The validity of eye blink rate in Chinese adults for the diagnosis of Parkinson's disease

Attentional modulation of eye blinking is altered by sex, age, and task structure

Spontaneous eye blinking is gaining popularity as a proxy for higher cognitive functions, as it is readily modulated by both environmental demands and internal processes. Prior studies were impoverished in sample size, sex representation and age distribution, making it difficult to establish a complete picture of the behavior. Here we present eye-tracking data from a large cohort of normative participants (n=604, 393 F, aged 5-93 years) performing two tasks: one with structured, discrete trials (interleaved pro/anti-saccade task; IPAST) and one with a less structured, continuous organization in which participants watch movies (free-viewing; FV). Sex- and age-based analyses revealed that females had higher blink rates between the ages of 22 and 58 years in the IPAST, and 22 and 34 years in FV. We derived a continuous measure of blink probability to reveal behavioral changes driven by stimulus appearance in both paradigms. In the IPAST, blinks were suppressed near stimulus appearance, particularly on correct anti-saccade trials, which we attribute to the stronger inhibitory control required for anti-saccades compared to pro-saccades. In FV, blink suppression occurred immediately after scene changes, and the effect was sustained on scenes where gaze clustered among participants (indicating engagement of attention). Females were more likely than males to blink during appearance of novel stimuli in both tasks, but only within the age bin of 18-44 years. The consistency of blink patterns in each paradigm endorses blinking as a sensitive index for changes in visual processing and attention, while sex and age differences drive interindividual variability.Significance Statement Eye-tracking is becoming useful as a non-invasive tool for detecting preclinical markers of neurological and psychiatric disease. Blinks are understudied despite being an important supplement to saccade and pupil eye-tracking metrics. The present study is a crucial step in developing a healthy baseline for blink behavior to compare to clinical groups. While many prior blink studies suffered from small sample sizes with relatively low age- and sex-diversity (review by Jongkees & Colzato, 2016), our large cohort of healthy participants has permitted a more detailed analysis of sex and age effects in blink behavior. Furthermore, our analysis techniques are robust to temporal changes in blink probability, greatly clarifying the relationship between blinking, visual processing, and inhibitory control mechanisms on visual tasks.

Wearable and Invisible Sensor Design for Eye-Motion Monitoring Based on Ferrofluid and Electromagnetic Sensing Technologies

For many human body diseases, treatments in the early stages are more efficient and safer than those in the later stages; therefore, detecting the early symptoms of a disease is crucial. One of the most significant early indicators for diseases is bio-mechanical motion. This paper provides a unique way of monitoring bio-mechanical eye motion based on electromagnetic sensing technology and a ferro-magnetic material, ferrofluid. The proposed monitoring method has the advantages of being inexpensive, non-invasive, sensor-invisible and extremely effective. Most of the medical devices are cumbersome and bulky, which makes them hard to apply for daily monitoring. However, the proposed eye-motion monitoring method is designed based on ferrofluid eye make-up and invisible sensors embedded inside the frame of glasses such that the system is wearable for daily monitoring. In addition, it has no influence on the appearance of the patient, which is beneficial for the mental health of some patients who do not want to attract public attention during treatment. The sensor responses are modelled using finite element simulation models, and wearable sensor systems are created. The designed frame of the glasses is manufactured based on 3-D printing technology. Experiments are conducted to monitor eye bio-mechanical motions, such as the frequency of eye blinking. Both the quick blinking behaviour with an overall frequency of around 1.1 Hz and the slow blinking behaviour with an overall frequency of around 0.4 Hz can be observed through experimentation. Simulations and measurements results show that the proposed sensor design can be employed for bio-mechanical eye-motion monitoring. In addition, the proposed system has the advantages of invisible sensor set-up and will not affect the appearance of the patient, which is not only convenient for the daily life of the patient but also beneficial for mental health.

