Saccade generation and suppression in schizophrenia: effects of response switching and perseveration

Decomposing mechanisms of abnormal saccade generation in schizophrenia patients: Contributions of volitional initiation, motor preparation, and fixation release

Clinical and theoretical models suggest deficient volitional initiation of action in schizophrenia patients. Recent research provided an experimental model of testing this assumption using saccade tasks. However, inconsistent findings necessitate a specification of conditions on which the deficit may occur. The present study sought to detect mechanisms that may contribute to poor performance. Sixteen schizophrenia patients and 16 healthy control participants performed visually guided and two types of volitional saccade tasks. All tasks varied as to whether the initial fixation stimulus disappeared (fixation stimulus offset) or continued during saccade initiation, and whether a direction cue allowed motor preparation of the specific saccade. Saccade latencies of the two groups were differentially affected by task type, fixation stimulus offset, and cueing, suggesting abnormal volitional saccade generation, fixation release, and motor preparation in schizophrenia. However, substantial performance deficits may only occur if all affected processes are required in a task.

Neural correlates of impaired volitional action control in schizophrenia patients

Slowed initiation of volitional but not visually guided saccades indicates impaired volitional action control in schizophrenia patients (SZ). The present study aimed at identifying neural correlates of this specific deficit. Fourteen SZ and 13 healthy control participants (HC) underwent functional magnetic resonance imaging while performing volitional and visually guided saccades. SZ showed increased latencies in volitional but not in visually guided saccades. Brain activation during volitional saccades compared to visually guided saccades was increased in SZ compared to HC in several areas: the supplementary eye fields, suggesting inefficient production of volitional saccades; the prefrontal cortex, pointing to altered top down control on complex eye movements; and the left middle temporal area, suggesting changes in early sensory and attention processing during the volitional control of saccades in SZ.

Inflexible information acquisition strategies mediate visuo-spatial reasoning in stabilized schizophrenia patients

OBJECTIVES

Cognitive deficits are of fundamental importance to the clinical picture of schizophrenia and are on the verge to be included as diagnostic criteria in the DSM-V. While focusing on information processing deficits, no emphasis has been put on whether patients' deficits can be accounted for by maladaptive information acquisition strategy deployment.

METHODS

We tested 24 stabilized patients with schizophrenia and 25 matched controls in a visuo-spatial analogy task with graded difficulty. Eye movement recordings served to identify information acquisition strategies.

RESULTS

Patients compared to healthy controls showed slower reaction times in the easiest condition and higher error rates in the more difficult conditions. Eye movement recordings illustrated that overall mean fixation duration increased with increasing task difficulty in healthy controls only. Further, patients deployed a more efficient strategy ("constructive matching") less often than healthy controls in the easier conditions.

CONCLUSIONS

These results suggest that information acquisition strategies mediate visuo-spatial cognitive performance in schizophrenia. Patients adopt a less efficient strategy independently of task difficulty indicated by a characteristic behavioural pattern. Our results point to a powerful tool of improving patients' performance in cognitively demanding tasks by training them in more flexible cognitive (e.g., information acquisition) strategy deployment.

Response switching in schizophrenia patients and healthy subjects: effects of the inter-response interval

Schizophrenia patients show impaired saccadic response switching, pointing to action control deficits at the level of response selection. Previous studies on healthy subjects suggested that response switch effects might decrease if the prior response is longer ago, reflecting a slow dissipation of the response program persisting from the previous trial. The present study aimed at directly investigating whether response switch effects in schizophrenia patients and healthy subjects depend on the inter-response interval (IRI). Effects of response switching on pro- and antisaccade performance were analyzed in 19 schizophrenia patients and 19 healthy controls at 3 different IRIs (2,500, 3,000, 4,000 ms). Response switch effects of healthy subjects did not vary with the IRI, suggesting that the previous response program persists as long as no contrary response program is activated. In schizophrenia, response switch deficits were replicated at an IRI of 3,000 ms, whereas at IRIs of 2,500 and 4,000 ms, effects of response switching did not significantly differ from healthy subjects. This might suggest that there is a specific IRI range particularly sensitive to response switch deficits in schizophrenia. However, effects of response switching at different IRIs remain to be consolidated.