The circuit of addiction

meso cortico limbic dopamine

• therse regions and their interaction matter for addcition

• VTA- sneding out and realsing dopamine

• limic system- lizard brain, matters for emotions

• cortical pathway- orbital frontal cortex

• prefrontal cortex- human brain

• dopamine goes all over brain

Dopamine has far reaching effects

• Salience

  • attenition

  • perception

• Decison making

• motivation

  • hunger

  • thirst

  • sex

  • grades

  • money

• Domapine effects lots of things and lots of functions

How to test that this circuit is real?

• Operant condishioning

• shape behvaior by rewarding desired behavior

• drugs provide powerfull reward

Directly modifiy the function of the circuit assoctaied with addiction'

• Can directly stimulate a part of brain

  • VTA

  • Nucleus accubens

• Can release drugs in regons

• Can release neurotrasnmoiters

• can block neurotranmiters

Injection into the relevant structure

• Agonists

  • Enhance activity

• Antagonists

  • Block activity

Parts of the circuit

• VTA- Dopamine neurons

• Nucleus accombins

  • core

  • shell

  • part of sraitum

• frontal cortex

  • Oribital frontal cortex

  • Anterior cingulate

  • Dorsal prefrontal

• The rest of brain

VTA

• cluster of dopamine nureons

• hits all over the brain

• encodes reward predition error signals

  • idenitfiers rewars

  • what stimuli predicts rerwards

  • when is prediction is correct

  • when predition is inncorrect

  • generalizes stimuli

• important for motivation, pleasure, desion making, movement planing, perception, attenion, memory

Nucleus accumbens (NAc)

• Core and shell

• part of straitum

  • part of basil ganglia

• Intergrates the reward sig into movement opptions

• learning about how prediction maps movement

• intergrates top down control from frontal cortex with bottom up motivation from dopamine, emotion from amygidula, mem from hippocampus, hemostatic drives from hippocampus

• regulates the effort expened to achive goal

NAc connectivity

• imputt and output from lots of places

NAc shell and core

• division of responiblites between subdivioon

• processing pathway if new has more flexablity

NA shell

NAc core

basal ganglia: procdual learning and mottor output\

• gating movement

• direct

  • disinhibits motor output (opens yhe gait)

• Indirect

  • Can disinhibit or increase inhibition

  • hyperdirct

The straitum in the basil ganglia [

Frontal cortex

• lots

• desion making

• idenity

• attention

• morality

• guy with pole thro brain

Dopamine

• VTA: generalized reward prediction error signal

• Based on changes in firing rates (How many action potentionals per second)

• Based on firing rate

Reward sensitivity

• No CS: Nothing predicts rewards

• R: reward (juce) happens at the line

• Lots of trials across rows (each dot is an action potenial)

• Overtime as an assocation (sound) is pared with reward (juice) the monkeys brain creates dopamine upon hearing assocation, the dopamine will acctally be connected to the bell

• If you take reward away brain still fires at bell but are blocked when they re supposed to be given jucie

Dopamine reward predictiom

dopamine sig

• reward

• predition

• error

• last peice: generalzed across similar stimuli

VTA vs substantia nigra (SNr/SNc)

• should motor movement happen or not

Drugs hijacxk thgis reward prediction error signal