PMID-18958234 Endocannabinoid Signaling is Critical for Habit Formation.
- quick review (the intro is packed with grat information):
- in goal-directed learning, behavior is highly sensitive to the incentive value of the outcome, and contingency between the action and the outcome.
- with repetition actions become both more efficient and more automatic.
- after extensive training, rats move from goal-directed behavior to more habitual response independent of outcome value.
- random interval schedules favor this more than random ratio reward schedules.
- in mice, random interval schedules promoted habit formation, whereas random ratio schedules promoted acquisition of goal-directed behaviors. does this also apply to humans? I would guess so. Might be an interesting tool to have in the toolbox.
- interval schedules promoted the exploration of a random lever whereas ratio schedules promoted the exploitation of the reward lever.
- the underlying circuitry supporting goal-directed behav and habit formation are different:
- goal directed behavior seems to require the associative BG/cortex including:
- dorsomedial or associative striatum (medial!)
- COMT, a transporter, is more highly expressed here than DAT.
- pre-limbic ctx
- mediodorsal thalamus
- habit formation requries:
- dorsolateral or sensorimotor striatum (lateral!)
- DAT, dopamine transporter, is highly expressed here.
- infralimbic cortex
- amphetamine sensitization can lead to increased spine density in medium spiny neurons in the dorsolateral striatum, while decreasing spine density in the dorsomedial striatum. (interesting!)
- lesions of nigrostriatal input to dorsolateral striatum impairs habit formation;
- infusion of dopamine into the ventral medial prefrontal cortex favors goal-directed behavior
- that is a rather broad statement to make ...
- endocannabinoid release in the striatum is required for LTD induction.
- endocannabinoid signaling regulated bt DA.
- CB1 (the receptor implicated in addiction) is highly expressed in the dorsolateral striatum (habit!) at both excitatory and inhibitory terminals.
- used mice with CB1 mutations therefore!
- CB1 mutant mice have impaired habit formation and enhanced exploration.
- suggest that endocannabinoid signaling is critical for both habit formation and increased exploration in interval schedules.
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