# The neural basis of habit formation measured in goal-directed response switching

## TL;DR

This study explores how the brain switches from habitual actions to goal-directed behaviors, identifying key brain regions and mechanisms involved in habit formation and control.

## Contribution

The study identifies specific cortical-striatal networks and the causal role of the premotor cortex in habit control using fMRI and TMS.

## Key findings

- Overtraining increases RT switch costs, indicating stronger habitual behavior.
- fMRI shows distinct brain regions for habit expression and overriding.
- TMS of the left premotor cortex enhances habit control performance.

## Abstract

Replacing a habitual action with goal-directed control involves a cost whose neural mechanisms in humans are not well established. Our study quantifies this cost and uncovers its neural correlates using fMRI and neurostimulation. Training S-R links in overtrained stimuli (compared to less trained ones, termed standard-trained stimuli) increased RT switch costs, explained by drift diffusion modeling. Training engaged sensorimotor areas and the posterior putamen, whereas standard-trained behaviors recruited the posterior caudate, insula, and prefrontal regions. A cortical network orchestrated habit expression (right S1 with the left anterior insula/prefrontal areas) while also implicating the basal ganglia when overriding habits (left premotor with the putamen). Importantly, stimulation of the left premotor cortex played a causal role in habit control, enhancing performance across both the training and devaluation phases. Our findings reveal an interaction between habitual and goal-directed brain regions, highlighting shared neural dynamics when overriding habitual behaviors.

•RT switch cost increases with overtraining, indexing human habit strength•fMRI reveals cortical-striatal networks for both habit expression and overriding•TMS shows a causal role of the premotor cortex in both habit acquisition and reversal•Computational modeling links automaticity to drift-diffusion decision parameters

RT switch cost increases with overtraining, indexing human habit strength

fMRI reveals cortical-striatal networks for both habit expression and overriding

TMS shows a causal role of the premotor cortex in both habit acquisition and reversal

Computational modeling links automaticity to drift-diffusion decision parameters

Behavioral neuroscience; Cognitive neuroscience; Medical imaging