Delayed verbal reactions are specifically impaired in patients with schizophrenia

Recent neuropsychological, psychophysiological and neuroimaging studies have shown that specific changes in attention and information processes occur in schizophrenic disorders. A verbal delayed reaction methodology, determined by our group since 1992, has provided similar quantitative data. Visual verbal stimuli, occurring in random sequence, are presented to the subject who is requested to utter immediately the perceived word in a first trial; in a second one, a delay (foreperiod) between the word presentation and a 'go' signal (eight asterisks) is interposed. Acousticograms and orbicularis oris EMG are recorded as responses. The ratio of the 1.5-s foreperiod delayed reaction time to the immediate reaction time reveals a facilitation of the executive system occurring during sustained purposeful attention, a characteristic function of the prefrontal cortex. A further ratio, with a 0.1-s foreperiod, has been measured to investigate the effect of interference processes. These trials have been performed including 18 patients with schizophrenia, 31 with idiopathic Parkinson's disease, four patients with extrapyramidal degenerative diseases, five affected by obsessive compulsive disorder and in age-matched normal controls. Both ratios were significantly increased in schizophrenic patients and, on the contrary, decreased in patients with obsessive-compulsive disorder. These changes are in agreement with the neuroimaging findings of 'hypofrontality' in the schizophrenic patients. Verbal delayed reaction methodology seems a reliable and easily applicable tool for investigating sustained purposeful attention processes in clinical conditions.