@article {185, title = {Neural language processing in adolescent first-language learners.}, journal = {Cereb Cortex}, volume = {24}, year = {2014}, month = {2014 Oct}, pages = {2772-83}, abstract = {

The relation between the timing of language input and development of neural organization for language processing in adulthood has been difficult to tease apart because language is ubiquitous in the environment of nearly all infants. However, within the congenitally deaf population are individuals who do not experience language until after early childhood. Here, we investigated the neural underpinnings of American Sign Language (ASL) in 2 adolescents who had no sustained language input until they were approximately 14 years old. Using anatomically constrained magnetoencephalography, we found that recently learned signed words mainly activated right superior parietal, anterior occipital, and dorsolateral prefrontal areas in these 2 individuals. This spatiotemporal activity pattern was significantly different from the left fronto-temporal pattern observed in young deaf adults who acquired ASL from birth, and from that of hearing young adults learning ASL as a second language for a similar length of time as the cases. These results provide direct evidence that the timing of language experience over human development affects the organization of neural language processing.

}, keywords = {Adolescent, Adult, Age Factors, Cerebral Cortex, Critical Period (Psychology), Deafness, Female, Functional Laterality, Humans, Language Development, Learning, Magnetoencephalography, Male, Semantics, Sign Language, Young Adult}, issn = {1460-2199}, doi = {10.1093/cercor/bht137}, author = {Ferjan Ramirez, Naja and Leonard, Matthew K and Torres, Christina and Hatrak, Marla and Halgren, Eric and Mayberry, Rachel I} } @article {204, title = {Independence of early speech processing from word meaning.}, journal = {Cereb Cortex}, volume = {23}, year = {2013}, month = {2013 Oct}, pages = {2370-9}, abstract = {

We combined magnetoencephalography (MEG) with magnetic resonance imaging and electrocorticography to separate in anatomy and latency 2 fundamental stages underlying speech comprehension. The first acoustic-phonetic stage is selective for words relative to control stimuli individually matched on acoustic properties. It begins \~{}60 ms after stimulus onset and is localized to middle superior temporal cortex. It was replicated in another experiment, but is strongly dissociated from the response to tones in the same subjects. Within the same task, semantic priming of the same words by a related picture modulates cortical processing in a broader network, but this does not begin until \~{}217 ms. The earlier onset of acoustic-phonetic processing compared with lexico-semantic modulation was significant in each individual subject. The MEG source estimates were confirmed with intracranial local field potential and high gamma power responses acquired in 2 additional subjects performing the same task. These recordings further identified sites within superior temporal cortex that responded only to the acoustic-phonetic contrast at short latencies, or the lexico-semantic at long. The independence of the early acoustic-phonetic response from semantic context suggests a limited role for lexical feedback in early speech perception.

}, keywords = {Adult, Brain, Brain Mapping, Female, Humans, Magnetic Resonance Imaging, Magnetoencephalography, Male, Speech Perception, Young Adult}, issn = {1460-2199}, doi = {10.1093/cercor/bhs228}, author = {Travis, Katherine E and Leonard, Matthew K and Chan, Alexander M and Torres, Christina and Sizemore, Marisa L and Qu, Zhe and Eskandar, Emad and Dale, Anders M and Elman, Jeffrey L and Cash, Sydney S and Halgren, Eric} } @article {190, title = {Signed words in the congenitally deaf evoke typical late lexicosemantic responses with no early visual responses in left superior temporal cortex.}, journal = {J Neurosci}, volume = {32}, year = {2012}, month = {2012 Jul 11}, pages = {9700-5}, abstract = {

Congenitally deaf individuals receive little or no auditory input, and when raised by deaf parents, they acquire sign as their native and primary language. We asked two questions regarding how the deaf brain in humans adapts to sensory deprivation: (1) is meaning extracted and integrated from signs using the same classical left hemisphere frontotemporal network used for speech in hearing individuals, and (2) in deafness, is superior temporal cortex encompassing primary and secondary auditory regions reorganized to receive and process visual sensory information at short latencies? Using MEG constrained by individual cortical anatomy obtained with MRI, we examined an early time window associated with sensory processing and a late time window associated with lexicosemantic integration. We found that sign in deaf individuals and speech in hearing individuals activate a highly similar left frontotemporal network (including superior temporal regions surrounding auditory cortex) during lexicosemantic processing, but only speech in hearing individuals activates auditory regions during sensory processing. Thus, neural systems dedicated to processing high-level linguistic information are used for processing language regardless of modality or hearing status, and we do not find evidence for rewiring of afferent connections from visual systems to auditory cortex.

