The taste of champagne, the sound of a train, the flash of a pop fly into left field – indeed all of human perception – begins in the brain’s center. That’s where sensory information passes from the thalamus to the neocortex for processing.
That critical transfer is a bit of a brain science mystery: Instead of reacting to information from the thalamus with a burst of excitatory chatter, most cortical cells are quickly and strongly inhibited or silenced. Why does that happen?
In new work published in Nature Neuroscience, Brown University and University of California–Davis researchers provide the surprising answer.
The research team found that cortical inhibitory cells, which suppress communication, are relatively insensitive to inputs from the thalamus compared with excitatory cells, which encourage communication. Instead, inhibitory cells react strongly because they get much more stimulation from the thalamus. In fact, the researchers found, inhibitory cells get about eight times the amount of neurotransmitter, the signal-spurring chemicals that initiate nerve impulses. The result is that their silencing effect on brain cell communication overrides the noisy effect from their excitatory neighbors.
Scott Cruikshank, an assistant research professor in the Department of Neuroscience at Brown and lead author of the article, said the team’s secondary finding was also unexpected. Inhibitory cells in the cortex not only receive more input from the thalamus – they get that input faster than excitatory cells do.
"What we found is that the amount of information these cells receive as well as the speed of their response is what causes this fast inhibition," Cruikshank said. "What’s exciting about these findings is that they help to explain how the cortex handles information at the very earliest stages of processing. And understanding the cortex is critical to understanding not only perception, but memory, language, cognition."
Barry Connors, chair of the Department of Neuroscience and the senior scientist on the project, said the findings may also shed light on the causes of some forms of epilepsy, where the brain’s ability to inhibit cell activity is hampered.
"If nothing keeps the excitatory cells in check, it’s as if all the cells are shouting at once," Connors said, "and that cacophony causes a seizure."
The experiments were conducted by stimulating excitatory and inhibitory cells in the brains of mice with electrodes. But identifying these precise types of cells is akin to finding a needle in a haystack. So Cruikshank and Connors used cells from a mouse carrying a gene that makes its inhibitory cells glow green from a jellyfish protein -- creating a natural flag for the scientists.
Timothy Lewis, an assistant professor of mathematics at the University of California–Davis, made the models used to calculate how the speed of the cortical cells’ responses affected their circuit behavior.
Source: Brown University
Related stories:
Study of learning disabled mice shows balance in the brain is key
A new study in the October 31st issue of
Cell, a Cell Press journal, has revealed the molecular and cellular underpinnings of one of the most common, single gene causes for learning disability in humans. The findings made in learning disabled mice offer new insight into what happens in the brain when we learn and remember.
A fine balance
Once a toddler has mastered the art of walking, it seems to come naturally for the rest of her life. But walking and running require a high degree of coordination between the left and right sides of the body. Now researchers at the Salk Institute for Biological Studies have shown how a class of spinal cord neurons, known as V3 neurons, makes sure that one side of the body doesn't get ahead of the other.
Balancing the brain
Neuroscientists at Children's Hospital Boston have identified the first known "master switch" in brain cells to orchestrate the formation and maintenance of inhibitory synapses, essential for proper brain function. The factor, called Npas4, regulates more than 200 genes that act in various ways to calm down over-excited cells, restoring a balance that is thought to go askew in some neurologic disorders. The findings appear in the September 24 advance online edition of the journal
Nature.
Memory enhanced by sports-cheat drug
A drug used to increase blood production in both medical treatments and athletic doping scandals seems also to improve memory in those using it. New research published in the open access journal
BMC Biology shows that the memory enhancing effects of erythropoietin (EPO) are not related to its effects on blood production but due to direct influences on neurons in the brain. The findings may prove useful in the treatment of diseases affecting brain function, such as schizophrenia, multiple sclerosis, and Alzheimer's.
Trigger for brain plasticity identified
Researchers have long sought a factor that can trigger the brain's ability to learn – and perhaps recapture the "sponge-like" quality of childhood. In the August 8 issue of the journal
Cell, neuroscientists at Children's Hospital Boston report that they've identified such a factor, a protein called Otx 2.
The APCs of nerve cell function
Rapid information processing in the nervous system requires synapses, specialized contact sites between nerve cells and their targets. One particular synapse type, cholinergic, uses the chemical transmitter acetylcholine to communicate between nerve cells. Cholinergic synapses are essential for normal learning and memory, arousal, attention, and all autonomic (involuntary) nervous system functions. Malfunction of cholinergic synapses is implicated in Alzheimer's disease, age-related hearing loss, autonomic neuropathies, and certain forms of epilepsy and schizophrenia. Despite the importance of cholinergic synapses for cognitive and autonomic functions, little is known about the mechanisms that direct their assembly during development.
Deafness and seizures result when mysterious protein deleted in mice
Scientists have discovered that mice genetically engineered to lack a particular protein in the brain have profound deafness and seizures. The finding suggests a pathway, they say, for exploring the hereditary causes of deafness and epilepsy in humans.
Autism-related Proteins Control Nerve Excitability, Researchers Find
Two proteins that are implicated in autism have been found to control the strength and balance of nerve-cell connections, researchers at UT Southwestern Medical Center have found.