Research On The Ability Of Response Inhibition Of OCD Patients With Stop Signal Task

In our daily life, people can casually stop a certain behavior according to the environmental needs. Whether this control over the action about to occur succeeds or not depends on response inhibition function. Response inhibition is essential for people when they take flexible and Goal-directed action which based on environmental changes. Response inhibition disorder can lead to many neurological diseases and mental illness, such as children attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD) and Parkinson’s, etc.OCD is common in the clinical practice, but it’s one of the most difficult to cure mental disorders. The main symptoms of OCD patients are the obsessions and compulsions. Obsessions may be caused by the inability to inhibit certain stimuli, while compulsions may be caused by the inability to inhibit certain dominant responses. Studies have shown that the defective response inhibition is the core damage of the OCD patients when executing function. Also, some studies found out that the OCD damaged brain region overlapped the brain regions which involved in response inhibition brain mechanisms. Most findings support that the OCD patients have response inhibition defects, while some other literatures suggest that they have selective inhibition defects, or even have no obvious defects compared with the control group. The reason is that different studies have different experimental paradigm as well as different group designs. Also, it is related to the limitations of the methods and techniques.At present, the most common used response inhibition experimental paradigms are Go/NoGo task and stop signal task. Some researchers believe that in the Go/NoGo task, the stimuli to NoGo may not be inhibited, but just be ignored by selective attention mechanism. And subjects selectively make responses to Go stimuli. Stop-It is a classic experimental paradigm for response inhibition ability study. It simulates the real life situations and requires the subjects to fast and accurately take or stop an action in the experiment. The stop signal task is a process to inhibit an activated reaction, which can display the implementation process of response inhibition more comprehensively. In addition, the detected SSRT in the stop signal task is the only objective indicator which can reflect the inhibitory control ability, it may be a more pure detection method of response inhibition function. We will study the response inhibition ability of OCD in the stop signal paradigm.Objective: To study obsessive-compulsive disorders’(OCD) effects on patients’ response inhibition ability, to reveal the difference between healthy control group and them. To use the principle of stop signal paradigm as well as neural and psychological mechanisms to investigate the neural and psychological mechanisms, which cause OCD symptoms.Methods:The experimental group consisted of30OCD patients. The inclusion criteria:①meet the diagnostic criteria of OCD CCMD-3(Chinese classification of mental disorders).②exclude cerebral organic diseases, no serious physical disease history, with normal vision or normal corrected vision.③take no medicine or stop taking medicine for no less than4weeks after first visit to the doctor’s.④the Y-BOCS (Yale-Brown Obsessive Compulsive Scale) scores the mild to moderate.⑤ is right-handed.⑥informed consent and co-operate. The healthy control group consisted of30people, whose gender, age and years of education are matched with OCD group.Both two groups were rated by the attending physicians of high qualification, using Hamilton Anxiety Scale (HAMA) and depression scale (HAMD). Only those who scored less than7in HAMA and less than8in HAMD could be involved, in order to exclude the interference in OCD response inhibition from anxiety, depressive tendencies and other comorbidity factors.Use the stop-signal task to test the stop signal reaction time (SSRT) and reaction time on no-signal trials (NSRT) of30OCD patients, to measure their reaction and response inhibition abilities, and compare the results with age matched healthy control group.To ensure data effectiveness, this research selected the part of more accurate data (P close to50%) and Got rid of the part of bad data (P(r/s)>80%or<20%), which remained21cases in OCD group and23cases in control group. To test our hypotheses, we performed various analyses in SPSS19.0for Windows program, and the measurement data was expressed by the way mean value plus or minus standard deviation. First,t-test of independent sample (two sides) was conducted between two groups. Second, multiple regression analysis was performed between SSRT and intraclass variables as well as participants’ social variables (age, mean education year, and the score of psychological scale). Third, covariance analysis (ANCOVA) was conducted in which the NSRT was as covariate and SSRT was as dependent variable, which to test the relationship between response inhibition ability and overall response ability. Last, paired sample t-test for SRRT and NSRT was performed to test the interference effect of the stimulus of stop on response time. The significance level was0.05. There was no difference between two P(r/s) groups (either close to50%), t=-1384,P=0.174， which means the reasonable data lays a foundation for comparison of SSRT.There was no significant difference in SSD between the OCD and control groups:t=0.469, P=0.642; SSRT in OCD group was also obviously higher than that of control group:t=3206,P=0.003; NSRT in OCD group was significantly higher than that of control group:t=2.894,P=0.006; NS-HIT in OCD group was significantly lesser than that of control group: t=-2.795, P=0.008, whereas MISS in OCD group was significantly higher than that of control group:t=2258,P=0.029.Covariance analysis was conducted in which the NSRT was as covariate and SSRT was as dependent variable, and there was no difference in homogeneity test of variances (F=0.175, P=0.68=78) and regression homogeneity (F=0.056, P=0.81) between two groups. And the results show that after removing the influence of NSRT, SSRT in OCD group is still obviously higher than that of control group (F=21.98,P=0.001).For OCD group, Multiple regression analysis was performed between SSRT and other variables like age and education, and the results showed there was no significant relationships in SSRT and age (t=-O.830, P=0418); SSRT and education (t=-1.409,P=0.177) as well as SSRT and Y-BOCS score (t=1.751, P=0.098). For control group, results of Multiple regression analysis also showed there was no significant relationship in SSRT and age(t=-0.19, P=0.851) as well as SSRT and education(t=-1.473, P=0.166).Paired t-tests were performed respectively for SRRT and NSRT in two groups, the results of OCD group showed that, SRRT is100.15ms significantly lower than NSRT (t=-13.355, P=0.000), and the results of control group SRRT is88.76ms significantly lower than NSRT (t=-14.073, P=0.000). Results of Multiple regression analysis between SSRT and other intraclass factors are as follows:in control group, SSRT negative correlated with SSD (t=-225.063, P=0.000), positive correlated with NSRT (t=75.129, P=0.000) and SRRT (t=2.225, P=0.038), but not with NS-HIT (t=0.694, P=0.497) and NS-MISS (t=0.590, P=0.563). In OCD group, SSRT negative correlated with SSD (t=-8.5,P=0.000) and positive correlated with NSRT(t=6.115, P=0.000), but not with NS-HIT (t=0.023, P=0.982) and NS-MISS (t=-0.224,P=0.811).Conclusion:1. Stop signal task shows that the OCD patients have response inhibition defects.2. OCD patients’response inhibition defects play an important role in pathogenesis.3. Stop signal stimuli have interference in subjects’reaction.4. For response inhibition ability study, stop signal task paradigm is the most scientific experimental one.