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Abstract:
Abstract: Neuromagnetic fields to speech were pre-surgically
modeled as single equivalent current dipoles (ECDs) and compared to
intraoperative speech and naming sites in eight neurosurgery
patients (6 right handed 2 left handed) undergoing tumor resection.
The MEG neuromagnetic field sources elicited by vowel stimuli /a/
and /u/ during a passive listening task were co-registered onto
MRIs to form magnetic source images (MSI). Hemispheric asymmetry
was calculated by summing the number of sequential ECD sources in
the left (L) and right (R) late fields (150-400 ms) and computing
the laterality index [(LI) = (L-R)/(L+R)]. The MSI locations were
consistent with intraoperative electrocortical stimulation mapping
(ESM) speech and naming sites in four right-handed patients who
showed a positive LI, or leftward asymmetry. In four other patients
ESM sites were not found during surgery. The left-handed patients,
who were confirmed right hemisphere language dominant by
intracarotid amobarbital test, and had tumors in the right
hemisphere, showed negative MEG LI, or rightward asymmetry. In
conclusion: 1) Sequential, single ECD asymmetry in the late
neuromagnetic field to speech is consistent with intracarotid
amobarbital tests of hemispheric language dominance; and 2)
Presurgical neuromagnetic field sources co-localize with ESM sites
for speech and naming.
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