In my research I’ve learned a lot about language acquisition and processing and it has opened my eyes to how the brain is able to work and process in such a complex way.  First, I learned that when learning a second language, your brain uses the strong preexisting connections from your first language to learn the second faster and more effectively.  Also, there are specific areas of the brain that are associated with particular components of language and it is intriguing as to how we are able to determine the function of these specific areas.  These researchers as well as many others have suggested a critical period for learning languages which is pretty much up until puberty and then there is slight aphasia causing less plasticity or flexibility in the neurons.  One study had supporting evidence for this hypothesis given that one area of the brain was only activated in native signers and those that learned it after puberty did not have any activation at all in this area of the brain.  While there has been other evidence supporting this I think it’s important to point out that this decline in the plasticity and ability to learn a language is highly variable between individuals.  Another paper had provided a possible hypothesis for why babies are able to learn any language and that is because when they are born their brains are wired to understand any language but as their parents and others talk to them in their native language the babies’ are able to differentiate sounds and begin to piece together components of the language.  This researcher also proposed a social gating hypothesis stating that it is very important that infants have social interactions because without this they can’t truly become fluent in their native language and this could be an explanation as to why other animals who have computing systems as great as ours don’t use language.  In a more structural sense, one study found that there was less gray matter in bilinguals than people who learned a second language later in life which could mean that they have more streamlined and efficient neural systems, but the opposite has been found in many other studies where bilinguals have more gray and white matter volume than those who learned a second language after puberty or are monolinguals.  One suggestion in this paper that I thought was fascinating talked about Alzheimer’s and how the greater white matter density in bilinguals is able to compensate for the gray matter atrophy that occurs and therefore deters the disease.  This was of particular importance to me because I previously worked in a lab that investigated a possible cause for Alzheimer’s that involved the cell cycle and from that research I truly understand the importance of having anything that is able to deter Alzheimer’s from progressing in an individual.  Another study I read asked the exact question I did, what connections in the adult brain allow for better learning of a second language?  They found that for lexical retrieval success a stronger connection between the left insula/frontal operculum and the left posterior superior temporal gyrus was needed and the stronger the connection the greater the improvement in the individual.  Generally, the preexisting connections between these areas of the brain are what allow certain adults to have more ease in learning a second language compared to others.  A different study looked at individuals who were exposed to and learned a second language for 5 months and found that those who had a greater increase in proficiency had a greater increase in gray matter density in areas that are associated with language.  One interesting point that a different paper investigated was the effect of your first language on your ability to learn a second language.  They found that activation in an area of the brain that was earlier in Koreans than Chinese and this could be explained by the fact that Korean has somewhat similar structures to English while Chinese has no correlational structure.  Upon further research however, they found that their language proficiency determines the detection of their measurements rather than the grammatical structures, essentially meaning that the first language does not necessarily make a difference in the long term knowledge of the language but those with completely different structures might take longer or have a more difficult time learning it.  Lastly I read a dissertation on adult second language acquisition and the neural substrates and found that there is most likely a dual-system since regular and irregular verbs are processed differently but it’s not a simple separation between words and rules, it is more complex than that.  Then they looked into syntax and semantics and found that syntactical errors activated a different part of the brain than they were expecting but this has been found in other experiments previously, and for semantical errors it activated an area of the brain that has been shown to be associated with semantics.  In their last study they found that people who were native signers had greater activation in their right hemisphere compared to people who learned to sign after puberty.  There was also a region of the right hemisphere that was not activated at all in the late signers suggesting that there is a critical period for the plasticity in this area of the brain.  Overall, I learned a lot from this research and have found it very interesting along the way, I hope that more research is done to get to the real bottom of my question but during my research I truly realized one thing: the brain is extremely complex and fascinating.  

The Dissertation

In my research I came across a dissertation that discusses how adults learn a second language and the effects on the brain.  First it talks about the individual components of language like sound structure, structure of words, sentence structure, meaning of words, and the meaning of more complex sentences.  The beginning discusses the different approaches to how we are able to differentiate between word forms and past tense differentiations.  There has been lots of banter and debate about which system and structure is truly how the brain works but as of now we’re still unsure as to how the brain is able to determine correct and incorrect words and sentences.  On to acquisition, this paper also suggests that there is a critical period as to when we are best able to learn a second language, but that the declines after this period are highly variable between individuals. The first study mentioned in this dissertation investigated potentials in the brain when participants read English sentences either with correctly conjugated past tense verbs or when they were incorrectly in their infinitive.  There have been many debates as to the system under which the brain works, and there are suggestions of a dual-system where we have all of the words in one section of the brain and rules in the other and then apply the rules to the verbs, or it could be a  single-system where it is the organization of the lexicon rather than separate processes.  The first experiment in this study included sentences with only alterations in the verbs and they found that there were significant differences in the trials with the correct regular verbs and the incorrect regular ones in all 100 ms time frames after the stimulus, however with the irregulars there was no significance between the correct and incorrect in the 100-1000 ms time frame.  These results suggest that regular and irregular conjugation is treated differently by the brain in the early stages of processing.  The second experiment they included sentences that were syntactically incorrect or there were violations in the meaning of the sentence this was done to ensure that the participants hadn’t been using another process in the previous experiment because they were just focusing on the verb rather than the sentence.  The results for the regular verbs were similar to those in the first experiment but the results for the irregulars were slightly different in that there were significant interactions in the 500-900 ms time frame and for the sentence structure violations there was a significant effect on the wavelengths that were measured compared to the controls.  These results could mean that these are similar processes given that they have similar effects on the brain but at slightly different times.  Experiment three had identical procedures and stimuli to experiment two, but they altered the preceding words to the verbs to ensure that it didn’t affect their measurements.  The results from the regular verbs differed from both of the preceding experiments, the irregular verb results were the same as in experiment two, and the sentence structure results were similar to what was found in experiment two.  Overall, this study suggests that regular and irregular verbs are treated differently at the neural level, and possibly supports the dual-systems hypothesis.  The second study discussed in this paper looked into the brain regions that are involved in syntactic and semantic processing.  Before technology really skyrocketed linguists would observe people who had a lesion in a certain part of their brain and see if it affected their speech or language in any way, the data from these studies have been further confirmed by technological data from healthy individuals.  In this experiment they had right-handed males read sentences which were correct or had a syntactical, words in the wrong order, or semantic, a word doesn’t make sense, error.  Syntactic violations had a greater activation in regions in the superior frontal gyrus and these locations corresponded with Brodmann’s area and the semantic violations had greater activation in the temporal and temporo-parietal regions of the brain.  The regions that were activated by syntactic violations were odd in that they weren’t expecting this, but they were not unique since previous studies have had similar findings, they were surprised however that Broca’s area was not activated but they suggested that it might be activated only to the same extent as it is with a correct sentence.  In regards to the areas activated by the semantic violations they have been previously shown as storage regions but overall the regions have previously been shown to be involved in semantic memory, both encoding and retrieval of information, and storage.  The third study examined in this dissertation focuses on the neural regions involved in language processing of bilinguals of English and ASL compared to the age of acquisition.  It has been shown previously that there is significant activation in the right hemisphere of bilinguals and deaf signers suggesting that sign language demands processing in the right hemisphere compared to oral languages.  When looking at the results from the participants reading English sentences they were virtually identical and there were equivalent activations in the right hemisphere along the anterior and middle superior temporal sulcus in both groups when reading ASL sentences, suggesting this activation is irrespective of the age of acquisition.  While the areas of activation were the same, there was significantly less activation in the late signers than in the native signers and late signers have a strong left hemisphere dominance when reading ASL while native speakers have no left hemisphere dominance when reading ASL.  There was also significant activation in one area of the right hemisphere in native signers but was not activated at all in late signers, suggesting that there is a critical period for this region as well as generally using the right hemisphere to understand sign language.  Overall from this dissertation, they supported the theory of a dual-system given that the regular and irregular violations had different activations at different time points, suggesting there is different processing at the neural level for regular and irregular verbs.  They also found that syntactic violations activate a part of the brain where they weren’t expecting to get results but semantic violations were found to activate areas that previously were shown to be involved in semantic-pragmatic processing.  Lastly, they found that in native signers there was activation in one region of the right hemisphere that was not present in late signers, even though they generally had similar areas of activation in the right hemisphere, suggesting that plasticity in this region declines with aging and maturation.

