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Abstract

The mammalian neocortex has an amazing capacity for plastic remodelling. This is the basis for lifelong adaptation to alterations in sensory environments and behavioural demands.
Hebbian mechanisms seem to play a key role in use- and input-dependent cortical plasticity.
We used functional MRI together with a spatial discrimination task to investigate in detail
the effects of synchronous and asynchronous tactile coactivation on cortical organisation in
the human primary somatosensory cortex (SI) and its behavioural consequences. Coactivation,
which is the Hebbian-like associative pairing of tactile stimulation, was applied for three
hours to the distal phalanges of index, middle and ring ngers of the right hand either synchronously
or asynchronously. Strengthening previous ndings we show here that somatosensory
cortical representations in SI for synchronously coactivated ngers move closer together
resulting in an integration of those representations. On the other hand, cortical representations
for asynchronously coactivated ngers become segregated and move further apart. This coincides
with a reduced number of mislocalisations between ngers that have been coactivated
asynchronously and an increased number of mislocalisations between ngers that have been
coactivated synchronously. These results were reversible within one week after stimulation.
Thus, not only synchronous but also asynchronous coupling of passive tactile stimulation is
able to induce short-term cortical reorganisation that is associated with functionally relevant
changes in the perceptual and behavioural capacities of an individual without active training or
attention directed to the stimuli.