O sweet spot where art thou? Light treatment of Seasonal Affective Disorder and the circadian time of sleep

Change in Seasonal Beliefs Mediates the Durability Advantage of Cognitive-Behavioral Therapy Over Light Therapy for Winter Depression

In treating an acute episode of winter depression, cognitive-behavioral therapy for seasonal affective disorder (CBT-SAD) and light therapy are comparably efficacious, with improvement in depression symptoms during CBT-SAD mediated by reduced seasonal beliefs (i.e., maladaptive thoughts about the seasons, light availability, and weather). Here, we tested whether the enduring benefit of CBT-SAD over light therapy following treatment is associated with offsetting seasonal beliefs during CBT-SAD. Currently depressed adults with Major Depression, Recurrent with Seasonal Pattern (N = 177) were randomized to 6 weeks of light therapy or group CBT-SAD and followedup one and two winters after treatment. Outcomes measured during treatment and at each follow-up included depression symptoms on the Structured Clinical Interview for the Hamilton Rating Scale for Depression-SAD Version and Beck Depression Inventory-Second Edition. Candidate mediators measured at pre-, mid-, and posttreatment were SAD-specific negative cognitions (Seasonal Beliefs Questionnaire; SBQ); general depressogenic cognitions (Dysfunctional Attitudes Scale; DAS); brooding rumination (Ruminative Response Scale-Brooding subscale; RRS-B); and chronotype (Morningness-Eveningness Questionnaire; MEQ). Latent growth curve mediation models found a significant positive path from treatment group to the slope of SBQ during treatment, with CBT-SAD showing larger improvements in seasonal beliefs with overall change in seasonal beliefs in the medium-effect range, and significant positive paths from SBQ slope to depression scores at the first and second winter follow-ups, indicating greater change towards more flexible seasonal beliefs during active treatment was associated with less severe depression symptoms following treatment. Estimated indirect effects (treatment group → SBQ change * SBQ change → outcome) were also significant at each follow-up for each outcome with βindirect ranging from .091 to .162. Models also found significant positive paths from treatment group to the slope of MEQ and RRS-B during treatment, with light therapy showing a greater increase in "morningness" and CBT-SAD showing a greater decrease in brooding during active treatment; however, neither construct emerged as a mediator of follow-up depression scores. Change in seasonal beliefs during treatment mediates both the acute antidepressant and long-term effects of CBT-SAD and explains lower depression severity following CBT-SAD relative to light therapy.

Second-generation antidepressants for treatment of seasonal affective disorder

BACKGROUND

Seasonal affective disorder (SAD) is a seasonal pattern of recurrent depressive episodes that is often treated with second-generation antidepressants (SGAs), light therapy, or psychotherapy.

OBJECTIVES

To assess the efficacy and safety of second-generation antidepressants (SGAs) for the treatment of seasonal affective disorder (SAD) in adults in comparison with placebo, light therapy, other SGAs, or psychotherapy.

SEARCH METHODS

This is an update of an earlier review first published in 2011. We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2020, Issue 1) in the Cochrane Library (all years), Ovid MEDLINE, Embase, and PsycINFO (2011 to January 2020), together with the Cochrane Common Mental Disorders Controlled Trials Register (CCMDCTR) (all available years), for reports of randomised controlled trials (RCTs). We hand searched the reference lists of all included studies and other systematic reviews. We searched ClinicalTrials.gov for unpublished/ongoing trials. We ran a separate update search for reports of adverse events in the Ovid databases.  SELECTION CRITERIA: For efficacy we included RCTs of SGAs compared with other SGAs, placebo, light therapy, or psychotherapy in adult participants with SAD. For adverse events we also included non-randomised studies.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened abstracts and full-text publications against the inclusion criteria. Data extraction and 'Risk of bias' assessment were conducted individually. We pooled data for meta-analysis where the participant groups were similar, and the studies assessed the same treatments with the same comparator and had similar definitions of outcome measures over a similar duration of treatment.

