Searching for meaning: research into hallucinations
Our brains are wired to see patterns, faces and objects where there are none. Research is taking advantage of this phenomenon to help us understand hallucinations.
--
A hallucination is seeing, hearing, feeling, smelling or tasting something that doesn’t really exist. Visual hallucinations are the most common, affecting up to 74% of people living with Parkinson’s for 20 years or more.
Hallucinations can be difficult symptom for people with Parkinson’s to cope with. They may be threatening, scary or upsetting as described by one Parkinson’s UK forum user:
“My husband thinks there are people in the house and talks to them and gets upset because some of them are disfigured or are tiny babies with no one to look after them. I try to keep calm and not confrontational — he will ask me what I am going to do about the tall man in his chair or will I be giving the assorted people in our sitting room some tea! I will just say that although I know they are real to him I can’t see them. I also try to give him lots of reassurance that I love him and that he is safe. Even so I am only human and sometimes get impatient with him — then I feel guilty.”
This comment also highlights how difficult it may be for family members or carers to cope with hallucinations, and how unsure they may feel about how to respond.
The most commonly used drugs to treat hallucinations in people who do not have Parkinson’s are typical anti-psychotics. These drugs work by reducing dopamine levels in the brain. As people with Parkinson’s don’t have enough dopamine, these drugs are not appropriate as they can exacerbate movement problems.
Management of hallucinations in Parkinson’s is usually done by adjusting medication to reduce the occurrence of hallucinations without worsening movement symptoms. Atypical anti-psychotics, which target a different brain chemical, may be also be helpful.
We also don’t fully understand what causes hallucinations in Parkinson’s. One barrier to this understanding is the difficulty of studying visual hallucinations in a clinical setting. People can be less likely to experience a hallucination while with a health professional, and hallucinations are believed to be under-reported in surveys and questionnaires.
An unusual way to study hallucinations
Pareidolia is a phenomenon where we see, patterns, shapes, faces or objects where they do not exist. This helps us to understand the world around us — our brain is constantly sifting through visual information and trying to make sense of what we see. Usually we do this very accurately — recognising trees as trees and people as people. But sometimes we assign meaning where it is not there — think seeing animals in the clouds and perhaps even prophets in your breakfast.
So how is this naturally occurring phenomenon helping us to understand hallucinations? Researchers in Japan asked people with two different types of dementia — dementia with Lewy bodies and Alzheimer’s — as well as those without dementia to take a ‘Pareidolia Test’. They found that people with dementia with Lewy bodies were most likely to report meaning in ambiguous images, a ‘false response’. And the number of false responses that people reported also correlated with the severity of their hallucinations. This suggests that there may be an overlap in visual hallucinations and pareidolia, which could be exploited in order to study hallucinations.
The researchers also found that a dementia drug called donepezil reduced the number of pareidolias and visual hallucinations that people experienced, providing further evidence for a common mechanism underlying the two.
Dr Alan Bowman is a clinical psychologist and academic tutor at Teeside University. Alan was interested in using the pareidolia test to find out if an ambiguous environment affects people who regularly report hallucinations and those who do not hallucinate differently.
Alan explains:
Our eyes can “play tricks” on us when our visual environment is ambiguous. We have all experienced this at one time or another, for example when that shadow in the forest looks like a person for a fleeting moment, or when we momentarily see a face in a sky full of clouds.
The study
Alan and his team recruited people with Lewy body disorders (either Parkinson’s, dementia with Lewy bodies or Parkinson’s dementia) who did not hallucinate and those that did, as well as people without one of these conditions.
They were interested in:
- sensitivity — how well the participants detected images that were there
- response bias — the tendency to report the presence of an image, regardless of if it was really there or not
The team measured this using pareidolia images like these:
Did you see the teapot in image a?
In participants with a Lewy body disorder, those who reported experiencing hallucinations found it much trickier to separate the “signal” (image a) from the “noise” (image b).
A second key finding from the study was that when presented with ambiguous visual “noise” (like image b), participants prone to hallucinations tended to see illusory objects more frequently than participants who did not hallucinate.
Alan suggests that although internal changes in the brain that cause perceptual problems contribute to hallucinations, an ambiguous environment may also play a role by encouraging the brain to ‘compensate’.
Alan uses a metaphor to describe this:
Imagine a radio that is not fully operational. The aerial may be broken, and it is not receiving the external signals very well as a result. This means that the radio station it is trying to pick up is quiet, buzzing, and quite hard to hear. There is a lot of ‘white noise’, and it is hard to hear what is being said amongst all this information.
As a means of compensating for this problem, the user of the radio turns it up to full volume. The consequence is that the poor-quality radio signal becomes a little easier to hear. However, at the same time, the white noise becomes very loud, to the extent that some of it starts to sound like music, or a voice, when in fact it is nothing. In other words, there is a cost for this compensation — meaningless, ambiguous sensory information is wrongly perceived as meaningful.
Research has shown that people with Lewy body disorders have impaired visual perception. We are suggesting that the brain compensates for this loss of vision by “turning the volume dial up” and therefore becomes more likely to perceive things.
Priming
Alan also wanted to establish if people’s responses to the images were affected by priming. If you read the words lunch, bread and cafe, what do you think of when you see the following word?
so_p
Most likely, what came to mind was soup. The words I gave you primed you to think of soup. But if I’d given you the words shower, towel and wash, you’d probably have thought of soap instead. And images can also be used to prime people.
In Alan’s experiment, the image of the teabags could help to prime the participants to see the teapot in image a. What effect did this have on the participants? Back to Alan:
Presenting a prime reduced the overall number of illusory objects that hallucinating participants saw in each trial, although even with a prime, hallucinating participants still reported significantly more pareidolia than control groups did.
This suggests that creating environments with visual cues, sometimes referred to as ‘dementia-friendly environments’, could be helpful in the management of hallucinations. By making the environment easier to understand and navigate, people may be less likely to hallucinate in order to ‘fill in’.
What’s next for this research? Could the pareidolia test be used as a diagnostic tool? Alan is hopeful that this could be true in the future:
There is a growing body of research to suggest that the pareidolia test can be useful in discriminating dementia with Lewy bodies from Alzheimer’s. The test also appears to be good at discriminating people who hallucinate from non-hallucinators.
So the test may one day help ensure people receive an accurate diagnosis and may even be able to predict if someone will experience this symptom.
You can read the full scientific paper here, or watch this video to find out more about how hallucinations affect people with Parkinson’s:
