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 : “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 control the movement of arms and 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 .

Based on research results in rats and monkeys, the team led by Yuri Saalmann from the University of Wisconsin in Madison, USA, assumed that the state of consciousness is regulated from the thalamus.

This control center in the diencephalon 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.

When the scientists activated the electrodes that had previously been installed in the thalamus, the animals awoke . 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

When the researchers stopped electrical stimulation, the animals fell asleep again. The level of alertness was dependent both on the frequency of the electrostimulation - ideally 50 Hertz - and on the location of the 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 Do not wake animals from anesthesia.

Measurements showed that stimulation of the CL region changed the way of communication between the thalamus and other brain regions - similar to how these patterns of nerve impulses also differ between normal sleep and wakefulness, i.e. unconscious and conscious states. Did the researchers find a " neuronal correlate of consciousness " in this communication pattern of nerve cells, to a certain extent the "consciousness signature"?

Probably not. The state of the “awakened” monkeys is not identical to a normal awake consciousness, says the neurologist Nicholas Schiff from Cornell University: “The state activated by the stimulation that the model creates 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 what the sensations are in the minimally conscious state."

It's about more than waking and sleeping

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, one speaks of perception, attention, alertness or the like in order 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 really awoke from anesthesia, what they perceived, it remains a challenge to find out, says Laureys, "because we neither verbally nor with macaques can communicate non-verbally. "

However, the experiment shows that people are not the only ones who are aware of their and their environment , according to Laureys. "And now we are seeing for the first time how the concept of" awareness "can be transferred from animals to humans."

Experiments that could help coma patients

However, the president of the Allen Institute for Brain Research in Seattle would "be cautious, despite the promising results, to draw conclusions on the basis of this study on clinical implications." Thus, the conditions of the coma and the anesthetic anesthetic would differ "to a large extent" , But they are comparable in terms of complete loss of consciousness.

Deployment is still a long way off

In fact, there are already attempts to treat coma patients and people with impaired consciousness. Schiff's research group has already stimulated people in the CL region "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 ongoing on patients who have recovered from coma or a serious brain injury but still have cognitive impairments, says Schiff.

In 2007 , Schiff was the first to use deep brain stimulation in a 38-year-old American who had woken up after a coma and had opened his eyes but was unable to communicate. After the treatment, he was able to eat and speak independently again