DYSMETRIA OF VOLUNTARY SACCADES IN SCHIZOPHRENIA
In schizophrenia occur structural and functional changes in frontal and temporal cortex, thalamus, amygdala and hippocampus, an increase in ventricular volume, a decrease in the size of the corpus callosum. These changes are considered as the neurobiological basis of cognitive deficit observed in patients. These structures are involved in the generation of saccadic eye movements. This fact allows us to use the oculography method to search for objective criteria for assessing the functional state of the brain in schizophrenia. In works devoted to assessing the accuracy of the amplitude of voluntary eye movements is reported about an increase in the proportion of hypometrical visually induced saccades in patients with schizophrenia compared with the control group. The detected saccade dysmetry is associated with a spatial memory deficit and lacking of control from the frontal cortex. It should be noted that most of the known studies have been conducted with the participation of patients undergoing heterogeneous drug treatment. And the methodological approaches to the study of oculomotor activity in these studies are different. This does not allow to make a detailed profile of oculomotor reactions in schizophrenia. In this regard, it seems appropriate to study the absolute and relative indices of voluntary saccades in patients with schizophrenia who are not receiving drug therapy, in order to identify possible oculomotor markers that can further help in the diagnosis of this disease. In the study participated 42 people: 16 schizophrenia patients (3 males and 13 females, average age 37.6±4 years) and 26 healthy subjects (3 males and 23 females, average age 22±1.5 years). Schizophrenia patients did not take any antipsychotic drugs before admission to the hospital and participated in the study no later than twenty-four hours after the start of drug treatment. The procedure research: participants made vertical and horizontal voluntary saccades in response to a tree-dot stimulus. Time of one presentation of a stimulus - 20 seconds. Before presenting the stimulus, the participant received instructions to move their eyes from dot to dot as quickly as possible without moving their head. The video camera recorded in the infrared range with frequency 50 Hz was located next to the monitor (30-40 angular degrees relative to the monitor-participant axis) from the side of the patient’s leading eye. Registration was carried out in a room with ambient light, using infrared illumination. The proportion of dysmetric saccades was calculated as the ratio of the number of cases of dysmetria to the total number of gaze movements from point to point during the presentation of the stimulus. Statistical analysis was done using the SPSS statistical software package. To determinant the nature of the distribution, the Kolmogorov-Smirnov criterion was used, the significance of differences (independent samples) was determined by the Student t-test. One-way ANOVA was used to evaluate the effect of the disease on the proportion of dysmetric saccades. Both with horizontal and vertical arrangement of stimulus, patients with schizophrenia made fewer fixations in 20 seconds than healthy subjects. Also, patients with schizophrenia commit significantly more dysmetric saccades compared to the healthy subjects. Both in the experimental and in the control groups, a predominance of hypometrical errors over hypermetric ones is observed. Moreover, in patients with schizophrenia, this difference is significantly higher. The presence of the disease "schizophrenia" (one-way ANOVA) significantly affects the proportion of multisaccades, as well as the proportion of dynamic hypersaccades in the horizontal direction. An increase in the proportion of hyposaccades is usually associated with an interruption of control from the prefrontal cortex, which can be explained by the phenomenon of hypofrontality observed in schizophrenia. It can be assumed that the increase in the proportion of saccadic hypometria is a manifestation of the endophenotype of schizophrenia. Although low productivity in performing voluntary saccades in people with schizophrenia is probably not a specific symptom, it represents part of the overall profile of oculomotor reactions in this disease. The detected predominance of dysmetria in patients with schizophrenia compared with the control in respect to horizontal, but not vertical saccades, may be due to differences in neuronal control. Perhaps the involvement of different cortical areas in the control of vertical eye movements compensates dysfunction of the frontal cortex, which leads to a lack of statistically significant differences in the vertical saccades accuracy and the presence of such differences in the horizontal saccades accuracy.