Israeli study on neural activity could lead to treatment for Alzheimer's disease

How exactly do brain waves transmit information, and what can this mean for the connection between decreased brain activity and neurodegenerative diseases?

 A healthy brain compared to a brain suffering from Alzheimer's Disease (photo credit: National Institutes of Health)
A healthy brain compared to a brain suffering from Alzheimer's Disease
(photo credit: National Institutes of Health)

There might be a correlation between decreased brain wave activity, caused by lower synchronization levels in neural activity, and cognitive impairment in neurodegenerative diseases such as Alzheimer’s, a research team from Bar-Ilan University has discovered.

The research was published in a new study titled “Upstream y-synchronization enhances odor processing in downstream neurons” in the peer-reviewed online Cell Reports journal earlier this week. The study was led by doctoral student Tal Dalal in the laboratory of Prof. Rafi Haddad, of the Goldschmied Multidisciplinary Brain Research Center at Bar-Ilan.

The study focuses on brain waves and the transmission of information to the brain. The research team attempted to understand exactly how it is that brain waves transfer information, and the impact that varying levels of neural synchronization can have.

What are brain waves?

Brain waves were first discovered in the early 20th century by scientists using electrodes attached to scalps. In doing this, they discovered brain activity characterized by slow and rapid ascending and descending signals, which became known as brain waves.

 The synchrony-inducing neurons are marked in green to reflect the ability to silence their activity via flashes of light. (credit: TAL DALAL) The synchrony-inducing neurons are marked in green to reflect the ability to silence their activity via flashes of light. (credit: TAL DALAL)

Since then, brain waves have been studied intensively, specifically in the context of the processing and transmitting of information between different regions of the brain.

As they are currently understood, brain waves are the expression of synchronized activity carried out by tens of thousands of neurons, with a normal increase in wave activity expressing the synchronized activity of multiple different groups of neurons as they transmit information. But how and why do these waves contribute to the proper transmission of information to the brain?

Various studies throughout the years have shown that changes in brain wave intensity and frequency can indicate neurological disorders such as epilepsy and autism, or neurodegenerative diseases including Parkinson’s and Alzheimer’s.

Alzheimer’s, 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.

Carrying out the study

The Bar-Ilan study focused on altering the level of synchronization in the area of the brain that transmits information, before examining how this affected both the transfer itself and the understanding levels of the brain area receiving it.

The scientists focused primarily on the brain’s olfactory system (the sense of smell), as it is characterized by particularly strong brain wave activity.

The scientists focused primarily on the brain’s olfactory system (the sense of smell), as it is characterized by particularly strong brain wave activity.

In order to increase and decrease neuron synchronization, the researchers used a method called optogenetics, which allows neural activity to be turned on and off at will. Optogenetics works through the projection of flashes of light over specific areas of the brain, allowing for the synchronizing neurons to be turned on or off.

Manipulating the olfactory system

The initial processing of information in the olfactory system takes place in the primary or “upstream” area, and it was in this area that the researchers increased and decreased neural synchronization before the information was processed in the downstream area of the system.

They found that manipulating the system to increase neural synchronization in the upstream region led to a significant improvement in the transmission and processing of the information downstream. Similarly, decreasing neural synchronization upstream led to impaired processing in the downstream region.

However, they also discovered something unexpected. Activating the synchrony-inducing neurons also caused a decrease in the overall activity level in the upstream region, explained Dalal.

Because of this, he said, “We would have expected less information to be transferred to the downstream region. But the very fact that the output from the upstream region is synchronized, compensated for the overall reduced activity and even improved the transfer of information.”

Results and study conclusions

Through researching the neural synchronization in the olfactory system, the team understood that when thousands of neurons are synchronized, the transmission of information in the brain is done more powerfully and reliably, compared to a situation where the activity is asynchronous and each neuron operates independently regardless of the group.

This can be likened to a demonstration of tens of thousands of people in a public square compared to demonstrators scattered widely over a larger area, explained Dalal. The power of shared and synchronized activity is much stronger and more powerful in comparison to independent, non-synchronized activity.

The results of the study can lead to an increased understanding of cognitive impairment in neurodegenerative diseases, and could possibly even lead to new treatment options. It’s possible that the stimulation of specific neurons through the same optogenetics method used in the study could restore synchronization to the level required for normal brain activity.

“To date, studies have shown a correlation between decreased synchronicity and neurodegenerative disease, but haven’t shown why and how it happens,” said Dalal. 

In our study, we've shown how synchronization contributes to the transmission and processing of information in the brain, and this may be the reason why we eventually see cognitive impairment in patients.

Doctoral student Tal Dalal