Spontaneous eye blink rate mediates the relationship between sleepiness and impulsivity to negative stimuli

Previous studies have demonstrated that sleep deprivation results in a negativity bias, especially in the context of impaired response inhibition. In the present study we investigated spontaneous eye blink rate (EBR), a correlate of dopamine function, as a mediator of the relationship between subjective sleepiness and impulsivity toward negative stimuli on a Go/NoGo task. Participants rated their sleepiness on a number of measures including the Epworth Sleepiness Scale (ESS), the Karolinska Sleepiness Scale (KSS) and subscales of the Chronic Sleep Reduction Questionnaire (CSRQ). The findings revealed that EBR mediated the relationship between sleepiness as measured by the Karolinska Sleepiness Scale (KSS) and commission errors on negatively valanced stimuli. These findings suggest that reduced inhibition in responding to negative stimuli can be found as a function of subjective sleepiness and that changes in dopamine function may be one contributing factor explaining this relationship.

Spontaneous Eye Blinks Predict Executive Functioning in Seniors

As the world’s population is aging rapidly, cognitive training is an extensively used approach to attempt improvement of age-related cognitive functioning. With increasing numbers of older adults required to remain in the workforce, it is important to be able to reliably predict future functional decline, as well as the individual advantages of cognitive training. Given the correlation between age-related decline and striatal dopaminergic function, we investigated whether eye blink rate (EBR), a non-invasive, indirect indicator of dopaminergic activity, could predict executive functioning (response inhibition, switching and working memory updating) as well as trainability of executive functioning in older adults. EBR was collected before and after a cognitive flexibility training, cognitive training without flexibility, or a mock training. EBR predicted working memory updating performance on two measures of updating, as well as trainability of working memory updating, whereas performance and trainability in inhibition and switching tasks could not be predicted by EBR. Our findings tentatively indicate that EBR permits prediction of working memory performance in older adults. To fully interpret the relationship with executive functioning, we suggest future research should assess both EBR and dopamine receptor availability among seniors.

Effects and mechanisms of information saliency in enhancing value-based decision-making in younger and older adults

Aging attenuates frontostriatal network functioning, which could lead to deficits in value computation when decision-making involves uncertainty. Although it has been shown that visually enhancing information saliency of outcome probability can improve decision-making in old age, mechanisms of this effect are still unclear. In the present study, the saliency of outcome probability was increased using a color-coding scheme as a decision aid in a mixed lottery choice task, and spontaneous eye-blink rate and pupillary responses were assessed in younger and older adults. Older adults showed lower value sensitivity than younger adults; however, increasing information saliency benefitted choice behaviors in both age groups. Furthermore, the decision aid reduced pupil size during decision-making in both age groups, suggesting that enhancing information saliency decreases cognitive demands of value computation. Baseline value sensitivity was negatively correlated with benefit of enhancing information saliency only in older adults. As value representations in older decision makers are less distinctive at baseline, they may have required more environmental compensation than younger adults.

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.

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.

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.

Interactive Effects of Dopamine Baseline Levels and Cycle Phase on Executive Functions: The Role of Progesterone

Estradiol and progesterone levels vary along the menstrual cycle and have multiple neuroactive effects, including on the dopaminergic system. Dopamine relates to executive functions in an “inverted U-shaped” manner and its levels are increased by estradiol. Accordingly, dopamine dependent changes in executive functions along the menstrual cycle have been previously studied in the pre-ovulatory phase, when estradiol levels peak. Specifically it has been demonstrated that working memory is enhanced during the pre-ovulatory phase in women with low dopamine baseline levels, but impaired in women with high dopamine baseline levels. However, the role of progesterone, which peaks in the luteal cycle phase, has not been taken into account previously. Therefore, the main goals of the present study were to extend these findings (i) to the luteal cycle phase and (ii) to other executive functions. Furthermore, the usefulness of the eye blink rate (EBR) as an indicator of dopamine baseline levels in menstrual cycle research was explored. 36 naturally cycling women were tested during three cycle phases (menses–low sex hormones; pre-ovulatory–high estradiol; luteal–high progesterone and estradiol). During each session, women performed a verbal N-back task, as measure of working memory, and a single trial version of the Stroop task, as measure of response inhibition and cognitive flexibility. Hormone levels were assessed from saliva samples and spontaneous eye blink rate was recorded during menses. In the N-back task, women were faster during the luteal phase the higher their progesterone levels, irrespective of their dopamine baseline levels. In the Stroop task, we found a dopamine-cycle interaction, which was also driven by the luteal phase and progesterone levels. For women with higher EBR performance decreased during the luteal phase, whereas for women with lower EBR performance improved during the luteal phase. These findings suggest an important role of progesterone in modulating dopamine-cycle interactions. Additionally, we identified the eye blink rate as a non-invasive indicator of baseline dopamine function in menstrual cycle research.

