The hallucinating brain

What is a hallucination?
29 January 2021

Interview with 

Colleen Rollins, Cambridge University




Colleen Rollins is a 4th year psychiatry PhD student at Cambridge University, who looks at how the structure and function of the brain supports the experience of hallucinations, and Katie Haylor asked Colleen about her research...

Colleen - Hallucinations are a sensory experience, often with a compelling sense of reality, that occurs in the absence of a corresponding stimulus in the physical world. So for instance, hearing someone speak to you when there's in fact, no one there. Or seeing a person or an animal run across your visual scene, when that wasn't actually caused by anything. It can also occur in other sensory modalities, such as smelling or tasting things that aren't there, or even feeling someone touch you.

Katie - Wow. You can have a smell hallucination. Really?

Colleen - Yeah. I've heard someone telling me that they smell death, which sounds quite distressing.

Katie - What are they like?

Colleen - It often depends on the condition that they can occur in. So for people with a diagnosis of Schizophrenia, we know that these hallucinations are more often auditory. They usually manifest as hearing voices, which often say quite nasty or critical things. Whereas in older age, in people with Parkinson's or Lewy body dementia, they're often more visual. People may see either figures or animals that don't seem to acknowledge them. But there's also a lot of variation within that. So different people can have different experiences.

Katie - Are hallucinations always tied into a health problem?

Colleen - No, they're definitely not. And there's actually increasing recognition that these experiences can occur on a spectrum from health to illness and people without a clinical diagnosis can experience them too. They can also occur in situations that involve stress, isolation, or bereavement, but they can also occur for seemingly no rhyme or reason. And may also sort of either be neutral experiences or even contribute to meaningful experiences.

Katie - I want to ask you why they occur and I've got the sense that this might be quite a big question. Could you perhaps categorise hallucinations for us in any way? How do scientists like you tend to think about them?

Colleen - Historically they've been classified more by clinical diagnosis. So we might talk about hallucinations and Schizophrenia, which is more what I focus on, compared to those as a cause of Charles Bonnet syndrome, for instance. But as I mentioned before, there's increasing recognition and also research that these occur in people without a psychiatric diagnosis as well, or without any clinical history. So there's increasing efforts to understand the variety of hallucinations and maybe have a better classification system for them.

Katie - So does the mechanism behind the hallucination depend on why you're having it? Would how a Schizophrenic hallucination works be different to if you're hallucinating because you're incredibly tired? Are there any sort of fundamental mechanisms that you can talk about?

Colleen - Bit of a basic explanation - hallucinations are thought to emerge from different connectivity or different communication between brain regions. So we think that hallucinations certainly involve sensory regions. So auditory or visual regions for auditory or visual hallucinations. And these seem to interact or speak to higher order prefrontal areas of the brain that are involved more with monitoring where the sensory information is coming from, whether it's internal or external. There are likely different mechanisms that support these varieties of hallucinations, but we think there are also commonalities between them as well. So from the perspective of brain science, which is what I research, we can think of hallucinations as manifesting from differences in patterns of brain connectivity, between different brain regions or networks, and some of these brain regions or networks might be the same that would give cause to different hallucinations, and others might be very different.

Katie - You said you study Schizophrenia and hallucinations associated with Schizophrenia. Before I ask you a bit more about your research, what actually is Schizophrenia?

Colleen - Yeah. That is a very good question that I'm sure many clinicians might have trouble giving you a clear answer to. It's a psychiatric illness that often involves symptoms that sort of dissociate from reality. So hallucinations or delusions or disorganised perceptions or thoughts. There's a lot of variety in how it presents in different people. And so this certainly poses different challenges to researching it and also treating it. My interest comes in in the specific symptom of hallucinations that around 60 to 80% of people with a diagnosis of Schizophrenia will experience.

Katie - How exactly are you studying this?

Colleen - I use some cognitive research about the psychology or mental processes, some qualitative research about the lived experience, but mainly I use neuroimaging. So magnetic resonance imaging, or functional MRI, to study how the structure and function of the brain supports hallucinations.

Katie - So what are you looking for? Do you know which bits of the brain probably are active in hallucinations?

Colleen - It likely involves both sensory areas of the brain. So for auditory hallucinations, that likely involves brain regions or networks that process hearing and language. It also seems to involve medial prefrontal bits of the brain. So that is towards the front and middle of the brain. And these regions are involved more in self-monitoring or directing attention to salient stimuli.

Katie - What exactly is the question you're trying to answer?

Colleen - So I'm really interested in how the different ways that the brain is folded can contribute to these experiences. Research by myself and others has shown that differences in brain folding patterns are actually associated with whether people with Schizophrenia will experience hallucinations. And this is really interesting because the way the brain folds is developed in utero in the second or third trimester of pregnancy. So it's suggesting that something during brain development might scaffold the way people experience the world and influence whether or not they'll have these unusual sensory experiences.

Katie - Hallucinations can be very varied in their modality, in their content, in their emotional content, in why they're occurring in the first place. Where does the research need to go in terms of better understanding this phenomenon?

Colleen - A helpful direction and also where it does seem to be going is better understanding these varieties of experiences. So like you said, the variety of conditions that can cause hallucinations, probably more research about what they're actually like. A lot of our clinical assessments simply involve sort of, "do you hear or see things that aren't there?" But that says nothing about the content of what they're like, that says nothing about sort of the emotions that that's associated with or how it impacts the daily life.

I think more research about what the experiences are like as well as the different ways and the different risk factors that can produce these hallucinations. I've spoken a lot about the biology of hallucinations and the brain science, but of course there are many different levels of explanation that you can speak to them about. And we know that stress trauma or intense negative emotions can be risk factors for hallucinations as well.


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