Eye movements of patients with schizophrenia in a natural environment

Alterations of eye movements in schizophrenia patients have been widely described for laboratory settings. For example, gain during smooth tracking is reduced, and fixation patterns differ between patients and healthy controls. The question remains, whether such results are related to the specifics of the experimental environment, or whether they transfer to natural settings. Twenty ICD-10 diagnosed schizophrenia patients and 20 healthy age-matched controls participated in the study, each performing four different oculomotor tasks corresponding to natural everyday behavior in an indoor environment: (I) fixating stationary targets, (II) sitting in a hallway with free gaze, (III) walking down the hallway, and (IV) visually tracking a target on the floor while walking straight-ahead. In all conditions, eye movements were continuously recorded binocularly by a mobile lightweight eye tracker (EyeSeeCam). When patients looked at predefined targets, they showed more fixations with reduced durations than controls. The opposite was true when participants were sitting in a hallway with free gaze. During visual tracking, patients showed a significantly greater root-mean-square error (representing the mean deviation from optimal) of retinal target velocity. Different from previous results on smooth-pursuit eye movements obtained in laboratory settings, no such difference was found for velocity gain. Taken together, we have identified significant differences in fundamental oculomotor parameters between schizophrenia patients and healthy controls during natural behavior in a real environment. Moreover, our data provide evidence that in natural settings, patients overcome some impairments, which might be present only in laboratory studies, by as of now unknown compensatory mechanisms or strategies.

Dysconnectivity of the inferior frontal gyrus: implications for an impaired self-other distinction in patients with schizophrenia

Ego disturbances in schizophrenia might be caused by a failure of the efference copy mechanism, which compares efferent with reafferent signals and attenuates the sensory consequences of self-produced movements. We carried out a functional magnetic resonance imaging study in which 16 patients with schizophrenia and 16 healthy matched controls were studied while performing both intentional and unintentional continuous hand movements in two consecutive experiments. We periodically varied the delay of visual feedback to create a sensory-motor discrepancy. Exclusively for intentional movements the activation pattern of the inferior frontal gyrus (IFG) in patients was opposite to that of controls: less attenuated during time-congruent feedback and less activated during time-incongruent feedback. Additionally, several functional connections within the mismatch detection network (IFG with insula, putamen, medial orbitofrontal cortex) were affected. Also, activity of the dysconnected orbitofrontal cortex was correlated with ego disturbance in patients. We discuss that in healthy individuals the IFG might enable a distinction between self and non-self using time-characteristics of feedback, whereas in patients this sensory mismatch detection appears to be altered. Moreover, due to the dysconnectivity of the IFG, the efferent and reafferent signal exchange between perceptual and motor areas seems to be affected. This might cause self-monitoring deficits in patients, phenomena that contribute to the emergence of ego disturbances.

Hyperintentionality during automatic perception of naturalistic cooperative behavior in patients with schizophrenia

Social cognition and the corresponding functionality of involved brain networks are essential for effortless social interaction. Patients with schizophrenia exhibit impaired social functioning. In this study, we focused on the neural networks involved in the automatic perception of cooperative behavior and their alterations in schizophrenia. We performed a functional magnetic resonance imaging study of 19 schizophrenia patients and 19 healthy matched controls. Participants watched a set of short videos with two actors manipulating objects, either with (C+) or without cooperation (C-). Additionally, we assessed delusional symptoms in patients using the Scales for the Assessment of Positive Symptoms and psychosis proneness in healthy controls using the brief schizotypal personality questionnaire. The observed group-by-condition interaction revealed a contrasting activation pattern for patients versus healthy controls in the medial and lateral prefrontal cortex, the middle cingulate cortex, and the left angular gyrus. Furthermore, increased activation of the middle prefrontal areas, left angular gyrus, and the posterior sulcus temporalis superior in response to the noncooperative condition (C-) was positively correlated with delusional symptoms in patients. Our findings suggest an overactivated "theory of mind" network in patients for the processing of noncooperative behavior. Thus, "overmentalizing" might be based on delusions and altered processing of cooperative behavior in patients with schizophrenia.