MAIN RESULTS

In this update we identified no new RCT on the effectiveness of SGAs in SAD patients. We included 2 additional single-arm observational studies that reported on adverse events of SGAs.  For efficacy we included three RCTs of between five and eight weeks' duration with a total of 204 participants. For adverse events we included two RCTs and five observational (non-randomised) studies of five to eight weeks' duration with a total of 249 participants. All participants met the DSM (Diagnostic and Statistical Manual of Mental Disorders) criteria for SAD. The average age ranged from 34 to 42 years, and the majority of participants were female (66% to 100%). Results from one trial with 68 participants showed that fluoxetine (20/36) was numerically superior to placebo (11/32) in achieving clinical response; however, the confidence interval (CI) included both a potential benefit as well as no benefit of fluoxetine (risk ratio (RR) 1.62, 95% CI 0.92 to 2.83, very low-certainty evidence). The number of adverse events was similar in both groups (very low-certainty evidence). Two trials involving a total of 136 participants compared fluoxetine versus light therapy. Meta-analysis showed fluoxetine and light therapy to be approximately equal in treating seasonal depression: RR of response 0.98 (95% CI 0.77 to 1.24, low-certainty evidence), RR of remission 0.81 (95% CI 0.39 to 1.71, very low-certainty evidence). The number of adverse events was similar in both groups (low-certainty evidence). We did not identify any eligible study comparing SGA with another SGA or with psychotherapy. Two RCTs and five non-randomised studies reported adverse event data on a total of 249 participants who received bupropion, fluoxetine, escitalopram, duloxetine, nefazodone, reboxetine, light therapy, or placebo. We were only able to obtain crude rates of adverse events, therefore caution is advised regarding interpretation of this information. Between 0% and 100% of participants who received an SGA suffered an adverse event, and between 0% and 25% of participants withdrew from the study due to adverse events.

AUTHORS' CONCLUSIONS

Evidence for the effectiveness of SGAs is limited to one small trial of fluoxetine compared with placebo showing a non-significant effect in favour of fluoxetine, and two small trials comparing fluoxetine against light therapy suggesting equivalence between the two interventions. The lack of available evidence precluded us from drawing any overall conclusions on the use of SGAs for SAD. Further, larger RCTs are required to expand and strengthen the evidence base on this topic, and should also include comparisons with psychotherapy and other SGAs. Data on adverse events were sparse, and a comparative analysis was not possible. The data we obtained on adverse events is therefore not robust, and our confidence in the data is limited. Overall, up to 25% of participants treated with SGAs for SAD withdrew from the study early due to adverse events.

Detecting Critical Decision Points during Cognitive-Behavioral Therapy and Light Therapy for Winter Depression Nonremission and Recurrence

Using data from a clinical trial comparing cognitive-behavioral therapy (CBT-SAD) and light therapy (LT) for winter seasonal affective disorder (SAD; N = 177), we explored critical decision points, or treatment weeks, that predict likelihood of nonremission at post-treatment and depression recurrence following treatment. In receiver operator characteristic (ROC) curve analyses, we used weekly Structured Clinical Interview for the Hamilton Rating Scale for Depression-SAD Version (SIGH-SAD) scores during treatment to predict nonremission at post-treatment (Week 6) and recurrence one winter later (Winter 1), two winters later (Winter 2), and any recurrence. Although several C-statistics of ≥ .70 were found, only Week 4 SIGH-SAD scores in CBT-SAD for nonremission had enough predictive ability to inform clinical decision-making (C-statistic = .80; sensitivity = .91; specificity = .68). Week 4 of CBT-SAD may be a critical time point to identify likely nonremitters who need tailoring of intervention, based on SIGH-SAD cutpoint score ≥ 13. This study illustrates how clinical trial data can inform detecting optimal decision points in treatment for identifying patients unlikely to remit, a critical first step to developing adaptive treatment strategies using decision rules to operationalize when and for whom treatment should change to maximize clinical benefit.

Applying experimental therapeutics to examine cognitive and chronological vulnerabilities as mediators of acute outcomes in cognitive-behavioral therapy and light therapy for winter depression

OBJECTIVE

We applied the experimental therapeutics approach to test whether acute treatment outcomes for winter seasonal affective disorder (SAD) are mediated by a cognitive mechanism in cognitive-behavioral therapy (CBT-SAD) versus a chronobiologic mechanism in light therapy (LT).

METHOD

Currently depressed adults with major depression, recurrent with seasonal pattern (N = 177; 83.6% female, 92.1% non-Hispanic White, M age = 45.6) were randomized to 6 weeks of LT or group CBT-SAD. SAD symptoms were assessed weekly on the Structured Clinical Interview for the Hamilton Rating Scale for Depression-SAD Version. At pre-, mid-, and posttreatment, participants completed measures of general depressogenic cognitions (Dysfunctional Attitudes Scale; DAS); SAD-specific negative cognitions (Seasonal Beliefs Questionnaire; SBQ); chronotype (Morningness-Eveningness Questionnaire; MEQ); and depressive symptoms (Beck Depression Inventory-Second Edition).

