Circadian rhythms in physiology and behavior are synchronized by a central pacemaker, the suprachiasmatic nuclei (SCN) of the hypothalamus. Shift work, jet lag and sleep disorders can disrupt circadian rhythms, negatively impacting health and well-being. The SCN pacemaker resets rapidly in response to changes in the daily light cycle, however, adjustment of peripheral oscillators to changing time zones or work shifts is more gradual, leading to internal desynchrony. In addition, many diseases can impair the SCN’s ability to adjust to changes in the light cycle. My research investigated whether combined pharmacological inhibition of neuropeptide Y and serotonin could enhance resetting and attenuate transient cycles in locomotor activity following a sudden change in light exposure. I found that simultaneously blocking neuropeptide Y and serotonin receptors potentiated phase shifts during the late subjective night and significantly reduced transient cycles of locomotor activity in hamsters. Development of treatments that enhance the circadian system’s response to light may alleviate some of the negative health consequences experienced by travelers, shift workers and individuals with disease-related circadian desynchrony.

No description available.

Abstract In addition to the visual information, external light causes non-image-forming (NIF) effects that modulate brain function and induce psychophysiological effects. The light signal is traditionally assumed to only be mediated via the eyes. Recent studies have suggested the existence of putatively light sensitive structures in the rodent and human brain and penetration of light into the skull and brain tissue has been observed. The brain activation observed during transcranial bright light (TBL) exposure indicates a direct light responsivity of brain tissue. The aim of this thesis was to explore the psychophysiological responses related to TBL. The studies comprising this thesis were conducted in healthy subjects and patients suffering from seasonal affective disorder. TBL exposure was administered via the ear canals in all study settings using light-emitting diodes (LEDs). The comparisons in studies I, II, and III were conducted against the inactivated sham device. Study IV explored the effect of TBL dose. Neither melatonin nor cortisol secretions were altered when acutely exposed to nocturnal TBL. Circadian profiles in TBL setting were in parallel to control conditions for both hormones. Intermittent TBL exposure led to alleviation of jet lag symptoms. Overall post-travel jet lag symptoms as well as subjective feelings of fatigue, inertia, and forgetfulness were reduced. The time to execute the motor response i.e. motor time with a visual warning signal was improved by the TBL treatment. TBL alleviated both depressive and anxiety symptoms related to seasonal affective disorder (SAD). A dose-response relationship regarding the intensity of dose administered via the ear canals was not found. Altogether, TBL seems to affect human brain function by alleviating symptoms of jet lag and SAD and improving psychomotor performance. The acute effect is suggested to be mediated via structures unrelated to acute melatonin secretion i.e. the retinohypotalamic tract (RHT). These results support the light sensitivity of the human brain although the mechanism of action is not yet established. / Tiivistelmä Visuaalisen informaation lisäksi valo aiheuttaa käytöksellisiä ja fysiologisia vaikutuksia, jotka eivät liity kuvan muodostamiseen. Yleisesti vaikutuksen ajatellaan välittyvän aivoihin ainoastaan silmien kautta. Viimeaikaiset tutkimukset ovat havainneet jyrsijöiden ja ihmisten aivoissa mahdollisesti valolle vasteellisia rakenteita. Valon on osoitettu lisäksi läpäisevän kallon ja saavuttavan aivokudoksen. Aivojen aktivoituminen kallon läpi annettavan valoaltistuksen aikana viittaa myös suoraan aivojen valovasteellisuuteen. Tämän väitöskirjan tavoitteena oli tarkastella vaikuttaako kallon läpi annettava valo ihmisen psykofysiologiaan. Tähän väitöskirjaan sisällytetyt tutkimukset tehtiin terveillä vapaaehtoisilla tutkittavilla ja kaamosmasennuspotilailla. Ledin avulla tuotettu valo annettiin kaikissa tutkimusasetelmissa korvakäytävien kautta. Tutkimukset I, II ja III tehtiin lumekontrolliasetelmassa. Tutkimuksessa IV tarkasteltiin valon annosvastetta. Akuutin yöaikaisen valoaltistuksen ei havaittu muuttavan melatoniinin tai kortisolin eritystä. Molempien hormonien vuorokausieritysprofiilit olivat kontrolliasetelman kaltaiset. Jaksottaisen valoaltistuksen havaittiin lievittävän aikaerorasituksen kokonaisoireita ja vähentävän väsymystä, inertiaa ja hajamielisyyttä. Motorisen nopeuden havaittiin paranevan kolmen viikon valohoitojakson aikana. Lisäksi neljän viikon valohoitojakso lievitti kaamosmasennukseen liittyviä masennus- ja ahdistusoireita. Vaikutuksessa ei havaittu eroa eri valoannoksen saaneiden ryhmien välillä. Kallon läpi annettava kirkasvalo näyttäisi vaikuttavan ihmisen aivotoimintaan lievittämällä aikaerorasituksen ja kaamosmasennuksen oireita sekä parantamalla psykomotorista suorituskykyä. Vaikutus ei ole yhteydessä akuuttiin melatoniinin erityksen estämiseen. Tämän tutkimuksen tulokset tukevat ajatusta aivojen valovasteellisuudesta. Kallon kautta annettavan valon vaikutusmekanismia ei kuitenkaan tiedetä vielä.

