People often have good intentions but fail to adhere to them. Implementation intentions, a form of strategic planning, can help people to close this intention–behavior gap. Their effectiveness has been proposed to depend on the mental formation of a stimulus–response association between a trigger and target behavior, thereby creating an “instant habit.” If implementation intentions do indeed lead to reliance on habitual control, then this may come at the cost of reduced behavioral flexibility. Furthermore, we would expect a shift from recruitment of corticostriatal brain regions implicated in goal-directed control toward habit regions. To test these ideas, we performed a fMRI study in which participants received instrumental training supported by either implementation or goal intentions, followed by an outcome revaluation to test reliance on habitual versus goal-directed control. We found that implementation intentions led to increased efficiency early in training, as reflected by higher accuracy, faster RTs, and decreased anterior caudate engagement. However, implementation intentions did not reduce behavioral flexibility when goals changed during the test phase, nor did it affect the underlying corticostriatal pathways. In addition, this study showed that “slips of action” toward devalued outcomes are associated with reduced activity in brain regions implicated in goal-directed control (ventromedial prefrontal cortex and lateral orbitofrontal cortex) and increased activity of the fronto-parietal salience network (including the insula, dorsal anterior cingulate cortex, and SMA). In conclusion, our behavioral and neuroimaging findings suggest that strategic if–then planning does not lead to a shift from goal-directed toward habitual control.

Despite good intentions, people often fail to cross the “intention–behavior gap,” especially when goal achievement requires repeated action. To bridge this gap, the formation of automatized routines may be crucial. However, people may differ in the tendency to switch from goal-directed toward habitual control. To shed light on why some people succeed in forming routines while others struggle, the present study related the automatization of a novel, daily routine to individual differences in white-matter connectivity in corticostriatal networks that have been implicated in goal-directed and habitual control. Seventy-seven participants underwent diffusion-weighted imaging and formed the daily routine of taking a (placebo) pill for 3 weeks. Pill intake was measured by electronic pill boxes, and participants filled out a daily online questionnaire on the subjective automaticity of this behavior. Automatization of pill intake was negatively related to striatal (mainly caudate) connectivity with frontal goal-directed and cognitive control regions, namely, ventromedial pFC and anterior cingulate gyrus. Furthermore, daily pill intake was positively related to individual differences in striatal (mainly caudate) connectivity with cognitive control regions, including dorsolateral and anterior pFC. Therefore, strong control networks may be relevant for implementing a new routine but may not benefit its automatization. We also show that habit tendency (assessed with an outcome-devaluation task), conscientiousness, and daily life regularity were positively related to routine automatization. This translational study moves the field of habit research forward by relating self-reported routine automatization to individual differences in performance on an experimental habit measure and to brain connectivity.

This study presents the first direct investigation of the hypothesis that dopamine depletion of the dorsal striatum in mild Parkinson disease leads to impaired stimulus–response habit formation, thereby rendering behavior slow and effortful. However, using an instrumental conflict task, we show that patients are able to rely on direct stimulus–response associations when a goal-directed strategy causes response conflict, suggesting that habit formation is not impaired. If anything our results suggest a disease severity–dependent deficit in goal-directed behavior. These results are discussed in the context of Parkinson disease and the neurobiology of habitual and goal-directed behavior.