Neurobiological correlates of impulsivity in healthy adults: Lower prefrontal gray matter volume and spontaneous eye-blink rate but greater resting-state functional connectivity in basal ganglia-thalamo-cortical circuitry

Studies consistently implicate aberrance of the brain's reward-processing and decision-making networks in disorders featuring high levels of impulsivity, such as attention-deficit hyperactivity disorder, substance use disorder, and psychopathy. However, less is known about the neurobiological determinants of individual differences in impulsivity in the general population. In this study of 105 healthy adults, we examined relationships between impulsivity and three neurobiological metrics - gray matter volume, resting-state functional connectivity, and spontaneous eye-blink rate, a physiological indicator of central dopaminergic activity. Impulsivity was measured both by performance on a task of behavioral inhibition (go/no-go task) and by self-ratings of attentional, motor, and non-planning impulsivity using the Barratt Impulsiveness Scale (BIS-11). Overall, we found that less gray matter in medial orbitofrontal cortex and paracingulate gyrus, greater resting-state functional connectivity between nodes of the basal ganglia-thalamo-cortical network, and lower spontaneous eye-blink rate were associated with greater impulsivity. Specifically, less prefrontal gray matter was associated with higher BIS-11 motor and non-planning impulsivity scores, but was not related to task performance; greater correlated resting-state functional connectivity between the basal ganglia and thalamus, motor cortices, and prefrontal cortex was associated with worse no-go trial accuracy on the task and with higher BIS-11 motor impulsivity scores; lower spontaneous eye-blink rate was associated with worse no-go trial accuracy and with higher BIS-11 motor impulsivity scores. These data provide evidence that individual differences in impulsivity in the general population are related to variability in multiple neurobiological metrics in the brain's reward-processing and decision-making networks.

The developmental relationship between central dopaminergic level and response inhibition from late childhood to young adulthood

Dopamine (DA) is known to modulate response inhibition (RI). In contrast to the abundant adult studies, only few developmental studies have focused on this topic. Moreover, the mechanism underlying the modulation of RI by the DA system from childhood to adulthood remains unclear. We aimed to assess whether the relationship between DA and RI during late childhood and young adulthood is similar. Accordingly, DA function was measured using the spontaneous eye blink rate (EBR), whereas RI ability was tested using the Go/Nogo task. Experiment 1 included 149 adults (age range, 18-25years) who completed the EBR test and the Go/Nogo task; the results showed that higher EBR was associated with lower commission error in the Nogo trials. Experiment 2 included 45 children (age range, 10-12years) and 37 adults (age range, 18-19years) who completed the EBR test and Go/Nogo tasks (similar to experiment 1); in both the child and adult groups, higher EBR was related to better RI ability. As EBR is closely related to central DA function, these findings suggest that DA plays a similar role in the processing of RI in late childhood and young adulthood.

Spontaneous eye blink rate as predictor of dopamine-related cognitive function-A review

An extensive body of research suggests the spontaneous eye blink rate (EBR) is a non-invasive indirect marker of central dopamine (DA) function, with higher EBR predicting higher DA function. In the present review we provide a comprehensive overview of this literature. We broadly divide the available research in studies that aim to disentangle the dopaminergic underpinnings of EBR, investigate its utility in diagnosis of DA-related disorders and responsivity to drug treatment, and, lastly, investigate EBR as predictor of individual differences in DA-related cognitive performance. We conclude (i) EBR can reflect both DA receptor subtype D1 and D2 activity, although baseline EBR might be most strongly related to the latter, (ii) EBR can predict hypo- and hyperdopaminergic activity as well as normalization of this activity following treatment, and (iii) EBR can reliably predict individual differences in performance on many cognitive tasks, in particular those related to reward-driven behavior and cognitive flexibility. In sum, this review establishes EBR as a useful predictor of DA in a wide variety of contexts.

