This article on premised on gaining an understanding on nicotine addiction on cigarette smokers. The author posits that nicotine in the cigarettes when injected in rats increases the need for an immediate reward instead of a delayed reward. It is from this observation that the author concludes that cigarette smokers exhibit impulsivity when they prefer immediate rewards instead of larger delayed rewards given at delayed intervals when compared to non-smokers.
- Goal/Question Tested
The objectives of the study determine whether acute and sub-chronic nicotine increased impulsivity when the subjective reward values were manipulated through changes in probability as opposed to magnitude. The hypothesis in this study was that when the subjective reward values are changed in terms of probability rather than the size of the reward, nicotine increases impulsive choices in smokers. The findings of the study are significant as they can help understand causes addiction in cigarette smokers and therefore aid in the termination of smoking.
- How the research question was tested
The rats used in the study weighed between 250-300 grams. They were previously trained though water deprivation and forced trials for each delay interval. The study used rats and presented them with two levers. One of the levers delivered immediate rewards while the other delivered delayed rewards. The reward in the experiment was water. The immediate reward was delivered on half of all the trials while the delayed reward was delivered on every reward although after increasing delays. Half of the rats were injected with 0.8mg/kg nicotine subcutaneously while the other half was injected with 1.2mg/kg of nicotine. Table 1 show the sequence of delays with which the delayed rewards were administered.
Figure one show the effect of the doses of nicotine on the rats. The 0.8mg/kg dose had minimal effects on the rats when compared to the 1.2mg/kg dose of nicotine. The figure also shows that the percentage response on delayed reward levers decreased with increasing interval of delays. The three asterisks on the graph indicate that unlike the 0.8mg/kg dose of nicotine, the 1.2mg/kg dose affected the responses on the delayed reward lever negatively at intermediate delays. Figure two presents data on the latency in seconds required to complete the first lever press for every trial.
Figure 2a shows that with increased delay, the latency tended to increase. The asterisk in figure 2b denotes that for the ten rats and at 95% confidence level, the 0.8mg/kg dose of nicotine caused an increase in the amount of time needed to complete the requirement under the longest interval of delay. Figure three shows the results for the two doses over the span of six consecutive days. From the graph, it is apparent that two daily injections of 0.8mg/kg dose of nicotine caused a decrease of the mean percentage responses on the delayed reward lever in the period of six consecutive days.
- Interpretation of Results
The experiment showed that unlike the 0.8mg/kg dose of nicotine, the 1.2mg/kg dose increases the impulsive choice for the immediate, although less certain reward. This implies that increased nicotine intake increases the probability for impulsive choices. Additionally, two daily doses of 0.8mg/kg nicotine over a period of six consecutive days also increased the impulsive choice for immediate rewards. The nicotine injections did not affect the latency for the first response. This shows that whether the reward is manipulated by probability or size, the nicotine has similar effects on impulsive choices. This implies that nicotine probably affects delay discounting. This means that the manipulation approach notwithstanding, nicotine potentially aids in developing and maintaining addiction through the increase of impulsivity.
- Strengths and weaknesses
The use of rats was important because propensity for addiction and impulsivity is correlated in animals and humans. The experiment was also carried out over a period of six days allowing the researcher to note any outliers in the data reported. However, a control experiment might have given more perspective as the researcher would have had a data set on which to draw a comparison. Additionally, the rats that were used did not have a uniform weight. The differences in body weight and by extension mass might have affected the outcome of the study.