The findings of a study conducted at Tel Aviv University indicate that the brain's response to sounds is powerful even during sleep, in all but one measure: the level of alpha-beta waves related to the degree of attention and attention. the meaning: In the sleep state the brain hears the sound but fails to focus on it and form a full identification and conscious perception
A new discovery by Tel Aviv University may help solve the scientific mystery - how does the waking brain transform the sensory input into a conscious experience? As part of the groundbreaking study, the researchers relied on data from electrodes implanted in the depths of the human brain for medical purposes in order to examine differences in the cerebral cortex's response to different sounds played to the subject, at the level of the individual neuron, in states of wakefulness versus sleep.
The researchers were surprised to find that the brain's response to sounds is powerful even during sleep, in all measures except one: the level of alpha-beta waves related to the degree of attention, attention, and expectations regarding sounds received. The meaning: in a state of sleep the brain hears the sound but fails to focus on it and identify it, and therefore a conscious perception of the sound does not exist in a state of sleep.
The researchers: "For the first time, we have a quantitative measure that differs dramatically between an awake person who is aware of sounds and an audio response in sleep states characterized by unconsciousness and disconnection from the environment."
The research was conducted under the leadership of Dr. Hana Hayit and with the assistance of Dr. Amit Marmelstein from the laboratory of Prof. Yuval Nir from the Sackler School of Medicine, the Segol School of Neuroscience, and the Department of Biomedical Engineering, as well as under the leadership of Prof. Yitzhak Fried from the Medical Center of UCLA University in the USA. Also participating in the study were: Dr. Aharon Krum and Dr. Yaniv Sela from Prof. Nir's research group as well as Dr. Ido Strauss and Dr. Firas Pahum from the Tel Aviv Medical Center (Ichilov). The study was published in the prestigious journal Nature Neuroscience.
Prof. Nir explains that the uniqueness of the research is that it relies on data from electrodes implanted in the depths of the human brain that monitor brain activity with high resolution, including at the level of the individual neuron (nerve cell). According to him, for obvious reasons, it is not possible to implant electrodes in the brains of humans for the purposes of science, but in this study, the researchers were helped by a special medical situation in which electrodes were implanted in the brains of epilepsy patients to monitor the brain activity in the various areas in preparation for an operation designed to help them. The patients volunteered to examine the brain's response to audio stimuli in states of wakefulness versus sleep.
As part of the study, speakers were placed next to the patients' beds that play different sounds, and the researchers compared the data obtained from the electrodes - nerve cell activity and local electrical waves in different areas of the brain - while awake and during different stages of sleep. In total, data was collected from about 700 neurons, about 50 neurons from each subject, over a period of 8 years.
Dr. Hait: "After sounds are received in the ear, the signal is transmitted from station to station inside the brain. Until recently, it was widely believed that in sleep states, these signals quickly fade when they reach the cerebral cortex. In our research, we discovered to our surprise that even during sleep the brain response is stronger and richer than expected, and spreads to many areas of the cerebral cortex and ignites a response similar in strength to that measured in the awake state. However, in one specific feature, we discovered a dramatic difference in brain activity in waking and sleeping states - the level of activity of alpha-beta waves."
The researchers explain that alpha-beta waves (between 10 and 30 Hz) are associated with the processes of attention and anticipation, which are controlled by feedback from higher areas of the brain. In fact, at the same time as the "bottom-up" information is transmitted from the sensory receptors to higher processing areas, the opposite movement also occurs: the higher areas, which rely on prior knowledge accumulated in the brain, act as a kind of directed and active hand that sends information "from top to bottom" to guide the sensory areas on what to concentrate on, from what ignore, etc. Thus, for example, when a certain sound is received by the ear, those higher regions identify whether the sound is familiar or new, whether it deserves attention, or perhaps it does not need to be addressed. This brain activity is reflected as a suppression of alpha-beta waves, and indeed, previous studies have identified a high level of these waves in states of rest and anesthesia. According to the current study, the strength of the alpha-beta waves is actually the main difference between waking and sleeping states when it comes to the brain's response to audio stimuli.
Prof. Nir concludes: "Our findings have a wide significance, beyond the limits of the experiment itself. First, they provide an important key to the oldest and most intriguing question of all: What is the secret of consciousness? What is the unique brain activity that allows us to be aware of what is happening around us, and disappears when we sleep? We discovered a new thread, and in future studies we will delve deeper into the mechanisms responsible for this difference.
In addition, since we have identified a specific brain characteristic that differentiates between states of consciousness and unconsciousness, we have for the first time a quantitative measure that allows us to assess the subject's level of awareness in response to sounds. By perfecting the measurement of the level of alpha-beta waves in the brain, using accessible non-invasive monitoring means (such as EEG), we hope that it will be possible, for example, to verify during surgery that the patient is under deep anesthesia and does not feel anything. In a similar way, it will be possible to examine the degree of awareness of the environment of a demented person or a person in a nursing state who is unable to communicate with his environment. In such cases, a low level of alpha-beta waves in response to sounds may even indicate that a person who is considered unconscious actually perceives and understands what is being said around him. We hope that our findings will serve as a basis for the development of effective and accessible methods for measuring the level of consciousness of people apparently in various states of unconsciousness."
More of the topic in Hayadan:
