Inhibitory control and spatial working memory: a saccadic eye movement study of negative symptoms in schizophrenia.

The negative symptoms of schizophrenia are perhaps the most unremitting and burdensome features of the disorder. Negative symptoms have been associated with distinct motor, cognitive and neuropathological impairments, possibly stemming from prefrontal dysfunction. Eye movement paradigms can be used to investigate basic sensorimotor functions, as well as higher order cognitive aspects of motor control such as inhibition and spatial working memory - functions subserved by the prefrontal cortex. This study investigated inhibitory control and spatial working memory in the saccadic system of 21 patients with schizophrenia (10 with high negative symptoms scores and 11 with low negative symptom scores) and 14 healthy controls. Tasks explored suppression of reflexive saccades during qualitatively different tasks, the generation of express and anticipatory saccades, and the ability to respond to occasional, unpredictable ("oddball") targets that occurred during a sequence of well-learned, reciprocating saccades between horizontal targets. Spatial working memory was assessed using a single and a two-step memory-guided task (involving a visually-guided saccade during the delay period). Results indicated significant increases in response suppression errors, as well as increased response selection impairments, during the oddball task, in schizophrenia patients with prominent negative symptoms. The variability of memory-guided saccade accuracy was also increased in patients with prominent negative symptom scores. Collectively, these findings provide further support for the proposed association between prefrontal dysfunction and negative symptoms.