Conventional wisdom until now held that the brain entered a state of “hibernation” while sleeping, and that the senses could be activated only by outside stimuli, or by the body's internal clock. This explanation of the electrical activity registered among neurons during sleep now seems to be a bit on the dumb side, since researchers have discovered only recently that slow electrical fluctuations exist in the cortex even during the deepest states of sleep. Thus far, the investigating team has not managed to find an explanation as to why this is happening, but its members have some theories.

When an individual is awake and keeps their eyes open, the visual cortex, located at the back of the head, is bombarded with a burst of electrical signals, which represents the enormous amount of data the brain records and processes at once, information such as who moved where in a crowd, or identifying a missing object among others. The brain usually protects itself from having to record that many data by simply not noticing the objects, which is why most people can easily walk past something they have been looking for for several times, before actually finding it.

Yuval Nir, a neurobiology student at the Weizmann Institute, who has also been involved with the current study, says that “In the old approach, the senses are 'turned on' by the switch of an outside stimulus. This is giving way to a new paradigm in which the brain is constantly active, and stimuli change and shape that activity.”

“The use of clinical data enabled us to solve a riddle of basic science in a way that would have been impossible with conventional methods. These findings could, in the future, become the basis of advanced diagnostic techniques,” Rafael Malach, an Institute professor, adds. He is also the lead researcher of the new paper, which details the finds in a recent issue of the journal Nature Neuroscience.

Researchers hypothesize that a minimum level of activity among neurons in the visual cortex is necessary from something called the “philosophical perspective,” meaning that the brain cells have to actually transmit information in order for them to survive. If they were to stop, they would die instantly. Another explanation for this eternal state of half-sleep would be that it allows the cortex to be solicited at any point, in case of emergency.