I emailed Dr Caterina Cinel and she sent me the following summary of her work with permission to post it here.
In our study we are investigating a technique called audio-visual entrainment to reduce tremor in people with Parkinson's disease.
Very briefly, entrainment is a technique where the brain activity is induced to synchronise at particular frequencies, through a form of visual and/or auditory stimulation (the Wikipedia page "Brainwave entrainment" gives some basic and simple information http://en.wikipedia.org/wiki/Brainwave_entrainment
which can help you to understand how it works).
The principle is very simple: our brain produces normally neural activity that can be detected through EEG (electroencephalogram). Depending on whether a persons is active, relaxed, half asleep or sleeping, this brain activity (or brainwaves) will have particular features and frequencies: the more a person is relaxed, the slower and the more regular these brainwaves will be. This is something that occurs all the time in our brain. Entrainment is simply a technique that induces the brain to produce regular brainwaves at a particular frequency, exploiting the natural tendency of our brain to synchronise with external, regular stimulation (sounds and/or images).
Entrainment can induce relaxation and has been shown to be effective to treat, for example, stress and headache and some research seems to suggest that it can enhance cognition in particular circumstances.
Here at Essex we have started to investigate whether audio-visual entrainment can help to reduce tremor in PD patients (tremor itself is associated with some particular cortical brain activity). While entrainment is a well known technique and there are many studies that investigate its effects, we are the very first researchers who are studying the effects of entrainment on PD tremor (that's why nothing can be found about it on the internet).
We are at the early stages of our study, and we have just finished testing our first few volunteers, but the results at the moment are positive and encouraging, so we are testing more volunteers and we hope to publish soon our first results.
We have contacted local Parkinson's UK groups to find volunteers to our study and had a good response.
Hope my reply has helped you to understand what we are doing, but do not hesitate to contact me if you have any questions.