low frequencies. The right STN blink-related beta power modulation correlated negatively with the DAT density of the contralateral putamen. The left STN blink-related beta power correlated with the DAT density of the putamen in the less dopamine-depleted hemisphere. Both correlations were specific to the walking condition and to beta power following a blink.

CONCLUSION

Our findings show that spontaneous blinking is related to striatal dopamine and has a frequency specific deployment in the STN. This correlation depends on the current movement state such as walking.

SIGNIFICANCE

This work indicates that subcortical activity following a motor event as well as the relationship between dopamine and motor events can be dependent on the motor state. Accordingly, disease related changes in brain activity should be assessed during natural movement.

Motor synchronization and impulsivity in pediatric borderline personality disorder with and without attention-deficit hyperactivity disorder: an eye-tracking study of saccade, blink and pupil behavior

Shifting motor actions from reflexively reacting to an environmental stimulus to predicting it allows for smooth synchronization of behavior with the outside world. This shift relies on the identification of patterns within the stimulus - knowing when a stimulus is predictable and when it is not - and launching motor actions accordingly. Failure to identify predictable stimuli results in movement delays whereas failure to recognize unpredictable stimuli results in early movements with incomplete information that can result in errors. Here we used a metronome task, combined with video-based eye-tracking, to quantify temporal predictive learning and performance to regularly paced visual targets at 5 different interstimulus intervals (ISIs). We compared these results to the random task where the timing of the target was randomized at each target step. We completed these tasks in female pediatric psychiatry patients (age range: 11-18 years) with borderline personality disorder (BPD) symptoms, with (n = 22) and without (n = 23) a comorbid attention-deficit hyperactivity disorder (ADHD) diagnosis, against controls (n = 35). Compared to controls, BPD and ADHD/BPD cohorts showed no differences in their predictive saccade performance to metronome targets, however, when targets were random ADHD/BPD participants made significantly more anticipatory saccades (i.e., guesses of target arrival). The ADHD/BPD group also significantly increased their blink rate and pupil size when initiating movements to predictable versus unpredictable targets, likely a reflection of increased neural effort for motor synchronization. BPD and ADHD/BPD groups showed increased sympathetic tone evidenced by larger pupil sizes than controls. Together, these results support normal temporal motor prediction in BPD with and without ADHD, reduced response inhibition in BPD with comorbid ADHD, and increased pupil sizes in BPD patients. Further these results emphasize the importance of controlling for comorbid ADHD when querying BPD pathology.

Effects of DPTQ, a novel positive allosteric modulator of the dopamine D1 receptor, on spontaneous eye blink rate and spatial working memory in the nonhuman primate

RATIONALE

Dopamine (DA) signaling through the D1 receptor has been shown to be integral to multiple aspects of cognition, including the core process of working memory. The discovery of positive allosteric modulators (PAMs) of the D1 receptor has enabled treatment modalities that may have alternative benefits to orthosteric D1 agonists arising from a synergism of action with functional D1 receptor signaling.

OBJECTIVES

To investigate this potential, we have studied the effects of the novel D1 PAM DPTQ on a spatial delayed response working memory task in the rhesus monkey. Initial studies indicated that DPTQ binds to primate D1R with high affinity and selectivity and elevates spontaneous eye blink rate in rhesus monkeys in a dose-dependent manner consistent with plasma ligand exposures and central D1activation.

RESULTS

Based on those results, DPTQ was tested at 2.5 mg/kg IM in the working memory task. No acute effect was observed 1 h after dosing, but performance was impaired 48 h later. Remarkably, this deficit was immediately followed by a significant enhancement in cognition over the next 3 days. In a second experiment in which DPTQ was administered on days 1 and 5, the early impairment was smaller and did not reach statistical significance, but statistically significant enhancement of performance was observed over the following week. Lower doses of 0.1 and 1.0 mg/kg were also capable of producing this protracted enhancement without inducing any transient impairment.

CONCLUSIONS

DPTQ exemplifies a class of D1PAMs that may be capable of providing long-term improvements in working memory.

Activation of brain arousal networks coincident with eye blinks during resting state

Eye-blinking has been implicated in arousal and attention. Here we test the hypothesis that blinking-moments represent arousal surges associated with activation of the ascending arousal network (AAN) and its thalamic projections. For this purpose, we explored the temporal relationship between eye-blinks and fMRI BOLD activity in AAN and thalamic nuclei, as well as whole brain cluster corrected activations during eyes-open, resting-state fMRI scanning. We show that BOLD activations in the AAN nuclei peaked prior to the eye blinks and in thalamic nuclei peaked prior to and during the blink, consistent with the role of eye blinking in arousal surges. Additionally, we showed visual cortex peak activation prior to the eye blinks, providing further evidence of the visual cortex's role in arousal, and document cerebellar peak activation post eye blinks, which might reflect downstream engagement from arousal surges.

A proxy measure of striatal dopamine predicts individual differences in temporal precision

The perception of time is characterized by pronounced variability across individuals, with implications for a diverse array of psychological functions. The neurocognitive sources of this variability are poorly understood, but accumulating evidence suggests a role for inter-individual differences in striatal dopamine levels. Here we present a pre-registered study that tested the predictions that spontaneous eyeblink rates, which provide a proxy measure of striatal dopamine availability, would be associated with aberrant interval timing (lower temporal precision or overestimation bias). Neurotypical adults (N = 69) underwent resting state eye tracking and completed visual psychophysical interval timing and control tasks. Elevated spontaneous eyeblink rates were associated with poorer temporal precision but not with inter-individual differences in perceived duration or performance on the control task. These results signify a role for striatal dopamine in variability in human time perception and can help explain deficient temporal precision in psychiatric populations characterized by elevated dopamine levels.

Spontaneous Eye Blink Rate During the Working Memory Delay Period Predicts Task Accuracy

Spontaneous eye blink rate (sEBR) has been linked to attention and memory, specifically working memory (WM). sEBR is also related to striatal dopamine (DA) activity with schizophrenia and Parkinson’s disease showing increases and decreases, respectively, in sEBR. A weakness of past studies of sEBR and WM is that correlations have been reported using blink rates taken at baseline either before or after performance of the tasks used to assess WM. The goal of the present study was to understand how fluctuations in sEBR during different phases of a visual WM task predict task accuracy. In two experiments, with recordings of sEBR collected inside and outside of a magnetic resonance imaging bore, we observed sEBR to be positively correlated with WM task accuracy during the WM delay period. We also found task-related modulation of sEBR, including higher sEBR during the delay period compared to rest, and lower sEBR during task phases (e.g., stimulus encoding) that place demands on visual attention. These results provide further evidence that sEBR could be an important predictor of WM task performance with the changes during the delay period suggesting a role in WM maintenance. The relationship of sEBR to DA activity and WM maintenance is discussed.

