Behind closed eyes

Feb 04, 2009

Even when our eyes are closed, the visual centers in our brain are humming with activity. Weizmann Institute scientists and others have shown in the last few years that the magnitude of sense-related activity in a brain that's disengaged from seeing, touching, etc., is quite similar to that of one exposed to a stimulus. New research at the Institute has now revealed details of that activity, explaining why, even though our sense centers are working, we don't experience sights or sounds when there's nothing coming in through our sensory organs.

The previous studies of Prof. Rafael Malach and research student Yuval Nir of the Neurobiology Department used functional magnetic resonance imaging (fMRI) to measure brain activity in active and resting states. But fMRI is an indirect measurement of brain activity; it can't catch the nuances of the pulses of electricity that characterize neuron activity.

Together with Prof. Itzhak Fried of the University of California at Los Angeles and a team at the EEG unit of the Tel Aviv Sourasky Medical Center, the researchers found a unique source of direct measurement of electrical activity in the brain: data collected from epilepsy patients who underwent extensive testing, including measurement of neuronal pulses in various parts of their brain, in the course of diagnosis and treatment.

An analysis of this data showed conclusively that electrical activity does, indeed, take place even in the absence of stimuli. But the nature of the electrical activity differs if a person is experiencing a sensory event or undergoing its absence. In results that appeared recently in Nature Neuroscience, the scientists showed that during rest, brain activity consists of extremely slow fluctuations, as opposed to the short, quick bursts that typify a response associated with a sensory percept. This difference appears to be the reason we don't experience hallucinations or hear voices that aren't there during rest. The resting oscillations appear to be strongest when we sense nothing at all - during dream-free sleep.

The slow fluctuation pattern can be compared to a computer screen-saver. Though its function is still unclear, the researchers have a number of hypotheses. One possibility is that neurons, like certain philosophers, must 'think' in order to be. Survival, therefore, is dependant on a constant state of activity. Another suggestion is that the minimal level of activity enables a quick start when a stimulus eventually presents itself, something like a getaway car with the engine running. Nir: '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.'

Malach: '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.' Such techniques might not necessarily require the cooperation of the patient, allowing them to be used, for instance on people in a coma or on young children.

Paper: For the scientific paper, please see: www.nature.com/neuro/journal/v… n9/full/nn.2177.html

Source: Weizmann Institute of Science

Explore further: First successful vaccination against 'mad cow'-like wasting disease in deer

add to favorites email to friend print save as pdf

Related Stories

Nanotubes may restore sight to blind retinas

Dec 02, 2014

The aging process affects everything from cardiovascular function to memory to sexuality. Most worrisome for many, however, is the potential loss of eyesight due to retinal degeneration.

Drone in flight test learns on the fly with special chip

Nov 05, 2014

The great computer challenge for many scientists centers around how well a computer can learn, react and adapt from the environment. Tom Simonite of MIT Technology Review on Tuesday had a report about recent ...

Novel robotic walker helps patients regain natural gait

Nov 21, 2014

Survivors of stroke or other neurological conditions such as spinal cord injuries, traumatic brain injuries and Parkinson's disease often struggle with mobility. To regain their motor functions, these patients ...

Tomorrow's degradable electronics

Nov 20, 2014

When the FM frequencies are removed in Norway in 2017, all old-fashioned radios will become obsolete, leaving the biggest collection of redundant electronics ever seen – a mountain of waste weighing something ...

Bacteria become 'genomic tape recorders'

Nov 13, 2014

MIT engineers have transformed the genome of the bacterium E. coli into a long-term storage device for memory. They envision that this stable, erasable, and easy-to-retrieve memory will be well suited for ap ...

Recommended for you

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

KBK
not rated yet Feb 04, 2009
These scientists have 'come to new conclusions of possibility' based on research, they have not 'explained why'. Even they say that in the article.

The author of the article should understand that. I'm getting very sick of this need for 'facts' in these websites. People generally don't like to confront that which a good scientists knows, which is that the only thing that really exists is theory-and there are no 'facts'.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.