ABSTRACT

Heritable features evolving during evolutionary time spans are of ultimate advantage for survival and are, without exception, structurally fixed. To cope successfully with the ongoing changes of environmental conditions occurring during the lifespan of individuals, additional mechanisms are required that allow rapid and effective adaptations that are not specified by genetic constraints. In spite of the substantial amount of adaptational capacities, systems must possess sufficient generic stability to allow secure processing. Conceivably, there is a trade-off between modifiability and stability. In contrast to developmental plasticity, adaptations of adult brains do not, in the first place, rely on maturational and growth processes. Specifically, for learning-induced alterations there is a consensus that there is a crucial role for so-called functional plasticity, based on rapid and reversible modifications of synaptic efficacy. However, large-scale amputations have been shown to involve sprouting and outgrowth of afferent connections into neighbouring regions at cortical and subcortical levels (Florence et al., 1998; Jain et al., 2000). Technically, the term “adaptation” is used in a rather neutral sense, i.e. there are no implicit assumptions whether “adaptational changes” might yield a positive or negative outcome. Given this general overview, it appears conceivable that plastic-adaptive capacities of various forms represent a general and ubiquitous cortical feature present in all sensory modalities as well as in higher cortical areas. Before summarizing details and possible deviations from that scheme, some basic properties of cortical plasticity, observable in early sensory areas are briefly discussed.