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/v11/n9/full/nn.2177.html

Source: Weizmann Institute of Science

Explore further: A high-fat diet may alleviate mitochondrial disease

Related Stories

BBC explores mind control over TV program choice

Jun 18, 2015

The world is growing increasingly digital, and so will modes of interaction. TV watchers might welcome an alternative to under-the-cushion clickers, a thought not lost on the people at BBC. What if our viewers ...

Functioning brain follows famous sand pile model

Jun 22, 2015

One of the deep problems in understanding the brain is to understand how relatively simple computing units (the neurons), collectively perform extremely complex operations (thinking).

Wearable tech 2.0 aims to alter mind, body

Jun 11, 2015

Grandmothers are wearing Fitbit, Jawbone bracelets pack the shelves of big-box stores and Apple's smartwatch is expected to be one of the most coveted Christmas gifts this year.

The wonders of bioluminescent millipedes

Jun 08, 2015

There's something inherently magical, even surreal, about seeing hundreds of glowing millipedes scattered across the ground of a sequoia grove on a moonless night in Sequoia National Park.

Recommended for you

A high-fat diet may alleviate mitochondrial disease

5 hours ago

Mice that have a genetic version of mitochondrial disease can easily be mistaken for much older animals by the time they are nine months old: they have thinning grey hair, osteoporosis, poor hearing, infertility, ...

Cheek muscles hold up better than leg muscles in space

6 hours ago

It is well known that muscles need resistance (gravity) to maintain optimal health, and when they do not have this resistance, they deteriorate. A new report published in the July 2015 issue of The FASEB Journal, however, sugges ...

Sialic acid: A key to unlocking brain disorders

9 hours ago

A new report published in the July 2015 issue of The FASEB Journal suggests that a common molecule found in higher animals, including humans, affects brain structure. This molecule may play a significant role in how brain ...

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.