Neuroimaging methods vs. lesion studies FOCUSING ON LANGUAGE

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1 Neuroimaging methods vs. lesion studies FOCUSING ON LANGUAGE

2 Pioneers in lesion studies Their postmortem examination provided the basis for the linkage of the left hemisphere with language C. Wernicke P. Broca

3 Studying cognitive functions of the brain: language Lesion studies Neuroimaging methods Offered insight into: Locus & differentiality of mental operations Causation of abnormalities that affect cognition Multifaceted phenomenon: language postmortem patients The sophistication of technology rediscovered neurology: Lesion studies findings may be corroborated in spite of time lapse ( Broca was correct) living experiment participants & patients

4 Before neuroimaging methods Difficult to localise lesions Scientists drew conclusions based on autopsy information or on inferences from co-occurring symptoms Lesions do not manifest themselves in a stable manner across patients, despite symptom similarity

5 Neuroimaging methods Computed Tomography (CT): emits x-ray radiation and measures the density of tissues by producing cross-sectional images of the body Electroencephalography (EEG): measures the electrical signals of the brain & demonstrates activity in different behavioural states Event-Related Potential (ERP): provides a precise temporal measure of a neural activity (stimulus response) Magnetoencephalography (MEG): depicts the source of signal activation within small magnetic fields

6 Prominent neuroimaging methods Positron Emission Tomography (PET): a) introduces radioactive tracers in the bloodstream b) measures local variation in cerebral blood flow that reveal heightened neural activity functional Magnetic Resonance Imaging (fmri): a) does not introduce radioactive tracers b) employs increased blood flow in certain brain areas c) creates a map of changes in regional blood flow following local neuronal activity d) emits magnetic signal experimentally manipulated

7 Despite their limitations, PET & fmri penetrate deeper and beyond and obviously damaged region have elucidated language functioning more than lesion studies exempli gratia: Broca s area is not entirely responsible for Broca s aphasia damaged insula in aphasic patients Broca s area has been implicated in speech processing (both in aphasic patients & healthy subjects) Temporo-parietal region: a) responsible for phonological coding in spoken language; b) associated with aphasic symptoms Wernicke s area does not cause Wernicke s aphasia syndrome the white matter or the surrounding temporal cortex

8 However, PET and fmri studies have not frequently shown expected activation following specific tasks co-activation of nearby areas may complement each other in studies which use specific tasks, seeking to identify the activation loci of cognitive functions (e.g. speech production, speech processing, working memory, phonological processing, grammar & syntax, speech analysis)

9 Interesting findings may emerge If a foreign language is learned at an early age, there is an overlap within Broca s area concerning the regions engaged in the acquisition of both native and foreign language If a foreign language is learned later in life, different brain areas are involved than those involved in native language learning Wernicke s area is not age sensitive with respect to the age of language acquisition

10 Language acquisition & sensory impairments Tactile reading activates the posterior left temporal region other areas involved in lexical or conceptual access may be involved The focus on signing hands and facial expressions may activate an area similar to spoken language locus, apart from the ventral temporal cortex Right lateralisation of auditory language processing may also project onto sign language processing

11 Compensatory strategy case Objective: locus of semantic processing Focus: semantic activations in patients with semantic dementia all presented with anterior temporal lobe atrophy Results: bilateral activation, right hemisphere more than controls Contradiction: right anterior temporal lobe cannot entirely support semantic processing compensatory strategy??

12 Invaluable contribution Deeper and more precise understanding of the mapping and functioning of complex neural processes Revelation of different missions accomplished by regions traditionally correlated with specific functions, as substantiated by lesion studies Localisation of the activation following mental tasks and justification of emerging picture Neuroimaging findings careful replication before verifying validity of implications; depict more accurately brain specialization

13 Bibliography Cabeza, R., & Nyberg, L. (2000). Imaging Cognition II: An Empirical Review of 275 PET and fmri Studies. Journal of Cognitive Neuroscience, 12(1), Campbell, R., Calvert, G., & MacSweeney, M. (in press). Brain Bases for Seeing Speech: fmri Studies of Speechreading. Eysenck, M.W., & Keane, M. (2000). Cognitive Psychology: A Student s Handbook (4 th edition). Hove, UK: Psychology Press. Hickok, G., Bellugi, U., & Klima, E.S. (1998). What s Right about the Neural Organisation of Sign Language? A Perspective on Recent Neuroimaging Results. Trends in Cognitive Sciences, 2(12), Gazzaniga, M.S., Ivry, R.B., & Mangun, G.R. (1998). Cognitive Neuroscience: The Biology of the Mind. New York: W.W. Norton & Company Inc. Martin, G.N. (in press). Human Neuropsychology. Prentice Hall Harvester Wheatsheaf. Mummery, C.J., Ashburner, J., Scott, S.K., & Wise, R.J.S. (1999). Functional Neuroimaging of Speech Perception in Six Normal and Two Aphasic Subjects. Journal of the Acoustical Society of America, 106(1), Mummery, C.J., Patterson, K., Wise, R.J.S., Vandenbergh, R., Price, C.J., & Hodges, J.R. (1999). Disputed Temporal Lobe Connections in Semantic Dementia. Brain, 122, Neville, H.J., Bavelier, D., Corina, D., Rauschecker, J., Karni, A., Lalwani, A., Braun, A., Clark, V., Jezzard, P., & Turner, R. (1998). Cerebral Organisation for Language in Deaf and Hearing Subjects: Biological Constraints and Effects of Experience. Proceedings of the National Academy of Sciences USA (Colloquium Paper), 95, Petersen, S.E., Fox, P.T., Snyder, A.Z., & Raichle, M.E. (1990). Activation of Extrastriate and Frontal Cortical Areas by Visual Words and Word-Like Stimuli. Science, 249, Scott, S.K., Blank, C.C., Rosen, S., & Wise, R.J.S. (2000). Identification of a Pathway for Intelligible Speech in the Left Temporal Lobe. Brain, 123, Signoret, J.L., Castaigne, P., Lhermitte, F., Abelanet, R., & Lavorel, P. (1984). Rediscovery of Leborgne s Brain: Anatomical Description with CT Scan. Brain and Language, 22,

14 Thank you for your attention EVANGELIA TIGKA, MSC 1 ST TECHNICAL/VOCATIONAL SPECIAL NEEDS SECONDARY SCHOOL O F NEA IONIA M A G NESIA E_TIGKA@YAHOO.CO.UK