Altered Pain Processing Associated with Administration of Dopamine Agonist and Antagonist in Healthy Volunteers

Striatal dopamine dysfunction is associated with the altered top-down modulation of pain processing. The dopamine D2-like receptor family is a potential substrate for such effects due to its primary expression in the striatum, but evidence for this is currently lacking. Here, we investigated the effect of pharmacologically manipulating striatal dopamine D2 receptor activity on the anticipation and perception of acute pain stimuli in humans. Participants received visual cues that induced either certain or uncertain anticipation of two pain intensity levels delivered via a CO₂ laser. Rating of the pain intensity and unpleasantness was recorded. Brain activity was recorded with EEG and analysed via source localisation to investigate neural activity during the anticipation and receipt of pain. Participants completed the experiment under three conditions, control (Sodium Chloride), D2 receptor agonist (Cabergoline), and D2 receptor antagonist (Amisulpride), in a repeated-measures, triple-crossover, double-blind study. The antagonist reduced an individuals’ ability to distinguish between low and high pain following uncertain anticipation. The EEG source localisation showed that the agonist and antagonist reduced neural activations in specific brain regions associated with the sensory integration of salient stimuli during the anticipation and receipt of pain. During anticipation, the agonist reduced activity in the right mid-temporal region and the right angular gyrus, whilst the antagonist reduced activity within the right postcentral, right mid-temporal, and right inferior parietal regions. In comparison to control, the antagonist reduced activity within the insula during the receipt of pain, a key structure involved in the integration of the sensory and affective aspects of pain. Pain sensitivity and unpleasantness were not changed by D2R modulation. Our results support the notion that D2 receptor neurotransmission has a role in the top-down modulation of pain.

Motor restrictions impair divergent thinking during walking and during sitting

Creativity, specifically divergent thinking, has been shown to benefit from unrestrained walking. Despite these findings, it is not clear if it is the lack of restriction that leads to the improvement. Our goal was to explore the effects of motor restrictions on divergent thinking for different movement states. In addition, we assessed whether spontaneous eye blinks, which are linked to motor execution, also predict performance. In experiment 1, we compared the performance in Guilford’s alternate uses task (AUT) during walking vs. sitting, and analysed eye blink rates during both conditions. We found that AUT scores were higher during walking than sitting. Albeit eye blinks differed significantly between movement conditions (walking vs. sitting) and task phase (baseline vs. thinking vs. responding), they did not correlate with task performance. In experiment 2 and 3, participants either walked freely or in a restricted path, or sat freely or fixated on a screen. When the factor restriction was explicitly modulated, the effect of walking was reduced, while restriction showed a significant influence on the fluency scores. Importantly, we found a significant correlation between the rate of eye blinks and creativity scores between subjects, depending on the restriction condition. Our study shows a movement state-independent effect of restriction on divergent thinking. In other words, similar to unrestrained walking, unrestrained sitting also improves divergent thinking. Importantly, we discuss a mechanistic explanation of the effect of restriction on divergent thinking based on the increased size of the focus of attention and the consequent bias towards flexibility.

The confounding effects of eye blinking on pupillometry, and their remedy

Pupillometry, thanks to its strong relationship with cognitive factors and recent advancements in measuring techniques, has become popular among cognitive or neural scientists as a tool for studying the physiological processes involved in mental or neural processes. Despite this growing popularity of pupillometry, the methodological understanding of pupillometry is limited, especially regarding potential factors that may threaten pupillary measurements' validity. Eye blinking can be a factor because it frequently occurs in a manner dependent on many cognitive components and induces a pulse-like pupillary change consisting of constriction and dilation with substantive magnitude and length. We set out to characterize the basic properties of this "blink-locked pupillary response (BPR)," including the shape and magnitude of BPR and their variability across subjects and blinks, as the first step of studying the confounding nature of eye blinking. Then, we demonstrated how the dependency of eye blinking on cognitive factors could confound, via BPR, the pupillary responses that are supposed to reflect the cognitive states of interest. By building a statistical model of how the confounding effects of eye blinking occur, we proposed a probabilistic-inference algorithm of de-confounding raw pupillary measurements and showed that the proposed algorithm selectively removed BPR and enhanced the statistical power of pupillometry experiments. Our findings call for attention to the presence and confounding nature of BPR in pupillometry. The algorithm we developed here can be used as an effective remedy for the confounding effects of BPR on pupillometry.

Patterns of eye blinks are modulated by auditory input in humans

Previous studies could elaborate a link between attentional processes and eye blinking in both visual and auditory attention tasks. Here we show that this link is active at a fundamental level of perception: presentation of a series of bare sine tones is sufficient to induce a modulation of temporal blink patterns, allowing to determine which series was presented to participants even when they are not required to interactively engage in processing the auditory input. In particular, we monitored eye blinking during an auditory attention task using two series of sine tones, differing in the predictability of the timing of tone onsets. Whereas inter-onset intervals in one tone series corresponded to uncorrelated samples from a normal distribution, they were distributed according to a Gaussian random walk in the other tone series. We find that blink patterns are dynamically modulated by both purely auditory inputs. The magnitude, form, and coherence of the temporal associations between tone onsets and blink events depend strongly on the requirement to respond to the presented stimuli. The predictability of the tone series appears to modulate pre-stimulus blink inhibition given that a response is required. Altogether, these findings suggest eye blink as a readily available, non-invasive behavioral marker for context-sensitive, moment-to-moment allocation of attention.

Modulation of dopamine tone induces frequency shifts in cortico-basal ganglia beta oscillations

Βeta oscillatory activity (human: 13-35 Hz; primate: 8-24 Hz) is pervasive within the cortex and basal ganglia. Studies in Parkinson's disease patients and animal models suggest that beta-power increases with dopamine depletion. However, the exact relationship between oscillatory power, frequency and dopamine tone remains unclear. We recorded neural activity in the cortex and basal ganglia of healthy non-human primates while acutely and chronically up- and down-modulating dopamine levels. We assessed changes in beta oscillations in patients with Parkinson's following acute and chronic changes in dopamine tone. Here we show beta oscillation frequency is strongly coupled with dopamine tone in both monkeys and humans. Power, coherence between single-units and local field potentials (LFP), spike-LFP phase-locking, and phase-amplitude coupling are not systematically regulated by dopamine levels. These results demonstrate that beta frequency is a key property of pathological oscillations in cortical and basal ganglia networks.

