Inverse zombies studied using anaesthesia

Hospital medicine takes a pretty crude approach to consciousness. You're considered mentally AWOL if you don't respond to simple commands or physical prodding. But studies of post-operative patients have found that many of them recall having dreamt during anaesthesia. And in some disturbing cases they've even felt pain or heard the surgeons talking. This suggests that it's possible to be outwardly dead to the world, but conscious inside (locked-in patients and imaging studies of brain-injured patients in a persistent vegetative state also imply the same thing). Researchers have nicknamed people in this state "inverse zombies" - a play on the standard philosophical zombie concept, in which a person may appear to be outwardly conscious, but is in fact, dead inside.

A problem with much of the research into "inverse zombies" is that it's been conducted opportunistically in hospitals. The experimental set-up is messy, the patients have a variety of health complications, and they've often been given a cocktail of anaesthetic drugs. These studies have found rates of awareness during anaesthesia at around 0.023 to 1 per cent and rates of anaesthesia dreaming at rates of 6 to 53 per cent.

Now Valdas Noreika and his collaborators have performed a carefully controlled lab study of subjective (or "phenomenal") consciousness during anaesthesia, with the help of 40 healthy male university students. These brave souls were given progressively higher doses of one of four different anaesthetic drugs: dexmedetomidine; propofol (the drug that tragically killed Michael Jackson, who was using it as a sleeping aid); sevoflurane; and xenon. Dexmedetomidine and propofol are given intravenously; the other two are inhaled.

After the doping had begun, the researchers gave the participants the verbal command "Open your eyes!" at five minute intervals. Once a participant stopped responding they were considered to be unconscious in the traditional medical sense and the dose was gradually lowered until they responded again. Throughout, the researchers recorded the surface electrical activity from the front of the participants' brains using a "Bispectral Index Monitor (BIS)" - a form of electroencephalography (EEG), which provided an objective measure of the depth of sedation.

The induction phase - from the last response to "Open your eyes!" to the loss of responsiveness - lasted typically from around 5 to 10 minutes; the period of sedation or loss of responsiveness itself lasted around 10 minutes; this was followed by a 2 minute recovery phase and then 5 minutes of EEG scanning. At this point, the participants were interviewed about their subjective experiences during the time they were knocked out.

The key finding is that dreams or sensations were experienced during nearly 60 per cent of the anaesthesia sessions. These ranged from perceptual sensations (including "quick visual experiences"; out-of-body sensations; an altered sense of time); dream-like experiences (had a fragmentary dream about "a trip in Eastern Europe" said one participant); vision-based dreams related to the lab situation ("one of the nurses got suspended from her work"); and dreams with auditory content based on the lab situation ("a friend's roommate ... sitting next to me here in the lab, telling me we have to go to the city"). Sometimes these experiences were accompanied by negative emotions ("a bit anxious"); other times positive ("felt extraordinarily good"). The type of experiences didn't vary with the particular anaesthetic given.

Noreika and his team say these findings are important because they highlight the inadequacy of the standard medical definition of loss of consciousness (i.e. a loss of responsiveness), which is used in many anaesthesia-based studies into the neural correlates of consciousness. This standard definition, they argue, fails to take into account the frequent persistence of phenomenal consciousness in the absence of responsiveness. "Arguably, if one aims to explore the neural correlates of phenomenal consciousness, it would be fruitful to contrast the neural activity during dreaming anaesthesia vs. the neural activity during dreamless anaesthesia," they said.

The study is vulnerable to some obvious criticisms. The depth of sedation was shallower than is typically used in surgery, so the results may not generalise to higher doses of anaesthesia. Also, the participants were forewarned that they would be interviewed about any experiences they had whilst unconscious, which could have led them to come up with the kind of answers that they felt the researchers were after. Defending the validity of their results, Noreika's team pointed out that subjective reports of experience were more frequent when the objective BIS measure indicated shallower sedation - just as you'd expect if the experiences were real. "The results confirm that subjective experience may occur during clinically defined unresponsiveness," the researchers said.

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Noreika, V., Jylhänkangas, L., Móró, L., Valli, K., Kaskinoro, K., Aantaa, R., Scheinin, H., and Revonsuo, A. (2011). Consciousness lost and found: Subjective experiences in an unresponsive state. Brain and Cognition, 77 (3), 327-334 DOI: 10.1016/j.bandc.2011.09.002

Further reading: Check out this recent New Scientist feature article on consciousness and anaesthesia.


Post written by Christian Jarrett for the BPS Research Digest.

Paraplegics walk in their dreams

In the land of dreams, the shackles of disability are cast asunder. That's the revelation from a new dream diary study featuring 15 paraplegics, 5 of whom were born with their condition. These volunteers (aged 22 to 84 years), recruited from a military hospital and a care home for people with motor disabilities, recorded their dreams for 6 weeks and French researchers compared the content with similar diaries kept by age-matched, able-bodied control participants.

