The Effect On Response Inhibition Function Of Reward Motivation And Its Neural Mechanism

Response inhibition is usually defined as a capacity to prevent or suppress the appropriate or unwanted behaviors which interferes movement or cognitive goals. Response inhibition plays a very important role in human behavior control. The person of higher impulsivity usually is non-foresight actor, instant gratification’s favorer, unable to inhibit inappropriate behavior, tended to risk, sensitive to extraneous stimulus and reward. Stop signal task is one of the most commonly used experimental paradigms to investigate the response inhibition function. This task require participants to respond to advantage stimulation (Go stimulation), however, to inhibit the response to stop stimulations. High impulsive individuals usually present that SSRT significant increased in stop signal task.Many factors influence the response inhibition function. In recent years, a growing number of studies began to pay attention to the interaction of motivation (especially the reward motivation) and specific cognitive function which included attention. However, the effects of reward motivation on the inhibition function is positive (response inhibition function increase) or negative (response inhibition function decrease), which is not yet clear. Studies of attention deficit/hyperactivity disorder with the stop signal task suggested that the participants would receive a certain amount of reward (small gifts or money) when they succeeded to inhibit the stop signal stimulus. However, there was no reward when they succeeded to response the go stimulus. In this experiment condition, compared to non-reward condition, participants’ response inhibition function was significantly increased (SSRT was significantly short). In the experimental condition that participants succeed to response the go stimulus would get a certain amount of reward, and there was no reward when they succeed to inhibit the stop signal stimulus, participants’ response inhibition function was significantly decreased (SSRT was significantly long). Although previous studies have preliminarily explored reward motivation how to affect the response inhibition. However, previous studies have been limited by the design of study and the object of study (ADHD patients), there were not consistent and many limitations in these study results. Many studies suggested that reward motivation often leads to high impulsive behavior, such as aggressive behavior, addiction behavior etc. Impulsive behavior is the response inhibition impairment behavior. Therefore, we suggested that reward motivation would cause the decrease of response inhibition function. With the development of neuroimaging, a growing number studies begin to investigate the neuromechanism of response inhibition which is turned into focus. However, how the neuromechanism of reward motivation affect response inhibition is still unknown. Therefore, This article would use healthy university students, a new stop signal task and fMRI technology to investigate the affects of reward motivation on response inhibition and its neural mechanism.The first study explored the effect of reward motivation on response inhibition function of health college students using reward stop signal task. The second study explored the effect of reward motivation on response inhibition function of college students with different impulsive trait using reward stop signal task. The third study explored the neuromechanism of reward motivation affect response inhibition by functional magnetic resonance technology (fMRI).The first study explored the effect of reward motivation on response inhibition function of health college students using reward stop signal task and non-reward stop signal task by within-subjects design. We recruited 44 Southwest University students (20 males, 24 females) by leaflet and advertising, whose average age is 21.40±1.65, visual acuity or corrected visual acuity is normal, no color weakness or achromatopsia. Stop signal task was divided into two parts, reward task and non-reward task. Each part included two experimental run. The experimental sequence was ABBA. All the participants joined two tasks. The experimental process:In the experiment a stimulus cue which point out that the yellow cue press 1 to react and the blue cue press 2 to react will be showed; followed by a fixation point that hint the stimulation coming. After the fixation point disappeared, the stimulation began to appear. Participants were asked to make response based on stimulation. In study, the subjects were asked to respond as quickly as possible when they see the stimulus appeared, not deliberately delay. When the stimulus is followed by a stop signal, participants must stop button response. In the reward program, there will be 1 yuan award if response correct for Go stimulation, response error without reward or punishment. There will be 1 yuan punishment if failed to stop the reaction for Stop stimulation. Give a feedback in time after the end of the reaction, the content of the current feedback for the total amount of reward. The reward will cumulate if response correct for Go stimulation. If failed to stop the reaction for Stop stimulation not instantly lose lyuan, it will be deducted in the end of a small phase of the experiment (32 trails). At the end of the experiment, the total prize amount will be showed on the screen. In the non reward program, only the correct or error were feedback after reaction to Go or Stop stimulation. The total number of the correct responses to Go stimulation and success inhibit the responses to Stop stimulation were presented on the screen. Results showed that compared with the non reward conditions, GoRT were significantly decreased (t(43)=2.25,p=0.03) and SSRT were significantly increased (t(43)=-4.61,p=0.00) in reward conditions. The second study explored the effect of reward motivation on response inhibition function of college students with different impulsive trait using stop signal task, Using 2 (non-reward and reward stop signal) ×2 (high impulsive group and low impulsive group) mixed experimental design. Firstly, the participants were screened by BIS-11 scale. 