Reading Exercise 2
How the brain reorganizes itself
The work that Tim Pons and his colleagues published last week is basic research into the portion of the brain, the cortex, that one scientist says is ‘responsible for all the interesting things we do’. The cortex is a layer between two and five millimetres thick that covers the brain and each area of the cortex has a different function. The area Pons and his colleagues are interested in receives ‘somatic’ sensation, in other words, information about touch, position, heat, cold and pain. The somatic sensory cortex can be represented as a topographic map, sub-divided into specific regions that receive nerve signals from specific areas of the body.
About twelve years before Pons and his colleagues carried out their experiments, the Macaque monkeys being studied had the nerves cut which carried signals from the fingers, palm, upper limb, neck and the back of the head. The regions bordering this part of the somatic sensory cortex receive signals from the face and trunk*.
Under anaesthetic Pons and his colleagues inserted electrodes into the region of the cortex where the nerves had been cut and recorded the neuronal** response. They found to their surprise that the whole region, covering an area of between ten and fourteen square millimetres, now responded to stimulation of the lower face. Previously, scientists had thought that the cortex of adult animals could not reorganize itself over an area greater than one or two millimetres.
*trunk = the main part of the body
**neuronal = areas of the nerves