Spontaneous eye blink rate in winter seasonal affective disorder

Neural control of blinking

Blinking is a motor act characterized by the sequential closing and opening of the eyelids, which is achieved through the reciprocal activation of the orbicularis oculi and levator palpebrae superioris muscles. This stereotyped movement can be triggered reflexively, occur spontaneously, or voluntarily initiated. During each type of blinking, the neural control of the antagonistic interaction between the orbicularis oculi and levator palpebrae superioris muscles is governed by partially overlapping circuits distributed across cortical, subcortical, and brainstem structures. This paper provides a comprehensive overview of the anatomical and physiological foundations underlying the neural control of blinking. We describe the infra-nuclear apparatus, as well as the supra-nuclear control mechanisms, i.e., how cortical, subcortical, and brainstem structures regulate and coordinate the different types of blinking.

Seasonal variation of spontaneous blink rate and beta EEG activity

Seasonal variations of the photoperiod have been shown to regulate biological and behavioral functions, with also effects on clinical symptom and course of several psychiatric conditions. Although melatonin is considered the principal signal used to transmit informations about the light and dark cycle, a dopamine (DA) role in regulating seasonal changes has been suggested. Few studies have addressed a seasonal pattern of dopamine, and human studies have been conducted on inter-subject differences, comparing measures obtained during fall-winter with those of spring-summer. We studied within-subject seasonal changes of blink rate (BR), a indirect marker of central DA activity, in 26 normal subjects (15 females and 11 males, mean age: 24.7 ± 4.0) during winter, spring, summer and fall. Occipital EEG activity and subjective measures of vigilance and mood were also assessed to account for variations on arousal and fatigue. A significant seasonal effect was found for BR, with higher rate in summer, and for EEG beta activity, with higher activity in spring and summer. Subjective fatigue was found higher in winter. According to our data, it is possible that higher BR and increased EEG beta activity result by an arousal activation sustained by dopamine systems during the months with a long photoperiod.

Light therapy: is it safe for the eyes?

OBJECTIVE

Light therapy has become an increasingly popular treatment for depression and a range of other neuropsychiatric conditions. Yet, concerns have been raised about the ocular safety of light therapy.

METHOD

We conducted the first systematic review into the ocular safety of light therapy. A PubMed search on January 4, 2017, identified 6708 articles, of which 161 were full-text reviewed. In total, 43 articles reporting on ocular complaints and ocular examinations were included in the analyses.

RESULTS

Ocular complaints, including ocular discomfort and vision problems, were reported in about 0% to 45% of the participants of studies involving light therapy. Based on individual studies, no evident relationship between the occurrence of complaints and light therapy dose was found. There was no evidence for ocular damage due to light therapy, with the exception of one case report that documented the development of a maculopathy in a person treated with the photosensitizing antidepressant clomipramine.

CONCLUSION

Results suggest that light therapy is safe for the eyes in physically healthy, unmedicated persons. The ocular safety of light therapy in persons with preexisting ocular abnormalities or increased photosensitivity warrants further study. However, theoretical considerations do not substantiate stringent ocular safety-related contraindications for light therapy.

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.

Mood seasonality: a cross-sectional study of subjects aged between 10 and 25 years

BACKGROUND

Most of the earlier studies on mood seasonality were conducted in adults and there are few available data on children and adolescents. In two cross sectional surveys, we examined the role of age and gender on seasonal sensitivity in subjects aged 10 to 25 years.

METHODS

In survey one, the Seasonal Pattern Assessment Questionnaire for Children and Adolescents (SPAQ-CA) was administered to 1709 subjects (845 females and 864 males) from 10 to 17 years. In survey two, the Seasonal Pattern Assessment Questionnaire (SPAQ) was administered to 1867 subjects (1061 females and 806 males) from 18 to 25 years.

RESULTS

Only in survey one was a significant positive correlation found between age and Global Seasonality Score (GSS) (r=.29; p<.00001). Significant gender differences were found at age 14 years and above in survey one, and at all ages in survey two.

CONCLUSIONS

The results support the hypothesis that seasonal sensitivity is higher in female subjects.

Lidschlagaktivität während der Bildschirmarbeit

Up to three-fourths of visual display operators complain about ocular discomfort after lengthy work at a monitor. The increase of displays at work has resulted in a problem area with growing impact for the economy and healthcare. Symptoms overlapping the complaints of dry eye disease point to the joint pathophysiological origin. In numerous studies the drastic decrease in blinking frequency was shown to be an essential cause of dry eye symptoms. Lid movements not only have the purpose of smoothing the precorneal tear film ("windshield effect"), but also affect the composition and stability of the different layers. Unfortunately, previous work has often been limited by the heterogeneity of measurement settings, leading to inconsistent results.

