Researchers uncover mechanism responsible
In the early 20th century, scientists began recording brain activity using electrodes attached to the scalp. To their surprise, they found that brain activity was characterized by slow and fast rising and falling signals that were later called “brain waves.”
Since then, brain waves have been intensively studied for their involvement in the processing and transmission of information between different regions of the brain. In the healthy brain, a change in wave intensity has been observed in the context of a wide range of cognitive activities such as memory and learning. In addition, many studies have shown that changes in wave intensity and frequency indicate epilepsy, autism or neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease. Alzheimer’s disease, for example, is characterized by a sharp decrease in wave intensity at a certain frequency, while epilepsy is characterized by a very sharp and abnormal increase in wave intensity at a different frequency. .
It is currently known that brain waves express the synchronized activity of tens of thousands of nerve cells (neurons), so that a normal increase in wave intensity expresses the synchronized activity of different groups of neurons with the aim of transmit information. But why and how do these waves contribute to the proper transmission of information in the brain?
A new study led by PhD student Tal Dalal in the lab of Professor Rafi Haddad, from the Gonda (Goldschmied) Multidisciplinary Brain Research Center at Bar-Ilan University in Israel, focuses on this key question. In the study published in Cell reports, the researchers changed the level of synchronization in the area of the brain that transmits information. They then looked at how this affected the transfer of information and how the area of the brain that received the information understood it.
The research focused on regions of the brain that are part of the olfactory system, or sense of smell, which is characterized by high brain wave intensity. A particular type of neuron in this region is responsible for creating synchronized brain wave activity. To increase or decrease synchronization, the researchers used optogenetics, a method that turns neuronal activity on and off, much like a switch, by projecting flashes of light onto the brain. In this way, the activity of synchronization neurons can be turned on or off to examine how changing the synchronized activity of many neurons in one region affects the transmission of information to the next region, which reads the information..
The primary or “upstream” zone, manipulated by increasing or decreasing synchronization, is where the initial processing in the olfactory system takes place. From there, information synchronized or not, depending on the manipulation, is transferred to the secondary or “downstream” area of the olfactory system responsible for higher level processing.
The researchers found that increasing the synchronization of neurons in the upstream brain region that transmits information led to a significant improvement in information transmission and processing in the downstream region. Conversely, when synchronization was reduced, the representation of information in the downstream region was impaired.
An unexpected discovery also occurred. “We were surprised to find that activation of synchronization-inducing neurons also caused a decrease in overall activity level in the upstream region, so we would have expected less information to be transferred to the upstream region. But the very fact that the output from the upstream region is synchronized, compensated for the overall reduced activity and even improved information transfer,” says Dalal.
The researchers concluded the importance of synchronized brain activity for the transfer and processing of information. When thousands of neurons are synchronized, the transmission of information in the brain is more powerful and reliable, compared to a situation where the activity is asynchronous and each neuron works independently regardless of the group. Dalal says it can be compared to a protest of tens of thousands in a public square versus protesters scattered in different places. The power of a shared and synchronized activity is immense compared to an independent and unsynchronized activity.
This discovery may explain why a decrease in synchronized activity, which expresses a decrease in brain wave intensity, can lead to cognitive impairment in neurodegenerative diseases such as Alzheimer’s disease. “Studies to date have shown a correlation between decreased synchronicity and neurodegenerative disease, but have not shown why and how this occurs,” says Dalal. “In our study, we showed how synchronization helps in the transmission and processing of information in the brain, and this may be why we eventually see cognitive impairment in patients.”
Dalal and Professor Haddad’s study offers new options for the treatment of neurodegenerative diseases. It is possible that abnormal brain activity will be corrected in the future by specific stimulation of certain neurons, such as the flashes of light used for manipulation in this study, to restore synchronization to the level required for normal brain activity..
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Upstream synchronization improves odor processing in downstream neurons
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