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What is the 'substantia nigra'?

Parkinson's Effects On The Brain

Neal Hermanowicz (Director of the Movement Disorders Program) gives expert video advice on: What hallucinations are associated with Parkinson's? and more...

What is the 'substantia nigra'?

Substantia nigra is a very small part of the brain that sits at the top of the section called the brain stem. It's about half the size of your thumbnail, but it's a crucial part for the normal maintenance of mobility and it is the site classically in the destruction of brain cells in Parkinsons disease. These are where a large number of Dopamine-synthesizing brain cells are located and are being lost by whatever this process of Parkinsons disease is.

What is a 'Lewy body,' and how does it factor into Parkinson's?

A Lewy body is—it's Lewy, L-E-W-Y, which is the name of a pathologist who recognized a microscopic finding in the brain tissue of people with Parkinsons disease. If you take a piece of the brain and stain it in a certain way and look at it under a microscope, one can find this spherical-looking clump of what turns out to be abnormal protein within the actual neuron - the neuron being the brain cell that's affected by Parkinsons disease. It still, to this day, is regarded as one of the very key features in terms of confirming the diagnosis by tissue analysis. We don't do this in clinical practice; we don't do brain biopsies, but if we are wondering about the diagnosis of somebody after they've passed away, for example, the way that diagnosis is confirmed is by identifying Lewy bodies in a microscopic analysis of the brain.

What hallucinations are associated with Parkinson's?

There are many side effects that the medications that are used to treat the symptoms of Parkinsons disease can create; and one of them includes hallucinations. The hallucinations that are caused by these medications are usually visual in form, they're sometimes auditory - people will hear things that are not actually there, or they can be what are called olfactory, or people will smell things that are not actually there. But far and away, the most common hallucination is of a visual nature, and people see very well formed hallucinations. They will see people in their home that are not actually present. They may see bugs on the floor, they may see an animal scurrying in the corner of the room or they may see their deceased parents sitting on the couch. These things are not uncommon, it's estimated that about a third of people who are treated for Parkinsons disease will experience these side effects at some point. They're not always as disruptive as they might sound to be, although if they continue over time, they can evolve into more troubling and frightening symptoms in some cases. Often, people who have these hallucinations are able to identify them as exactly that. They realise that this is a medication side effect, that the person is not exactly or truly there. On occasions, people don't have insight retained. They don't recognize that this is a medication side effect and not real, and in that circumstance it can at least be bewildering and sometimes downright frightening to people, if they think that there's a stranger in the home who may intend to do them harm. It can cause a great deal of difficulty for people.

What is 'dopamine,' and how does it relate to Parkinson's?

Dopamine is a naturally-occuring brain chemical that we all have and need, and one of the key features, again identified quite some time ago is that in the brains of people with Parkinsons disease the production of dopamine is diminished. There is a lowering of the concentration in the brain of someone with Parkinsons disease. The consequences of this are that the symptoms emerge; that people do develop slowness or stiffness or tremor as a consequence of this reduction of the synthesis of dopamine. The reason dopamine is reduced is that the brain cells, the neurons that are creating dopamine or that are principally responsible for the synthesis of dopamine, are reducing in number.