This new brain circuit, described in Nature Neuroscienceplays a role in modulating the attention and perceptionand may hold the key to treating attention disorders such as ADHD that to this day are still not well understood or adequately treated, despite the abundance of research on the role of neurons.
This new brain circuitry plays a role in modulating attention and perception.
Scientists have discovered that the noradrenalinea neurotransmitter that can be thought of as adrenaline for the brain, sends a chemical message to neurons to make them more alert, while sending another to astrocytes to calm overactive neurons.
“When you’re scared or overwhelmed, there’s so much activity in your brain that you can’t take in any more information,” he said. Kira Poskanzer, PhD, assistant professor of biochemistry and biophysics and lead author of the study.
Until this study, it was assumed that brain activity simply calmed down over time as the amount of norepinephrine in the brain dissipated. “We showed that it is, in fact, the astrocytes that pull the parking brake and bring the brain into a more relaxed state,” said Poskanzer.
a missing piece
Astrocytes are star-shaped cells woven between neurons in the brain in a grid-like pattern. Its many stellar arms connect a single astrocyte with thousands of synapses, which are the connections between neurons. This arrangement positions astrocytes to listen to neurons and regulate their signals.
These cells have traditionally been regarded as simple support cells for neurons, but new research over the past decade shows that astrocytes respond to a variety of neurotransmitters and may play critical roles in neurological conditions such as Alzheimer’s.
michael reitmannPhD, the paper’s first author who was a graduate student in Poskanzer’s lab when he conducted the research, wanted to know whether astrocyte activity could explain how the brain recovers from a burst of norepinephrine.
“It felt like there was a missing centerpiece to explain how our brains recover from such acute stress,” Reitman said. “There are these other cells very close by that are sensitive to norepinephrine and can help coordinate what the neurons around them are doing.”
guardians of perception
The team focused on understanding perception, or how the brain processes sensory experienceswhich can be very different depending on what state a person (or any other animal) is in at the moment.
For example, if you hear thunder as you settle in, the sound may seem comforting and your brain may even shut down. But if you hear the same sound while walking, your brain may be more alert and focused on safety. “These differences in our perception of a sensory stimulus occur because our brains process information differentlydepending on the environment and the state we’re already in,” said Poskanzer, who is also a member of the Kavli Institute for Fundamental Neuroscience.
To do this, Poskanzer and Reitman looked at how mice responded when given a drug that stimulated the same receptors that respond to norepinephrine. They then measured how much the mice’s pupils dilated and looked at brain signals in the visual cortex. But what they found seemed counterintuitive: instead of exciting the rats, the drug relaxed them..
“That result really doesn’t make sense given the models we have, and it led us to think that another cell type might be important here,” Poskanzer said. “It turns out that these two things are united in one feedback loop. Given the number of neurons each astrocyte can communicate with, this system makes them really important and differentiated regulators of our perception.”
The researchers suspect that astrocytes may play a similar role for other neurotransmitters in the brain, as being able to seamlessly transition from one brain state to another is essential for survival.