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PhD defence: Liv Vadskjær Hjordt
Friday, 24. August 2018, 15:00 - 17:00
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by peje
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On Friday August 24th at 3 pm in Auditorium 93 at Rigshospitalet, Cand. psych. Liv Vadskjær Hjordt, will defend her PhD thesis entitled "I should have been a bear. Bears are allowed to hibernate; humans are not".

Assessment committee:
Professor Martin Balslev Jørgensen, MD, DMSc, Copenhagen University, Denmark (Chairman)
Adjunct professor Nicole G. K. Rosenberg, Cand. Psych., Århus University Hospital, Denmark
Professor Kelly Rohan, Department of Psychological Science, University of Vermont, USA

Primary supervisor:
Professor Gitte Moos Knudsen, MD, DMSc, Neurobiology Research Unit, Copenhagen, Denmark.

Summary:
People living in countries far north or south of Equator are subjected to cold, dark and long winters. Although most people cope well with the winter season, about 12% of the population in Copenhagen fulfil the diagnostic criteria for Seasonal Affective Disorder (SAD); an occurrence of recurrent seasonal depressions that most often develop during autumn or winter and remits the following spring or summer. Individuals with depression often exhibit cognitive impairments, but it is unclear which aspects of cognition are affected in SAD, whether they are state or trait features of depression, and are implicated in the development of depressive symptoms. Similarly, the impact of personality traits on SAD severity, and whether such self-reported traits fluctuate with the seasons is also unknown.

The overall aim of this thesis is to gain more knowledge on how cognitive functions and self- perceived personality traits are involved in SAD, and how they associate with depressive symptoms. This thesis is based on three published studies that have been undertaken in a group of 29 medication-free individuals diagnosed with SAD and 30 demographically matched healthy controls. All participants completed an extensive neuropsychological test battery, self-report questionnaires and psychiatric interviews once in summer and once in winter.

We observed that in winter, individuals with SAD showed impairments in the ability to inhibit responses to angry and sad faces and in the identification of happy faces compared with controls. In summer, individuals with SAD and controls performed similarly on these tasks (study 1). We also found that in summer and in winter individuals with SAD showed season-independent impairments in tasks measuring working memory, cognitive processing speed and motor speed compared to controls. Cognitive processing speed was negatively associated with the seasonal change in SAD depressive symptoms in SAD (study 2). Finally, we observed that in summer, the groups scored similarly on their personality traits, whereas in winter, individuals with SAD scored higher on Neuroticism and lower on Extraversion, compared with controls and to their own summer scores. Controls did not score any different in winter compared to summer. High scores on Neuroticism in summer were associated with more severe depressive symptoms in winter in the SAD group only (study 3).

The results obtained in this thesis suggest that impaired inhibition of angry and sad faces, reduced identification of happy faces, high levels of Neuroticism and low levels of Extraversion characterize individuals with SAD in winter compared to controls, and may thus constitute sensitive state- dependent markers of SAD pathology. Interestingly, in winter, individuals with SAD scored higher on Neuroticism and lower on Extraversion compared to their own summer scores. One interpretation of these results is that individuals suffering from SAD, experience seasonal fluctuations at the very core of their self-perceived personality. Impaired working memory, cognitive processing- and motor speed may constitute more trait-like characteristics of SAD, as these impairments did not change as individuals with SAD moved from their depressive phase to their asymptomatic phase. Cognitive processing speed and Neuroticism appear to be related to depressive symptoms in SAD and may thus constitute SAD vulnerability trait-like markers.

Our findings provide a psychological link between cognitive mechanisms and personality characteristics and SAD. This could guide future longitudinal studies aiming to study which psychological factors are involved in the development of SAD.

Location Auditorium 93, Rigshospitalet