At night when the brain breaks up into islands
Exhausting job! Establish peak brain function throughout the day. It's understandable that the neurons need some rest from the raising awareness - they don't want to hear anything more from their work colleagues for the time being.
Almost three thousand years ago, the ancient Indians in their holy scriptures, the Upanishads, distinguished three fundamental states of the mind: waking, dreaming and dreamless deep sleep. Today's neuroscientists agree without hesitation after countless EEGs and brain tomographies. The researchers would also agree with the wise men from the East that consciousness disappears when you fall asleep. However, when it comes to the question of what this ominous consciousness is, there are still no sealed answers to this day.
The division of night rest into two different types of sleep was first scientifically identified by American physiologists in the 1950s when they discovered REM sleep. This is characterized by rapid eye movements (rapid eye movements) below the closed eyelids. As a result, it turned out that test sleepers who were awakened during a REM phase often report vivid dreams. For those who were awakened during the rest of the time – non-REM sleep (NREM) – the pages of the dream log remained blank.
The Italian physician Giulio Tononi is also interested in the connection between the phenomena of sleep and consciousness. He made a name for himself in 2000 when he proved that even the fruit fly Drosophila occasionally allows itself a nap. Now he's at the University of Wisconsin-Madison studying the sleep cycles of a slightly more complicated animal.
In his sleep laboratory, he used state-of-the-art equipment to observe the waking phase and NREM sleep of human subjects. Tononi suspected that the nightly dozing of consciousness must be accompanied by some measurable change in the functioning of the brain. And indeed he found what he was looking for.
Using so-called transcranial magnetic stimulation (TMS), he administered precise current pulses to the test subjects' premotor cortex. When the test persons were awake, the electrical signals propagated from the excited region via nerve cell extensions to neighboring and some distant brain areas. On the other hand, when people slept in dreamless NREM sleep, the TMS produced a local reaction, but the neurons there no longer communicated the stimulation to their neighbors.
Tononi concludes from the results that the networked connections in the cerebral cortex break down during the NREM phase: "When consciousness disappears, the cortex disintegrates into many small islands that can no longer speak to one another." According to this, only a continuous, collective whispering of the neurons would produce consciousness. However, Tononi does not yet know how the human brain cuts off the communication channels during NREM sleep.
Next, the researcher wants to devote himself to REM sleep and use his sober method to put dream consciousness, which is entwined with legends, to the test. However, it will probably not be possible to definitively clarify who is whispering the often bizarre dream dramaturgy into our brains.