Examining the effect of depressive symptoms on habit formation and habit-breaking

BACKGROUND AND OBJECTIVES

Dysfunction in reward processing is a hallmark feature of depression. In the context of reinforcement learning, previous research has linked depression with reliance on simple habit-driven ('model-free') learning strategies over more complex, goal-directed ('model-based') strategies. However, the relationship between depression and habit-breaking remains an under-explored research area. The current study sought to bridge this gap by investigating the effect of depressive symptoms on habit formation and habit-breaking under monetary and social feedback conditions. Additionally, we examined whether spontaneous eyeblink rate (EBR), an indirect marker for striatal dopamine levels, would modulate such effects.

METHODS

Depressive symptoms were operationalized using self-report measures. To examine differences in habit formation and habit breaking, undergraduate participants (N = 156) completed a two-stage reinforcement learning task with a devaluation procedure using either monetary or social feedback.

RESULTS

Regression results showed that in the monetary feedback condition, spontaneous EBR moderated the relationship between depressive symptoms and model-free strategies; individuals with more depressive symptomatology and high EBR (higher dopamine levels) exhibited increased reliance on model-free strategies. Depressive symptoms negatively predicted devaluation sensitivity, indicative of difficulty in habit-breaking, in both monetary and social feedback contexts.

LIMITATIONS

Social feedback relied on fixed feedback rather than real-time peer evaluations; depressive symptoms were measured using self-report rather than diagnostic criteria for Major Depressive Disorder; dopaminergic functioning was measured using EBR rather than PET imaging; potential confounds were not controlled for.

CONCLUSIONS

These findings have implications for identifying altered patterns of habit formation and deficits in habit-breaking among those experiencing depressive symptoms.

Dopamine, religiosity, and utilitarian moral judgment

Our goal was to examine the relationship between biological and sociocultural factors that predict utilitarian moral judgment. Utilitarian moral judgments occur when a specific action is based on the outcome rather than its consistency with social norms. We predicted that (1) individuals with higher levels of dopamine will make more utilitarian decisions and (2) individuals who express greater religiosity will make less utilitarian judgments. We measured dopamine using spontaneous eyeblink rate, an indirect measure associated with striatal dopaminergic transmission. A total of 96 participants completed a utilitarian moral judgment task where they made judgments regarding nonmoral, impersonal, personal low-conflict, and personal high-conflict moral dilemmas. Then, participants completed a questionnaire measuring religiosity. We found a negative relationship between religiosity and the proportion of "yes" judgments participants made in the high-conflict personal dilemmas, which was consistent with our second hypothesis. None of our other hypotheses were supported. Understanding biological and cultural factors that relate to utilitarian moral judgment may also help in developing artificial intelligence that more closely mimic human behavior.

Tear metabolomics highlights new potential biomarkers for differentiating between Sjögren's syndrome and other causes of dry eye

PURPOSE

The lacrimal exocrinopathy of primary Sjögren's syndrome (pSS) is one of the main causes of severe dry eye syndrome and a burden for patients. Early recognition and treatment could prevent irreversible damage to lacrimal glands. The aim of this study was to find biomarkers in tears, using metabolomics and data mining approaches, in patients with newly-diagnosed pSS compared to other causes of dry eye syndrome.

METHODS

A prospective cohort of 40 pSS and 40 non-pSS Sicca patients with dryness was explored through a standardized targeted metabolomic approach using liquid chromatography coupled with mass spectrometry. A metabolomic signature predictive of the pSS status was sought out using linear (logistic regression with elastic-net regularization) and non-linear (random forests) machine learning architectures, after splitting the studied population into training, validation and test sets.

RESULTS

Among the 104 metabolites accurately measured in tears, we identified a discriminant signature composed of nine metabolites (two amino acids: serine, aspartate; one biogenic amine: dopamine; six lipids: Lysophosphatidylcholine C16:1, C18:1, C18:2, sphingomyelin C16:0 and C22:3, and the phoshatidylcholine diacyl PCaa C42:4), with robust performances (ROC-AUC = 0.83) for predicting the pSS status. Adjustment for age, sex and anti-SSA antibodies did not disrupt the link between the metabolomic signature and the pSS status. The non-lipidic components also remained specific for pSS regardless of the dryness severity.

CONCLUSION

Our results reveal a metabolomic signature for tears that distinguishes pSS from other dry eye syndromes and further highlight nine key metabolites of potential interest for early diagnosis and therapeutics of pSS.

The latency of spontaneous eye blinks marks relevant visual and auditory information processing

Eye blinks are influenced by external sensory and internal cognitive factors, as mainly shown in the visual domain. In previous studies, these factors corresponded to the time period of task-relevant sensory information and were often linked to a motor response. Our aim was to dissociate the influence of overall sensory input duration, task-relevant information duration, and the motor response to further understand how the temporal modulation of blinks compares among sensory modalities. Using a visual and an auditory temporal judgment task, we found that blinks were suppressed during stimulus presentation in both domains and that the overall input length had a significant positive relationship with the length of this suppression (i.e., with the latency of the first blink after stimulus onset). Importantly, excluding the influence of the overall sensory input duration we could show that the duration of task-relevant input had an additional influence on blink latency in the visual and the auditory domain. Our findings further suggest that this influence was not based on sensory input but on top-down processes. We could exclude task difficulty and the timing of the motor response as driving factors in the blink modulation. Our results suggest a sensory domain-independent modulation of blink latencies, introduced by changes in the length of the task-relevant, attended period. Therefore, not only do blinks mark the timing of sensory input or the preparation of the motor output, but they can also act as precise indicators of periods of cognitive processing.

Dopamine and the interdependency of time perception and reward

Time is a fundamental dimension of our perception of the world and is therefore of critical importance to the organization of human behavior. A corpus of work - including recent optogenetic evidence - implicates striatal dopamine as a crucial factor influencing the perception of time. Another stream of literature implicates dopamine in reward and motivation processes. However, these two domains of research have remained largely separated, despite neurobiological overlap and the apothegmatic notion that "time flies when you're having fun". This article constitutes a review of the literature linking time perception and reward, including neurobiological and behavioral studies. Together, these provide compelling support for the idea that time perception and reward processing interact via a common dopaminergic mechanism.

