Background
It has been proposed that proprioceptive input can modulate neural excitability in both primary motor cortices (M1) simultaneously, although direct evidence for this is still lacking. Previous studies showed that proprioceptive accuracy of one hand is reduced after the application of one-Hz repetitive transcranial magnetic stimulation (rTMS) for 15 minutes over the contralateral somatosensory cortex. The aim of this study was to investigate the effect of rTMSinduced central proprioceptive deafferentation to excitability of both M1 as reflected in ipsilateral and contralateral motor evoked potentials (MEP).
Methods: MEPs of both abductor pollicis bravis (APB) muscles were recorded using single-pulse TMS over right M1 in seven healthy subjects. Immediately after one-Hz rTMS was applied for 15 minutes over the right somatosensory cortex, the MEP measurement was repeated. The proprioceptive function of the left thumb was assessed, before and after rTMS, using a position-matching task.
Results: There was an increase in ipsilateral MEP after the rTMS: whereas no MEPs were recorded on the ipsilateral hand before the rTMS, MEPs were recorded in both ipsilateral and contralateral hand in three of seven subjects. At the same time, the mean log amplitude was reduced and the mean latency was prolonged in the contralateral MEP.
Conclusions: rTMS-induced central proprioceptive deafferentation reduces the MEP generation in the contralateral hand, and fascilitates that in the ipsilateral hand. A further study with a larger sample seems warranted to confirm this finding and to elucidate the neurophysiology underlying it.

Visual Segmentation is an important function of our visual system as it eventually enables us to form correct representation of the outer world objects or events. We used fMRI in search for cortical activity related to the perception of visual scene segmented by contrast of three visual cues in human beings. The stimuli used were three kinds of flickering random dot checkerboard: defined by 1)texture orientation contrast 2)color contrast 3)motion direction contrast. Using these stimuli, 9 healthy subjects were functionally scanned with 1.5T MR machine while they fixated their eyes and passively viewed the stimuli presented. In experiment 1, these three conditions sequentially appeared from a flickering random dot field, while in experiment2 they appeared from a dark screen with fixation point in the center. Even though all three checkerboard conditions were the same in both experiments, the overall activation patterns were quite different. The extrastriate areas, especially V4, and Parietal lobe were activated cue-invariantly in the first experiment, while only V1 was activated cue-invariantly in the second experiment. To investigate the effect of the flickering random dot field, experiment3 was carried out with 4 of the ex-subjects and it showed activation of V1 and deactivation of extrastriate area including MT area for the flickering random dot field perception. As flickering effect might have removed the V1 activation in experiment1 while comparing checkerboard conditions with flickering random dot field condition, it can explain the absence of V1 activation in experiment1, still it cannot explain the absence of V4 activation or Parietal lobe activation in experiment2. As V1 has been localized for boundary perception and V4 for shape perception and parietal lobe for binding different visual attributes, activation of these areas can be interpreted as such. However, the differences in the results of experiment1 and experiment2 suggest that differences of the start line in perceptual flow can activate visual cortices differentially.

Basic concept of functional magnetic resonance imaging(fMRI) is the detection of changing magnetic field during the activation of a neural network. The change of magnetic field depends on the hemoglobin oxidation-reduction ratio which corresponds to the degree of neural activation and following blood supply. Repeated execution of certain task and subsequent fast MRI scanning represent neuronal activation of responsible foci for the task. As it has a siginificant role in functional neuroimaging, fMRI is currently applied in many filed of brain research, particularly on the evaluation of brain function and structure. fMRI is particularly useful in the clinical field of neurodegenerative disease including dementia, cerebrovascular disease, and epilepsy.