Human Brain Continues to Dream and Process Words During Anesthesia

Two research teams meticulously studied the effects of anesthesia on human consciousness and discovered that it creates a state similar to sleep.
Loukia Papadopoulos

A new study entitled "The Conscious Mind: Integrating subjective phenomenology with objective measurements" by the University of Turku and the Hospital District of Southwest Finland has revealed some interesting findings regarding human consciousness. It turns out that even under anesthesia, consciousness continues to function only in an altered state similar to sleep.


The research saw Adjunct Professor of Pharmacology and Anesthesiologist Harry Scheinin's team, a group centered on the study of anesthesia mechanisms, collaborate with Professor of Psychology Antti Revonsuo's team, a group focused on human consciousness. Together, the groups analyzed changes in the brain caused by anesthetics using electroencephalogram (EEG) and positron emission tomography (PET).

Dream-like experiences

The first part of the study, saw volunteers anesthetized either with dexmedetomidine or propofol and monitored until they regained responsiveness. The participants, nearly all said they experienced "dream-like experiences that sometimes mixed with reality," according to Revonsuo.

The researchers also conducted tests to evaluate whether subjects could detect words or even entire phrases when anesthetized. The EEG revealed that the brain under anesthesia attempted but could not process sentences.

"When we used dexmedetomidine, also the expected words created a significant response, meaning that the brain was trying to interpret the meaning of the words. However, after the participants woke from the anesthesia, they did not remember the sentences they had heard and the results were the same with both drugs." said Senior Researcher, Adjunct Professor Katja Valli who participated in the study.

The subjects were also exposed to unpleasant sounds under the influence of anesthesia. The research group found that, although the participants could not remember hearing the sounds once awake, they showed distinct responses to a replay of the sounds meaning that subconsciously they recognized them.

"In other words, the brain can process sounds and words even though the subject did not recall it afterward. Against common belief, anesthesia does not require the full loss of consciousness, as it is sufficient to just disconnect the patient from the environment," explained Scheinin

Consciousness remains

The team also used PET imaging to analyze the impact of four different anesthetics on the regional cerebral glucose metabolism. In the end, all analysis pointed to the fact that some consciousness remained during anesthesia despite the individual losing the ability to respond, a state very similar to sleep.

"The state of consciousness induced by anesthetics can be similar to natural sleep. While sleeping, people dream and the brain observes the occurrences and stimuli in their environment subconsciously," concluded Revonsuo.

The study was funded by the Academy of Finland and the Jane and Aatos Erkko Foundation and supported by research teams from the University of Michigan, Ann Arbor, and the University of California, Irvine, USA. The research's results have been published in four separate studies in the July issues of two leading journals in anesthesiology. 

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