The neurotransmitter norepinephrine plays a significant role in the conscious reception of sensory information

The findings may lead to the development of future treatments for problems related to the level of sensitivity to the environment such as sleep difficulties, hypersensitivity in autistic people, and the identification of dangerous driving situations * The study was published late last week in the scientific journal Current Biology.

A study carried out in Dr. Yuval Nir's laboratory at the School of Medicine and the Segol School of Neuroscience at Tel Aviv University led to an important discovery in a question that has occupied science for a long time: why does information absorbed by the senses sometimes reach the mind and sometimes not? What distinguishes these situations? The researchers found that one of the most important substances in the process is a neurotransmitter called norepinephrine. They believe that their discovery may form the basis for developing treatments for conditions associated with over- or under-sensitivity to environmental stimuli.

The research was jointly led by Dr. Hagar Galbard-Shagiv and Efrat Magidov from Dr. Nir's laboratory, and it was carried out in collaboration with Prof. Thelma Hendler and Dr. Hagai Sharon from the Segol Center for Brain Functions at the Tel Aviv Medical Center (Ichilov). The study was published late last week (July 2018) in the scientific journal Current Biology.

"Noradrenaline is a well-known neurotransmitter that affects brain activity," says Dr. Nir. "Among other things, it is known that it is found in the brain in high amounts when we are awake, and that its level drops significantly during sleep, when we are disconnected from our surroundings. These data led us to hypothesize that the presence of norepinephrine is important for the reception of sensory information in the mind."

To test their hypothesis, the researchers conducted an experiment with the participation of 30 healthy subjects. Each subject participated in three sessions, one week apart. At the beginning of each session, the subject swallowed a pill that was placed in front of him, when neither he nor the examiners knew what was in it: Raboxetine, which increases the level of noradrenaline in the brain, clonidine, which lowers the level of noradrenaline, or a placebo (powdered sugar) that has no effect. During the three sessions, each subject received all three drugs, in random order.

Under the influence of each of the substances, the subjects were asked to perform tasks of visual perception: identify weak images on a screen that are very difficult to distinguish, on the threshold of the ability to perceive. The researchers compared the performance of the participants before and after the administration of the drug, and also checked the brain activity while performing the tasks - using an EEG that measures the electrical activity in the brain, and with the help of fMRI technology that provides a functional imaging of the brain activity.

"The findings revealed that the ability of the subjects to notice the pictures and identify what appears in them gradually improved as the level of noradrenaline in their brains increased," says Dr. Hagar Galbard-Shagiv. "Accordingly, the EEG tests showed that the electrical response in the brain improved as the level of noradrenaline in the brain was higher, but only at a relatively late stage of the image processing process. The fMRI tests completed and strengthened the picture: norepinephrine did not affect the first stations of image reception in the brain, but strengthened the response in later stations of image processing in the cerebral cortex - in areas known as high visual areas. That is, in the two different measurements of brain activity - EEG and fMRI - an effect of norepinephrine was observed on the later stages of the processing process - the stages that lead to the image captured by the eye being registered in the mind, or in other words: that the person will be aware of what his eyes saw."

Efrat Magidov adds: "Until today, norepinephrine is considered a neurotransmitter involved in brain stimulation as well as in higher cognitive processes, such as storing information in memory, making decisions, emotional reactions to stress, etc. We have shown that it also plays a central role in apparently more 'basic' processes, such as sensory information processing. We discovered that the presence of norepinephrine dictates the chance that we will absorb stimuli in our environment. Norepinephrine is actually a kind of 'volume button' that controls the brain's response to what is happening in the world around us."

"We believe that our findings can lead in the future to new directions in the treatment of a variety of problems and disorders, related to the human's sensitivity to what is happening in his environment," concludes Dr. Nir. "For example, the ambition is to check whether people who suffer from sleep disorders - have difficulty falling asleep or wake up easily from any noise - suffer from higher levels of norepinephrine and the same may be true of autistic people who suffer from hypersensitivity and senses overwhelmed by any sensory stimulation; On the other hand, among those with neuropsychiatric disorders who are cut off from their environment, may low levels of the neurotransmitter be found? Our research may also develop tools for the early detection of moments of reduced sensitivity to the environment, which may lead to a life-threatening situation - for example in drivers or pilots."