Continued Research

In further research about my topic of how we learn languages, I found an article that discusses one of the experiments I mentioned in my previous post.  This other paper talks about the study in which 9 month old infants took 12 sessions with a fluent adult in a second language and tested their ability to recognize the phonemes from this language, but those who were exposed to the second language via the TV or audio tapes did not learn.  Again, this paper proposes the social gating hypothesis, stating that the infant focuses on the input from the adult because the intentions of the adult make it important to the infant and human interaction increases social awareness.  The goal of this paper however was to observe the phonetic learning and social interactions of the infants with a Spanish tutor.  They measured the gaze behaviors of the infants, how many times they looked at the tutor and then to a new toy introduced to them, and then measured the mismatch response.  They found that infants who had a higher amount of gaze shifts had a higher mismatch response indicating that they learned better than those infants who did not shift their gaze between the instructor and the toy.  The possible explanations for why this occurs are that the infants may have been learning word forms and therefore enhanced phonetic learning and another explanation is that the gaze shifting actually increase cognitive resources and general information processing.  Further studies that this article suggests is determining what part of the face that the infants are looking at when the tutor is introducing the toy.  Another paper that I read was truly aimed at the heart of my question.  The researchers looked at the connections in the brains of adults who went through a 12 week intensive French course and their success at learning the language.  Previous studies have shown that adults who have stronger connections between the left insula/frontal operculum have better performances when learning Hindi dental-retroflex sounds.  In this study they looked at lexical retrieval which utilized this region of the brain and they also looked at reading speed which has been connected with the left ventral temporo-occipital cortex, or the visual word form area.  They had the participants talk for 2 minutes about a day at the beach or zoo in both French and English and they calculated the total number of words correctly pronounced as an index of lexical retrieval success.  For the reading speed portion they had the participants read aloud an English or French passage and then they measured the number of words read per minute and this was used as an index of reading ability.  For the participants there was an increase in lexical retrieval and reading speed in French after they took the intensive course.  The connectivity between the left insula/frontal operculum and the left posterior superior temporal gyrus was correlated with improvement in lexical retrieval when producing spontaneous speech in French and those with a stronger connection had greater improvement in the usage of unique words.  They also found that the connectivity between the visual word form area and a cluster in the left mid-superior temporal gyrus was significantly correlated with the improvement in French reading speed, and those with a stronger connection had greater improvement.  This study generally shows that the pre-existing connections between these important areas of the brain are what set apart adults in their abilities to learn languages.  Another paper investigated the structural plasticity of the language areas of the brain after being exposed to and learning a second language for 5 months.  They found that the individuals who had a greater increase in second language proficiency had a greater increase in gray matter density in the brain areas that are associated with language, the prefrontal and temporal regions.  A possible alternate explanation for this correlation is just the enriched environment of being in Switzerland in the left ATL, but there is no alternate explanation for the correlation in the IFG.  This result has been found in other studies as I have discussed previously, even though this had an extremely small sample size and couldn’t specifically test what aspects of the second language learning were causing these increases in gray matter density.  In a separate paper they investigated how a first language influences the ability to learn a second language and increase proficiency.  Specifically, they looked at what is an index of structured reanalysis, a controlled process that occurs when there is a mismatch in a sentence, and to do this they had people go through an intense 9 week English course and tested them twice, once at the beginning and once during the last two weeks of the class.  They found that there was activation in the part of the brain they were imaging and found that this occurred at different time points for the native Korean speakers and the native Chinese speakers.  Activation occurred earlier in the Korean speakers because they have somewhat similar structures to the English they tested while the Chinese had no correlational structure.  Also, they determined that it is those who performed the highest had the highest amplitude in the measures and this suggests that second language proficiency determines the detection of what they attempted to measure rather than the grammatical structures of their first language.  These results essentially say the first language of the person attempting to learn a second language does not necessarily make a difference in the long term knowledge of the language but those with completely different structures may have a more difficult time and take longer to learn the language than others.  In this part of my reading I’ve learned quite a bit about second language acquisition and I found the data on the gaze shifts and social interaction from the study with the infants quite interesting and the study that included the participants who took the French course was exactly what I was looking for.  So far I believe my research has been successful in answering my questions.

