In subjects who responded well to the training, the EEG (Electroencephalography) revealed characteristic changes in brain activity, more specifically in the alpha waves.
These alpha waves show, among other things, how effectively the brain exploits the sensory information needed for learning.
"An exciting question now is to what extent the alpha activity can be deliberately influenced with biofeedback," said Hubert Dinse from the Neural Plasticity Lab of the Ruhr-Universitat Bochum, who led the study.
"This could have enormous implications for therapy after brain injury or, quite generally, for the understanding of learning processes," Dinse was quoted as saying in the Journal of Neuroscience.
The research team from the Ruhr-Universitat, the Humboldt Universitat zu Berlin, Charite-Universitatsmedizin Berlin, and the Max Planck Institute (MPI) for Human Cognitive and Brain Sciences were involved in the findings, according to a statement of Ruhr-Universitat Bochum.
How well we learn depends on genetic aspects, the individual brain anatomy, and, not least, on attention.
"In recent years we have established a procedure with which we trigger learning processes in people that do not require attention," said Dinse.
The researchers were, therefore, able to exclude attention as a factor. They repeatedly stimulated the participants' sense of touch for 30 minutes by electrically stimulating the skin of the hand.
Before and after this passive training, they tested the so-called "two-point discrimination threshold," a measure of the sensitivity of touch.
For this, they applied gentle pressure to the hand with two needles and determined the smallest distance between the needles at which the patient still perceived them as separate stimuli.
On average, the passive training improved the discrimination threshold by 12 percent - but not in all of the 26 participants.
Using EEG, the team studied why some people learned better than others.
The results, therefore, suggest that perception-based learning is highly dependent on how accessible the sensory information is.
The alpha activity, as a marker of constantly changing brain states, modulates this accessibility.