from neurolinguistics of bilingualism to cognitive control

From Neurolinguistics Of Bilingualism to Cognitive Control

Esli Struys, MuRe, CLIN, Vrije Universiteit Brussel

Campus Jette, 27 April 2010

Pag.27-4-2010 2Neurolinguistics, bilingualism and MRI

Broca & Wernicke revisited

-perisylvian language areas

-Broca: IFG -Wernicke: STG

-Broca’s patients under MRI (Dronkers et al., 2007)

-speaking still possible without Broca’s area (Plaza et al., 2009)

-Broca plays critical role in cognitive control (Koechlin & Jubault, 2003)


4 Branches of Neurolinguistics

-Aphasiology & dyslexia (language pathology)

-Localization of language processing (MRI & PET)

-Time course of language processing (EEG & MEG)

-Language Acquisition (L1 & L2) (interdisciplinary)


Studying the bilingual brain

-Norm rather than the exception

-Neuroplasticity (functional & physical changes)

-Education (training effects)


Research questions

1. Does a bilingual speaker represent each language in different areas of the brain?

2. What are the neural correlates of language switching?

3. Which variables affect neural representation of 1. & 2.?

4. Effect on other cognitive skills?


1. question

-aphasiology: selective recovery of bilingual’s language skills

-Broca’s area only for native language?

-fMRI & PET


Late vs. Early bilinguals (Kim et al., 1997)


Parallel lexical activity

-parallel activation of 2 languages in –word production (Kroll et al., 2008)

–word recognition (Van Hell & De Groot, 2008)

-morphological strategies (Portin et al., 2008)


Syntactical activity in L1 & L2

-fundamentally different (Ullman, 2001; Clahsen & Felser, 2006) or integrated?

-cross-linguistic priming effects (Hartsuiker & Pickering, 2008)

-syntactic violations & ambiguities (Kotz et al., 2008)


Convergence Hypothesis (Green, 2003)

-neural differences between native & L2 speakers may disappear as proficiency increases

-proficiency as predictor of neural representation


Then why selective recovery?

-networks involved in representation language components distinct from circuits involved in control of such networks (Green, 2005)

-training effects (proficiency) related to the latter?


The role of development

Comparable

proficiency L1 &

L2 reached

(balanced

bilingualism)

Differential activity for

L2

(i) In same L1-related

prefrontal networks

but engaged to

larger extent

(ii) Areas more

anterior to classical

language areas,

related to cognitive

control

Parallel activity L1 & L2


2. question

DLPFC (BA 9, 46) � during language switching in picture naming (Hernandez et al., 2000)

� highly fluent bil. show increase of DLPFC activity in « bilingual mode »

� neurological « signature » for bilingualism


3. question

-Age of Acquisition (AoA)– Early Bilinguals (Sim)

– Early-late Bilinguals (Seq).

-Manner of Acquisition– Implict vs. Explicit learning (unexplored)

-Proficiency (LEAP-Q, BAT)– Balanced vs. unbalanced


Role of AoA

-late L2 learners recruit more neural resources (Golestani et al., 2006)

-increase in LIFG activity for late learners (Hernandez et al., 2007)

-critical period for grammatical processing?


4. question

-advantages in metalinguistic skills (Cummins, 1978)

-disadvantages in lexical access– Corrected for if vocabulary size is taken into account (Bialystok et al., 2008)

– Compensated for by improved executive functioning?

-similar developmental pattern (Werker et al., 2008)

-delays onset of aging


Our research

-Centre for Linguistics

-Multilingual Research Unit–SLA

–Bi- and multilingualism

–Bilingual education–Positive effects on calculation scores (Comblain & Rondal, 1993; Jäppinen, 2005)

–STIMOB (Van de Craen et al., 2005)


Additive Bilingualism(Baetens Beardsmore, 1986)

-opposite to « semilingualism » or subtractive bilingualism

-increased metalinguistic awareness (Cummins, 1978; Cromdal, 1999)

-creativity (Kessler & Quinn, 1988) & cognitive flexibility (Kovacs & Mehler, 2009)

- knowledge of 2 languages « greater than the sum of the parts » (Hakuta & Bialystok, 1994)


Going beyond the language domain

-competition between lexical & grammatical activation in L1 & L2 (Green, 1998)

-solved by inhibiting any active, non-target language

-effect on non-linguistic skills, like cognitive control (or selective attention), arithmetic?


Bilingualism, Executive Functioning & Number

-bilinguals show clear advantages for executive control (Green, 1998; Bialystok et al., 2009)

-neurocognitive advantages for bilinguals in a selective attention task(Mondt, 2007)

-inhibitory control as a predictor of individual children’s mathematical ability (Bull & Scerif, 2001)– Lesion studies show possible link with arithmetic (Zamarian et al., 2006)


Research Setup

-Dependent variable– Brain activity during an arithmetic verification task as registered with fMRI (Hôpital Erasme, ULB, Anderlecht)

-Independent variable(s)– Mono- vs. Bilingualism (linguistic background)

– School- vs. Non-school language (educational background)

-Population of 31 children


Mental Calculation Paradigm (Menon et al., 2000)

-originally designed to dissociate prefrontal and parietal activation

-control condition– 5-digit chain (press if « zero »)

-two experimental conditions

– 3-operand equations (x + y = z)

– 4-operand equations (x + y = z – a)


Conclusions

-s-l bilinguals: least number of active brain regions, left lateralized brain activity

-n-s-l bilinguals and monolinguals: similar patterns of additional bilateral activity in frontal and subcortical areas

-no intraparietal activity (HIPS or AG) in children during arithmetic verification

-results indicate – a training effect (s-l bil vs. n-s-l bil)– an advantage for bilinguals (s-l bil vs. mono)?


Bilingualism & Simon task

-does bilingualism enhance nonverbal control processes?– Arithmetic facts still phonologically stored

-differential brain-behavior relations (Bialystok et al., 2005)– Fast responses in bilinguals related to left hem. regions bordering language areas

-executive functions boosted in children? (Bialystok et al., 2007)


Attention Network Task (Costa et al., 2008)

-early & balanced bilingualism aids conflict resolution

-ANT taps into 3 different nonverbal attentional mechanisms– Alerting

– Orienting

– Executive control


Why Simon & Stroop task?

-different types of conflict–Stimulus-reponse (Simon) versus stimulus-stimulus (Stroop)

–Conflict at stage of response selection (Simon) versus conflict at stage of stimulus identification (Stroop)

Green Red BluePurple Blue Purple 2 7 9 4


Differences in GM density (VBM)

-increased GM density in E-I bil. in left inferior parietal cortex (Mechelli et al., 2004)

-modulated by AoA & Prof.

-correspondence with verbal fluency?


Corpus callosum variability (Coggins et al., 2003)

-bundle of axons connecting 2 cerebral hemispheres

-largest WM structure in the brain


Structural differences

Table 1. Midsagittal corpus callosum regional area differences between

bilingual and monolingual individuals


Conclusions CC study

-CC undergoes adaptation to accommodate multiple language faculty

-difference due to increase in fibre numbers emanating from L hem to R hem?

-relationship with AoA & proficiency?


Conclusion

-different languages � same neural representations (AoA, Prof)

-how to avoid interference?

-selective attention to relevant language, suppression of other

-effect on cognitive control

-structural changes?

from neurolinguistics of bilingualism to cognitive control

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