Ocular measures during associative learning predict recall accuracy

The ability to form associations between stimuli and commit those associations to memory is a cornerstone of human cognition. Dopamine and noradrenaline are critical neuromodulators implicated in a range of cognitive functions, including learning and memory. Eye blink rate (EBR) and pupil diameter have been shown to index dopaminergic and noradrenergic activity. Here, we examined how these ocular measures relate to accuracy in a paired-associate learning task where participants (N = 73) learned consistent object-location associations over eight trials consisting of pre-trial fixation, encoding, delay, and retrieval epochs. In order to examine how within-subject changes and between-subject changes in ocular metrics related to accuracy, we mean centered individual metric values on each trial based on within-person and across-subject means for each epoch. Within-participant variation in EBR was positively related to accuracy in both encoding and delay epochs: faster EBR within the individual predicted better retrieval. Differences in EBR across participants was negatively related to accuracy in the encoding epoch and in early trials of the pre-trial fixation: faster EBR, relative to other subjects, predicted poorer retrieval. Visual scanning behavior in pre-trial fixation and delay epochs was also positively related to accuracy in early trials: more scanning predicted better retrieval. We found no relationship between pupil diameter and accuracy. These results provide novel evidence supporting the utility of ocular metrics in illuminating cognitive and neurobiological mechanisms of paired-associate learning.

The Effect of Dopaminergic Replacement Therapy on Creative Thinking and Insight Problem-Solving in Parkinson's Disease Patients

Parkinson's disease (PD) patients receiving dopaminergic treatment may experience bursts of creativity. Although this phenomenon is sometimes recognized among patients and their clinicians, the association between dopamine replacement therapy (DRT) in PD patients and creativity remains underexplored. It is unclear, for instance, whether DRT affects creativity through convergent or divergent thinking, idea generation, or a general lack of inhibition. It is also unclear whether DRT only augments pre-existing creative attributes or generates creativity de novo. Here, we tested a group of PD patients when “on” and “off” dopaminergic treatment on a series of tests of creative problem-solving (Alternative Uses Task, Compound Remote Associates, Rebus Puzzles), and related their performance to a group of matched healthy controls as well as to their pre-PD creative skills and measures of inhibition/impulsivity. Results did not provide strong evidence that DRT improved creative thinking in PD patients. Rather, PD patients “on” medication showed less flexibility in divergent thinking, generated fewer ideas via insight, and showed worse performance in convergent thinking overall (by making more errors) than healthy controls. Pre-PD creative skills predicted enhanced flexibility and fluency in divergent thinking when PD patients were “on” medication. However, results on convergent thinking were mixed. Finally, PD patients who exhibited deficits in a measure of inhibitory control showed weaker convergent thinking while “on” medication, supporting previous evidence on the importance of inhibitory control in creative problem-solving. Altogether, results do not support the hypothesis that DRT promotes creative thinking in PD. We speculate that bursts of artistic production in PD are perhaps conflated with creativity due to lay conceptions of creativity (i.e., an art-bias).

Preliminary effects of prefrontal tDCS on dopamine-mediated behavior and psychophysiology

The ability to manipulate dopamine in vivo through non-invasive, reversible mechanisms has the potential to impact clinical, translational, and basic research. Recent PET studies have demonstrated increased dopamine release in the striatum after bifrontal transcranial direct current stimulation (tDCS). We sought to extend this work by examining whether bifrontal tDCS could demonstrate an effect on behavioral and physiological correlates of subcortical dopamine activity. We conducted a preliminary between-subjects study (n = 30) with active and sham tDCS and used spontaneous eye blink rate (EBR), facial attractiveness ratings, and greyscales orienting bias as indirect proxies for dopamine functioning. The initial design and analyses were pre-registered (https://osf.io/gmnpc). Stimulation did not significantly affect any of the three measures, though effect sizes were often moderately large and were all in the predicted directions. Additional exploratory analyses suggested that stimulation's effect on EBR might depend on pre-stimulation dopamine levels. Our results suggest that larger samples than those that are standard in tDCS literature should be used to assess the effect of tDCS on dopamine using indirect measures. Further, exploratory results add to a growing body of work demonstrating the importance of accounting for individual differences in tDCS response.

The Early Effects of Alcohol Consumption on Functional Visual Acuity, Tear Functions, and the Ocular Surface

PURPOSE

We investigated the early effects of alcohol intake on tear functions and ocular surface health in this prospective controlled study.

METHODS

Forty-four eyes of 22 subjects (17 males, 5 females; mean age: 35.3 years) who drank 200 mL of 25% Japanese vodka and 44 eyes of age- and sex-matched 22 control subjects who drank water were investigated. Subjects were requested to refrain from alcohol consumption from the previous day and food ingestion 6 hr before the study. Each subject consumed exactly the same order prepared dinner and same quantity of alcohol over the same time frame. Subjects underwent breath alcohol level, tear evaporation and blink rate, tear lipid layer interferometry, tear film break-up time (BUT), fluorescein and Rose Bengal stainings, Schirmer test, and visual analog scale (VAS) evaluation of dry eye symptoms before, as well as 2 and 12 hr after alcohol intake.

RESULTS

The mean breath alcohol level was significantly higher in the alcohol group compared to the water group at 2 and 12 hr (P<0.001). The mean tear evaporation increased significantly from 2.5×10-7 to 8.8×10-7 gr/cm2/sec 12 hr after alcohol intake (P<0.001). The mean BUT shortened significantly from 15.0±5.0 to 5.0±2.5 sec 12 hr after alcohol intake. Lipid layer interferometry showed signs of tear film thinning 12 hr after alcohol intake in all subjects of the alcohol intake group, which was not observed in the water group. The mean blink rates increased significantly from 10.6±1.5 blinks/min to 13.5±0.9 blinks/min and 15.1±1.2 blinks/min at 2 and 12 hr, respectively, in the alcohol group (P<0.001). The Schirmer test values decreased significantly 12 hr after alcohol intake (P<0.001). The mean VAS score for dryness increased from baseline significantly in the alcohol group at 12 hr (P<0.001). No significant time-wise changes in tear functions were observed in the water group.

CONCLUSION

The tear film and ocular surface epithelia showed early and distinctive quantitative and qualitative changes associated with visual disturbances after alcohol intake.

