In assessing the causes of mental illness biological factors may be broadly juxtaposed against psychological ones. “Biological factors” include: genetics (heredity); brain damage (whether present at birth or caused by subsequent trauma); neurotransmitter activity; and other factors such as substance abuse, poor nutrition or exposure to environmental toxins. Conceptually “psychological factors” divide into two sub-groups. The first is what might be called cognitive and the second, social. “Cognitive” factors include psychodynamic theories of personality based on feelings of inferiority, neuroses, complexes and other life experiences. “Social” factors are cultural expectations and environmental constraints. There is some overlap between the two. For example, abuse, neglect or trauma when an infant may arise from factors such as low SES but then impact early childhood development, the child’s object relations and sense of self.
While possibly they did formerly few now believe these models are mutually exclusive. Rather to understand the etiology of mental disorder one must adopt an integrative, polythetic, multiaxial diagnostic approach. An example is the diathesis-stress model, which hypothesizes that environmental stress factors trigger genetic vulnerabilities.
Because it is “symptom” based DSM-IV more prominently focuses on cognitive psychological and socio-psychological diagnoses and outcomes. These readily permit inference of counterpart cognitive psychological and socio-psychological causes, which I will avoid simply repeating. For example DSM-IV states that one of the general diagnostic criteria for a personality disorder is “cognition” (i.e. ways of perceiving and interpreting self, other people, and events). From this one readily might infer the existence a psychological pathology involving self identity and self-concept. One cannot however readily infer the existence of any biological mechanisms that may be causally contributory. Once one takes a step back and regards the DSM as an exercise in the construction of explanatory narrative this lacuna becomes pervasive. Only when discussing serious psychotic disorders (e.g. schizophrenia) does the DSM offer etiological explanations that are not primarily psychologically driven. For this reason my primary focus in this essay will be to establish differential biological explanations as opposed to those that primarily are psychologically driven in connection with BPD, substance abuse disorder and schizophrenia.