RESULTS

Parallel-process growth models showed evidence for hypothesized mechanisms. For SAD-specific negative cognitions (SBQ), both symptom measures showed (1) an effect of treatment group on the slope of the mediator, with CBT-SAD demonstrating greater decreases, and (2) an effect of the slope of the mediator on the slope of the outcome. These effects held for the SBQ but not the broader measure of depressogenic cognitions (DAS). For the chronotype measure (MEQ), treatment assignment affected change, whereby LT was associated with reduced "eveningness," but this was unrelated to change in symptoms.

CONCLUSIONS

CBT-SAD promoted decreases in SAD-specific negative cognitions, and these changes were related to decreases in symptoms. Consistent with the theory that LT corrects misaligned circadian rhythms, LT reduced eveningness, but this did not correspond to symptom improvement. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Cognitive Vulnerabilities as Prognostic Predictors of Acute and Follow-up Outcomes in Seasonal Affective Disorder Treatment with Light Therapy or Cognitive-Behavioral Therapy

BACKGROUND

First-line treatments for winter seasonal affective disorder include light therapy and cognitive-behavioral therapy; however, it is unclear whether particular patient profiles respond differentially to each treatment type. This study examined baseline patient cognitive and chronobiological vulnerabilities as prognostic and prescriptive predictors of acute and follow-up treatment outcomes.

METHODS

177 adults with seasonal affective disorder were randomized to 6-weeks of either light therapy or cognitive-behavioral therapy. Participants completed baseline measures of cognitive vulnerabilities (Dysfunctional Attitudes Scale; Ruminative Response Scale; Seasonal Belief Questionnaire) and chronobiological vulnerability (Morningness-Eveningness Questionnaire). Depression was assessed at pre- and post-treatment and at follow-ups one and two winters later.

RESULTS

Pre-treatment depression severity correlated significantly with each cognitive vulnerability measure, and significantly predicted future depression. After controlling for pre-treatment depression, higher scores on the Morningness-Eveningness Questionnaire were prognostic of lower depression at treatment endpoint, but no cognitive vulnerability emerged as a prognostic or prescriptive predictor of outcome.

CONCLUSIONS

Greater morningness was associated with less severe post-treatment depression in both cognitive-behavior therapy and light therapy. No cognitive vulnerability emerged as a prognostic or prescriptive predictor, perhaps because they correlated with pre-treatment depression severity, a robust predictor of outcome. Future research should test alternative cognitive constructs.

Relationship Between the Cortisol-Estradiol Phase Difference and Affect in Women

Affective disorders impact women's health, with a lifetime prevalence of over twelve per cent. They have been correlated with reproductive cycle factors, under the regulation of hormonal circadian rhythms. In affective disorders, circadian rhythms may become desynchronized. The circadian rhythms of cortisol and estradiol may play a role in affective disorders. The purpose of this study was to explore the temporal relationship between the rhythms of cortisol and estradiol and its relationship to affect. It was hypothesized that a cortisol-estradiol phase difference (PD) exists that correlates with optimal affect. A small scale, comparative, correlational design was used to test the hypothesis. Twenty-three women were recruited from an urban university. Salivary samples were collected over a twenty-four-hour period and fitted to a cosinor model. Subjective measures of affect were collected. Relationships between the cortisol-estradiol PD and affect were evaluated using a second-degree polynomial equation. Results demonstrated a significant correlation in affect measures (p < 0.05). An optimal PD was identified for affect to be 3.6 hours. The phase relationship between cortisol and estradiol may play a role in the development of alterations in affective disorders.

Abnormalities in sleep patterns in individuals at risk for psychosis and bipolar disorder

AIM

To compare patterns of sleep and the presence of sleep disturbances in individuals in at-risk mental states (ARMS) for psychosis and bipolar disorder (BD) with a healthy control (HC) group.

METHODS

This was a comparative study involving 20 individuals in ARMS for psychosis or BD, according to the Comprehensive Assessment of At-Risk Mental States, and 20 age- and sex-matched healthy controls. Quality of sleep in the previous month was assessed using the Pittsburgh Sleep Quality Index, diurnal somnolence was evaluated using The Epworth Sleepiness Scale, and chronotype was determined using the Questionnaire of Morningness/Eveningness (QME). All of the participants underwent polysomnography (PSG) during the entire night for two consecutive nights. The first night aimed to adapt the subject to the environment, and only the data from the second night were used for the analysis.

RESULTS

Compared with the HC group, individuals in the ARMS group reported significantly worse sleep quality, as measured by the Pittsburgh Sleep Quality Index. Both groups had scores consistent with daytime sleepiness on the Epworth Sleepiness Scale, and there were no differences with regard to chronotype between the groups, with a predominance of the indifferent type in both groups. In the PSG assessment, we observed increased Sleep Latency (SL) and increased Rapid Eye Movement Sleep Onset Latency (REMOL) in the ARMS group, compared to the HC group.

CONCLUSION

The results of this study indicated that sleep abnormalities could be found early in the course of mental diseases, even in at-risk stages, and support the further investigation of their predictive value in the transition to psychosis and BD.

Treatment of seasonal affective disorder

Seasonal affective disorder (SAD), winter type, is characterized by the regular annual onset of major depressive episodes during fall or winter, followed by spontaneous remission and sometimes hypomanic or manic episodes during spring and summer. SAD is clinically important, since approximately 2-5% of the general population in temperate climates are affected. Since the first description of the syndrome, researchers have made attempts to elucidate the pathophysiological background of SAD. Bright light therapy has been proposed as the treatment of choice for this disorder. However, numerous studies have also investigated suitable psychopharmacological treatments for SAD. This report is aimed to provide an overview on the clinical management and current therapeutic options for SAD.

Do sleep abnormalities and misaligned sleep/circadian rhythm patterns represent early clinical characteristics for developing psychosis in high risk populations?

Sleep architecture changes, such as slow-wave sleep (SWS) percentage variations and reductions in latency and density of rapid eye movement (REM), are found in most patients with schizophrenia and are considered to be an important part of the pathophysiology of the disorder. In addition to these sleep parameters changes, disruptions in sleep homeostasis and the sleep/circadian rhythm also occur in these patients. Sleep/circadian rhythm abnormalities negatively affect neocortical plasticity and cognition and often precede the diagnosis of the illness. Thus, it has been suggested that the sleep/circadian rhythm might be involved in the pathophysiology of psychosis. Recent advances in the identification of individuals at a high risk for developing schizophrenia allow us to investigate several neurobiological processes involved in the development of psychosis. In this article, we review the current evidence of the effects of sleep parameter abnormalities, disruptions in sleep homeostasis and misalignments of sleep circadian rhythm on the early stages of schizophrenia. In addition, we discuss the preliminary evidence of sleep and circadian rhythm abnormalities during the prodromal stages of psychosis and propose that these abnormalities can be explored as potential predictors, as an adjunct to clinical diagnosis, of developing a psychotic disorder in at risk populations.

Chronobiology of mood disorders

OBJECTIVE

As part of a series of papers examining chronobiology ['Getting depression clinical guidelines right: time for change?' Kuiper et al. Acta Psychiatr Scand 2013;128(Suppl. 444):24-30; and 'Manipulating melatonin in managing mood' Boyce & Hopwood. ActaPsychiatrScand 2013;128(Suppl. 444):16-23], in this article, we review and synthesise the extant literature pertaining to the chronobiology of depression and provide a preliminary model for understanding the neural systems involved.

METHOD

A selective literature search was conducted using search engines such as MEDLINE/PubMed, combining terms associated with chronobiology and mood disorders.

RESULTS

We propose that understanding of sleep-wake function and mood can be enhanced by simultaneously considering the circadian system, the sleep homoeostat and the core stress system, all of which are likely to be simultaneously disrupted in major mood disorders. This integrative approach is likely to allow flexible modelling of a much broader range of mood disorder presentations and phenomenology.

CONCLUSION

A preliminary multifaceted model is presented, which will require further development and testing. Future depression research should aim to examine multiple systems concurrently in order to derive a more sophisticated understanding of the underlying neurobiology.

