When we dream, a strange phenomenon occurs inside our brains. We have an experience similar to being awake but also quite different from being awake simultaneously. Researchers are still attempting to pinpoint precisely what happens in that transitional condition. However, a recent finding from Tel Aviv University might solve the significant scientific puzzle: how does sensory information become a conscious experience in the awakened brain?
A recent study in the journal Natural Neuroscience showed that one key aspect of consciousness is put off while we sleep. This may provide insight into how our brains dream. Consciousness, in this sense, is the ability to recognize or be aware of sounds.
The study was headed by Dr Hanna Hayat and co-supervised by Prof. Itzhak Fried from UCLA Medical Center, and with significant contributions from Dr. Amit Marmelshtein at the lab of Prof. Yuval Nir from the School of Medicine, the Sagol School of Neuroscience, and the Department of Biomedical Engineering. Other participants included: Dr. Yaniv Sela and Dr. Aaron from Prof. Nir’s group, Dr. Firas Fahoum, and Dr. Ido Strauss from the Tel Aviv Sourasky Medical Center (Ichilov).
Data collected from implanted electrodes
The ground-breaking study used information from electrodes surgically inserted deep within the human brain for medicinal purposes. The data was used to compare the cerebral cortex responses to sounds during wakefulness and sleep at a resolution of single neurons.
It is challenging to map the brains of people awake and asleep. Few people would like electrodes inserted into their heads while they go about their daily lives. But in this case, the team benefited from medical studies conducted on people with epilepsy.
“This study is remarkable in that it relies upon data from electrodes inserted deep into the human brain. It allows high-resolution monitoring, down to the level of individual neurons, of the brain’s electrical activity,” explains neuroscientist Yuval Nir from Tel Aviv University in Israel. For obvious reasons, electrodes cannot be implanted into the human brain for research purposes. We can, however, make use of a unique medical method where electrodes are placed in the brains of epileptic patients to track activity in various sections of their brains for diagnostic and therapeutic purposes.
The subjects volunteered to assist in comparing the brain’s reaction to auditory stimulation during awake and sleep, the researcher continues. The electrodes allowed the researchers to observe, down to individual neurons, variations in the cerebral cortex’s response during various stages of sleep compared to when patients were awake.
The method of research
Researchers compared data from the implanted electrodes while playing a variety of sounds over speakers at the volunteers’ bedsides for the study. For eight years, the researchers gathered data from over 700 neurons, roughly 50 neurons in each patient.
The fact that the brain’s sensitivity to sound persisted during sleep in all respects came as a surprise to the researchers. On the other hand, Alpha-beta wave activity rises in response to attention to auditory information and associated expectations. It appears that incoming noises are evaluated by the brain but not communicated to subjects consciousness.
This contradicts earlier research. Thus, it’s impossible to concentrate on or recognize the sound while the brain processes auditory information when we are asleep. It’s simply that the sounds are processed very differently while we sleep – and that difference is a big one.
“Except for one particular aspect, where a marked variation was noticed, the brain’s response strength during sleep was comparable to that seen during waking: the activity level of alpha-beta waves,” says Hanna.
Alpha-beta waves (10-30Hz)
Higher-level brain feedback regulates the alpha-beta waves (10–30Hz). This feedback, which includes whether or not sounds are new, aids our minds in determining which sounds are significant and call for attention. Alpha-beta wave patterns have previously been seen to migrate higher in a similar manner in anesthetized patients. But it hasn’t been observed in those who are asleep. It is one approach to understanding the “fascinating riddle” of how the conscious and unconscious brains vary.
Additionally, this provides researchers with a quantitative and accurate way to determine if a patient is unconscious or not, whether it be during medical procedures, in comatose patients, when looking for dementia symptoms, etc.
Need for future findings
Dr. Nir clarified that their findings go much beyond this particular experiment. They start by offering a crucial solution to an intriguing old mystery:
The mystery of consciousness: what is it? What is the “X-factor,” the special brain activity associated with the consciousness that enables us to be aware of events taking place around us? At the same time, we are awake and vanish when we are asleep?
Additionally, we now have a separate quantitative measure – the first of its type – for evaluating an individual’s awareness of incoming noises thanks to discovering a particular brain characteristic that differs between stages of consciousness and unconsciousness. He also underlined the importance of further future research to determine the causes underlying this variation.
Feature image credit: Consciousness by Shutterstock.com