A Specific Role for Posterior Dorsolateral Striatum in Human Habit Learning - Tricomi

Question 1

fasen van de studie

Answer 1

The participants complete the tasks within an fMRI scanner. There are 3 phases and 2 groups of participants:
* 1-day group: performed two 8-minute training sessions on 1 day.
* 3-day group: performed 4 training sessions each day for 3 days (6 times as much training).

Phase 1: Instrumental learning
Participants are shown different blocks with an indication of which button to press (yellow filled-in square). They could press the button as much as they wanted within the block. A gray circle indicated that no reward would follow if the button was pressed, while an M&M or Frito cue indicated a reward. Reward cues were given on a variable interval: on average every 10 seconds.

Phase 2: Outcome devaluation
After the final training session, 1 of the 2 food outcomes was devalued by asking the participants to eat it until it was no longer pleasant. Then, they were placed back into the fMRI for the final phase.

Phase 3: Critical test
A short, 3-min extinction test (without rewards) followed to determine the degree of habituation. There were 2 possible outcomes, indicating whether behavior was goal-directed or habitual:
1. Goal-directed action: participants respond less for the food they no longer find pleasant than for the still valued food.
2. Habit-based action: both M&M and Frito cues elicit equal responding.

Question 1

doel van dit experiment

Answer 1

er achter komen of mensen goal-directed of habit-based actie uitvoeren

Question 2

resultaten van de test (behaviour)

Answer 2

Comparison of the 1- and 3-day group on showed that, during extinction:
* 1-day group: reduced response rates during presentation of the cue linked to the devalued food.
* 3-day group: continued to respond for the devalued food.

-> The 1-day group showed goal-directed behavior and the 3-day group showed habitual behavior

Question 3

resultaten van de fMRI data

Answer 3

1. Posterior putamen: the right posterior putamen/globus pallidus area in the dorsolateral striatum (DLS) showed an increasing response to the reward cues over the course of training sessions.

-> The posterior putamen/globus pallidus region seem to play a central role in the development and/or control of habitual behavior in humans.

2. vmPFC: increased activation as anticipation of an upcoming reward increased (number of seconds since the previous reward) and this pattern remained stable over the entire course of training.

-> The vmPFC seems to play a role in supporting goal-directed behavior by representing the value of an upcoming outcome. As it does not diminish with training, habitual behavior probably comes to preferentially influence behavior even when the individual remains aware of the outcome value.

Question 4

conclusies van het artikel

Answer 4

1. There is a clear shift from goal-directed to habitual behavior over repeated performance.
2. There is increasingly greater activation of a region in the posterior putamen extending into the globus pallidus with more experience: it became increasingly sensitive to stimuli associated with a particular behavioral response (greater S-R association).
3. Even when the vmPFC remained activated in response to reward anticipation, eventually the S-R association was so strong that goal-directed behavior transitioned into habitual behavior