Musculoskeletal pain during pregnancy and its impact on quality of life: A cross-sectional study.

Schizophrenia is a severe psychiatric condition that affects approximately 0.7% of the population worldwide (). Multiple genetic and environmental risk factors have been identified, but its pathogenesis remains largely unknown. While it is typically operationalized as a single disorder, it is widely recognized to be a heterogeneous syndrome with an unknown number of subtypes and/or dimensions. One reason for the lack of progress in characterizing heterogeneity (besides the fact that most research studies treat the condition as if it were a single disorder) is that it continues to be diagnosed based primarily on signs and symptoms that are not specific to the condition, that wax and wane over time (and so do not represent trait or vulnerability phenomena), and that have unknown biological bases (). Unlike for most diseases outside of psychiatry, there are no diagnostic or subtype biomarkers for schizophrenia, and many reliable biological findings are found in only a minority of patients (). This has led to suggestions that we need to, at a minimum, identify biological mechanisms involved in generating individual symptoms, even if it is understood that these may characterize only a subset of those who meet diagnostic criteria for schizophrenia along with others who do not fully meet these criteria. Ideally, it would be possible to identify mechanisms involved in clusters of symptoms and other features (e.g., perceptual and cognitive impairments) that can meaningfully define illness subtypes or dimensions that align with illness course characteristics and treatment response. To do so, however, requires determining which characteristics of schizophrenia are in fact primary rather than reflective of compensatory processes or consequences of other features. The characteristic symptoms of schizophrenia, as defined by the criteria by which it is currently diagnosed include: psychotic symptoms (also known as symptoms, so called due to the ‘addition’ of phenomena such as hallucinations and fixed delusional beliefs into consciousness), symptoms (so called due to the reduction of normative experience), such as restricted facial affect, loss of motivation and drive, and social withdrawal), and symptoms such as reduced coherence in speech, incongruence between ideation and emotion, and abnormal voluntary and involuntary motor behavior. Although there is a long history in psychiatry of focusing on these symptoms for diagnosis and monitoring of treatment response, it is possible for someone to ‘have schizophrenia’ but, at any given time, have none of these symptoms at threshold level. It is also not clear that all of these symptoms are direct reflections of the condition's primary neurobiological alterations. That is, some symptoms may be compensatory or adaptive responses to the primary neural changes, an idea expressed well over 100 years ago by Bleuler () with his distinction between primary (emerging from neurobiological impairments) and secondary symptoms, with the latter representing reactions to primary symptoms. In this view, loosening of associations, as typically observed through disorganized speech, was usually considered the most important primary symptom. This referred to a loosening of the associative linkages between mental representations, whether they involve perception, thought, memory, or other cognitive functions. A related contemporary concept was that schizophrenia involves an (), which can be translated as a lowering of the level of consciousness, or reduction in psychic tension. This refers to a less differentiated and less organized state of mental functioning () characterized by weakening of the normal connections between thoughts, the loss of control of mental contents, an inability to “promote the positive” or “inhibit the negative” (), the intrusion into consciousness of material that is normally non-conscious and as a consequence, inadequate or inappropriate emotional reactions (). The early hypothesis of a lowering of psychic tension in schizophrenia is consistent with Kurt Goldstein's later concept that sufficient excitability in cortical tissue is necessary for the perception of figure-ground relationships (). The latter refers to emergence of a focus of attention during visual perception, and the distinguishing between this focus (typically an object or an event) from the other, background, information that serves as visual context. In Goldstein's view, when brain structure and/or function is compromised, there is a dedifferentiation of the figure-ground process, especially for stimulus fields that are less familiar. This was thought to result in a number of phenomena that have been observed in schizophrenia, such as reduced visual acuity, problems in contour perception, reduced color perception, elevated sensory thresholds, reduced stability in bistable perceptions, and “simplification of the organizational units,” examples of which include reduced perceptual organization and reduced