}, keywords = {Adolescent, Adult, Brain Mapping, Deafness, Evoked Potentials, Female, Functional Laterality, Humans, Magnetic Fields, Magnetic Resonance Imaging, Magnetoencephalography, Male, Photic Stimulation, Semantics, Sign Language, Temporal Lobe, Time Factors, Young Adult}, issn = {1529-2401}, doi = {10.1523/JNEUROSCI.1002-12.2012}, author = {Leonard, Matthew K and Ferjan Ramirez, Naja and Torres, Christina and Travis, Katherine E and Hatrak, Marla and Mayberry, Rachel I and Halgren, Eric} } @article {192, title = {Language proficiency modulates the recruitment of non-classical language areas in bilinguals.}, journal = {PLoS One}, volume = {6}, year = {2011}, month = {2011}, pages = {e18240}, abstract = {

Bilingualism provides a unique opportunity for understanding the relative roles of proficiency and order of acquisition in determining how the brain represents language. In a previous study, we combined magnetoencephalography (MEG) and magnetic resonance imaging (MRI) to examine the spatiotemporal dynamics of word processing in a group of Spanish-English bilinguals who were more proficient in their native language. We found that from the earliest stages of lexical processing, words in the second language evoke greater activity in bilateral posterior visual regions, while activity to the native language is largely confined to classical left hemisphere fronto-temporal areas. In the present study, we sought to examine whether these effects relate to language proficiency or order of language acquisition by testing Spanish-English bilingual subjects who had become dominant in their second language. Additionally, we wanted to determine whether activity in bilateral visual regions was related to the presentation of written words in our previous study, so we presented subjects with both written and auditory words. We found greater activity for the less proficient native language in bilateral posterior visual regions for both the visual and auditory modalities, which started during the earliest word encoding stages and continued through lexico-semantic processing. In classical left fronto-temporal regions, the two languages evoked similar activity. Therefore, it is the lack of proficiency rather than secondary acquisition order that determines the recruitment of non-classical areas for word processing.

}, keywords = {Adult, Brain Mapping, Female, Humans, Language, Language Development, Magnetic Resonance Imaging, Magnetoencephalography, Male, Multilingualism, Young Adult}, issn = {1932-6203}, doi = {10.1371/journal.pone.0018240}, author = {Leonard, Matthew K and Torres, Christina and Travis, Katherine E and Brown, Timothy T and Hagler, Donald J and Dale, Anders M and Elman, Jeffrey L and Halgren, Eric} } @article {206, title = {Spatiotemporal neural dynamics of word understanding in 12- to 18-month-old-infants.}, journal = {Cereb Cortex}, volume = {21}, year = {2011}, month = {2011 Aug}, pages = {1832-9}, abstract = {

Learning words is central in human development. However, lacking clear evidence for how or where language is processed in the developing brain, it is unknown whether these processes are similar in infants and adults. Here, we use magnetoencephalography in combination with high-resolution structural magnetic resonance imaging to noninvasively estimate the spatiotemporal distribution of word-selective brain activity in 12- to 18-month-old infants. Infants watched pictures of common objects and listened to words that they understood. A subset of these infants also listened to familiar words compared with sensory control sounds. In both experiments, words evoked a characteristic event-related brain response peaking \~{}400 ms after word onset, which localized to left frontotemporal cortices. In adults, this activity, termed the N400m, is associated with lexico-semantic encoding. Like adults, we find that the amplitude of the infant N400m is also modulated by semantic priming, being reduced to words preceded by a semantically related picture. These findings suggest that similar left frontotemporal areas are used for encoding lexico-semantic information throughout the life span, from the earliest stages of word learning. Furthermore, this ontogenetic consistency implies that the neurophysiological processes underlying the N400m may be important both for understanding already known words and for learning new words.

}, keywords = {Adult, Brain Mapping, Cerebral Cortex, Evoked Potentials, Auditory, Female, Humans, Infant, Language Tests, Learning, Magnetic Resonance Imaging, Magnetoencephalography, Male, Neurons, Speech Perception, Vocabulary}, issn = {1460-2199}, doi = {10.1093/cercor/bhq259}, author = {Travis, Katherine E and Leonard, Matthew K and Brown, Timothy T and Hagler, Donald J and Curran, Megan and Dale, Anders M and Elman, Jeffrey L and Halgren, Eric} } @article {191, title = {Spatiotemporal dynamics of bilingual word processing.}, journal = {Neuroimage}, volume = {49}, year = {2010}, month = {2010 Feb 15}, pages = {3286-94}, abstract = {

Studies with monolingual adults have identified successive stages occurring in different brain regions for processing single written words. We combined magnetoencephalography and magnetic resonance imaging to compare these stages between the first (L1) and second (L2) languages in bilingual adults. L1 words in a size judgment task evoked a typical left-lateralized sequence of activity first in ventral occipitotemporal cortex (VOT: previously associated with visual word-form encoding) and then ventral frontotemporal regions (associated with lexico-semantic processing). Compared to L1, words in L2 activated right VOT more strongly from approximately 135 ms; this activation was attenuated when words became highly familiar with repetition. At approximately 400 ms, L2 responses were generally later than L1, more bilateral, and included the same lateral occipitotemporal areas as were activated by pictures. We propose that acquiring a language involves the recruitment of right hemisphere and posterior visual areas that are not necessary once fluency is achieved.

}, keywords = {Adolescent, Adult, Brain, Brain Mapping, Female, Functional Laterality, Humans, Magnetoencephalography, Male, Multilingualism, Nerve Net, Pattern Recognition, Visual, Reading, Semantics, Young Adult}, issn = {1095-9572}, doi = {10.1016/j.neuroimage.2009.12.009}, author = {Leonard, Matthew K and Brown, Timothy T and Travis, Katherine E and Gharapetian, Lusineh and Hagler, Donald J and Dale, Anders M and Elman, Jeffrey L and Halgren, Eric} }