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Symposia
OCT19 | 9:00 AM
Asymmetries in the human brain: Insights from structural and functional anatomy, and its relation to behavior
Chairs
Brain asymmetry has been observed in vertebrates and invertebrates structurally, functionally, and behaviorally, and can arise through several genetic, epigenetic, or neural mechanisms. It is considered an evolutionary advantage: a functionally asymmetric brain prevents conflicts between both hemispheres, performs a parallel processing of tasks, and avoids duplication of functions, increasing neural capacity. The more lateralized a function, the better it works, although extreme lateralizations are not good: the necessary degree of lateralization depends on the task. This symposium will address structural asymmetries in the human brain, and it will focus on regions involved in language processing, a strongly lateralized cognitive domain. Then, evidence from a behavioral paradigm which measures language lateralization will be presented. This original paradigm has the advantage of being transcultural, and its robust results have been replicated in speakers of different tongues. Finally, the clinical use of this paradigm as a presurgical brain mapping tool measuring language lateralization will be discussed.
Speakers
Anatomical substrates of functional hemisphere asymmetries
Mariana Bendersky
Universidad de Buenos Aires- ENyS
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Brain asymmetry has been observed in vertebrates and invertebrates structurally, functionally, and behaviorally, and can arise through several genetic, epigenetic, or neural mechanisms. It is considered an evolutionary advantage: a functionally asymmetric brain prevents conflicts between both hemispheres, performs a parallel processing of tasks, and avoids duplication of functions, increasing neural capacity. The more lateralized a function, the better it works, although extreme lateralizations are not good: the necessary degree of lateralization depends on the task. This symposium will address structural asymmetries in the human brain, and it will focus on regions involved in language processing, a strongly lateralized cognitive domain. Then, evidence from a behavioral paradigm which measures language lateralization will be presented. This original paradigm has the advantage of being transcultural, and its robust results have been replicated in speakers of different tongues. Finally, the clinical use of this paradigm as a presurgical brain mapping tool measuring language lateralization will be discussed.
The translingual lexical decision task: a measure of language lateralization
Markus Hausmann
University of Durham, UK
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The visual half-field technique is a reliable neuropsychological measurement of language lateralization, typically showing higher accuracy and faster correct responses for linguistic stimuli presented in the right visual field (RVF) than left visual field (LVF). The RVF advantage corresponds to the well-known dominance of the left hemisphere (LH) in processing language(s). However, neuroscientists around the globe use different variations of the visual half-field paradigm, preventing direct comparisons. The current study used a word/non-word visual half- field paradigm with translingual stimuli. In total, 496 participants from seven European countries were assessed: Belgium (64), England (49), Germany (85), Italy (34), The Netherlands (87), Norway (51), and Switzerland (126). All language groups revealed a significant RVF/LH advantage in accuracy and reaction times that accounted for up to 26.1% of the total variance in performance. We found some variation in the degree of the RVF/LH advantage across language groups, accounting for a maximum of 3.7% of the total variance in performance. The RVF/LH advantage did not differ between subsamples speaking English, French or German as first or second languages or between monolingual and early/ late bi/multilinguals. The translingual lexical decision task (TLDT) is a simple but reliable measurement of language lateralization that can be applied clinically and experimentally across linguistic and national boundaries.
Lateralization of lexical processing in refractory temporal epilepsy
Lucia Alba-Ferrara
ENyS - CONICET
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In temporal lobe epilepsy (TLE) language areas could be functionally affected. This research studied the lateralization of lexical processing in refractory TLE in a non-invasive manner that overcomes the idiom barrier. This paradigm called Lexical Decision Task (LDT) applies the half visual field technique. Patients with left TLE (LTLE) (N=12), right TLE (RTLE) (N=15) and controls (N=17) were evaluated using LDT. An ANCOVA analysis was performed, with the left, right and baseline stimulus side (SS) as a within subjects, and group as a between subject´s variable. A main effect of the SS was found. Pairwise comparisons show that baseline improved performance, right SS resulted in an intermediate performance and the left SS diminished performance. A main group effect was found (F(2.71)=10,P<0.05). Comparisons in pairs indicate that the controls outperformed both TLE groups. LTLE and RTLE did not differ from each other. An interaction between group and SS was found. Post hoc t tests showed between the SS of each group showed that controls benefit with right SS compared to left. Such advantage was not found in the LTLE group. The results validate a lateralization of the lexical processing, indicating the effectiveness of the LDT. The interaction between SS and LTLE might indicate diminished lateralization of lexical processing in LTLE, being understood as a sign of a reorganization of the lexical function by epileptogenic crises. Further data is being collected.