Effects of age and expertise on tactile perception: Investigation of underlying neural mechanisms using transcranial direct current stimulation

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Our overarching goal is to examine with transcranial direct current stimulation (tDCS) how age and expertise affect the mutual balance between excitation and inhibition within the somatosensory cortex. Tactile perception contributes importantly to manual dexterity and therefore to the mastering of many activities of daily living. Impairment of tactile perception in older age often results in loss of independence. However, age-related decline in tactile performance can be delayed or prevented by training and acquisition of tactile expertise in middle adulthood, for example on the job. Tactile aging is accompanies by alterations on the neural level which can be observed as changes in early (somatosensory) and late (cognitive) ERP components. Interestingly also these changes in ERP components seem to be reversible of delayed by tactile expertise. Supposedly, an altered balance between local excitation and inhibition play an important role in these processes. Although expertise and aging have been suggested to have different effects on inhibition and excitation during perception and learning, namely a focal increase of exciation with expertise and a decrease of lateral inhibition with aging, is seems that these different effects on the synaptic level have similar effects on the EEG measures. This question we want to further examine with this follow-up study to the Bremen Hand Study @ Jacobs. For this purpose we will use tDCS to modulate intracortical exciation and inhibition within the somatosensory cortex. To further investigate how sensory plasticity differs in experts and older adults we also aim to combine a tactile training paradigm with tDCS. Based on the assumption that effects of expertise and age on the balance between excitation and inhibition are basically different we expect on the electrophysiological level (measured with EEG) as well as on the behavioral level (tactile discrimination and learning progress) an interaction between the type of modulation (excitatory versus inhibitory) with the factors age and expertise. Particularly in older adults, inhibitory (cathodal) tDCS should counteract the hypothesized unspecific increase of excitation und improve tactile performance. Young adults and experts should reveal less effects on the behavioral level even with a reduced but still specific activation. Opposite effects are expected of anodal (excitatory) tDCS. For facilitation of tactile learning we hypothesize a comparable dissociation.