Effects of Smoking on P50 Waveform in Schizophrenic Patients

Objective: Smoking is very common in schizophrenic patients compared to general population. It is considered that nicotine improves cognitive disturbances in addition to its role in normalization of auditory sensory gating deficit in schizophrenia.P50 is an auditory evoked potential that appears about 50 msec as a positive cleflexion after stimulus onset and reflects neural response. This positive waveform is used to show sensory gating mechanism. In schizophrenia P50 is found to be non-suppressed due to the insufficiency of this mechanism.In this study we aimed to investigate the effects of smoking on P50 and the relationship of this effect on probable cognitive impairment in chronic schizophrenic patients.Methods: Forty-three schizophrenic inpatients who fully met the DSM-IV criteria for schizophrenia and forty-four healthy controls were included in the study. Nine of the patients were not taking any drug. Twenty-four of them were on atypical antipsychotics and 10 patients were on typical antipsychotics. The patients and controls were divided into two groups; smokers and non-smokers. Smoker patients and controls were asked to refrain from smoking after midnight. P50 measurement was performed the following morning. Smoker subjects were allowed to consume their usual amount of cigarettes for 30 minutes after the first measurement. Then P50 measurement was repeated, The Wechsler Digit Span Task was performed while smoking and at the end of the restriction of smoking. In non-smokers the procedure was performed only onceResults: There was a significant difference in P50 ratios between the four groups (F=19.01, p<0.001). Smoker patients after smoking restriction (before smoking) and non-smoker patients had significantly high P50 ratios than smoker and non-smoker controls (p<0.001 for all of the comparisons). P50 ratio of smoker patients decreased after 30 minutes' smoking compared to that before smoking (t=7.07, p<0.001) and became similar to that of the controls (t=1.96, p>0.05). P50 ratio of smoker patients after smoking was also lower than that of nonsmoker patients (t=3.32, p<0.005). When the patients were divided into subgroups as "no drug" (n=9), "atypical anti psychotics" (n=24) or "typical antipsychotic" (n=10), there was no significant difference in P50 ratios among subgroups, but all patient groups had higher P50 ratios than the controls (p<0.05, p<0.001, p<0.001; respectively). It was found that digit span scores were not different between the smoker and nonsmoker patients and between the smoker and nonsmoker controls.Conclusion: This study supports P50 non-supression which is a reflection of cognitive disturbances in schizophrenia. However, in schizophrenic patients smoking after overnight abstinence improves P50 deficit. Schizophrenic patients may be trying to treat their cognitive symptoms by smoking since antipsychotics and other known treatments are insufficient to ameliorate cognitive symptoms. It will be better to develop long-half life nicotine-like drugs to solve this problem.