People can hear while in a coma, researchers say

…but we can’t understand, TCD study finds

PEOPLE who are in a coma or under general anaesthetic can hear us, new research has revealed.

However, the study, led by neuroscientists at the School of Psychology at Trinity College Dublin, revealed that while the unconscious brain can hear, it may not understand what people are saying.

The study was carried out on healthy people who were unconscious under general anaesthetic and patients who became unconscious following a severe brain injury. Both groups then listened to the famous scene from Taken, where Liam Neeson threatened his daughter’s kidnappers over the phone.

It was found that in both groups their brain regions were highly interconnected, but had lost the ability to convey information.

This research discovered for the first time that sensory brain regions, such as those involved in hearing, and higher-order systems responsible for complex thought, do not shut off during unconsciousness as previously thought.

They also do not disconnect from one another in different unconscious states.

Lorina Naci, Assistant Professor at the School of Psychology and Trinity College Institute of Neuroscience, led the study.

She explained that when someone is unconscious, their brain experiences a confusion similar to being at a loud party, when you cannot clearly understand what people are saying.

‘While our personal experiences may be different, consciousness is a fundamental feature of human experience, common to all of us.

‘What makes our research unique is trying to understand how the brain processes complex information in different unconscious states.’

She continued: ‘Our findings suggest that, during unconsciousness, brain responses are all jumbled up and this leads to lack of understanding.’

Brain responses during consciousness were also investigated, and found the opposite results.

It was found that during conscious states, the fine-tuned specificity of brain responses were needed for understanding and critical thought.

Ms Naci said: ‘Indeed, individuals with higher intellectual abilities showed higher specificity, further demonstrating that the diversity of brain responses is an essential feature of conscious cognition and verbal intelligence.’

Meanwhile, patients who lose consciousness after severe brain injury shed light on the brain mechanism affected by loss of consciousness.

If entirely behaviorally nonresponsive, they are thought to lack consciousness and be in a vegetative state, or, if they have reproducible but inconsistent wilful responses, they are considered to be in a minimal conscious state.

The clinical, behavioral assessment of patients who are behaviorally non-responsive is particularly difficult and can result in a misdiagnosis rate of more than 40%.

Studies show that despite the apparent absence of external signs of consciousness, a minority of patients – almost 20% – thought to be in a vegetative state can show conscious awareness by wilful modulation of their brain activity.

lisa.o’donnell@dailymail.ie

‘Brain responses become jumbled’