Alternative Approaches to Understanding Habit Learning in the Dorsolateral Striatum

Our daily lives are full of habits. Yet, even though we know them intimately, habits are surprisingly hard to pin down in laboratory settings in order to study them and their basis in the brain. For over a century, scholarly work on habits has been dominated by the idea that they are, fundamentally, a routine of behavior that gets set in motion as a sort of reflex in a given circumstance. This is captured by the theory that habits reflect an association between a stimulus or context and a response. Habitual behaviors of this sort are very different from behaviors that are driven cognitively, with a goal in mind, which is argued to reflect an association between the behavior and the outcome that occurs. In this framework, we can identify habits as behaviors that remain unchanged when the outcome changes, as well as when other environmental changes occur, because they look reflexive and not cognitively guided. In the brain, this insensitivity of behavior to change is known to rely on networks that include the dorsal-lateral aspect of the striatum. Ergo, the dorsolateral striatum (DLS), is regarded as a home base for stimulus-response learning for habits. However, when one examines habits further, there are explanatory gaps. First, there are alternative options for defining habits based on behaviors that appear stuck and unchangeable and that deserve closer attention. Second, when one digs further into the function of the dorsolateral striatum—the habit zone of the brain—it is not stimulus-response learning that jumps out, but rather other types of activity that may cause behaviors to look like habits. We view the research field as in rather muddy waters for trying to operationally define what habits are and for trying to understand how areas like the striatum make behaviors appear habitual. Yet, having several different working models to lean on and advances being made in both brain analyses and behavioral analyses, progress in this domain seems promising.