DEGREE OF LANGUAGE LATERALIZATION DETERMINES

SUSCEPTIBILITY TO UNILATERAL BRAIN LESIONS

(Knecht et al., 2002)

Ana Cecilia UlloaApril 03, 2012

Language Left-hemisphere dominant

Plasticity Undamaged hemisphere or undamaged

parts of the injured hemisphere take over language representation

Thulborn, Carpenter, & Just (1999), Am Heart J, 30, 749-54

Language Lateralization Individual differences in language

organization in the brain could make some people more able to recover function after unilateral brain damage

Graded continuum from left hemispheric to right hemispheric language lateralization

Some individuals possess weak lateralization or bihemispheric activation

Studies done in epilepsy patientsCannot be generalized

Abnormal brains due to medication-resistant epilepsy Bilaterality of language may be due to

disorganization resulting from longstanding lesion.

Previous Research

Does bihemispheric representation of language occur in healthy subjects? Does it offer resistance to language deficits after unilateral brain lesion?

Methods 20 subjects from a cohort of 324 healthy

volunteers

Functional transcranial Doppler sonogropahy (fTCD)

fMRI

TMS

fMRI Results

Picture-Word Verification Task

Measured reaction time (RT) after TMS on either side of the brain

TMS over areas CP5 or CP6CP 5: Wernicke’s AreaCP 6: counterpart on right hemisphere

30 minute rest before each administration

Results

Subjects with left language dominance were significantly slower than subjects with right language dominance after TMS over CP5

Results

Subjects with right language dominance were significantly slower than subjects with left language dominance after TMS over CP6

Discussion &Implications After TMS on subjects lacking marked

hemispheric lateralization, subjects showed almost no slowing of verbal processing

Individuals with a more bilateral language representation will remain relatively unaffected in verbal functioning after stroke to either the right or left hemisphere

Pros and ConsPros Simple, straightforward Detailed explanations for methods and

results

Cons Not much background information Not much discussion of limitations,

confounds, or future research

Future Directions Finding ways in which we can apply this

knowledge of hemispheric lateralization as a way of treating stroke patients that suffer language deficits

Crosson et al. (2009), Brain Lang, 111(2), 73-85.

ReferencesCrosson, B., Moore, A. B., McGregor, K. M., Chang, Y. L., Benjamin, M.,

Gopinath, K., Sherod, M. E., Wierenga, C. E., Peck, K. K., Briggs, R. W., Rothi, L. J. G., & White, K. D. Regional changes in word-production laterallity after a naming treatment designed to produce a rightward shift in frontal activity.B Brain and Language, 111, 73-85.

Knecht, S., Floel, A., Drager, B., Breitenstein, C., Sommer, J., Henningsen, H., Ringelstein, E. B., & Pascual-Leone, A. (2002). Degree of language lateralization determines susceptibility to unilateral brain lesions. Nature Neuroscience, 5, 695-699.

Thulborn, K. R., Carpenter, P. A., & Just, M. A. (1999). Plasticity of language-related brain function during recovery from stroke. Stroke, 30, 749-754.