Effects of meditation practice on spontaneous eyeblink rate

A rapidly growing body of research suggests that meditation can change brain and cognitive functioning. Yet little is known about the neurochemical mechanisms underlying meditation-related changes in cognition. Here, we investigated the effects of meditation on spontaneous eyeblink rates (sEBR), a noninvasive peripheral correlate of striatal dopamine activity. Previous studies have shown a relationship between sEBR and cognitive functions such as mind wandering, cognitive flexibility, and attention-functions that are also affected by meditation. We therefore expected that long-term meditation practice would alter eyeblink activity. To test this, we recorded baseline sEBR and intereyeblink intervals (IEBI) in long-term meditators (LTM) and meditation-naive participants (MNP). We found that LTM not only blinked less frequently, but also showed a different eyeblink pattern than MNP. This pattern had good to high degree of consistency over three time points. Moreover, we examined the effects of an 8-week course of mindfulness-based stress reduction on sEBR and IEBI, compared to an active control group and a waitlist control group. No effect of short-term meditation practice was found. Finally, we investigated whether different types of meditation differentially alter eyeblink activity by measuring sEBR and IEBI after a full day of two kinds of meditation practices in the LTM. No effect of meditation type was found. Taken together, these findings may suggest either that individual difference in dopaminergic neurotransmission is a self-selection factor for meditation practice, or that long-term, but not short-term meditation practice induces stable changes in baseline striatal dopaminergic functioning.

Eye Blink Rate as a biological marker of Mild Cognitive Impairment

We investigated the relationship between dopamine activity (DA), as measured by Eye Blink Rate (EBR), and cognitive function in old adults with Mild Cognitive Impairment (MCI) and healthy controls. Research has been inconclusive so far about the factors responsible for the transition from MCI to dementia. However, some studies suggest that cortical hyperexcitability in very early stages of pathological aging may progressively lead to cell death, and thus to Alzheimer's disease. Hence, we speculated that a dysfunction of DA activity, as measured by EBR, may characterize people with MCI, and account for their poor cognitive function. Thirty three (33) healthy and thirty six (36) old adults with MCI (Mean age = 67.52 y.o.) participated in this study. The EBR was recorded under resting conditions, using two gold skin electrodes above and below the left eye. Cognitive function was assessed with a battery of neuropsychological tests. Participants with MCI showed significantly higher EBR than the healthy controls. Also, EBR was negatively related to scores on the Montreal Cognitive Assessment test (MoCA) test. We propose that abnormally increased dopamine activity, as indexed by relatively high EBR, may be partially responsible for the neurotransmitter imbalance in the central nervous system of people with MCI, and the overall impaired cognitive performance. In addition, this finding suggests that an abnormally high EBR may be a potential biomarker of the transition from healthy aging to dementia.

Case-control study of blink rate in Parkinson's disease under different conditions

Standard neurology texts list a reduced blink rate as one of the clinical features of Parkinson's disease. However, there are few clinical studies which have quantified this clinical sign. Here we present the results of a quantified study in a cohort of cases and controls using a standard protocol. Cases meeting standard criteria for a diagnosis of Parkinson's disease were studied together with age- and sex-matched controls. Baseline data included age, sex, duration of disease, Hoehn and Yahr stage, mini-mental state examination and treatment. Subjects were videoed undertaking three different tasks: being interviewed, watching a video, and reading from a book. Blink rates were calculated as a mean 'per minute' figure for each of the three tasks. A meta-analysis of previous studies of blink rate was undertaken. A total of 20 cases and 41 controls were studied. A decline in blink rate with increasing age was seen for cases but not controls. A significant reduction in blink rate was seen in cases when compared with controls for each of the test conditions. Blink rates were highest in subjects when being interviewed and were lowest whilst reading a passage in both cases and controls. No effect of disease duration, severity or treatment was observed. We have quantified the reduction in blink rate which has long been recognised as a feature of Parkinson's disease. We have identified factors which determine blink rate within individuals. We have also been able to define normal and abnormal levels for blink rate which may be of value clinically and for future research.