Strong age but weak sex effects in eye movement performance in the general adult population: Evidence from the Rhineland Study

Assessing physiological changes that occur with healthy ageing is prerequisite for understanding pathophysiological age-related changes. Eye movements are studied as biomarkers for pathological changes because they are altered in patients with neurodegenerative disorders. However, there is a lack of data from large samples assessing age-related physiological changes and sex differences in oculomotor performance. Thus, we assessed and quantified cross-sectional relations of age and sex with oculomotor performance in the general population. We report results from the first 4,000 participants (aged 30-95 years) of the Rhineland Study, a community-based prospective cohort study in Bonn, Germany. Participants completed fixation, smooth pursuit, prosaccade and antisaccade tasks. We quantified associations of age and sex with oculomotor outcomes using multivariable linear regression models. Performance in 12 out of 18 oculomotor measures declined with increasing age. No differences between age groups were observed in five antisaccade outcomes (amplitude-adjusted and unadjusted peak velocity, amplitude gain, spatial error and percentage of corrected errors) and for blink rate during fixation. Small sex differences occurred in smooth pursuit velocity gain (men have higher gain) and blink rate during fixation (men blink less). We conclude that performance declines with age in two thirds of oculomotor outcomes but that there was no evidence of sex differences in eye movement performance except for two outcomes. Since the percentage of corrected antisaccade errors was not associated with age but is known to be affected by pathological cognitive decline, it represents a promising candidate preclinical biomarker of neurodegeneration.

Catecholaminergic Modulation of Semantic Processing in Sentence Comprehension

Catecholamine (CA) function has been widely implicated in cognitive functions that are tied to the prefrontal cortex and striatal areas. The present study investigated the effects of methylphenidate, which is a CA agonist, on the electroencephalogram (EEG) response related to semantic processing using a double-blind, placebo-controlled, randomized, crossover, within-subject design. Forty-eight healthy participants read semantically congruent or incongruent sentences after receiving 20-mg methylphenidate or a placebo while their brain activity was monitored with EEG. To probe whether the catecholaminergic modulation is task-dependent, in one condition participants had to focus on comprehending the sentences, while in the other condition, they only had to attend to the font size of the sentence. The results demonstrate that methylphenidate has a task-dependent effect on semantic processing. Compared to placebo, when semantic processing was task-irrelevant, methylphenidate enhanced the detection of semantic incongruence as indexed by a larger N400 amplitude in the incongruent sentences; when semantic processing was task-relevant, methylphenidate induced a larger N400 amplitude in the semantically congruent condition, which was followed by a larger late positive complex effect. These results suggest that CA-related neurotransmitters influence language processing, possibly through the projections between the prefrontal cortex and the striatum, which contain many CA receptors.

Intra-subject consistency of spontaneous eye blink rate in young women across the menstrual cycle

The spontaneous eye blink rate (EBR) has been linked to different cognitive processes and neurobiological factors. It has also been proposed as a putative index for striatal dopaminergic function. While estradiol is well-known to increase dopamine levels through multiple mechanisms, no study up to date has investigated whether the EBR changes across the menstrual cycle. This question is imperative however, as women have sometimes been excluded from studies using the EBR due to potential effects of their hormonal profile. Fifty-four women were tested for spontaneous EBR at rest in three different phases of their menstrual cycle: during menses (low progesterone and estradiol), in the pre-ovulatory phase (when estradiol levels peak and progesterone is still low), and during the luteal phase (high progesterone and estradiol). No significant differences were observed across the menstrual cycle and Bayes factors show strong support for the null hypothesis. Instead, we observed high intra-individual consistency of the EBR in our female sample. Accordingly, we strongly encourage including female participants in EBR studies, regardless of their cycle phase.

Conscious perception and the modulatory role of dopamine: no effect of the dopamine D2 agonist cabergoline on visual masking, the attentional blink, and probabilistic discrimination

RATIONALE

Conscious perception is thought to depend on global amplification of sensory input. In recent years, striatal dopamine has been proposed to be involved in gating information and conscious access, due to its modulatory influence on thalamocortical connectivity.

OBJECTIVES

Since much of the evidence that implicates striatal dopamine is correlational, we conducted a double-blind crossover pharmacological study in which we administered cabergoline-a dopamine D2 agonist-and placebo to 30 healthy participants. Under both conditions, we subjected participants to several well-established experimental conscious-perception paradigms, such as backward masking and the attentional blink task.

RESULTS

We found no evidence in support of an effect of cabergoline on conscious perception: key behavioral and event-related potential (ERP) findings associated with each of these tasks were unaffected by cabergoline.

CONCLUSIONS

Our results cast doubt on a causal role for dopamine in visual perception. It remains an open possibility that dopamine has causal effects in other tasks, perhaps where perceptual uncertainty is more prominent.

Clinical Perspectives of Parkinson's Disease for Ophthalmologists, Otorhinolaryngologists, Cardiologists, Dentists, Gastroenterologists, Urologists, Physiatrists, and Psychiatrists

Parkinson's disease (PD) is a multisystemic disorder characterized by various non-motor symptoms (NMS) in addition to motor dysfunction. NMS include sleep, ocular, olfactory, throat, cardiovascular, gastrointestinal, genitourinary, or musculoskeletal disorders. A range of NMS, particularly hyposmia, sleep disturbances, constipation, and depression, can even appear prior to the motor symptoms of PD. Because NMS can affect multiple organs and result in major disabilities, the recognition and multidisciplinary and collaborative management of NMS by physicians is essential for patients with PD. Therefore, the aim of this review article is to provide an overview of the organs that are affected by NMS in PD together with a brief review of pathophysiology and treatment options.

Substance use is associated with reduced devaluation sensitivity

Substance use has been linked to impairments in reward processing and decision-making, yet empirical research on the relationship between substance use and devaluation of reward in humans is limited. We report findings from two studies that tested whether individual differences in substance use behavior predicted reward learning strategies and devaluation sensitivity in a nonclinical sample. Participants in Experiment 1 (N = 66) and Experiment 2 (N = 91) completed subscales of the Externalizing Spectrum Inventory and then performed a two-stage reinforcement learning task that included a devaluation procedure. Spontaneous eye blink rate was used as an indirect proxy for dopamine functioning. In Experiment 1, correlational analysis revealed a negative relationship between substance use and devaluation sensitivity. In Experiment 2, regression modeling revealed that while spontaneous eyeblink rate moderated the relationship between substance use and reward learning strategies, substance use alone was related to devaluation sensitivity. These results suggest that once reward-action associations are established during reinforcement learning, substance use predicted reduced sensitivity to devaluation independently of variation in eyeblink rate. Thus, substance use is not only related to increased habit formation but also to difficulty disengaging from learned habits. Implications for the role of the dopaminergic system in habitual responding in individuals with substance use problems are discussed.

