A progressive deterioration in people's will and emotional life was central to Kraepelin's concept of his newly described illness, dementia praecox. When Bleuler coined the term schizophrenia, the ‘four As’ that defined the fundamental symptoms of schizophrenia (alogia, affect blunting, autism and ambivalence) strongly resemble what we now call negative symptoms. The advent of the antipsychotic era brought about a focus on a disorder centred on positive symptoms, shunting motivation and emotional life to the outskirts of the disorder's definition. Although treatment frequently ameliorates psychosis, most people do not achieve a return to a satisfactory level of functioning owing to untreated negative and cognitive symptoms. Interest in these symptoms resurfaced in the 1970s under the ‘negative symptoms’ term, in part as a response to this clinical need. Fifty years later, these symptoms are still a major unmet therapeutic need in people diagnosed with schizophrenia.

The quest for defining and understanding negative symptoms resulted in the creation of new symptom scales, including the Scale for the Assessment of Negative Symptoms (SANS) and the Positive and Negative Syndrome Scale (PANSS). These were important contributions but unsatisfactory for several reasons, including the assessment of cognitive deficits and disorganisation, as well as poor coverage of motivation-related negative symptoms in the PANSS. Both scales rely on behavioural proxies for internal experiences that are at the core of motivation or experiential impairments in individuals with schizophrenia spectrum disorders. The recent second-generation scales,^{Reference Kirkpatrick, Fenton, Carpenter and Marder1} such as the Brief Negative Symptom Scale (BNSS) and the Clinical Assessment Interview for Negative Symptoms (CAINS), were developed to cover the five consensus domains of negative symptoms: anhedonia, asociality, avolition, blunted affect and alogia. Furthermore, they assess not only the observed behaviour but also internal experience in the experiential domains.^{Reference Kirkpatrick, Fenton, Carpenter and Marder1}

This themed issue of the BJPsych is intended to clarify and integrate, for researchers and clinicians, current knowledge of negative symptoms in four main areas: psychopathology, clinical course, pathophysiology and treatment.

There is growing evidence that negative symptoms is an umbrella term with at least two distinct dimensions: deficits in motivation/pleasure, i.e. an experiential dimension, and deficits in expression (alogia and blunted affect) that may have different underlying biological mechanisms. This issue contains some evidence for that idea, and for the need to study each of the five domains (anhedonia, asociality, avolition, blunted affect and alogia) independently.

Three papers explore the different factors of the negative symptoms construct, also discussed in Kirkpatrick et al's editorial.^{Reference Kirkpatrick, Fenton, Carpenter and Marder1} Canal-Rivero et al^{Reference Canal-Rivero, Ruiz-Veguilla, de la Foz, López-Díaz, Garrido-Torres and Ayesa-Arriola2} found that emotional expression, not motivation, correlated with thinning in specific frontal lobe areas in a cohort with first-episode psychosis over a 10-year follow-up. Wolpe et al^{Reference Wolpe, Chen, Kirkpatrick, Jones, Jenkins and Cardinal3} explored the longitudinal impact of the side-effects of antipsychotics as a source for secondary negative symptoms, finding that clozapine-induced sedation negatively affects the motivation and pleasure dimension (i.e. anhedonia, asociality and avolition) of the BNSS but not the expressive one (alogia and blunted affect). O'Brien et al^{Reference O'Brien, Ered, Korenic, Olino, Schiffman and Mittal4} explored the effect of anhedonia in three groups – a group at high risk of psychosis, a group with depression and a group without known psychiatric illness. They found that an abnormal perception of current stress in those reporting early abuse was a risk factor for anhedonia, independently of the disorder, suggesting that adverse childhood events are a risk factor for negative symptoms. Taken together, these three findings indicate the need to use specific scales to evaluate negative symptoms and consider the five separate domains of negative symptoms, as outlined by Kirkpatrick et al.^{Reference Kirkpatrick, Fenton, Carpenter and Marder1}

A reduction in motivational and emotional life is no longer considered the end state of schizophrenia. In this issue, the meta-analysis of Salazar and colleagues found a high prevalence of negative symptoms in children and adolescents during the early stages of a psychotic disorder, with 79.6% of those at risk of psychosis and 60.8% of those with early-onset psychosis exhibiting negative symptoms. It is unclear whether those negative symptoms represent the outcome of faulty developmental trajectories, are secondary to other psychopathological aspects, or result from some form of bias. In any case, these results indicate the need for early recognition of negative symptoms in psychotic disorders.

There has been relatively little progress in the pharmacological treatment of negative symptoms. Non-pharmacological treatments are widely recommended, and Cella and colleagues^{Reference Cella, Roberts, Pillny, Riehle, O'Donoghue and Lyne5} reviewed their efficacy. Unfortunately, their review highlights the relative methodological weakness of the studies conducted to date and the modest positive effect they show for ameliorating negative symptoms.