The fundamental disturbance (Grundstörung) of schizophrenia (Part 1): Acquiring a potent endophenotype, exploratory eye movement

It is important to identify the common fundamental disturbance (Grundstörung) in schizophrenia and to elucidate its real nature. A fundamental disturbance refers to a primary disturbance underlying the pathology of schizophrenia and is defined as something that can explain various pathological conditions. However, these aspects have not yet been determined. We have investigated them using exploratory eye movements. In this article, we describe our discovery of a potent endophenotype (Part I), while our elucidation of the fundamental disturbance will be presented in the next report (Part II). Exploratory eye movements are movements of the eye fixation ‐ point during free observation of objects. We found that these movements reflect an “attitude to get involved voluntarily and actively in the environment,” in other words, “subjective activity.” We also calculated the Responsive Search Score from exploratory eye movements recorded under conditions of interpersonal interaction and social recognition. This score was characteristically lower in patients with schizophrenia than in healthy individuals and patients with other psychiatric disorders. In addition, it reflected genetic predisposition to schizophrenia and was highly correlated with negative symptoms and the performance intelligence quotient on the Wechsler Intelligence Scale. Furthermore, the characteristics of the score with respect to genetic predisposition met all the criteria for an endophenotype. The Responsive Search Score appeared to be a potent marker for schizophrenia. Hence, we will elucidate the fundamental disturbance of schizophrenia by using this marker.