All bar one of the disabled participants had at least one dream in which they moved their legs, including all five of the congenital paraplegics. As a group, the disabled participants experienced dreams about walking twice as often as they had dreams featuring their paraplegia. Moreover, voluntary leg movements featured in the dreams of the disabled more often than in the dreams of the able-bodied (38.2 per cent of dreams vs. 28.7 per cent). "I was not in a wheelchair but walking to a night club, to go dancing," recalled a 22-year-old person with congenital paraplegia in one typical dream report. There were some dreams featuring wheelchairs - these were experienced by eight of the disabled group and none of the controls.

Of the leg-movement mentions in the disabled participants' dream reports, the majority (46 per cent) pertained to walking. This is a lower percentage than found in the able-bodied diaries (64 per cent), but that's because the disabled dreamt more often about dancing and standing up. Activities like running, cycling, swimming and driving featured equally often in the dreams of both groups.

The disabled participants dreamed of walking even though they'd either never walked or hadn't walked for years. For example, two of the participants had been paralysed since sustaining gun-shot wounds during World War II and the France-Algeria war. There was no evidence that walking dreams became less frequent with duration of paralysis.

How do people with paraplegia dream of walking if it's something they've never experienced or haven't done for years? The researchers, led by Marie-Thérèse Saurat, believe it could reflect the activity of a "genetic, inherent walking programme", or the action of mirror neurons, which are stimulated during the day by the sight of other people performing movements. The latter explanation is especially favoured for dreams about cycling and other complex activities - it's "difficult to imagine that there is an innate programme for riding a bicycle, as this is a highly specialised activity recently developed in human history," the researchers said.

Why do paralysed people dream of walking? The researchers dismiss the psychoanalytic idea that the dreams are an expression of a subconscious wish. They argue that people with paraplegia are open about their desires to walk, and that their dreams are not dominated by walking to the extent you'd expect if they were compensating for lack of walking in waking life (in fact their dreams contained less walking than the control participants). Saurat and her colleagues suggest instead that walking in dreams may have an adaptive function: helping "consolidate the relevant neuronal mapping ... Notably, motor imagery training improves the movement performance of the intact muscles and increases basal ganglia activation in subjects with spinal cord injury."

These new findings add to previous research that found people born blind have visual experiences in their dreams and people born deaf can hear spoken language in theirs.
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Saurat, M., Agbakou, M., Attigui, P., Golmard, J., and Arnulf, I. (2011). Walking dreams in congenital and acquired paraplegia. Consciousness and Cognition, 20 (4), 1425-1432 DOI: 10.1016/j.concog.2011.05.015

Post written by Christian Jarrett for the BPS Research Digest.

An afternoon nap tunes out negative emotions, tunes in positive ones

The perfect excuse for a siesta! People who stay awake throughout the day become progressively more sensitive to negative emotions. In contrast, those who take an afternoon nap are desensitised to negative emotions yet more responsive to positive ones. The new finding builds on past research by showing that not only does sleep deprivation cause emotional problems, a sleep boost can bring emotional advantages.

Ninad Gujar and his colleagues tested 36 participants (half were male; average age 21) on a face processing task, once at 12pm and then again at 5pm. Half the participants were given a 90-minute napping opportunity after the first task, whilst the others just went about their day as usual.

The task involved the participants looking at a computer screen that showed a male face pulling fearful, sad, angry and happy expressions at various intensities. The participants' goal quite simply was to rate each presentation of the face for intensity on a scale from 1 (definitely neutral) to 4 (mostly happy/sad etc).

For participants who stayed awake through the afternoon, their performance at 5pm, compared with at 12pm, demonstrated heightened sensitivity to fearful and angry facial expressions. By contrast, the participants who'd had a nap were less sensitive to fearful expressions at 5pm yet more sensitive to happy expressions. These emotional processing changes were also accompanied by mood differences: the no-nap group reported less positive mood later in the afternoon, compared with earlier, whereas the nap-group reported a decrease in negative mood.

The emotional processing changes observed among the nap-group were related to rapid-eye-movement (REM) sleep. EEG recordings taken while the nappers slept showed that those who obtained REM sleep were more likely to show the desensitisation to negative emotions and sensitisation to positive ones.

An alternative interpretation of the results is that napping affects visual processing, not emotional sensitivity. But the researchers don't think this stands up to much scrutiny, since any basic visual processing effects ought to have been uniform across the different emotions.

So, assuming the emotional sensitivity account is true, why might the non-napping participants have become more sensitive to negative emotions? One possibility, which is backed up by sleep deprivation research, is that the prefrontal cortex becomes fatigued through the day and therefore less able to dampen down emotional reactivity in the sub-cortex. Alternatively, perhaps heightened sensitivity to fear and anger is adaptive - as we fatigue through the day, it makes sense that we should become more vigilant towards these danger-based signals. Either way, a brief nap appears to give us an emotional recharge, altering the way we respond to other people's facial expressions. The implications for working practices are obvious.

'These data add to a growing collection of findings indicating a regulatory role for sleep in the optimal homeostasis of emotional brain function,' the researchers said, 'which if disrupted may have detrimental contributions to clinical symptomotology in affective disorders.'
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Gujar, N., McDonald, S., Nishida, M., and Walker, M. (2010). A Role for REM Sleep in Recalibrating the Sensitivity of the Human Brain to Specific Emotions. Cerebral Cortex, 21 (1), 115-123 DOI: 10.1093/cercor/bhq064

Earlier on the Digest: How to nap