Location
The Striatum surrounds the thalamus at the top of the brain stem. It's a subcortical (inside) part of the forebrain, and is the major input system of the basal ganglia.
Function
This region plays a crucial role in voluntary action directed at obtaining rewards (e.g. food, water, sex).
It's involved in planning out movement pathways (e.g. towards a reward goal), and is activated by dopamine neurons.
Degeneration
Degeneration of the striatum region results in Huntingtons Disease.
Huntingtons Disease is marked by abnormal writing or jerky movements, progressing until complete failure of motor control systems occurs. This is combined with cognitive impairments (somewhat akin to Alzheimer's).
Voluntary Action
(From main article dopamine).
The following dopaminergic pathways connect to the striatum and allow it to integrate information about reward into voluntary motor control systems to enable goal pursuit.
- Nigrostriatal: Substantia Nigra Pars Compacta (SNPC) cells project to the striatum (loss of dopamine neurons here is a marker for parkinsons).
- Mesolimbic: Ventral Tegmental Area (VTA) to the Nucleus Accumbens (key substrate of reward learning - within the ventral striatum)
From the below data we can conclude that the caudate mediates intentional goal pursuit and the putamen mediates habitual execution of extensively practiced voluntary behaviour.
Choice Tests - 2.5 year turning point
Setup:
- Two buttons, each with a different video reward
- Children press buttons equally
Devaluation phase:
- One video is played over and over again, devaluing it as a reward
Testing/Extinction phase:
- Video is no longer played, children press buttons
- Children <2.5 press buttons equally (habitual)
- Children >2.5 press the button that isn't devalued (intentional)
Further Research
In human imaging studies during the extinction test:
- the caudate is active following a small amount of training (learning phase) -> choie is intentional
- the putamen is active following a large amount of training -> choice is habitual
On this note, rats who've had a small amount of training perform habitually if they have lesions in their caudate, but intentionally otherwise.
Inversely, rats who've had a large amount of training perform intentionally if they have lesions in their putamen, but habitually otherwise.