Researchers from the University of Wisconsin-Madison have found that it’s possible to wake a monkey out of a deeply anesthetized sleep by electrically stimulating the central lateral thalamus, a bundle of grey matter located just above the brainstem used for arousal, awareness and executive cognitive functioning.
For the study, the researchers put two macaque monkeys under anesthesia and then stimulated different areas of their brains with electrodes at a frequency of 50 Hertz to see how they would respond to different parts of the brain being stimulated. Also studying the animals while they were awake and sleeping, the researchers tailored the positioning of each electrode to match the shape of the targeted brain area, as well as its frequency to match that of regular wakefulness
Co-author of the study, Michelle Redinbaugh, said, “A millimeter out of position, and you dramatically reduce the effect...And if you’re in that ideal location, but stimulating at two Hertz instead of 50? Nothing happens. This is very location- and frequency-specific.”
In the end, they found that after stimulating the central lateral thalamus, the monkeys woke up, and their brain function resumed as though they were lucidly awake. This came even though they were still under anesthesia. Then, seconds after the researchers switched off the electric stimulation, the monkeys went back to sleep. They found the same results each time they repeated the process.
Redinbaugh, said, “The animal went from being deeply anesthetized to opening his eyes, looking around the room, and even reaching out for objects within only a few seconds of the stimulation turning on...Shortly after the stimulation ended, he went back into unconsciousness like nothing happened.”
Although not yet tried on humans, as macaque monkeys are the best animal model available to compare with humans, the researchers hope that their findings may go on to inform further research into consciousness, as well as new therapies for people suffering from brain traumas, injuries or consciousness disorders.
Meanwhile, they hope that similar kinds of deep brain stimulation may start being used for medical purposes such as bringing people out of comas, and to ensure that patients under anaesthesia for surgical purposes do not wake up during their procedure.