Visual hallucinations are particularly common in people with Parkinson’s, who frequently describe seeing vivid and lifelike people and animals that are not present. They can be a source of comfort and intrigue, but at later stages can become distressing, when insight is lost. Although they are experienced in other neurological disorders such as strokes and with visual loss, they are surprisingly rare out of the context of Parkinson’s disease.

The underlying mechanisms of visual hallucinations had been elusive, in part due to their transient nature, but more recent work has converged on a model invoking breakdown in the processes underlying normal human perception.  These include both bottom-up and top-down processing, as well as a central role for the thalamus.

I will present work from our group and others, examining visual hallucinations in Parkinson’s, and also consider why hallucinations particularly occur in Parkinson’s, more frequently than in other conditions.