There is a lack of neurological models of reduced local connectivity without neural loss. However, such models can be easily obtained by an impoverished environment.53 For example, breeding rats without social interactions induces cortical shrinkage. This does not correspond to neuronal loss, but to a reduction in neuropiles and synapses.51-55 The same phenomenon of related gray matter adaptation to training is likely to also occur in man. Indeed, the size of the posterior hippocampus has been showed to be increased in London taxi drivers, probably because of job-related overuse.56-57 We recently observed in normal subjects that the more they spontaneously used their memory network, the more gray matter they had in the stimulated regions. Thus, gray matter volume can adapt, depending on practice (Foucher et al, unpublished material).
