Changes in Cortical Mapping over a period of days following increased or decreased sensory or motor activity probably involve modulation of the effectiveness of initially weak excitatory synapses. After loss of normal sensory input (eg through amputation or peripheral nerve section) cortical neurons that previously responded to that input might undergo “denervation by hyperspersensitivity” – up regulation of the strength of their responses to any remaining weak excitatory input.
A great many pathways allow for feedback from “higher” to “lower” sensory areas in the brain, and this extensive network may come under control of inputs from other sensory areas enabling them to activate regions of cortex normally used for a different sensory system.
Since multi model sensory processing centers already have input from several senses, it is not so surprising that loss of input from one sense should lead to enhanced response to remaining sensory inputs, perhaps through modulation of the strength of synapse from association connections.
This is a hot topic in neuroscience research and we hope answers about each form of cortical plasticity will be revealed in the near future.