Development and plasticity of cortical areas and networks

The development of cortical layers, areas and networks is mediated by a com bination of factors that are present in the cortex and are influenced by th alamic input. Electrical activity of thalamocortical afferents has a progre ssive role in shaping cortex. For early thalamic innervation and patterning , the presence of activity might be sufficient; for features that develop l ater, such as intracortical networks that mediate emergent responses of cor tex, the spatiotemporal pattern of activity often has an instructive role. Experiments that route projections from the retina to the auditory pathway alter the pattern of activity in auditory thalamocortical afferents at a ve ry early stage and reveal the progressive influence of activity on cortical development. Thus, cortical features such as layers and thalamocortical in nervation are unaffected, whereas features that develop later, such as intr acortical connections, are affected significantly. Surprisingly. the behavi oural role of 'rewired' cortex is also influenced profoundly indicating the importance of patterned activity for this key aspect of cortical function.