Abnormal Neural Responses During Reflexive Blinking in Blepharospasm: An Event-Related Functional MRI Study

BACKGROUND

The neurophysiological disruptions underlying blepharospasm, a disabling movement disorder characterized by increased blinking and involuntary muscle spasms of the eyelid, remain poorly understood.

OBJECTIVE

To investigate the neural substrates underlying reflexive blinking in blepharospasm patients compared to healthy controls using simultaneous functional MRI and surface electromyography.

METHODS

Fifteen blepharospasm patients and 15 healthy controls were recruited. Randomly timed air puffs to the left eye were used to induce reflexive eye blinks during two 8-minute functional MRI scans. Continuous surface electromyography and video recordings were used to monitor blink responses. Imaging data were analyzed using an event-related design.

RESULTS

Fourteen blepharospasm patients (10 female; 61.6 ± 8.0 years) and 15 controls (11 female; 60.9 ± 5.5 years) were included in the final analysis. Reflexive eye blinks in controls were associated with activation of the right hippocampus and in patients with activation of the left caudate nucleus. Reflexive blinks in blepharospasm patients showed increased activation in the right postcentral gyrus and precuneus, left precentral gyrus, and left occipital cortex compared to controls. Dystonia severity negatively correlated with activity in the left occipital cortex, and disease duration negatively correlated with reflexive-blink activity in the cerebellum.

CONCLUSIONS

Reflexive blinking in blepharospasm is associated with increased activation in the caudate nucleus and sensorimotor cortices, suggesting a loss of inhibition within the sensorimotor corticobasal ganglia network. The association between decreasing neural response during reflexive blinking in the cerebellum with disease duration suggests an adaptive role. © 2020 International Parkinson and Movement Disorder Society.

Spontaneous eye blink rate predicts individual differences in exploration and exploitation during reinforcement learning

Spontaneous eye blink rate (sEBR) has been linked to striatal dopamine function and to how individuals make value-based choices after a period of reinforcement learning (RL). While sEBR is thought to reflect how individuals learn from the negative outcomes of their choices, this idea has not been tested explicitly. This study assessed how individual differences in sEBR relate to learning by focusing on the cognitive processes that drive RL. Using Bayesian latent mixture modelling to quantify the mapping between RL behaviour and its underlying cognitive processes, we were able to differentiate low and high sEBR individuals at the level of these cognitive processes. Further inspection of these cognitive processes indicated that sEBR uniquely indexed explore-exploit tendencies during RL: lower sEBR predicted exploitative choices for high valued options, whereas higher sEBR predicted exploration of lower value options. This relationship was additionally supported by a network analysis where, notably, no link was observed between sEBR and how individuals learned from negative outcomes. Our findings challenge the notion that sEBR predicts learning from negative outcomes during RL, and suggest that sEBR predicts individual explore-exploit tendencies. These then influence value sensitivity during choices to support successful performance when facing uncertain reward.

The Effect of Mindfulness Meditation on Impulsivity and its Neurobiological Correlates in Healthy Adults

Interest has grown in using mindfulness meditation to treat conditions featuring excessive impulsivity. However, while prior studies find that mindfulness practice can improve attention, it remains unclear whether it improves other cognitive faculties whose deficiency can contribute to impulsivity. Here, an eight-week mindfulness intervention did not reduce impulsivity on the go/no-go task or Barratt Impulsiveness Scale (BIS-11), nor produce changes in neural correlates of impulsivity (i.e. frontostriatal gray matter, functional connectivity, and dopamine levels) compared to active or wait-list control groups. Separately, long-term meditators (LTMs) did not perform differently than meditation-naïve participants (MNPs) on the go/no-go task. However, LTMs self-reported lower attentional impulsivity, but higher motor and non-planning impulsivity on the BIS-11 than MNPs. LTMs had less striatal gray matter, greater cortico-striatal-thalamic functional connectivity, and lower spontaneous eye-blink rate (a physiological dopamine indicator) than MNPs. LTM total lifetime practice hours (TLPH) did not significantly relate to impulsivity or neurobiological metrics. Findings suggest that neither short- nor long-term mindfulness practice may be effective for redressing impulsive behavior derived from inhibitory motor control or planning capacity deficits in healthy adults. Given the absence of TLPH relationships to impulsivity or neurobiological metrics, differences between LTMs and MNPs may be attributable to pre-existing differences.

Examining the link between reward and response inhibition in individuals with substance abuse tendencies

BACKGROUND

Substance use problems are often characterized by dysregulation in reward sensitivity and inhibitory control. In line with this representation, the goal of this investigation was to determine how substance abuse tendencies among university students affect incentivized response inhibition. Additionally, this study examined whether striatal dopamine moderates the impact of substance use on response inhibition performance.

METHODS

The sample included ninety-eight university students. Participants completed this prospective experimental study at an on-campus laboratory. All participants completed substance abuse and disinhibition subscales of the Externalizing Spectrum Inventory-Brief Form. Using a within-subjects design, participants then performed the Stop Signal Task under both neutral (unrewarded) and reward conditions, in which correct response cancellations resulted in a monetary reward. Striatal tonic dopamine levels were operationalized using spontaneous eyeblink rate.

RESULTS

The outcome measures were Stop Signal Reaction Time (SSRT) performance in the unrewarded and rewarded phases of the task. A hierarchical linear regression analysis, controlling for trait disinhibition, age, gender, and cigarette smoking status, identified an interactive effect of substance use and striatal dopamine levels on incentivized SSRT. Substance abuse tendencies were associated with slower SSRT and thus poorer inhibitory control under reward conditions among individuals with low levels of striatal dopamine (F = 7.613, p = .007).

CONCLUSIONS

This work has implications for research examining advanced drug use trajectories. In situations in which rewards are at stake, drug users with low tonic dopamine may be more motivated to seek those rewards at the expense of regulating inhibitory control.

