What are habits and do they depend on the striatum? A view from the study of neuropsychological populations

What are the neural substrates of habit learning in humans? Studies in neuropsychological populations have been central to answering the question, and for decades, research appeared to have provided a fairly consistent answer. However, developments in assays of habits in animals, as well as new approaches to dissecting habitual versus goal-directed control of behavior in humans, point to further complexities in human habit learning. This has raised new questions about the status of habits in neuropsychological populations and our understanding of how the brain supports habitual behavior. I review these emerging challenges and suggest a more nuanced approach to habit learning.