It seems to be the most natural thing in the world: you sleep at night, you are awake during the day – apart from occasional exceptions. But if you still remember the famous “Professor Hastig” from Sesame Street, who suddenly fell asleep in the middle of his lectures, you may have already thought about how the brain actually controls sleep and waking .
Now an Israeli-American research team has found that the switch for alertness is located in a specific region in the brain thalamus, the central lateral nucleus (CL). If they stimulated this region with two previously anesthetized macaques with fine electrical impulses , the animals woke up again, the researchers write in the journal “Neuron”.
Bringing the brain in sync with electricity
The researchers used a technique that has long been used and approved as a therapy for certain brain diseases, such as Parkinson's shaking paralysis is: “deep brain stimulation”. In doing so, fine wires are led into the brain region affected by the respective disease in order to bring the nerve cells back in “clock” with the help of very weak electrical impulses.
In Parkinson's patients, this is the “substantia nigra” in which nerve cells die and the remaining ones only send uncoordinated signals to the brain regions that move the poor and control legs. The result is the typical tremor, which disappears in many cases as a result of the surge of the “brain pacemaker”. The method is also used with some success for muscle tremors (tremors) and even mental illnesses such as depression.
The team led by Yuri Saalmann from the University of Wisconsin in Madison, USA, based on research results in rats and monkeys, assumed that the state of consciousness is regulated from the thalamus.
This The control center in the midbrain processes the stimuli that reach the brain via the sensory organs and controls movements. To do this, it is in contact with many other brain regions, such as the frontal lobe of the brain.
To test the hypothesis, the researchers anesthetized the two macaques with a dose that would normally let the animals sleep for at least two hours.
Activated the Scientists then placed the electrodes previously in the thalamus, awakened the animals . That means, despite the sleeping pills, they opened their eyes, grabbed objects with their arms and reacted to sounds in the room with facial and body movements. Other body signals, such as breathing and heart rate, corresponded to the waking state.
The monkeys fell asleep again without stimulation
If the researchers stopped the electrostimulation, the animals fell asleep again. The level of alertness was both depending on the frequency of the electrostimulation – ideally 50 Hertz – as well as on Place of stimulation in the brain: If the researchers stimulated the animals just a little next to the central lateral nucleus of the thalamus, or elsewhere in the brain, they could not wake the animals out of anesthesia.
Measurements showed that stimulation of the CL region changed the way communication between the thalamus and other brain regions – similar to how these patterns of nerve impulses change between normal sleep and wakefulness, so differentiate between unconscious and conscious state. Did the researchers find a “ neuronal correlate of consciousness ” in this communication pattern of nerve cells, so to speak the “consciousness signature”?
Probably not. The state of the “awakened” monkeys is not identical to normal waking consciousness, says neurologist Nicholas Schiff from Cornell University: “The state activated by the stimulation that the model generates is very different from the normal waking state.”
In addition, the behavioral tests carried out are very limited and in human studies would correspond to the level in the transition from behavior in the vegetative state to early minimally conscious behavior. “We have no way of meaningfully experiencing how the sensations are in the minimally conscious state.”
It is about more than waking and sleeping states
In fact, there are not only the two states of waking and sleeping, of consciously and unconsciously, but various levels in between. And it is difficult to determine the condition of the “woken up” monkeys. For Steven Laureys, head of the “coma research group” at the Liège University Hospital in Belgium, the study is “much more than just wakefulness and sleep”.
So far, there has been talk of Perception, attention, alertness or the like to avoid the “ important concept of consciousness .“ So with this publication we can now speak about the consciousness of non-human primates. ”How these animals awakened from anesthesia really thought what they perceived, it was a challenge to find out, says Laureys, “because we can neither verbally nor non-verbally communicate with macaques.”
But the experiment shows that people are not the only ones who are aware of their and their environment , says Laureys. “And now we see for the first time how the concept of” awareness “changes from animals to animals Let people transfer. ”
Experiments, the comapatias could help
For coma and other patients, the monkey experiments in the future could have therapeutic benefits . “I think it could be possible to wake coma patients with this method of deep brain stimulation,” says Christof Koch.
The president of the Allen Institute for Brain Research in Seattle would “despite the promising results be careful to draw conclusions on the clinical implications based on this study. “The states of the coma and the anesthetic anesthetic would differ” to a great extent “. However, they are comparable in terms of complete loss of consciousness.
Deployment is still a long way off
In fact, therapy attempts have already been made to coma patients and people with impaired consciousness, so Schiff's research group already has people in the CL Region stimulates “to restore functions both in patients with impaired consciousness and in patients with a higher degree of recovery after a coma.”
A study is currently underway on P Patients who have recovered from coma or a severe brain injury but still have cognitive impairments, says Schiff.
2007 Schiff was the first to use deep brain stimulation, with one 38 – American, who had woken up after a coma and had opened his eyes, but could not communicate. After the treatment, he was able to eat and speak independently .
However, the field is still a long way off from an effective therapy. “We have to understand a lot more before we can really use such instruments in a clinical context,” says Laureys. It is “highly unlikely” that what is described as “consciousness” in humans will only arise in the CL region in the thalamus, says Igor Kagan, head of the decision-making and awareness-raising research group at the Leibniz Institute for Primate Research in Göttingen. Human consciousness could not be located in a central location . (with smc)