Changes in brain gray matter due to repetitive painful stimulation.

Using functional imaging, we recently investigated how repeated painful stimulation over several days is processed, perceived and modulated in the healthy human brain. Considering that activation-dependent brain plasticity in humans on a structural level has already been demonstrated in adults, we were interested in whether repeated painful stimulation may lead to structural changes of the brain. 14 healthy subjects were stimulated daily with a 20 min pain paradigm for 8 consecutive days, using structural MRI performed on days 1, 8, 22 and again after 1 year. Using voxel based morphometry, we are able to show that repeated painful stimulation resulted in a substantial increase of gray matter in pain transmitting areas, including mid-cingulate and somatosensory cortex. These changes are stimulation dependent, i.e. they recede after the regular nociceptive input is stopped. This data raises some interesting questions regarding structural plasticity of the brain concerning the experience of both acute and chronic pain.