A team of scientists in California successfully manipulated the consciousness of rats by directing flashes of laser pulses onto the animals' central thalamus, an area that controls arousal.
Dr. Jin Hyung Lee of Stanford University, the senior author of the study, said the central thalamus seems to act like a radio dial that tunes the brain to various states of activity and arousal, meaning the thalamus relays neurons from the body to the cortex.
When neurons in the central thalamus are damaged due to brain injury, the person will experience problems in attention, memory, sleep and more.
Previous research has shown that if the neurons in the central thalamus are stimulated, injured patients who are minimally unconscious can actually be woken up.
The new study, which is featured in the journal eLife, aimed to test this theory.
To Sleep or Not To Sleep
Lee and her colleagues flickered specific laser pulses onto the light-sensitive thalamic neurons of sleeping rats, causing these neurons to fire.
In a high-frequency stimulation of about 40 or 100 pulses per second, the sleeping rats were awakened. On the other hand, a low-frequency stimulation of 10 pulses per second caused the rats to go into a state that is similar to the seizures which trigger them to stare and stiffen before falling asleep.
The team used functional magnetic resonance imaging (fMRI) to scan the brain activity of these sleeping rats and confirmed the different ways that thalamic neurons fired when the frequency changed.
Changing the frequency affected the thalamus this way: during low-frequency stimulation, inhibitory neurons called the zona incerta, which are found in a nearby brain region, fires a unique pattern sent to the sensory cortex. The zona incerta neurons were triggered to move in a spindle pattern, which often occurs during sleep.
When researchers tried to block the firing of these neurons in the middle of low-frequency stimulation, the average activity in sensory cortex elevated.
Hope For Patients With Traumatic Brain Injury?
The stimulation of the central thalamus showed promise for the treatment of traumatic brain injury, but researchers said patients with decreased levels of consciousness display slow progress through these stimulation treatments.
Still, Lee said their study has shown how the hardwiring of the brain can regulate arousal states.
"We hope to use this knowledge to develop better treatments for brain injuries and other neurological disorders," said Lee.
