Other rarer affective disorders include the bipolar disorders and the seasonal affective disorders. Because of the important role of mania and hypomania in the diagnosis of bipolar disorders, we will hold the discussion of these until Chapter 10 when we discuss disorders of the basic emotion of happiness.
The key paper on seasonal affective disorder (SAD) was by Rosenthal et al. (1984). Rosenthal and his colleagues described a seasonal pattern for a sample of 29 individuals in which there was a regular occurrence of autumn or winter depression followed by spring or summer normal, hypomanic, or manic mood. An extremely high proportion of this first sample had a bipolar affective disorder (93%). This high figure has been found in some other samples, for example, Blehar and Lewy (1990) summarised figures of 90% bipolar disorders from a number of studies totalling 246 individuals, although Thompson (1989), for example, reported lower rates of 71% in an English sample. Whatever the true rates, DSM-IV has taken the view that the seasonal pattern can occur for both unipolar and bipolar disorders.
The main features of SAD include low mood, increased appetite and weight, hypersomnia, and low energy. Because of the seasonality of the disorder, most theories have examined biological hypotheses especially in relation to the lightsensitive hormone melatonin, although more recent approaches have also examined psychological factors. Despite early enthusiasm, however, the melatonin hypothesis has not been supported by the available data (Rosenthal & Wehr, 1992). There are a number of more recent biological hypotheses (see Dalgleish, Rosen, & Marks, 1996, for a summary), but there is as yet no clear support for any of them. Data collected by Dalgleish and colleagues (Dalgleish, Spinks, Golden, & du-Toit, 2004; Dalgleish, Spinks, Yiend, & Kuyken, 2001; Spinks & Dalgleish, 2001) suggest differences between seasonal depression and unipolar depression on tasks such as the Autobiographical Memory Task, though the equivalent comparisons still need to be made with those with bipolar disorders.
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