Seeking clarity in diversity: exploring cognitive heterogeneity in schizophrenia-spectrum disorders

Cognitive functions such as memory, language, attention, perception, learning, and
problem-solving play a crucial role in daily life activities. When these cognitive processes are impaired, several important aspects of daily life are affected. In schizophrenia- spectrum disorders, there is evidence of a broad range of cognitive impairments. The research described in this dissertation examined the heterogeneity of cognitive impairments across the schizophrenia spectrum using data-driven clustering techniques. The results presented strongly and consistently support cognitive heterogeneity in schizophrenia-spectrum disorders, delineated by three cognitive subtypes: one subgroup with relatively preserved cognitive functioning, one subgroup with moderately impaired cognition, and one group with severely impaired cognition. Importantly, a substantial subset of patients has been found to perform similarly to healthy controls. These subgroups of cognition offer useful information regarding disease characteristics such as symptom severity and global functioning and may be explained by differences in the underlying neurobiology. In conclusion, heterogeneity or diversity is a major challenge in schizophrenia-spectrum disorders and should be considered in both research and clinical practice. Moreover, creating subgroups with shared illness characteristics and similar needs for care is a step toward personalized treatment.