Bright-light therapy in the treatment of mood disorders

Bright-light therapy (BLT) is established as the treatment of choice for seasonal affective disorder/winter type (SAD). In the last two decades, the use of BLT has expanded beyond SAD: there is evidence for efficacy in chronic depression, antepartum depression, premenstrual depression, bipolar depression and disturbances of the sleep-wake cycle. Data on the usefulness of BLT in non-seasonal depression are promising; however, further systematic studies are still warranted. In this review, the authors present a comprehensive overview of the literature on BLT in mood disorders. The first part elucidates the neurobiology of circadian and seasonal adaptive mechanisms focusing on the suprachiasmatic nucleus (SCN), the indolamines melatonin and serotonin, and the chronobiology of mood disorders. The SCN is the primary oscillator in humans. Indolamines are known to transduce light signals into cells and organisms since early in evolution, and their role in signalling change of season is still preserved in humans: melatonin is synthesized primarily in the pineal gland and is the central hormone for internal clock circuitries. The melatonin precursor serotonin is known to modulate many behaviours that vary with season. The second part discusses the pathophysiology and clinical specifiers of SAD, which can be seen as a model disorder for chronobiological disturbances and the mechanism of action of BLT. In the third part, the mode of action, application, efficacy, tolerability and safety of BLT in SAD and other mood disorders are explored.

Second-generation antidepressants for seasonal affective disorder

BACKGROUND

Seasonal affective disorder (SAD) is a seasonal pattern of recurrent depressive episodes that is often treated with second-generation antidepressants (SGAs), light therapy or psychotherapy.

OBJECTIVES

To assess the efficacy and safety of SGAs for the treatment of SAD in adults in comparison with placebo, light therapy, other SGAs or psychotherapy.

SEARCH METHODS

We searched the Cochrane Depression, Anxiety and Neuorosis Review Group's specialised register (CCDANCTR) on the 26 August 2011. The CCDANCTR contains reports of relevant randomised controlled trials from The Cochrane Library (all years), EMBASE (1974 to date), MEDLINE (1950 to date) and PsycINFO (1967 to date). In addition, we searched pharmaceutical industry trials registers via the Internet to identify unpublished trial data. Furthermore, we searched OVID MEDLINE, MEDLINE In-process, EMBASE and PsycINFO to 27July 2011 for publications on adverse effects (including non-randomised studies).

SELECTION CRITERIA

For efficacy we included randomised trials of SGAs compared with other SGAs, placebo, light therapy or psychotherapy in adult participants with SAD. For adverse effects we also included non-randomised studies.

DATA COLLECTION AND ANALYSIS

Two review authors screened abstracts and full-text publications against the inclusion criteria. Data abstraction and risk of bias assessment were conducted by one reviewer and checked for accuracy and completeness by a second. We pooled data for meta-analysis where the participant groups were similar and the studies assessed the same treatments with the same comparator and had similar definitions of outcome measures over a similar duration of treatment.

MAIN RESULTS

For efficacy we included three randomised trials of between five and eight weeks duration with a total of 204 participants. For adverse effects we included two randomised trials and three observational (non-randomised) studies of five to eight weeks duration with a total of 225 participants. Overall, the randomised trials had low-to-moderate risk of bias, and the observational studies had a high risk of bias (due to small size and high attrition). The participants in the studies all met DSM (Diagnostic and Statistics Manual of Mental Disorders) criteria for SAD. The average age was approximately 40 years and 70% of the participants were female.Results from one trial with 68 participants showed that fluoxetine was not significantly more effective than placebo in achieving clinical response (risk ratio (RR) 1.62, 95% confidence interval (CI) 0.92 to 2.83). The number of adverse effects were similar between the two groups.We located two trials that contained a total of 136 participants for the comparison fluoxetine versus light therapy. Our meta-analysis of the results of the two trials showed fluoxetine and light therapy to be approximately equal in treating seasonal depression: RR of response 0.98 (95% CI 0.77 to 1.24), RR of remission 0.81 (95% CI 0.39 to 1.71). The number of adverse effects was similar in both groups.Two of the three randomised trials and three non-randomised studies contained adverse effect data on 225 participants who received fluoxetine, escitalopram, duloxetine, reboxetine, light therapy or placebo. We were only able to obtain crude rates of adverse effects, so any interpretation of this needs to be undertaken with caution. Between 22% and 100% of participants who received a SGA suffered an adverse effect and between 15% and 27% of participants withdrew from the studies because of adverse effects.

