our understanding Parkinson's is that it can be described as a control system issue. The part of the brain affected (at least initially) by the disease is part

our understanding Parkinson's is that it can be described as a control system issue. The part of the brain affected (at least initially) by the disease is part of a network (the basal ganglia/cerebellar network) that evaluates environmental inputs and generates the output necessary for fine/precise motor control, amongst other things. So a Parkinson's patient cannot plan their movements as well and the main symptoms are slowness of movement, abnormal limb tone; yes tremor as well but the 1st 2 are what cause the most issues for most people (keep in mind, not everyone follows the textbook so there are subtypes that have more cognitive issues, i.e. hallucinations, executive dysfunction etc) The stimulators seem to affect the signaling in that circuit (they are targeted by the implanting neurosurgeon to specific nodes in that circuit as best as targeting surgical technology allows) that seem to restore the ability to move well. Exactly why, no one knows. It's just a dumb signal at around 1-4 milliamps at 130-180 hz at those specific spots but presumptively it corrects some aberrant behavior in the whole network. It was observed in the '00s that recordings taken during or right after surgery often showed a strong peak at ~13-35 hz (give or take, but roughtly around 20 hz) during the disease state, and that's what Medtronic has been trying to target w/ these devices. Of note - there actually isn't a system-wide dopamine "deficiency" - dopamine in general is fine for most of the body, it's just that the particular part of the brain that is affected happens to use dopamine as its signaling neurotransmitter so it's deficient in just that connection within the network. Dementia is theorized to happen when the abnormal brain process spreads to other parts of the brain other than the substantia nigra (see the Braak hypothesis)