Improved characterization of human somatosensory cortex using simultaneous vibro-tactile stimulation of multiple digits

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Tactile sensation is encoded in the primary somatosensory cortex in topographical maps accordingly to the body surface. This topographical representation can be modified as the result of training and experience. This brain plasticity results from newly expressed or strengthened synaptic connections. The effect can be measured in humans noninvasively using magnetoencephalography (MEG) as increased activation or larger activated area on the cortical surface. Brain plasticity is an important factor for successful recovery from a stroke. We shall develop a new method for objectively monitoring of plastic reorganization in somatosensory cortex by measuring the size of the somatotopic hand area as indicated by the distance between finger representation. The finger representation in human somatosensory cortex can be localized with the MEG. The distance between fingers can be obtained from multiple MEG recordings with stimulating one finger after the other. However, head movements between recordings cause too large errors. With our new procedure we will stimulate multiple fingers at the same time with vibrations of different rate. We shall record brain activity at the frequencies of the vibration stimuli and can separate the responses from each finger. Those responses will be localized. The distance between finger representation can be measured with high precision because all recordings were done at the same time and were affected by head movements equally. We shall investigate the possible interactions between finger localizations and effects of attention in order to optimize the procedure. In summary we shall develop a highly precise method for measuring distances between body part representations in the cortex. Changes over time in the obtained distance measure indicate plastic reorganisation e.g. as the effect of therapeutic intervention.