22 high compulsive trait (10 males,12 females, average age:22.40±1.43) subjects and 22 low compulsiveness (10 males,12 females, average age:22.24±1.56) are recruited. Stop signal task was divided into two parts, reward task and non-reward task. Each part included two experimental run. The experimental sequence was ABBA. All the participants joined two tasks. The study process of study two is same as the study one. ANOVA analysis showed that there is significant difference in the mainly effect of GoRT and no significant difference in the interaction effect of GoRT. In addition, there is significant difference in the mainly effect of SSRT and no significant difference in the interaction effect of SSRT. Paired samples T test results showed that Non reward GoRT compared to reward GoRT, there is significant difference which reward GoRT is significantly short than non reward GoRT in high impulsive individuals. However, there is no significant difference in low impulsive individuals. Non reward SSRT compared to reward SSRT, there is significant difference which reward SSRT is significantly longer than non reward SSRT in high impulsive individuals. There is no significant difference in low impulsive individuals. Two sample T test results showed that both reward GoRT and non reward GoRT of high impulsive individuals significant lower than low impulsive individuals. However, both reward SSRT and non reward SSRT of high impulsive individuals significant longer than low impulsive individuals.The third study explored the neuromechanism of how reward motivation affect response inhibition by functional magnetic resonance technology (fMRI), using 2 (non-reward and reward stop signal) ×2 (high impulsive group and low impulsive group) mixed experimental design. The experimental procedure and subjects were same as second study. The third study was divided into three parts:Part A explored the neuromechanism of reward motivation on response inhibition (1)——based on brain regions activity. Part B explored the neuromechanism of reward motivation on response inhibition (2)——based on functional connectivity between brain regions. Part C explored the neuromechanism of reward motivation on response inhibition (3)——based on efficiency connectivity between brain regions. The results of study three A showed that compared with the non reward conditions, Stop-Go of reward condition leads to the activity of brain regions significantly decreased, and these brain regions included bilateral inferior frontal gyrus, bilateral anterior supplementary motor area, bilateral caudate nucleus, bilateral putamen, bilateral globus pallidus etc. there is no activity significant increased regions. In addition, compared with non reward condition, in reward condition, Stop-Go of high impulsive correlated brain regions activity showed significantly decreased, these brain regions include bilateral inferior frontal gyrus, bilateral anterior supplementary motor area, bilateral caudate nucleus, bilateral putamen, bilateral globus pallidus etc. there is no activity significant increased regions. Compared with non reward condition, in reward condition, Stop-Go of low impulsive correlated brain regions activity showed significantly decreased, these brain regions include bilateral inferior frontal gyrus, bilateral anterior supplementary motor area, left globus pallidus etc. there is no activity significant increased regions. The results of PPI analysis showed that some function connectivity between brain regions of high impulsive group significantly higher than low impulsive group in reward condition. These brain regions function connectivity include that between inferior frontal gyrus and anterior supplementary motor area, between anterior supplementary motor area and caudate nucleus, between putamen, bilateral globus pallidus and caudate nucleus. There is no function connectivity that high impulsive group significantly lower than low impulsive group in reward condition. The results of DCM analysis showed that in non reward condition, high impulsive individuals complete the response process by hyperdirect pathway and indirect pathway. But in reward condition, indirect pathway plays a mainly role. In non reward condition and reward condition, low impulsive individuals complete the response process by hyperdirect pathway and indirect pathway.The conclusions of this study are as follows:(1) Reward motivation causes the decrease of response inhibition function. The behavior expressions are significantly increased GoRT and significantly decreased SSRT in stop signal task.(2)The effects of reward motivation on response inhibition function of participants with different impulsive trait are different. The effect of reward motivation on response inhibition function of participants with high impulsivity is stronger and with the impulsivity increasing, the effects are significantly increased.(3)The activities of response inhibition related brain regions are significantly decreased by reward motivation. The function connectivity between response inhibition related brain regions are significantly decreased by reward motivation.(4)In reward condition, high impulsive participants complete the response inhibit ion on stop signal mainly using the indirect pathway.