Brain complexity: anesthesia allows dreaming (Introduction)

by David Turell , Wednesday, August 29, 2018, 15:08 (2278 days ago) @ David Turell

Anesthesia appears to work by disconnecting parts of the brain and dreams can oc cur:

https://www.sciencealert.com/altered-states-consciousness-anaesthesia-sleep-like-state

"When you're getting the kind of surgery that requires being put under, you definitely don't want to be awake for any of the slicing. But a new study shows that when it comes to some general anaesthetics, our brains might be in a more sleep-like state than previously realised.

"The discovery suggests that far from being switched off, some parts of the brain are still capable of processing sensations from their environment, even if the patient can't recall any of it on waking.

"Researchers from the University of Turku in Finland compared the neurological effects of a pair of drugs commonly used to render patients unresponsive before medical procedures.

"Their goal was to determine whether the lack of responsiveness was largely due to the direct influence of the drugs themselves, or whether there was a knock-on effect that sends us into la-la land.

"The difference isn't just academic. If it's a knock-on effect, anaesthesia simply triggers an altered state of consciousness rather than flicking our off switch, meaning some conscious processes are still ticking while we're knocked out.

"As the researchers say in their report, "unresponsiveness does not equal unconsciousness, as one may have conscious experiences without behavioural responsiveness."

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"In this study, 47 healthy volunteers were dosed with either the sedative dexmedetomidine or the general anaesthetic propofol before having their brain waves recorded.

"Both drugs result in unresponsiveness at a certain dosages, though propofol is a far more powerful anaesthetic.

"When barely out cold, half of the subjects in the dexmedetomidine group could be aroused with a brief shake and a loud shout. Surprisingly, 42 percent of those given propofol could also be woken into a groggy state.

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"Later, the volunteers in both the sedative and the anaesthetic groups could recall the event, if a little hazily.

"'Nearly all participants reported dream-like experiences that sometimes mixed with the reality," says pyschologist Antti Revonsuo.

"The two groups were also played recordings of sentences which ended unexpectedly, such as "The night sky was filled with shimmering tomatoes". Other recordings were completely normal.

"Electroencephalogram recordings indicated volunteers who were deeply sedated could still hear the confusing phrases and were trying to make sense of it, even if later they couldn't remember hearing the sentences.

***

"'Against common belief, anaesthesia does not require full loss of consciousness, as it is sufficient to just disconnect the patient from the environment."

"While previous research has matched brain waves with states of awareness under anaesthesia, the fine control over the dosing in this study allowed researchers to identify changes due to the drugs and those due to changing consciousness.

"The work falls in line with other studies that also suggest anaesthesia doesn't switch off parts of the brain, as much as prevents them from communicating freely.

"If this sounds like nightmare fuel, take a deep breath – this isn't implying we can feel the cut of the surgeon's scalpel while lying trapped on a table.

"Rather, much like natural sleep, our brain is still half-paying attention, even if our awareness is switched off."

Comment: Under anesthesia consciousness does not completely disappear.