Using poverty of speech as a case study to explore the overlap between negative symptoms and cognitive dysfunction

Background Negative symptoms and cognitive impairment are both regarded as important prognostic markers in schizophrenia. Although these two domains are viewed as distinct and separable, conceptual overlap exists. We sought to illustrate this overlap using speech deficits among patients with schizophrenia. Method Reductions in verbal output were rated by a clinician following an interview, and these ratings were taken to represent negative symptoms (i.e., alogia). Patients were also asked to recount words from specific categories in a standardized manner, and the number of words was recorded as per standard protocol for verbal fluency tests. These scores were taken to represent cognitive impairment. The cross-sectional and longitudinal relationships between these two variables were then examined. Results Patients with more severe alogia produced significantly less words on the verbal fluency tests. This relationship was stronger than that observed with other negative symptoms, and also held after controlling for a number of sociodemographic and clinical variables (e.g., severity of illness). Prospective increases in the number of words produced during the verbal fluency test were associated with improvements in clinical alogia ratings, a longitudinal relationship that was not observed with other negative symptoms. Conclusions Some negative symptoms are conceptually related and therefore not fully distinct from cognitive impairments. Here, we demonstrate that clinical ratings of alogia and words produced during a cognitive test are tapping into a similar construct. Whether a specific deficit is classified as a negative versus cognitive symptom may be matter of semantics rather than reflective of divisible underlying processes.