Individual differences in blink rate modulate the effect of instrumental control on subsequent Pavlovian responding

RATIONALE

Pavlovian conditioned responses to cues that signal threat are rapidly acquired and tend to persist over time. However, recent research suggests that the ability to actively avoid or exert control over an anticipated threat can diminish the subsequent expression of Pavlovian responses. Studies in animal models suggest that active avoidance behavior and its consequences may be mediated by dopaminergic function. In the present study, we sought to replicate the finding that active control over threat can attenuate subsequent Pavlovian responding in humans and conducted exploratory analyses testing whether individual differences in blink rate, a putative index of dopaminergic function, might modulate this effect.

METHODS

Participants underwent Pavlovian aversive conditioning, followed immediately by one of two conditions. In the active avoidance condition, participants had the opportunity to actively prevent the occurrence of an anticipated shock, whereas in a yoked extinction condition, participants passively observed the cessation of shocks, but with no ability to influence their occurrence. The following day, the conditioned stimuli were presented without shock, but both groups of participants had no opportunity to employ active instrumental responses. Blink rate was measured throughout the task, and skin conductance responses served as our index of Pavlovian conditioned responding.

RESULTS

Consistent with our previous findings, we observed that the group that could actively avoid the shock on day 1 exhibited attenuated recovery of Pavlovian conditioned responses. Further, we found that individuals in the active avoidance group with higher blink rates exhibited a more robust attenuation of spontaneous recovery.

CONCLUSION

This finding suggests that individual variation in dopaminergic function may modulate the efficacy with which active avoidance strategies can attenuate reactive Pavlovian responses.

Using pupil dilation, eye-blink rate, and the value of mother to investigate reward learning mechanisms in infancy

The brain is adapted to learn from interactions with the environment that predict or enable the procurement of rewards (Schultz, 2010). For infants, the main caregiver (often the mother) is most associated with primary biological rewards such as food and warmth, as well as the most likely provider of emotional and social rewards such as comfort and responsiveness. In this study we capitalize on the reward value of mother to examine reward learning mechanisms in infancy using multiple eye-tracking measures. Converging lines of research have demonstrated links between reward-related striatal dopamine activity and measurable changes in spontaneous eye-blink rate (EBR) and pupil dilation (Eckstein et al., 2017). We presented 7-month-old infants with video stimuli that parametrically increased in social-emotional value (male stranger, female stranger, mother) or in visual attention value (static image, slowed silent cartoon, dynamic cartoon). After establishing infants’ baseline responses to these stimuli, we paired the videos with arbitrary shape cues in an associative learning task. Infants showed superior learning from their own mother’s video and a heightened anticipatory arousal response to the mother-associated cue following learning. Both learning measures were predicted by infants’ baseline EBR to their mother’s video, providing the first evidence of reward learning and transfer in human infants.

The effects of expected reward on creative problem solving

Creative problem solving involves search processes, and it is known to be hard to motivate. Reward cues have been found to enhance performance across a range of tasks, even when cues are presented subliminally, without being consciously detected. It is uncertain whether motivational processes, such as reward, can influence problem solving. We tested the effect of supraliminal and subliminal reward on participant performance on problem solving that can be solved by deliberate analysis or by insight. Forty-one participants attempted to solve 100 compound remote associate problems. At the beginning of each problem, a potential reward cue (1 or 25 cents) was displayed, either subliminally (17 ms) or supraliminally (100 ms). Participants earned the displayed reward if they solved the problem correctly. Results showed that the higher subliminal reward increased the percentage of problems solved correctly overall. Second, we explored if subliminal rewards preferentially influenced solutions that were achieved via a sudden insight (mostly processed below awareness) or via a deliberate analysis. Participants solved more problems via insight following high subliminal reward when compared with low subliminal reward, and compared with high supraliminal reward, with no corresponding effect on analytic solving. Striatal dopamine (DA) is thought to influence motivation, reinforce behavior, and facilitate cognition. We speculate that subliminal rewards activate the striatal DA system, enhancing the kinds of automatic integrative processes that lead to more creative strategies for problem solving, without increasing the selectivity of attention, which could impede insight.

Contrast sensitivity and motion discrimination in cannabis users

RATIONALE

Cannabis use impairs visual attention; however, it is unclear whether cannabis use also impairs low level visual processing or whether low level visual deficits can be related to lower dopaminergic functioning found in cannabis users.

OBJECTIVES

To investigate whether spatiotemporal contrast sensitivity and motion discrimination under normal and low luminance conditions differ in cannabis users and non-users.

METHODS

Control (n = 20) and cannabis (n = 21) participants completed a visual acuity test, a saliva test and self-report measures. Spatial and temporal contrast thresholds, motion coherence thresholds for translational and radial motion and the spontaneous eye blink rate were then collected.

RESULTS

Cannabis users showed decreased spatial contrast sensitivity under low luminance conditions and increased motion coherence thresholds under all luminance levels tested compared to non-users. No differences in temporal contrast sensitivity were found between the groups. Frequency of cannabis use correlated significantly and negatively with contrast sensitivity, both spatial and temporal, in the cannabis group and higher motion coherence thresholds for radial motion were also associated with more frequent cannabis use in this group. The eye blink rate was significantly lower in cannabis users compared to non-users.

CONCLUSIONS

The present study shows that cannabis use is associated with deficits in low level visual processing. Such deficits are suggested to relate to lower dopamine, in a similar manner as in clinical populations. The implications for driving safety under reduced visibility (e.g. night) in abstaining cannabis users are discussed.

Differentiating positive schizotypy and mania risk scales and their associations with spontaneous eye blink rate

Positive schizotypy and mania risk scales are strongly correlated, and both are linked to alterations in striatal dopamine. Previous research has not examined whether these risk scales form distinct factors or whether they are differentially related to other measures of psychopathology risk or striatal dopamine. In the current study (N = 596), undergraduate students completed both positive schizotypy and mania risk scales as well as scales assessing related psychopathology (i.e., negative and disorganized schizotypy; self-reported manic-like episodes). Additionally, we measured spontaneous eye blink rate, which has been consistently associated with striatal dopamine levels. Positive schizotypy and mania risk factors were strongly correlated (factor correlation = 0.73). However, a two-factor model with positive schizotypy and mania risk as separate factors fit significantly better than a one-factor risk model. After removing shared variance, only positive schizotypy was positively associated with both negative and disorganized schizotypy, and only mania risk was related to self-reported manic-like episodes. Furthermore, positive schizotypy was associated with decreased spontaneous eye blink rate, and mania risk was associated with increased spontaneous eye blink rate. Overall, these results suggest that positive schizotypy and mania risk can be distinguished as separate factors and that they might be differentially associated with striatal dopamine measures.

