Sleep provides the main key to the mystery of consciousness

Overview: During sleep, the brain analyzes auditory inputs, but cannot focus on sound or identify noise. Therefore, there is no conscious awareness of the stimulus.

sauce: Tel Aviv University

New discoveries from Tel Aviv University may provide the key to a great scientific mystery: how does the awakening brain transform sensory input into a conscious experience?

Breakthrough research relied on data collected from electrodes embedded deep into the human brain for medical purposes.

Using this information, we investigated the difference in the response of the cerebral cortex to sleep and awake sounds at a single neuron resolution.

Researchers were surprised to find that the brain’s response to sound remained strong during sleep at all but one parameter. The level of alpha beta waves associated with attention to auditory input and associated expectations.

This means that during sleep, the brain analyzes auditory inputs, but cannot focus on or identify sounds, resulting in a lack of conscious recognition.

The study was led by Dr. Hannah Hayat and co-supervised in the laboratories of Professor Yuval Neil of the Faculty of Medicine, the Faculty of Neuroscience, and the Faculty of Biomedical Engineering, with the great contribution of Dr. Amit Mamelstein. Fried food from UCLA Medical Center by Professor Itzhak. Other participants included Dr. Aaron Krom and Dr. Yaniv Sela from Professor Nir’s group, and Dr. Ido Strauss and Dr. Firas Fahoum from Tel Aviv Sourasky Medical Center (Ichilov).

The paper was published in a prestigious journal Nature Neuroscience..

Professor Neil: “This study is based on rare data from electrodes embedded deep in the human brain and is unique in that it can monitor the electrical activity of the brain at high resolution down to the level of individual neurons. is.

“For comprehensible reasons, we cannot implant electrodes in the living human brain just for scientific research. However, in this study, we implant electrodes in the brains of patients with epilepsy and brain for diagnostic and therapeutic purposes. A special medical procedure was available to monitor the activity of various parts of the body.

“Patients volunteered to help examine the brain’s response to auditory stimuli during awakening and sleep.”

Researchers have placed speakers that emit different sounds on the patient’s bedside to capture data from embedded electrodes (nerve activity and radio waves in different areas of the brain) at different stages of awakening and sleep. I compared. Overall, the team collected data from over 700 neurons, about 50 neurons in each patient, over an eight-year period.

Dr. Hayato: “After the sound is received by the ear, the signals are relayed from one station in the brain to the next. Until recently, these signals were thought to decay rapidly when they reached the cerebral cortex during sleep. However, looking at the data from the electrodes, I was surprised that the brain’s response during sleep was much stronger and richer than expected.

“Furthermore, this powerful response spread to many areas of the cerebral cortex. The strength of the brain response during sleep was similar to that observed during awakening, except for one specific function. , A dramatic difference was recorded. Alpha beta wave activity level. “

Researchers explain that alpha beta waves (10-30Hz) are associated with a process of attention and expectation controlled by feedback from higher regions of the brain.

As the signal moves “bottom-up” from the sensory organs to higher areas, “top-down” movement also occurs. The higher areas rely on prior information stored in the brain to act as guides, instructing the sensory areas about which inputs the signal should focus on, which inputs should be ignored, and so on.

So, for example, if a particular sound is received by the ear, the higher areas can determine if it is new or familiar, and if it is noteworthy. This type of brain activity manifests itself in the suppression of alpha beta waves. In fact, previous studies have shown high levels of these waves at rest and under anesthesia.

According to current studies, the intensity of alpha beta waves is the main difference in the brain’s response to auditory input during wakefulness and sleep.

Professor Nir summarizes: First, they provide an important key to the fascinating mysteries of ancient times: what is the secret of consciousness? What is the “X Factor”, which is a brain activity peculiar to consciousness? Do you recognize what’s happening around us when we’re awake and allow us to disappear when we’re sleeping?

“In this study, we discovered a new lead. Future studies will further investigate the mechanisms responsible for this difference.

“Furthermore, we have identified specific brain features that differ between the conscious and unconscious states, so now we have the first clear quantitative measure of this kind to assess an individual’s ringtone perception.

“In the future, we hope that improved techniques for measuring alpha beta EEG and non-invasive monitoring methods such as EEG will enable us to accurately assess a person’s state of consciousness in a variety of situations. Through surgical procedures to ensure that the patient remains unconscious, monitor the consciousness of the person with dementia or determine if an individual allegedly in a coma is unable to communicate. That is really unaware of his / her surroundings.

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“In such cases, the low-level alpha beta waves that respond to sound may allow a person who is considered unconscious to perceive and understand the words that are actually being said around him. May suggest.

“We hope that our findings will serve as a basis for developing effective new methods for measuring the level of consciousness of individuals who appear to be in various unconscious states.”

About this awareness research news

author: Noga City
sauce: Tel Aviv University
contact: Noga Shahar – Tel Aviv University
image: Image credited to Ana Yael

Independent research: Open access.
“”Decreased neurofeedback signaling despite strong neurons and gamma auditory response during human sleepAccording to Hannah Hayat et al. Nature Neuroscience

Overview

Decreased neurofeedback signaling despite strong neurons and gamma auditory response during human sleep

During sleep, sensory stimuli rarely provoke behavioral responses or conscious perception. However, it remains unclear whether sleep interferes with certain aspects of sensory processing such as feedforward and feedback signals.

Here, we presented awake and sleep auditory stimuli (click trains, words, music, etc.) in patients with epilepsy while recording nerve cell spikes, local electric field potentials of microwires, intracranial EEG and polysomnography. ..

Auditory stimuli evoked strong, selective spikes and high gamma (80-200 Hz) power responses on the outside of the temporal lobe in both non-REM and REM sleep. Sleep is only a moderately attenuated response magnitude, primarily affecting late responses beyond the early auditory cortex and entrainment to rapid clicktrain in non-rem sleep.

In contrast, the hearing-induced alpha-beta (10-30 Hz) asynchronization (ie, power loss) that is common in wakefulness was significantly reduced during sleep. Therefore, extensive auditory response persists during sleep, but decreased alpha-beta power probably reflects the neural feedback process and is inadequate.

Broader, our findings suggest that feedback signaling is the key to conscious sensory processing.