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Auditory evoked neuromagnetic response in cerebrovascular diseases: a preliminary study
K Toyoda1, S Ibayashi, T Yamamoto
1Second Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Objectives:
Magnetoencephalography (MEG) measures aspects of the function of the auditory cortex of the human brain with high spatial resolution. The objective was to determine whether MEG also accurately identifies the auditory cortex of the brain in patients with ischaemic stroke.
Methods:
The auditory evoked magnetic field (AEF) was examined after stimuli of 1 kHz tone bursts in 24 stroke patients without apparent infarcts in the auditory cortex, and compared the topography of sources of 50 ms (P50m) and 100 ms latency deflections (N100m), the most prominent components of middle and long latency AEFs, with that of 12 normal subjects. Cerebral haemodynamics in and around the auditory cortex were evaluated using PET.
Results:
In nine of 24 stroke patients, the accurate magnetic sources of P50m or N100m were not identified. The distribution of P50m sources varied more widely than N100m. Eight of these nine patients had severe stenotic lesions in the carotid or middle cerebral arterial trunks. Patients with abnormal P50m responses had decreased supratemporal and hemispheric blood flow compared with patients with normal P50m responses.
Conclusions:
These findings suggest that large vessel disease with disturbed cerebral haemodynamics in and near the auditory cortex tend to affect AEFs, especially the middle latency components. This is the first combined study of MEG and PET to show a significant correlation between AEF responses in stroke patients and their PET indices.