Liz Else, associate editor
You and your family are on holiday, driving round a mountainous part of Greece, when suddenly a tyre bursts. You roll over and over down some 100 metres before a large olive tree blocks your fall. Amazingly, you all emerge from the battered heap. Some days later, at work, you recount the tale, struggling to capture for your colleagues one of the odder aspects of the experience. It was, you say, a bit like a dream - or maybe a slow-motion movie, it was like being outside yourself, unreal...
Traumatic events are well known for producing this sense of unreality as we watch a disaster unfold. Most of us can also produce this state far more pleasurably, by getting drunk, for example. For the less fortunate, though, it is also a known, if quite controversial, psychiatric diagnosis of dissociation.
This comes in two main flavours. Depersonalisation disorder (DPD) describes the state where people experience persistent or recurring feelings of detachment or disconnection from their own mental processes, emotions and/or body. DPD is frequently accompanied by derealisation, where people feel that their external surroundings are unfamiliar, or that the world is "unreal".
DPD and derealisation are of great interest to researchers trying to home in on the mysteries of consciousness, as researchers Nick Medford and Heather Berlin explained at the Association for the Scientific Study of Consciousness conference in Brighton, UK, this week.
DPD is often found linked with other psychiatric conditions, such as schizophrenia, anxiety or panic attacks, and Medford, from the University of Sussex's Sackler Centre for Consciousness Science in Brighton, and Berlin, from Mount Sinai School of Medicine, New York, are interested in what they can learn from people who have the disorder.
Healthy folk, of course, provide controls. People with DPD describe a bewildering series of counterintuitive symptoms, including: that they have "cotton wool" in their heads and that they cannot concentrate; that they don't feel emotions they know they should be feeling in an appropriate social context - while still feeling a lot of emotions internally; that they sense that they are about to "disappear"; that their bodies are generally not connected to them.
What Medford calls the "strange dissolution" of the sense of self and loss of contact with the body and surrounds have been well documented, but the syndromes associated with them are only just now being studied systematically.
Medford says that the point is to look for the neurobiological and neurocognitive underpinnings of DPD, which they see as a disturbance of self-consciousness involving abnormalities of bodily sensation and emotional experience. Various papers (including a 2010 review by Medfordworking with Hugo Critchley, also at the Sackler centre) have pinpointed two parts of the brain, the anterior cingulate cortex (ACC) and right anterior insular cortex (AIC), as being involved in producing subjective feelings, and in coordinating appropriate responses to internal and external events.
Evidence from fMRI backs up the idea that the two brain regions play a big role in self-awareness, and together may be responsible for what neuroscientist Antonio Damasio from the University of Southern California in Los Angeles calls the "core self". This is the mental representation of an innate feeling of subjective awareness, characterised by continuity and individuality.
So far, people with DPD and derealisation do seem to have unusual activity in the ACC and the AIC. Damasio and the other researchers plan more investigations of DPD involving fMRI imaging. Hopefully this will allow them to treat the disorder and more fully understand what underpins our connection with the external world
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