Light therapy increases visual contrast sensitivity in seasonal affective disorder

The purpose of this study was to investigate the effects of light therapy on visual contrast sensitivity in patients with seasonal affective disorder (n=10) and healthy control subjects (n=10). Static and dynamic visual contrast sensitivity was measured using a Venus system before and after 4 weeks of light therapy (10,000 lux, 30 min, 5 times a week). Light therapy increased static visual contrast sensitivity in the patients. We found no significant difference between the patients and controls either before or after light therapy. These results raise the possibility that light therapy induces retinal sensitization in seasonal affective disorder.

Seasonal photoperiod, gender, and P300

The photoperiod model of seasonal affective disorder (SAD) suggests that SAD is caused by abnormal responses to seasonal changes in day length. Clarifying the utility of event-related brain potentials (ERPs) as diagnostic aids or measures of therapeutic efficacy in SAD requires understanding the range of naturally occurring seasonal patterns of variation in human responses. This investigation studied ERPs from non-patients (402 from men, 415 from women) during the pronounced photoperiod variation of the Alaskan subarctic where light availability ranges from 3.20 h in winter to 21.98 h in summer. ANOVA showed significant (P=0.03) main effect of photoperiod in the amplitude and latency of P300 responses, as well as a main effect of sensory modality (P=0.002). There was neither a main effect of gender, nor any significant gender-interactive effect in ERP responses. In clients with SAD, the ERP variability attributed to seasonal photoperiod remains to be clarified.

Consideration of three types of spontaneous eyeblink activity in normal humans: during reading and video display terminal use, in primary gaze, and while in conversation

PURPOSE

To consider the conditions under which the so-called spontaneous (endogenous) eyeblink activity has been assessed by different investigators over the last 75 years and to consider the most appropriate terminology. The reason for this analysis was to try to identify why such different values for the spontaneous eyeblink rate (SEBR) have been reported.

METHODS

A retrospective evaluation of published articles was carried out to identify whether the SEBR assessments were consistently dependent on the activity of the subjects while spontaneous eyeblink activity was being investigated. These were compared with assessments of SEBR in young adult subjects under equivalent conditions.

RESULTS

Assessments of spontaneous eyeblink activity revealed that SEBR in a reading posture is lower than that in primary gaze, and SEBR is higher when subjects are in conversation. Such differences are also generally found in literature reports, especially if the primary gaze assessment is carried in silence. Electrophysiological measures of SEBR yield slightly higher values compared with observational techniques. Statistical analysis (with calculation of 95% confidence interval values) indicate that reading-SEBR should be between 1.4 and 14.4 eyeblinks/min, primary gaze-SEBR between 8.0 and 21.0 eyeblinks/min and conversational-SEBR between 10.5 and 32.5 eyeblinks/min for normal adults.

CONCLUSIONS

It is inappropriate to simply state a value for spontaneous eyeblink rate because it is so dependent on experimental conditions. It is further proposed that reports of SEBR measures should be prefixed by these experimental conditions, namely reading-SEBR, primary gaze-SEBR (in silence) and conversational-SEBR.

Diurnal variation in spontaneous eye-blink rate

The daily pattern of spontaneous eye-blink rate (BR), a non-invasive peripheral measure of central dopamine activity, was investigated in 24 healthy subjects. The spontaneous eye-blink rate showed a stable pattern in morning, midday and afternoon hours. A significant increase was found at the evening time point (20.30 h). The finding is suggestive of a late evening increase of central dopamine activity. An increased level of subjective sleepiness was also found at the same evening point, at a time corresponding to the 'evening wake maintenance zone' or the 'forbidden zone for sleep'. A possible hypothesis is that the 'forbidden zone for sleep' may reflect a dopamine-mediated activation that counteracts a rising sleep drive. The role of diurnal variation of dopamine function should be considered both in the choice of the drug treatment regimen, and in the evaluation of biological and neuropsychological parameters.

Gender differences in glycosylated hemoglobin levels in seasonal affective disorder patients and controls

Seasonal affective disorder (SAD) has been shown to manifest different symptoms in female and male patients. Specifically, women with SAD have been shown to have greater increases in overeating, weight gain, and increased sleep as compared with their male counterparts. Given these dietary changes, we predicted that female SAD patients would exhibit increased glycosylated hemoglobin (HbA1) levels, indicative of chronically elevated glucose levels. Twenty-two patients (15 women and seven men) and matched controls were enrolled during the winter season and tested for HbA1 levels. A three-way analysis of variance (ANOVA; gender x group x season) was insignificant and the result was a negative study. After the initial hypothesis was rejected, we undertook a post-hoc analysis of the data, from which emerged that in winter, women patients had higher HbA1 levels as compared with matched controls. As our original hypothesis was rejected, we cannot accept the results of the post-hoc study. However, numerous other studies have demonstrated that female and male SAD patients differ in their pathophysiology, and are suggestive that in future analyses ought to consider analyzing subjects separately across gender.

Circadian profiles of cortisol, prolactin, and thyrotropin in seasonal affective disorder

To determine whether circadian profiles of various plasma hormones are abnormal in patients with winter seasonal affective disorder (SAD), we obtained 24-hour profiles of plasma cortisol, prolactin, and thyrotropin in subsets of a sample of 22 depressed patients with SAD on and off light therapy and in subsets of a sample of 24 normal controls. Cortisol levels did not differ between patients and controls, and levels in patients were not affected by light therapy. Prolactin levels were lower in patients than in controls throughout the day (p < 0.03) but were unaffected by light therapy. Independent of patient vs. control status, prolactin levels were higher in women than in men throughout the day (p < 0.003). Thyrotropin levels were no different in patients and controls, but levels in patients were lower following light therapy (p < 0.05).

Mother's prior intrauterine position affects the sex ratio of her offspring in house mice

Sex ratio alterations related to environmental factors occur in several mammals, but no mechanism has been identified to explain the adjustment. Intrauterine position (IUP) may provide the context in which such alterations occur. Previous studies on house mice and gerbils reveal that the position of a fetus in the uterus in relation to the sex of its neighbors influences its later anatomy, physiology, and behavior. The anogenital distance (AGD) of females located between two males (2M) is longer than that of females not between two males (OM). We have found that the IUP, as determined by cesarean section and by an index of the AGD, correlates with the sex ratio of the litters produced by female mice. The sex ratio of the first litter born to 2M females was 58% males, for 1M females was 51% males and for OM females was 42% males. The effect on sex ratio continues into the second litter. The number of pups produced by mothers of different IUPs in her first two litters did not differ, suggesting that the sex ratio adjustment occurs prior to parturition. These results provide a basis for the natural variability observed in sex ratios of litter-bearing mammals and suggest that one or more intrauterine mechanisms may be responsible for environmentally related sex ratio alterations.

Effects of phototherapy on electrooculographic ratio in winter seasonal affective disorder

Low electrooculographic (EOG) ratios have been reported in patients with seasonal affective disorder (SAD). This study was undertaken to replicate these results and to consider the effects of light therapy on the EOG in SAD patients. Sixteen outpatients with SAD and 16 age-, sex-, and medication-matched control subjects had EOG testing before and after 1 week of light therapy during the winter. The EOG ratios in the SAD patients were only marginally lower than those in the normal control subjects. These differences persisted after light therapy. Although the slightly decreased EOG ratios in SAD patients might have resulted from an artifact of test variability, drowsiness, or other confounding factors, the difference between patients and control subjects raises the possibility of retinal abnormality in SAD.

Seasonal variation in behavioral responses to m-CPP in patients with seasonal affective disorder and controls

This paper reports the behavioral responses to m-chlorophenylpiperazine (m-CPP), a serotonin agonist, in patients with seasonal affective disorder (SAD) and controls during the summer. Results are compared with the responses of SAD patients and controls given m-CPP in the winter. Results of the winter study were reported earlier by our group. Baseline Hamilton depression ratings in SAD patients were significantly lower in the summer than in winter (p < 0.05). Additionally, in both SAD patients and controls, there were seasonal differences on the National Institute of Mental Health (NIMH) self-rating scale items: "depressed affect," "dysphoria," and "functional deficit" at baseline. The behavioral responses to m-CPP across seasons differentiated patients from normals only in the "activation/euphoria" item, on which a far greater response was seen in patients than in controls during the winter. This behavioral response may be a state marker for winter depression, as it was significantly reduced after light treatment of these patients in the winter, and in the summer. SAD patients responded differently from controls on "altered self-awareness" and "dysphoria" independently of seasons, and these responses may be considered as possible trait markers for this condition. These results provide further evidence of a possible deficiency in serotonergic transmission in seasonal affective disorder.