Depression (and anxiety) is based upon an amplification of emotional information processing, derived from the evolution of human intelligence (the Amplification Effect), and impaired cortical regulation of excessive limbic system activity. In line with the Continuum Principle (natural phenomena tend to occur on a continuum, and any instance of hypothesized discreteness requires unassailable proof), there is insufficient evidence for discrete types of depression. Melancholic depression arises as an emergent property from the severe end of the depression continuum. Cognitive regulatory techniques applicable to depression and anxiety are introduced. A continuous model based upon severity and duration is also presented.



Evidence for depression as a unitary entity ironically comes from the research by Parker and colleagues (Parker, 2013; Parker et al, 1988; Parker et al, 1991), purportedly supporting melancholic/endogenous depression as a discrete type. The non-endogenous factor they identified consisting of anxiety, personality, and other condition variables, is used to support the position that a discrete form of depression—melancholic/endogenous—alone exists, with reactive/neurotic “depression” a composite of anxiety and personality symptoms (Parker, 2013; Parker et al, 1988; Parker et al, 1991). The results of Cochrane (1977) also align with this perspective, the non-endogenous form of depression being indistinguishable from non-depressed psychiatric states. But then how are we to characterize scenarios where depression involves anxiety, hypomania-mania, psychosis, and personality disorders? Depression is commonly mixed with anxiety, hypomanic-manic symptoms, psychosis in some instances, and personality disorder symptoms (Benazzi, 2004; Benazzi, 2007; Bilder et al, 2000; Elvevag, & Goldberg, 2000; Fava et al, 2000; Fiszdon et al, 2007; Freeman & McElroy, 1999; Himmelhoch, 1998; Judd et al, 1998). One solid option for explaining the overlap between depressive and other symptoms is separate continuums interfacing with one another (Bowins, 2015). Hence, the depression continuum can interface with other continuums, such as that for anxiety, hypomania-mania, psychosis, and personality disorders.

Interfacing of the anxiety and depression continuums provides an example of how this process can work. Depression and anxiety commonly overlap, as with depression and social anxiety (Fava et al, 2000). This is not surprising given the emotional information processing overlap between anxiety and depression: Circumstances that entail threat or danger also frequently involve loss (Bowins, 2004). We might arrange depression and anxiety on a single dimension placing them at either extreme, a seemingly viable option. However, this arrangement produces serious obstacles. First, it would imply that depressive and anxiety symptoms must trade off against each other, such that greater depression means lesser anxiety, a clearly false scenario since both symptom types can occur together with varying severity levels. Second, moderate levels on the single dimension, representing a true mix of symptoms, must mean less severe depression than at the depression pole, and less severe anxiety than at the anxiety pole. This occurrence is not compatible with the comorbidity of depression and anxiety, because mixed scenarios commonly involve both intense depression and anxiety; indeed, comorbidity is often a sign of greater severity generally. The perspective might be taken that placement on the same dimension only pertains to the presence or absence of depressive and anxiety symptoms, such that depressive symptoms are maximal at that pole and decline to the anxiety pole. However, the dimension we are now considering is severity and not just presence of symptoms.

Watson (2005) presents another way that anxiety and depression overlap based on the interpretation of factor analytic studies: Certain types of anxiety, GAD and Posttraumatic Stress Disorder (PTSD), and depression, major and dysthymic, are linked on the basis of distress (distress disorders), while panic disorder, agoraphobia, social phobia, and specific phobia are distinct as “fear” disorders. This comorbidity perspective can only account for depression and anxiety, and hence is limited in its applicability to the overlap between depression and other disorders. As pertains to depression and anxiety together, a major problem is that it fails to consider the different emotional information processing underlying depression and anxiety: Depression as amplified sadness with the root emotion triggered by loss oriented cognitive activating appraisals, and anxiety as amplified fear with the root emotion derived from threat or danger oriented cognitive activating appraisals (Beck, 1991; Bowins, 2004, Bowins, 2006a; Clore & Ortony, 2000; Eley & Stevenson, 2000; Finlay-Jones & Brown, 1981; Lazarus, 1984; Lazarus, 1991; Shrout et al, 1989). A more specific problem with Watson’s (2005) model pertaining to the realities of comorbidity, is that depression frequently co-exists with “fear” conditions such as social phobia (Fava et al, 2000). Social anxiety actually appears to represent the primary trigger for depression in many instances (Schneier et al, 2002). In addition, panic disorder, agoraphobia, social phobia, and specific phobia can involve equal or greater levels of distress than with generalized anxiety disorder, PTSD, or depression. For instance, those with panic disorder often experience great distress. Hence, the notion of interfacing depression and anxiety continuums is more parsimonious and compatible with the realities of depression and anxiety comorbidity.