Thesis (MBA (Business Management))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Experimental research in psychology and economics indicates that depression causes heightened risk aversion. Previous research has documented robust links between seasonal variation in length of day, seasonal depression (known as seasonal affective disorder, or SAD), risk aversion and stock market returns. One such study provides international evidence that stock market returns vary seasonally with the length of the day, a result called the SAD effect. Stock returns are shown to be significantly related to the amount of daylight throughout the autumn and winter. Another study examines the SAD effect in the context of an equilibrium asset pricing model to determine whether the seasonality can be explained using a conditional version of the capital asset pricing model (CAPM) that allows the price of risk to vary over time. Given the above as the base departure point, this report analyses the SAD effect in the context of the South African capital market, where, firstly, the variation in length of day during the year is not so severe compared with other countries like Sweden and the UK and, secondly, a more recent dataset includes the effects of integrated markets and globalisation, that possibly resulted in a shift of seasonal behaviour in the market. It quantifies the SAD effect in general, across industry sectors, over time periods and confirms that a conditional CAPM holds in explaining the seasonality due to SAD. The results differ substantially from those of prior studies. The expected signs of the SAD and Aut coefficients are reversed. Closer analysis shows that seasonality in stock returns has undergone a shift compared to seasonality in an older dataset. A prior finding that effects, such as the SAD, are better explained using excess returns than using raw total returns of the market, is reinforced. The analysis of SAD over time sheds some light on the unexpected outcome of the SAD and Aut coefficients by providing evidence that the validity of regression models deteriorated over time and, more conclusively, that in two consecutive periods, the SAD and Aut coefficients decreased in absolute value. It also found that the coefficients are linearly related to excess returns during the latter period only. The conditional CAPM provides evidence that the effect of SAD is captured in the time variation in the price of risk. The factor of reducing the remainder of SAD in error terms is, however, remarkably smaller. The implication is that market risk already accounts for the SAD effect, but only to a degree, and that the remaining contribution of the SAD effect contained in varying the price of risk is substantially less significant. This finding coupled with the contradictory results in the signs of SAD and Aut coefficients renders evidence of SAD in the South African market rather inconclusive. / AFRIKAANSE OPSOMMING: Navorsing in die gebied waar sielkunde en ekonomie oorvleuel, toon dat depressie ‘n verlaagde risiko-aptyt meebring. Meer spesifiek, vorige navorsing dokumenteer dat robuuste skakels tussen seisoenale lengtes van dae, seisoenale depressie (beter bekend as winter depressie), risiko-aptyt en opbrengste op die andelebeurs bestaan. Een van hierdie studies, wat uitgevooer was op ’n aantal hoof internasionale markte, bevind dat opbrengste op die aandelebeurse wel seisoenaal varieer in ooreenstemming met die lengtes van dae. In dié studie word daar getoon dat opbrengste noemenswaardig ooreenstem met die hoeveelheid sonlig gedurende herfs en winter. ’n Ander studie bestudeer weer seisoenale depressie in konteks met ’n ekwilibrium kapitaal-bate prysmodel om vas te stel of seisoenaliteit verklaar kan word deur ’n kondisionele weergawe van hierdie model waar die prys van risiko varieer oor tyd. Met bogenoemde as vertrekpunt, analiseer die verslag wat volg winterdepressie in die Suid-Afrikaanse aandelemark waar, eerstens, die variasie in lengtes van dae gedurende die jaar minder is as vir ander lande soos Swede en Engeland, en tweedens, waar ’n meer onlangse datastel die effekte van geintegreerde markte en globalisasie insluit. Die verslag kwantifiseer seisoenale depressie in die algemeen op die effektebeurs, pas dan regressie-modelle toe op verskeie industrie-sektore en oor verskillende periodes. Ten einde, word bevestig dat ’n kondisionele kapitaal-bate prysmodel seisoenaliteit as gevolg van winterdepressie kan verklaar. Vergeleke met vorige studies, word daar teenstrydighede in die resultate opgemerk ten opsigte van die verwagte tekens van die koeffisiënte. Met nadere ondersoek word bevind dat die seisoenaliteit in opbrengste ’n verskuiwing ondergaan het vergeleke met ’n ouer datastel. ’n Vorige bevinding dat faktore, tipies soos seisoenale depressie, beter verklaar kan word deur alpha opbrengste (risiko vrye obrengste afgetrek) as rou opbrengste, word bevestig. Die analise oor tyd verklaar gedeeltelik die onverwagte koeëfisiënte. Daar word waargeneem dat die geldigheid van regressie modelle oor twee opeenvolgende tydperke verswak het. Verder word daar ook bevind dat die absolute waardes van die koeëfisiënte verklein het en dat koeëfisiënte ’n liniêre verwantskap met opbrengste toon, slegs in die latere tydperk. Die toepassing van ‘n kondisionele kapitaal-bate prysmodel bevestig dat seisoenale depressie teenwoordig is in die prys van risiko. Daar word verder bevestig dat mark risiko gedeeltelik seisoenale depressie verklaar en dat die oorblywende teenwoordigheid daarvan in die prys van risiko heelwat minder statistiese geldigheid het. Gegewe dit, tesame met die teenstrydigheid in die tekens van die koeëfisiënte, word enige duidelike konklusies ten opsigte van seisoenale depressie se teenwoordigheid in die Suid-Afrikaanse mark verhoed.

Thesis (M.S.)--Uniformed Services University of the Health Sciences, 2005. / Typescript (photocopy).

Thesis (Ph. D.)--Uniformed Services University of the Health Sciences, 2005. / Typescript (photocopy).

Thesis (M.S.) -- Uniformed Services University of the Health Sciences, 2005. / Title from title screen (viewed Aug. 14, 2007). Includes bibliographical references (p. 95-106).

Thesis (M.S.)--Uniformed Services University of the Health Sciences, 2005. / Typescript (photocopy).

Thesis (M.S.)--Uniformed Services University of the Health Sciences, 2005. / Running title: Seasonal affective disorder and melanopsin. Typescript (photocopy).