Sending rats to sleep sheds light on brain circuitry
A team of researchers at Stanford University has demonstrated the ability to manipulate states of consciousness by altering brain activity. By changing the firing rates of neurons in the central thalamus, scientists have been able to wake rats and/or send them back to sleep. This latest study on the brain's circuitry may help to develop new and effective methods to treat brain injuries and other neurological disorders.
Within the brain, the thalamus serves to process and relay sensory information and motor signals to the cortex. The thalamus also plays a role in regulating states of sleep and arousal, and previous studies had suggested that stimulating thalamic neurons could awaken patients from minimally-conscious states.
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Led by Jin Hyung Lee, Ph.D., assistant professor of neurology, neurosurgery, and bioengineering at Stanford University, the team used lasers to stimulate the light-sensitive thalamic neurons of sleeping rats. They discovered that flashing pulses at high frequencies of 40 and 100 Hz woke the rats, while low frequencies at 10 Hz sent the animals into a state similar to that of absence seizures, causing them to stiffen and stare before falling back asleep.
The scientists observed that the high and low frequency stimulation triggered completely different states. Functional magnetic resonance imaging (fMRI) was used to scan activity in cortical brain areas. Regions with elevated activity during high frequency stimulation became inhibited with low frequency stimulation.
Electrical recordings confirmed the results, but also showed that low frequencies caused specific neurons to fire in a pattern that often occurs during sleep. When the scientists blocked the firing of these zona incerta neurons during low frequency stimulation, the average activity of the sensory cortex increased.
"Our results suggest the central thalamus works like a radio dial that tunes the brain to different states of activity and arousal," says Dr. Lee. "We showed how the circuits of the brain can regulate arousal states, and hope to use this knowledge to develop better treatments for brain injuries and other neurological disorders."
A paper on the research was recently published in the journal eLife Sciences.