Spontaneous eye blink rate and dopamine synthesis capacity: preliminary evidence for an absence of positive correlation

Dopamine is central to a number of cognitive functions and brain disorders. Given the cost of neurochemical imaging in humans, behavioural proxy measures of dopamine have gained in popularity in the past decade, such as spontaneous eye blink rate (sEBR). Increased sEBR is commonly associated with increased dopamine function based on pharmacological evidence and patient studies. Yet, this hypothesis has not been validated using in vivo measures of dopamine function in humans. To fill this gap, we measured sEBR and striatal dopamine synthesis capacity using [¹⁸F]DOPA PET in 20 participants (nine healthy individuals and 11 pathological gamblers). Our results, based on frequentist and Bayesian statistics, as well as region‐of‐interest and voxel‐wise analyses, argue against a positive relationship between sEBR and striatal dopamine synthesis capacity. They show that, if anything, the evidence is in favour of a negative relationship. These results, which complement findings from a recent study that failed to observe a relationship between sEBR and dopamine D2 receptor availability, suggest that caution and nuance are warranted when interpreting sEBR in terms of a proxy measure of striatal dopamine.

Impaired β-arrestin recruitment and reduced desensitization by non-catechol agonists of the D1 dopamine receptor

Selective activation of dopamine D1 receptors (D1Rs) has been pursued for 40 years as a therapeutic strategy for neurologic and psychiatric diseases due to the fundamental role of D1Rs in motor function, reward processing, and cognition. All known D1R-selective agonists are catechols, which are rapidly metabolized and desensitize the D1R after prolonged exposure, reducing agonist response. As such, drug-like selective D1R agonists have remained elusive. Here we report a novel series of selective, potent non-catechol D1R agonists with promising in vivo pharmacokinetic properties. These ligands stimulate adenylyl cyclase signaling and are efficacious in a rodent model of Parkinson's disease after oral administration. They exhibit distinct binding to the D1R orthosteric site and a novel functional profile including minimal receptor desensitization, reduced recruitment of β-arrestin, and sustained in vivo efficacy. These results reveal a novel class of D1 agonists with favorable drug-like properties, and define the molecular basis for catechol-specific recruitment of β-arrestin to D1Rs.

Individual differences in eye blink rate predict both transient and tonic pupil responses during reversal learning

The pupil response under constant illumination can be used as a marker of cognitive processes. In the past, pupillary responses have been studied in the context of arousal and decision-making. However, recent work involving Parkinson's patients suggested that pupillary responses are additionally affected by reward sensitivity. Here, we build on these findings by examining how pupil responses are modulated by reward and loss while participants (N = 30) performed a Pavlovian reversal learning task. In fast (transient) pupil responses, we observed arousal-based influences on pupil size both during the expectation of upcoming value and the evaluation of unexpected monetary outcomes. Importantly, after incorporating eye blink rate (EBR), a behavioral correlate of striatal dopamine levels, we observed that participants with lower EBR showed stronger pupil dilation during the expectation of upcoming reward. Subsequently, when reward expectations were violated, participants with lower EBR showed stronger pupil responses after experiencing unexpected loss. Across trials, the detection of a reward contingency reversal was reflected in a slow (tonic) dilatory pupil response observed already several trials prior to the behavioral report. Interestingly, EBR correlated positively with this tonic detection response, suggesting that variability in the arousal-based detection response may reflect individual differences in striatal dopaminergic tone. Our results provide evidence that a behavioral marker of baseline striatal dopamine level (EBR) can potentially be used to describe the differential effects of value-based learning in the arousal-based pupil response.

Transient heart rate acceleration in association with spontaneous eyeblinks

The reason why people spontaneously blink several times more frequently than is necessary for ocular lubrication has been a mystery. However, spontaneous eyeblinks selectively occur at attentional breakpoints of information processing, suggesting the involvement of spontaneous eyeblink in attentional disengagement from external stimuli. Physiological activity also changes considerably according to attention state. Heart rate decreases when attention is directed at stimuli, while it increases as attention is released. Therefore, we examined the temporal dynamics between spontaneous eyeblinks and instantaneous heart rate under natural circumstances. Our results showed that the heart rate momentarily increases after each spontaneous eyeblink while participants were freely viewing a movie or listening to a story. This phenomenon was consistently observed even when the participants were placed in a dark room. The skin conductance level on the fingers also increased after each spontaneous eyeblink, suggesting that the blink-related heart rate acceleration was induced by an increase in sympathetic nervous system activity. In contrast, no heart rate acceleration was observed to accompany spontaneous eyeblinks at rest or volitional eyeblinks. These results demonstrated that the generation of spontaneous eyeblinks and the activity of the autonomic nervous system are correlated under attentional influence of natural circumstances.

Bereitschaftspotential preceding eyelid blinks in Parkinson's disease

METHODS

Ten PD patients in stages 1 and 2 of the Hoehn & Yahr classification were compared to 18 healthy controls. Artifact-free EEG segments of two seconds preceding the onset of the blink potential were averaged and analyzed, and the statistical significance of the measured amplitudes were evaluated by analysis of variance models.

RESULTS

The presence of a BP in the PD patients was demonstrated. The mean amplitudes at 0 ms were respectively 0.6 µV and 3.3 µV for the BP patients and the normal controls, respectively.

CONCLUSIONS

The BP amplitudes were significantly smaller in PD patients than normal participants. The amplitudes of the BP were not modified by levodopa.

Eyelid Dysfunction in Neurodegenerative, Neurogenetic, and Neurometabolic Disease

Eye movement abnormalities are among the earliest clinical manifestations of inherited and acquired neurodegenerative diseases and play an integral role in their diagnosis. Eyelid movement is neuroanatomically linked to eye movement, and thus eyelid dysfunction can also be a distinguishing feature of neurodegenerative disease and complements eye movement abnormalities in helping us to understand their pathophysiology. In this review, we summarize the various eyelid abnormalities that can occur in neurodegenerative, neurogenetic, and neurometabolic diseases. We discuss eyelid disorders, such as ptosis, eyelid retraction, abnormal spontaneous and reflexive blinking, blepharospasm, and eyelid apraxia in the context of the neuroanatomic pathways that are affected. We also review the literature regarding the prevalence of eyelid abnormalities in different neurologic diseases as well as treatment strategies (Table 1).