Blink detection robust to various facial poses

Applications based on eye-blink detection have increased, as a result of which it is essential for eye-blink detection to be robust and non-intrusive irrespective of the changes in the user's facial pose. However, most previous studies on camera-based blink detection have the disadvantage that their performances were affected by the facial pose. They also focused on blink detection using only frontal facial images. To overcome these disadvantages, we developed a new method for blink detection, which maintains its accuracy despite changes in the facial pose of the subject. This research is novel in the following four ways. First, the face and eye regions are detected by using both the AdaBoost face detector and a Lucas-Kanade-Tomasi (LKT)-based method, in order to achieve robustness to facial pose. Secondly, the determination of the state of the eye (being open or closed), needed for blink detection, is based on two features: the ratio of height to width of the eye region in a still image, and the cumulative difference of the number of black pixels of the eye region using an adaptive threshold in successive images. These two features are robustly extracted irrespective of the lighting variations by using illumination normalization. Thirdly, the accuracy of determining the eye state - open or closed - is increased by combining the above two features on the basis of the support vector machine (SVM). Finally, the SVM classifier for determining the eye state is adaptively selected according to the facial rotation. Experimental results using various databases showed that the blink detection by the proposed method is robust to various facial poses.

Postoperative parkinsonism and lupus anticoagulant: A model of autoantibody-mediated neurotoxicity in stress

PRIMARY OBJECTIVE

Nigrostriatal hypodopaminergism is the fundamental basis in parkinsonism. It may arise secondarily from a variety of disorders but is rarely mentioned shortly after surgery.

METHODS AND PROCEDURES

To report the clinical course of five patients who had had symptomatic parkinsonism developed shortly after surgery (lumbar laminectomy, prostatectomy and cholestectomy). Appropriate investigations were done to elucidate their pathogenesis.

MAIN OUTCOMES AND RESULTS

There was no remarkable finding of their anesthetic agents, duration of surgery, type of surgery, medical conditions or preoperative screening test. Extensive investigations did not reveal consistent abnormality. However, an abnormal presence of lupus anticoagulant was detected in four patients; primary antiphospholipid antibody syndrome was fulfilled in two of them. The lupus anticoagulant restored to the reference range in another two patients later. Catastrophic antiphospholipid antibody syndrome was not seen. Initially, their parkinsonian symptoms rapidly progressed but slowed down after six months.

CONCLUSION

Lupus anticoagulant possesses neurotoxic property and has been found in cases of movement disorder involving with the central dopaminergism. Surgery, a form of traumatic stress, has been reported to bring on lupus anticoagulant and catastrophic antiphospholipid antibody syndrome. These relationships remind a generation or an enhancement of pathognomic autoantibody vulnerable for dopaminergic toxicity, such as lupus anticoagulant or other antiphospholipid antibody.

Spontaneous blinking in healthy persons: an optoelectronic study of eyelid motion

PURPOSE

To develop a method for the non-invasive detection and quantification of eyelid movements during spontaneous blinking.

METHODS

Spontaneous eyelid movements were monitored using an optoelectronic motion analyzer with passive markers in a younger group aged 20-30 years (13 men, 12 women) and in an older group over 50 years (10 men and nine women). Blink rate, eyelid displacement as a percentage of maximum excursion, and maximum eyelid velocity in closing and opening were calculated.

RESULTS

Spontaneous blink rate was significantly larger in women than in men (19 vs 11 blinks per minute); older women blinked more frequently than younger women. On average, young men closed the eyes completely (or almost completely) 44% of times, whereas the eyelid closure of young and older women was more frequently between 51 and 75% of the maximum excursion. Older men rarely closed completely and showed a similar frequency of blinks with up to 25%, 50% and 75% of maximum excursion. During eyelid closure and opening, the maximum velocity reduced with age: older subjects moved their eyelids approximately 80-70% slower than younger subjects. In all subjects, closing was performed 40-47% faster than opening; women moved faster than men. Eyelid displacement was greater in young than in older subjects.

CONCLUSIONS

The method used in this study allowed the non-invasive detection of eyelid movements during spontaneous blinking, providing a set of descriptive and kinematic data. The method could also be used to assess blink characteristics in patients with movement disorders, without invasive or time-consuming procedures.