Neuronal plasticity of the haptic system

Christoph Braun


To survive in a continuously changing environment either as individual or species, organisms need to adapt. Since environmental changes occur on different time scales ranging from milliseconds to hundreds of centuries, nature provides an arsenal of different mechanisms and strategies of adaptation. Immediate adaptations are necessary in life-threatening situations. Alternatively, changes in climate, food availability, and the appearance of competitors and predators alter an individual’s behaviour, and might, on a longer timescale, even shape organisms across generations. Adaptation of the latter type occurs mainly on an evolutionary basis, which acts on genetic information. In contrast, adaptation referring to changes in individual’s behaviour is realised by learning which is mediated on a neuronal level.
In this chapter, we will focus on learning as a specific capability of adaptation and also on its underlying neuronal mechanisms. In psychology and ethology, learning is described as a change of individuals’ cognition and behaviour due to a previous experience. Learning is reflected in the acquisition of new abilities and is associated with alterations in neuronal connectivity by forming new neuronal networks. The brain’s capacity of rewiring the nervous system according to its history of activation is commonly referred to as neuroplasticity. Neuroplastic changes of connectivity are assumed to persist at least for some period of time, even if inducing factors like effects of training or an altered environment are no longer present.
Unfortunately, the concept of neuroplasticity is still rather vague. So far, there exists no clear definition of a minimum time duration for which the altered connectivity has to persist in order for it to be referred to as being plastic. Usually, changes in neuronal processing that are acquired during at least several weeks of motor skill training or during the experience of an altered environment are referred to as longterm plasticity. By contrast, short-term plasticity relates to immediate but volatile changes in neural connectivity that is induced within hours or even seconds due to different experimental conditions. Yet, there is no clear-cut distinction between short-term plasticity on the one hand and modulation of neuronal activity due to taskswitching on the other.