OBJECTIVE: In 90% of normal subjects, the left hemisphere is dominant for l
anguage function. We investigated whether congenital lesions of the left pe
risylvian regions altered cortical language representation in right-handed
individuals.
METHODS: Using functional magnetic resonance imaging, we studied language h
emispheric dominance in five right-handed adult patients with congenitally
acquired arteriovenous malformations (AVMs) originating from left hemispher
ic cortical language regions. The AVMs had not caused neurological symptoms
during early development, but patients presented as adults with migraine,
seizure, or minor hemorrhage. Results obtained from the AVM patients were c
ontrasted to those from right-handed brain-injured stroke patients recoveri
ng from aphasia and to those from right-handed normal subjects.
RESULTS: During silent picture naming and verb generation tasks, cortical l
anguage networks lateralized primarily to the right hemisphere in the AVM g
roup, compared with the left hemisphere in the normal group. This right hem
isphere-shifted language network in the AVM group exceeded the shifts towar
d right hemispheric dominance found in the stroke group.
CONCLUSION: Patients with AVMs affecting the left perisylvian regions recru
ited the right hemisphere into language processing networks during early de
velopment, presumably in response to congenitally aberrant circulation. Thi
s early right hemisphere recruitment in the AVM patients exceeded the simil
ar process in the brains of stroke patients whose left cortical language ne
tworks were damaged in adulthood. Our data provide evidence of effective pl
asticity in the developing human brain compared with the mature brain respo
nse to injury. Knowledge of cortical language representation should assist
presurgical planning in patients with developmental anomalies affecting app
arently language-dominant brain regions.