18 January 2010

A Burst of Consciousness: Out of Chaos

The line between mental chaos and a clear awareness is measured in milliseconds. If the brain can be distracted at just the right time, it will not be able to see what is in front of its nose. Researchers at the Weizman Institute of Science studied patients with implanted brain electrodes (in preparation for surgery). They were able to observe the sudden burst of brain activity in the higher visual brain centers signifying comprehension of an image.
The subjects looked at a computer screen, which briefly presented a 'target' image -- a face, house, or man-made object.

This image was followed by a 'mask' -- a meaningless picture for distraction -- at different time intervals after the target image had been presented. This allowed the experimenter to control the visibility of the images -- the patients sometimes recognized the targets and sometimes failed to do so. By comparing the electrode recordings to the patients' reports of whether they had correctly recognized the image or not, the scientists were able to pinpoint when, where and what was happening in the brain as transitions in perceptual awareness took place.

Malach: 'We found that there was a rapid burst of neural activity occurring in the high-order visual centers of the brain -- centers that are sensitive to entire images of objects, such as faces -- whenever patients had correctly recognized the target image.' The scientists also found that the transition from not seeing to seeing happens abruptly. Fisch: 'When the mask was presented too soon after the target image, it 'killed' the visual input signals, resulting in the patients being unable to recognize the object. The patients suddenly became consciously aware of the target image at a clear threshold, suggesting that the brain needs a specific amount of time to process the input signals in order for conscious perceptual awareness to be 'ignited.'' _SD

Consciousness is a time-critical process. The time constraints of conscious awareness depend upon electro-physiological activity across the cortical and sub-cortical brain. These electro-physiological activities are in turn dependent upon lower level physiological and biochemical activities in cerebral neurons, glia, and vasculature. But there is a great deal of subtle detail hidden out of sight, for now. It will require our brightest scientists to tease out the complexity from the chaos.

Earlier research by same researchers using fMRI to identify neuronal correlates of conscious activity

Global Neuronal Workspace Theory of Consciousness

PDF Look at how prefrontal activity can be temporarily "shut down" by perceptual processes PDF

PDF A glimpse at active unconscious assistance processes in conscious reading of handwritten materials PDF

300 milliseconds to conscious awareness

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