Somatosensory evoked magnetic fields elicited by dorsal penile, posterior tibial and median nerve stimulation

The aim of this study is to localize the primary sensory cortex of urogenital organs in the human brain. Using a newly developed MRI-linked magnetoencephalography system, we measured somatosensory evoked magnetic fields (SEFs) for unilateral stimuli on the dorsal penile nerve (DPN), posterior tibial nerve (PTN) and median nerve (MN). In five healthy male subjects, SEFs were clearly observed. Peak latencty of the first cortical components were 63.8±9.2 ms for DPN, 39.8±3.0 ms for PTN and 20.7±0.7 ms for MN stimuli. Peak amplitude of the first cortical components were 63.1±10.8 fT for DPN, 160.2±50.1 fT for PTN and 335.2±70.3 fT for MN stimuli. Isofield map for the peak latencies indicated a single dipolar pattern for DPN as well as for PTN and MN stimuli. Using a single current dipole model, all SEF sources were localized on the contralateral central sulcus to the stimuli, indicating the primary sensory cortex. The DPN sources were localized on the interhemispheric surfaces, corresponding to previous speculations by direct cerebral stimulation. This non-invasive SEF technique promises further brain functional mapping for the urogenital organs.