What are the neurophysiologic changes in the basal ganglia in Parkinsons disease (PD)?
Neuronal loss in the SNc with consequent dopamine depletion in the striatum is the neurochemical–pathologic hallmark of PD.
This dopaminergic deafferentation produces an imbalance in the striatal activity, with hypoactivity of the striatonigral (direct) pathway and hyperactivity of striatopallidal (indirect) pathways.
This imbalance results in decreased inhibition (disinhibition) of the STN and increased activity of the GPi/SNr neurons, causing increased inhibition of the thalamic ventral tier nuclei.
Because these thalamic nuclei are responsible for the activation of the cortical areas involved in the generation of movements, the final effect of dopamine deficiency is poverty or slowness of movements (hypokinesia).
