PS263 Lec 13: Decision Making

Cortico-basal gangliar loops

signaling loops (neural pathway) from the cortex through the basal ganglia and back to the cortex

Does the striatum have dopamine receptors?

Yes, it has both D1 receptors (direct pathway, excitatory) and D2 receptors (indirect pathway, inhibitory)

Do both D1 and D2 receptors signal the same or different regions of the basal ganglia 

D1 receptors tend to signal the direct pathway whereas D2 receptors tend to signal the indirect pathway of basal ganglia 

exploration 

Choosing a new, uncertain, or less familiar option to learn more about it.

• involves attraction and aversiveness 

  • curiousity vs risk

exploitation

Choosing a familiar or known option to maximize benefits, often involving less uncertainty, as it focuses on optimizing rewards from prior experiences.

What guides your decisions in the brain?

Your decisions are guided by how much value your brain assigns to each option, with value signals coming from the OFC, striatum, dopamine system, and prefrontal cortex.

Deliberation 

comparing relative values of alternative actions/outcomes 

Vicarious trial and error

hesitation as animal appears to mentally compare different options

How do different brain regions contribute to deliberation during decision-making

The prefrontal cortex and hippocampus “imagine” or pre-play future situations, and these imagined outcomes activate the ventral striatum, which assigns reward value to each option.

How does dopamine help us choose between options?

Reward signals in the ventral striatum trigger dopamine release, which strengthens the GO pathway for the preferred option and suppresses alternatives, biasing the brain toward selecting the most rewarding choice.

How does dopamine promote a considered action in the basal ganglia?

Dopamine excites D1 neurons in the direct “GO” pathway and inhibits D2 neurons in the indirect “STOP” pathway, making the chosen action easier to initiate and more likely to be selected.

How does reduced dopamine bias against an action?

Low dopamine weakens the GO pathway and strengthens the STOP pathway, leading to greater inhibition of movement and making actions harder to start or choose.

Direct Pathway

makes movement more likely by creating a chain of inhibition → inhibition → disinhibition, which ultimately excites the cortex and allows the action to occur.

How does direct pathway work?

Frontal cortex sends excitatory signals to striatum → striatum (D1) sends inhibitory signals to GPi → GPi sends weak inhibition to Thalamus → Thalamus becomes more active due to weak inhibition from GPi, causing it to send stronger excitatory signals to Frontal Cortex  

What is the key action of the striatum in the direct pathway?

The striatum facilitates movement by inhibiting the internal globus pallidus, reducing its inhibitory control over the thalamus, thus promoting motor activity.

What neurotransmitters are used?

FC - Striatum → Glutamate 

Striatum - GPi → GABA 

GPi - Thalamus → GABA 

Thalamus - FC → Glutamate 

Indirect Pathway

Its job is to suppress or stop a movement. It is the “brake” system of the basal ganglia.

How does the Indirect Pathway work?

Frontal cortex sends striatum glutamate signals → striatum sends GABA inhibitory signals to GPe → GPe cannot inhibit GPi as much → GPi heavily inhibits thalamus → thalamus cannot send strong excitatory signals to cortex → movement stops. 

When dopamine is increased..

• D1 neurons get excited (direct pathway) → gets ready to promote movement/action

• D2 neurons inhibit themselves (indirect pathway) → reduces its breaks

This lets the D1 neurons to excite the movement.

When dopamine is decreased…

D2 neurons become more active → strengthens STOP pathway

D1 neurons are less activated → weakens GO pathway