AUTHORS' CONCLUSIONS

Evidence for the effectiveness of SGAs is limited to one small trial of fluoxetine compared with placebo, which shows a non-significant effect in favour of fluoxetine, and two small trials comparing fluoxetine against light therapy, which suggest equivalence between the two interventions. The lack of available evidence precludes the ability to draw any overall conclusions on the use of SGAs for SAD. Further larger RCTs are required to expand and strengthen the evidence base on this topic, and should also include comparisons with psychotherapy and other SGAs.Data on adverse events were sparse, and a comparative analysis was not possible. Therefore the data we obtained on adverse effects is not robust and our confidence in the data is limited. Overall, up to 27% of participants treated with SGAs for SAD withdrew from the studies early due to adverse effects. The overall quality of evidence in this review is very low.

Circadian rhythms and sleep in bipolar disorder

OBJECTIVE

Biological rhythm pathways are highlighted in a number of etiological models of bipolar disorder, and the management of circadian instability appears in consensus treatment guidelines. There are, however, significant conceptual and empirical limitations on our understanding of a hypothesised link between circadian, sleep, and emotion regulation processes in bipolar disorder. The aim of this article is to articulate the limits of scientific knowledge in relation to this hypothesis.

METHODS

A critical evaluation of various literatures was undertaken. The basic science of circadian and sleep processes, their involvement in normal emotion regulation, and the types of evidence suggesting circadian/sleep involvement in bipolar disorder are reviewed.

RESULTS

Multiple lines of evidence suggest that circadian and sleep-wake processes are causally involved in bipolar disorder. These processes demonstrably interact with other neurobiological pathways known to be important in bipolar disorder, but are unique in that they are open to behavioural manipulation.

CONCLUSION

Further research into biological rhythm pathways to bipolar disorder is warranted. Person-environment feedback loops are fundamental to circadian adaptation, and models of circadian pathogenesis (and treatment) should recognize this complexity.

Morningness-eveningness and depression: preliminary evidence for the role of the behavioral activation system and positive affect

There is considerable evidence of circadian rhythm abnormalities in mood disorders. Morningness-eveningness, the degree to which people prefer organizing their activity and sleep patterns toward the morning or evening, is related to circadian phase and is associated with mood, with relatively greater psychological distress among evening types. Given that circadian rhythms may also relate to the Behavioral Activation System (BAS) and positive affect (PA), but not to the Behavioral Inhibition System (BIS) or negative affect (NA), it was hypothesized that individual differences in BAS sensitivity and levels of PA, but not BIS and NA, would explain the association between morningness-eveningness and depression in a sample of 208 individuals with a range of depressive symptomatology. As predicted, increasing eveningness was associated with greater depression, lower BAS, and lower PA, but not directly associated with NA. Path analyses supported a model wherein morningness-eveningness is associated with depression via multi-step indirect paths including BAS-Reward Responsiveness, PA, and NA. A path between BIS and depression was distinct from the one involving morningness-eveningness. A variety of alternative path models all provided a weaker fit to the data. Thus, results were consistent with the BAS and PA mediating the effects of morningness-eveningness on depression.

Sleep and circadian rhythm disturbances: multiple genes and multiple phenotypes

Sleep is regulated by two broad mechanisms: the circadian system, which generates 24-h rhythms of sleep propensity and a wake-dependent homeostatic sleep process whereby sleep pressure increases during wake and dissipates during sleep. These, in turn, regulate multiple brain structures and neurotransmitter systems. In view of the complexity of sleep it is not surprising that there is considerable variation between individuals in both sleep timing and propensity. Furthermore, marked abnormalities in sleep are commonly encountered in psychiatric and neurodegenerative disorders. Teasing apart the genetic versus environmental contributions to normal and abnormal sleep is complex. Here we attempt to summarise what recent progress has been made, and what will be needed in the future to gain a more complete understanding of this fundamental aspect of physiology.

The chronobiology and neurobiology of winter seasonal affective disorder

This review summarizes research on the chronobiology and neurobiology of winter seasonal affective disorder (SAD), a recurrent subtype of depression characterized by a predictable onset in the fall/winter months and spontaneous remission in the spring/summer period. Chronobiological mechanisms related to circadian rhythms, melatonin, and photoperiodism play a significant role in many cases of SAD, and treatment of SAD can be optimized by considering individual differences in key chronobiological markers. Converging evidence also points to a role for the major monoamine neurotransmitters serotonin, norepinephrine, and dopamine in one or more aspects of SAD. Ultimately, as with other psychiatric illnesses, SAD is best considered as a complex disorder resulting from the interaction of several vulnerability factors acting at different levels, the various genetic mechanisms that underlie them, and the physical environment. Models of SAD that emphasize its potential role in human evolution will also be discussed.