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[The clinical study of somatosensory evoked magnetic fields in patients with acute cerebral infarction by magnetoencephalography].

OBJECTIVE
To investigate the characteristics of somatosensory evoked magnetic fields (SEF) in patients with acute cerebral infarction by magnetoencephalgraphy (MEG).


METHODS
SEFs were recorded from 17 patients with acute cerebral infarction and 18 healthy volunteers using 306-channel whole-head MEG. The electric stimuli were presented with interstimulus intervals of 0.5 s. The peaks of SEF were estimated by equivalent current dipole (ECD), which were superimposed on MRI.


RESULTS
M20 was the most elemental components of SEF in all subjects, originating from the area close to the "hand area" of the primary somatosensory cortex. There appeared several abnormal SEF parameters in the patient group: (1) the value of interhemispheric difference of the M20 positions was (8 +/- 4) mm in the normal group and (11 +/- 3) mm in the patient group (P < 0.01); (2) the peak latency of M20 responses in the healthy group was (20.7 +/- 1.1) ms, significantly shorter than those in both the unaffected hemisphere and affected hemisphere in the patient group, (21.8 +/- 1.2) ms and (23.6 +/- 1.9) ms, (both P < 0.01); (3) the strength of ECD in the affected hemisphere was (17 +/- 10) nAm, significantly smaller than that in the unaffected hemisphere, (26 +/- 10) nAm (P < 0.01).


CONCLUSION
Latent cortical impairment may be evaluated by MEG with higher spatial and temporal resolution. MEG provides objective and sensitive indexes to evaluate the function of somatosensory cortex in patients with acute cerebral infarction.