Striatum
The basal ganglia are a connected collection of nuclei that can influence movement, decisions, learning, and reward processing.
A Circuit for Influencing Action
Imagine the brain weighing an action while processing sensory input, internal state, motor activity, and reward-related significance. The basal ganglia are a connected collection of neuron groups, also called nuclei, that can influence this kind of processing. Their contributions include voluntary movement, decision-making, learning, reward processing, and cognitive functions such as planning.
The basal ganglia are a connected collection of nuclei that can influence movement, decisions, learning, and reward processing.
The striatum is the main input structure of the basal ganglia. It is therefore useful to begin with the route that information takes through the circuit rather than treating the striatum as an isolated brain structure.
Following the Information Loop
Cortical neurons provide the striatum with information about sensory input, internal states, and motor activity. The striatum then sends output through other basal ganglia nuclei and the thalamus. From there, the circuit reaches toward frontal areas of cortex and also connects with motor areas. This means that information enters through the striatum but does not simply stop there: activity in the circuit can influence movement, abstract decisions, and reward processing.
Tracing One Information Route
Trace the route when cortical activity carries information about sensory input, internal state, and motor activity.
Input: Cortical neurons provide the striatum with information about the organism's sensory input, internal states, and motor activity.
Entry point: The information enters the basal ganglia through the striatum, which is the main input structure of the system.
Circuit passage: Striatal output passes through other basal ganglia nuclei and the thalamus.
Cortical influence: The circuit reaches toward frontal areas of cortex and connects with motor areas, allowing striatal activity to influence decisions and movement.
The striatum is an entry point into a wider loop: cortex to striatum, through other basal ganglia nuclei and the thalamus, and toward frontal and motor cortex.
Dorsal and Ventral Emphases
The striatum has dorsal and ventral subdivisions with different broad functional emphases. The dorsal striatum is primarily implicated in influencing action selection. The ventral striatum is thought to be critical for different aspects of reward processing, including assigning affective value to sensations.
| Subdivision | Broad emphasis |
|---|---|
| Dorsal striatum | Influencing action selection |
| Ventral striatum | Reward processing, including assigning affective value to sensations |
Signals Meeting at a Spine
A useful way to understand reinforcement learning in the striatum is to focus on a medium spiny neuron's dendritic spine. Cortical neurons provide information to the striatum. Medium spiny neurons receive that cortical input and provide the main input/output neurons of the striatum. Dopamine neurons contact the same dendritic spine region. In this arrangement, cortical and dopamine signals come into close cellular relationship near the spine rather than acting as unrelated messages.
Dopamine is not merely another version of the cortical message. Its importance includes helping determine when cortical-to-striatal connections are modified.
Why Timing Changes Learning
Information flow and learning-related change are related but distinct questions. Information flow asks where cortical information travels through the basal ganglia circuit. Learning-related change asks when the efficacy of a corticostriatal synapse may be modified. The source describes this change as depending on appropriately timed dopamine signals in relation to the cortical activity at the striatal spine. Therefore, the presence of dopamine alone is not a complete explanation of synaptic change; its timing matters.
What do you think happens?
Is this explanation complete: Dopamine is present, so the corticostriatal synapse changes?
Reveal answer
Answer: No, the timing of dopamine signals also matters
The source states that corticostriatal synaptic efficacy may change when dopamine signals are appropriately timed. Dopamine acts in relation to cortical signals at striatal spines, not as an isolated explanation.
Common Explanatory Errors
Treating the striatum as the entire basal ganglia circuit.
The striatum is the main input structure, but its output passes through other basal ganglia nuclei and the thalamus toward frontal and motor areas of cortex.
Fix:
Describe the striatum as the entry point into a wider circuit.Describing the dorsal and ventral striatum as completely isolated systems.
They are subdivisions of the striatum within the wider basal ganglia circuit.
Fix:
Use action selection as the dorsal emphasis and reward processing as the ventral emphasis, while keeping both in the shared circuit.Treating dopamine as an independent teaching signal that explains synaptic change by itself.
The source emphasizes the relationship between cortical signals and dopamine signals near striatal spines and the importance of appropriate timing.
Fix:
Explain that appropriately timed dopamine helps determine when corticostriatal synaptic efficacy may change.Giving a precise before-versus-after rule that is not supplied by the source.
The source does not specify those separate outcomes.
Fix:
State only that appropriate timing matters for possible changes in corticostriatal synaptic efficacy.
Apply the Circuit Model
Rewrite this explanation so that it correctly describes the circuit: The striatum receives cortical information, chooses an action by itself, and dopamine independently teaches the brain what was good.
Hints
- State what happens to striatal output after cortical information enters.
- Use action selection for the broad emphasis of the dorsal striatum and reward processing for the broad emphasis of the ventral striatum.
- Explain that cortical and dopamine signals meet near medium spiny neuron spines.
- Mention that appropriately timed dopamine can be associated with changes in corticostriatal synaptic efficacy.
A Complete Correction
Construct a source-grounded explanation of how cortical information and dopamine-related learning signals work in the striatum.
Circuit role: The striatum is the main input structure of the basal ganglia, not the whole circuit.
Output route: Striatal output passes through other basal ganglia nuclei and the thalamus toward frontal and motor areas of cortex.
Subdivision roles: The dorsal striatum has a broad emphasis on action selection, while the ventral striatum has a broad emphasis on reward processing.
Learning-related change: Cortical and dopamine signals meet near medium spiny neuron dendritic spines, and appropriately timed dopamine can help determine when corticostriatal synaptic efficacy changes.
The striatum is a central input structure in a wider basal ganglia loop. Its subdivisions have different broad emphases, and dopamine contributes to learning-related synaptic change through its appropriately timed relationship with cortical activity near medium spiny neuron spines.
Key Takeaways
- The basal ganglia are connected nuclei that can influence movement, decisions, learning, reward processing, and cognitive functions such as planning.
- The striatum is the main input structure: cortical information enters there, and striatal output travels through other basal ganglia nuclei and the thalamus toward frontal and motor areas of cortex.
- The dorsal striatum has a broad emphasis on action selection, while the ventral striatum has a broad emphasis on reward processing and assigning affective value to sensations.
- Cortical signals and dopamine signals meet near medium spiny neuron dendritic spines in the striatum.
- Appropriately timed dopamine signals help determine when corticostriatal synaptic efficacy may change, supporting reinforcement learning.
Key Takeaways
- The basal ganglia are connected nuclei that can influence movement, decisions, learning, reward processing, and cognitive functions such as planning.
- The striatum is the main input structure, and its output travels through other basal ganglia nuclei and the thalamus toward frontal and motor areas of cortex.
- The dorsal striatum broadly emphasizes action selection, while the ventral striatum broadly emphasizes reward processing.
- Cortical signals, medium spiny neuron activity, and dopamine signals meet near striatal dendritic spines.
- Appropriately timed dopamine helps determine when corticostriatal synaptic efficacy may change.