How electrical traffic is routed through the brain has always been of great interest to psychologists. It was once thought that electrical signals always followed set paths through the brain, much in the way the heart pushes blood through the cardiovascular system. Many signals do, in fact, follow the same paths over and over again, but what is now more generally understood is that these pathways are in no way hardwired. The plasticity of the brain, or its ability to change based on the needs of the organism, has now been verified using a number of independent experiments. Scientists have now found yet another piece of evidence displaying the extraordinary ability of the brain to change by studying a curious condition called blindsight - a condition where people can see despite damage to the part of the brain that processes visual information.
Blindsight occurs in some people who have suffered damage to their visual cortex. The visual cortex is the primary place to which the brain routs information from the eyes. It is responsible for decoding visual information and can detect patterns and motion. Damage to this area, therefore, can lead to complete blindness - even in a person with healthy eyes.
Often, however, whatever damages the visual cortex (usually a stroke) damages only a part. This condition, called a scotoma, creates a large "hole" in the vision of the affected person where they cannot consciously detect any visual stimuli. In addition, they are often unable to accurately reproduce a drawing, leaving out the section the lies in the affected region of their vision.
When shown a stimulus in the affected region of their vision, patients will deny that they see anything. However, when pressed just to make a guess as to where the stimulus came from, they can often identify the direction of the source with an accuracy far better than chance. Some people can even identify whether the stimulus was an "x" or an "o", despite not consciously knowing either way. Psychologists were quick to recognize the huge implications of this - apparently, visual processing occurred in places other than the visual cortex.
In addition, a research team led by Prof. Tadashi Isa and Dr. Masatoshi Yoshida of the National Institute for Physiological Sciences, Japan, demonstrated that monkeys with damage to their visual cortex can be trained to recognize stimuli in their blind spots. The team trained monkeys to look at a visual stimulus at all points in their visual field. At first, the monkeys were mostly unable to track any stimulus in the affected region of their vision, but after 2-3 months they were tracking visual stimuli in all areas of their vision with the same accuracy. This result suggests that visual information can take pathways around the visual cortex and still provide useful information - something that could perhaps be used for therapeutic purposes in humans.
