From our review of the history of negative symptoms, as well as current research on this construct, we have shown that negative symptoms in schizophrenia can be mapped onto two phenomenological domains: “Expressive Deficits,” which represents a constellation of expressive gestures including speech, facial expression and other non-verbal signs, and “Avolition,” which encompasses amotivation and asociality.
The concept of “negative symptoms” has a long history in neuroscience and the delineation of negative symptoms in schizophrenia was based on observation and theory long before any empirical studies found evidence for their clustering. Kraepelin identified most of the currently studied negative symptoms and grouped them according to their common psychopathology, a deficit in the process of emotions. He believed negative symptoms were the result of a disconnect between cognition and emotion. When negative symptoms were united in the 1970’s and grouped in opposition to the “favored” positive symptoms, what was a disconnection between cognitions and emotions became a loss of normal function, a deficit. Whereas Bleuler thought that affectivity as a mental function was intact, psychiatrists in the 1980’s thought of negative symptoms (and negative schizophrenia) as permanent and inaccessible to treatment.
However, current understanding of cognitive processes in schizophrenia suggests that defining negative symptoms as a loss of function is problematic. Some investigators have shown that positive symptoms such as hallucinations and delusions are linked to impairments that are the absence of normal cognitive functions such as deficits in source monitoring, poor executive functioning, and jumping to conclusions (Bentall et al., 2009
; Brunelin et al., 2007
). Despite these findings that hallucinations and delusions may result from the loss of normal functions, these psychotic symptoms are clearly different from negative symptoms.
We argue that negative symptoms are heterogeneous and distinct from other symptoms of schizophrenia. Redefining negative symptoms as specific and separate impairments in emotional expressiveness and volition offers the best approach to this construct for both research and clinical treatment. This is supported by our review of factor analytic studies of negative symptoms, which consistently show “Expressive Deficits” and “Avolition” as two separate negative symptom domains.
These two domains differ in their assessment and our knowledge of their etiology. Expressive deficits can be observed during a clinical interview, whereas the diagnosis of avolition needs specific inquiries to be ascertained. Similarly, expressiveness is a constellation of observable behaviors, whose common or unique psychopathologies remain to be clarified, whereas avolition refers to a specific psychopathological process, whose behavioral manifestations need clarification.
We propose that impairments in expressiveness and volition are distinct domains and should be assessed separately in DSM-5. Separating these concepts provides a more focused approach for research on negative symptoms. Likewise, distinguishing between these two domains offers the best hope for developing new treatment approaches that target these specific core phenomena. Based on our review of research on negative symptoms, we recommend that ratings only consider behavioral manifestations of these two dimensions which may be exhibited as follows:
- For expressiveness: Four types of behavior are the most relevant and their impairments can be easily observed by clinicians and researchers: Communicative facial expressions, prosody, hand coverbal gestures, and language output.
- For volition: Reduction in self-initiated and maintained behaviors can be observed in four categories: spontaneous motor activity, grooming/hygiene, work/recreation/leisure, and social engagement.
To be classified as negative symptoms, and to have a diagnostic value, deficits in expressiveness and volition should be separated from other phenomenological components of psychotic disorders. To achieve this, the symptoms must be distinct from or present in the absence of clinically-significant depressed mood or anhedonia, serious extrapyramidal side-effects, and active avoidant behaviors (i.e. due to anxiety or paranoia).
Initially negative symptom classification was developed within the fields of psychopathology and clinical phenomenology. Current research in schizophrenia, however, is driven by cognitive, affective and social neurosciences that influence and enhance our symptom classification paradigms. Expressive deficits can be considered a specific deficit in social communication, overlapping with affective processes. Avolition can be seen as a deficit in functional outcomes until we can further identify which motivational processes are impaired in schizophrenia. Although, clarification is still needed regarding the nature of anhedonia and other affective processes in schizophrenia, at this time we do not consider anhedonia to fall under either domain. We recommend additional research on anticipatory anhedonia as it relates to avolition in schizophrenia. Future studies are also needed to clarify whether expressive deficits and avolition are merely separate observable dimensions or whether they have different neurobiological underpinnings requiring separate treatment approaches.