Our research aims at the identification of the relationship between perceptual changes in the tactile domain and cortical reorganization in the somatosensory cortex of human healthy subjects and stroke patients through specific, but passive stimulation protocols on the one hand, and through learning in everyday life on the other hand. By combining psychophysical tests and non-invasive imaging techniques we study the interrelationship between perceptual (i.e. behavioural) and cortical changes.
In previous work we used two different types of passive stimulation protocols ─ coactivation (1-3) and rTMS (4,5) ─ to modulate somatosensory perception. Both approaches have in common a reliance on the principles of Hebbian learning (6), according to which simultaneity of inputs is a prerequisite to drive plastic changes. For both coactivation and rTMS we found that perceptual and plastic cortical changes can be evoked solely by varying the inputs, without invoking attention, reinforcement or behavioural information. This shows that even unattended passive stimulation can induce cortical plasticity and behavioural improvements. Strikingly, our results are in good agreement with literature on learning-induced plasticity suggesting that passive stimulation protocols, combined with the right set of stimulation parameters, initiate learning-like network reorganization.
A second part of our research was devoted to exploring the relationship between behavioural and cortical changes under various conditions, namely ‘natural’ motor learning (7), learning-dependent increases in proprioceptive feedback (8), and reward-related discrimination learning (9,10). These findings from scenarios close to everyday life suggest that complementary forms of learning induce complementary changes in behaviour and cortical reorganization.
One key finding of our research is that both artificially-induced plasticity and ‘natural’ learning share a close relationship with cortical reorganization and behaviour, suggesting a common mechanism where gains in performance go hand in hand with the expansion of cortical representations, possibly through recruitment of processing resources.
Pleger, B., Dinse, H. R., Ragert, P., Schwenkreis, P., Malin, J. P., and Tegenthoff, M. (2001). Shifts in cortical representations predict human discrimination improvement. Proc Natl Acad Sci U S A 98, 12255-12260.
Pleger, B., Foerster, A.-F., Ragert, P., Dinse, H. R., Schwenkreis, P., Malin, J. P., Nicolas, V., and Tegenthoff, M. (2003). Functional imaging of perceptual learning in human primary and secondary somatosensory cortex. Neuron 40, 643-653.
Dinse, H. R., Ragert, P., Pleger, B., Schwenkreis, P., and Tegenthoff, M. (2003). Pharmacological modulation of perceptual learning and associated cortical reorganization. Science 301, 91-94.
Tegenthoff, M., Ragert, P., Pleger, B., Schwenkreis, P., Foerster, A.-F., Nicolas, V., and Dinse, H. R. (2005). Persistent improvement of tactile discrimination performance and enlargement of cortical somatosensory maps after 5 Hz rTMS. PLoS Biol 3, e362.
Pleger, B., Blankenburg, F., Bestmann, S., Ruff, C. C., Wiech, K., Stephan, K. E., Friston, K. J., and Dolan, R. J. (2006). Repetitive transcranial magnetic stimulation-induced changes in sensorimotor coupling parallel improvements of somatosensation in humans. J Neurosci 26, 1945-1952.
Hebb, D. O. (1949). The organization of behaviour (New York, Wiley and Sons).
Pleger, B., Schwenkreis, P., Grunberg, C., Malin, J. P., and Tegenthoff, M. (2004). Fluoxetine facilitates use-dependent excitability of human primary motor cortex. Clin Neurophysiol 115, 2157-2163.
Pleger, B., Schwenkreis, P., Dinse, H. R., Ragert, P., Hoffken, O., Malin, J. P., and Tegenthoff, M. (2003). Pharmacological suppression of plastic changes in human primary somatosensory cortex after motor learning. Exp Brain Res 148, 525-532.
Pleger, B., Blankenburg, F., Ruff, C. C., Driver, J., and Dolan, R. J. (2008). Reward facilitates tactile judgments and modulates hemodynamic responses in human primary somatosensory cortex. J Neurosci 28, 8161-8168.
Pleger, B., Ruff, C. C., Blankenburg, F., Kloppel, S., Driver, J., and Dolan, R. J. (2009). Influence of dopaminergically mediated reward on somatosensory decision-making. PLoS Biol 7, e1000164.