Dorsal Striatum
The basal ganglia are a connected collection of nuclei that can influence movement, decisions, learning, and reward processing.
A Circuit for Choosing and Learning
Imagine the brain weighing a possible action while also processing sensory input, internal state, motor activity, and reward-related significance. The basal ganglia are a connected collection of neuron groups, called nuclei, that can influence this kind of processing. They participate in voluntary movement, decision-making, learning, reward processing, and cognitive functions such as planning. The dorsal striatum is especially important for understanding how this circuit can influence action selection.
The basal ganglia are a connected collection of nuclei located at the base of the forebrain that can influence movement, decisions, learning, reward processing, and other cognitive functions.
Following Cortical Information
The striatum is the main input structure of the basal ganglia. Cortical neurons provide it with information about sensory input, internal states, and motor activity. Information does not simply stop in the striatum. Striatal output passes through other basal ganglia nuclei and the thalamus before reaching frontal areas of cortex. The circuit also connects with motor areas, so activity within the striatum can influence movement as well as more abstract decisions and reward processing.
Tracing One Information Stream
Trace the route of information related to a possible action.
Input: Cortical neurons provide the striatum with information related to sensory input, internal state, and motor activity.
Entry: The information enters the basal ganglia through the striatum, which is the system's main input structure.
Transmission: Striatal output passes through other basal ganglia nuclei and then through the thalamus.
Return: The pathway 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 larger loop, not the endpoint of cortical information.
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. These are broad emphases rather than completely isolated systems: both subdivisions belong to the striatum and participate in the wider basal ganglia circuit.
| Subdivision | Broad emphasis | How to interpret it |
|---|---|---|
| Dorsal striatum | Action selection | Helps frame the circuit in terms of influencing which action is selected. |
| Ventral striatum | Reward processing | Includes assigning affective value to sensations. |
Signals at a Striatal Spine
Reinforcement learning in this circuit can be understood by separating information flow from learning-related change. 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. A spine therefore brings cortical and dopamine neuron signals into a close cellular relationship with medium spiny neuron activity.
Separating Message From Modification
Why is dopamine not simply another version of the cortical message?
Cortical message: Cortical neurons provide information about sensory input, internal states, and motor activity.
Striatal response: A medium spiny neuron receives cortical input and participates as a main input/output neuron of the striatum.
Dopamine signal: Dopamine neurons contact the same dendritic spine region, bringing dopamine activity into close cellular relationship with the cortical input and medium spiny neuron activity.
Learning-related consequence: When dopamine signals are appropriately timed, the efficacy of the corticostriatal synapse may change. Dopamine therefore helps determine when the cortical-to-striatal connection is modified.
Cortical activity carries information, while dopamine helps regulate when a corticostriatal connection is modified.
Why Timing Changes Learning
The timing of dopamine activity matters because corticostriatal synapses do not change simply because cortical activity occurred. The source describes synaptic change as depending on dopamine signals being appropriately timed in relation to cortical and medium spiny neuron activity. Dopamine helps determine when cortical-to-striatal connections are modified, so it is part of the learning-related mechanism rather than merely another description of the cortical message.
What do you think happens?
If cortical activity and medium spiny neuron activity occur but the dopamine signal is not appropriately timed, should you conclude that the corticostriatal synapse must change?
Reveal answer
Answer: No, the source makes appropriate dopamine timing part of the modification process.
The learning-related change is described as occurring when dopamine signals are appropriately timed. Dopamine helps determine when cortical-to-striatal connections are modified.
Common Interpretive Mistakes
Treating the striatum as the entire basal ganglia.
The striatum is the main input structure, but its output passes through other basal ganglia nuclei and the thalamus.
Fix:
Describe the striatum as the entry point into a connected basal ganglia 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 their broad emphases as a guide: dorsal for action selection and ventral for reward processing.Treating dopamine as merely another cortical message.
Dopamine signals meet cortical signals at striatal spines and help determine when corticostriatal connections are modified.
Fix:
Separate cortical information flow from dopamine's learning-related role in synaptic modification.Ignoring temporal relationships at the synapse.
The source states that corticostriatal synaptic efficacy may change when dopamine signals are appropriately timed.
Fix:
Treat timing as part of the condition for learning-related synaptic change.
Practice the Circuit Trace
A learner says: The cortex sends information to the dorsal striatum, where the information ends. Dopamine then independently creates learning. Rewrite this explanation so that it correctly describes information flow, the roles of medium spiny neurons, and the importance of dopamine timing.
Hints
- Start with the striatum's role as the main input structure of the basal ganglia.
- Include the route through other basal ganglia nuclei and the thalamus toward frontal and motor areas.
- Explain that cortical and dopamine signals meet near medium spiny neuron dendritic spines.
- State that appropriately timed dopamine helps determine when corticostriatal synapses are modified.
When explaining the dorsal striatum, keep two levels separate. First trace the circuit: cortical information enters the striatum and striatal output continues through basal ganglia nuclei and the thalamus toward frontal and motor cortex. Then explain learning: cortical input, medium spiny neuron activity, and dopamine signals meet at striatal spines, and appropriately timed dopamine can help determine when corticostriatal synaptic efficacy changes.
Key Takeaways
- The basal ganglia are connected nuclei involved in movement, decision-making, learning, reward processing, and cognitive functions such as planning.
- The striatum is the main input structure: cortical information enters there, and striatal output continues through other basal ganglia nuclei and the thalamus toward frontal and motor areas.
- The dorsal striatum has a broad emphasis on action selection, while the ventral striatum has a broad emphasis on reward processing and affective value.
- Cortical input, medium spiny neuron activity, and dopamine signals come into close relationship at striatal dendritic spines.
- Dopamine timing matters because appropriately timed dopamine helps determine when corticostriatal synaptic efficacy may change.
Key Takeaways
- The basal ganglia form a connected circuit that can influence movement, decisions, learning, reward processing, and cognition.
- Cortical information enters through the striatum, and striatal output travels through other basal ganglia nuclei and the thalamus toward frontal and motor cortex.
- The dorsal striatum is broadly associated with action selection, whereas the ventral striatum is broadly associated with reward processing.
- At striatal spines, cortical and dopamine signals meet in close relationship with medium spiny neuron activity.
- Dopamine contributes to reinforcement learning partly through its timing: appropriately timed signals help determine when corticostriatal synaptic efficacy changes.