Neurotransmitter homeostasis and habit formation: the predominant role of reward speed in behavior selection

Habits may persist not only because of limits in willpower but also because everyday behavior helps the brain maintain a preferred level of reward. We tested a homeostatic account that predicts a stronger influence of reward speed than of reward amount on short term choice. Nineteen participants completed a twelve day within subject protocol that included a baseline, an intervention that removed each person’s fast reward behavior, a washout, and a second intervention that removed a distinct high amount behavior. Participants recorded time spent on other activities each day, and analyses used complete paired observations for each comparison with nonparametric confirmations. When the fast reward behavior was removed, participants increased the time they devoted to other activities; this increase was statistically significant before correction, although it did not reach the Bonferroni correction level of significance. When the high amount behavior was removed, the increase in time devoted to other activities was smaller and not statistically significant in the subset who completed that phase. These findings suggest that short horizon behavior follows the rate and timing of reinforcement more than the total amount accumulated over longer intervals, which is consistent with a homeostatic selection process. The results suggest practical steps for habit change. Early efforts should increase the immediacy, frequency, and availability of reinforcement in the desired behavior and reduce the effort needed to begin, while moderating the immediacy of the undesired behavior. Limitations in this study included a small sample, a fixed intervention order, no logging during washout, potential partial overlap of fast and high amount behaviors and reliance on self-report to classify activities as fast reward or large amount.