The Beginning of the Reading

So far the beginning of my reading has been quite interesting.  The first paper I read was a journal article that discussed the sections of the brain that were active in twins, either 13 or 19, when they were given a task in Japanese, their first language, and in English, their second language.  When given a task in Japanese the section of the brain that was activated was very specific and when they were given the same task in English the activation was more widespread, but the areas of activation were similar between the two possibly suggesting that the cortical plasticity, or the reorganization of neural connections, for second language acquisition occurs in a way to match the specialization of first language activation.  This makes sense as the brain is using the preexisting, strong neural connections from the primary language to help learn and remember the secondary language better and it also displays that there are certain areas of the brain that are activated depending on whether the task is sentence construction, syntax or grammar.  I found it interesting that these researchers and others suggest that there is a sensitive period from birth until puberty where there is increased neural plasticity and flexibility that then declines after puberty due to aphasia, or the loss of ability to understand speech.  Also, in this paper they showed a possible network of linguistic functions including sentence comprehension, syntax, phonology, and lexico-semantics, which I thought was very intriguing.  Another paper provided a possible hypothesis as to the greater ability of infants to learn languages, and that is that when babies are born their brains are wired to understand any language and as parents and others talk to them they start to distinguish different phonemes before they are even able to speak.  Another curious hypothesis that this researcher proposed is that there is a social “gate” which explains why other animals who have very powerful computing systems are not able to speak and it provides a possible explanation for why those with autism  have deficits in social cognition and language.  When the researchers looked at 7.5 month old children and observed their brain waves when given phonetic sounds of their native and nonnative language they looked at the mismatch negativity, which is how well the children were able to detect odd phonemes.  If a child had better native phonetic discrimination this allows them to detect words and leads them towards language, but if they had better nonnative discrimination then that signified the infant was at an earlier stage in development.  The ability of the infant to recognize phonetic units in their native language while inhibiting their attention towards phonetic units that don’t work in this language is what allows them to proceed towards language themselves.  In a separate study 9 month old infants took 12 sessions with either a native Mandarin speaker or a native English speaker and after these sessions each infant was tested using the Mandarin phonetic units that were different from English and those that had Mandarin exposure had a much higher ability to recognize these units and therefore they concluded that infants are still able to learn even when their brain starts to differentiate into their native language.  They also found that when the infants were taught through audiotapes or TV they did not learn and were equivalent to those that were exposed to only the native English speakers.  One other paper discussed the gray matter volume, the tissue in the brain that contains the neuron bodies and synapses, in the language associated areas in the brain in multilinguals, those that spoke 3 or more languages.  They hypothesized that there would be higher levels of gray matter in those that learned the languages successively, meaning they learned one at a young age, another at a later point in their life and the third much later, compared to those that learned their first two languages simultaneously and the third later in life.  This hypothesis suggests that those who learned two languages simultaneously had a more efficient neural networks and they are able to better incorporate a second language into the same network as the first language instead of the brain creating all new connections.  They found that there was greater gray matter volume in those that learned their languages successively in regions that are associated with language in the brain.  Their results were bilateral, in that they had similar results in the right and left hemispheres of the brain, while other previous studies had found that there was only an increase in gray matter density in the left hemisphere.  This paper was interesting because it investigates essentially the efficiency of language processing in those that have learned languages when they were young or as they aged.  In one review they researched the functional and anatomical alterations that occur in the brain and they found different evidence for the gray matter changes in the previously discussed paper in this post.  Other studies have looked into cortical thickness or white matter integrity.  One article included in this review observed bilinguals and measured their gray matter density in one area of the brain that is associated with vocabulary and found that there was more gray matter in bilinguals compared to monolinguals and the more vocabulary they learned the more gray matter was present.  Another article looked at white matter integrity and found that there was higher white matter integrity in the monolinguals compared to bilinguals in older subjects while the opposite was true in younger subjects.  Suggesting that the age of acquisition is an important factor in learning languages.  It was suggested in one paper that there is usually gray matter atrophy in Alzheimer’s patients and that those who are bilingual with greater white matter integrity can compensate for this loss and therefore is a deterrent for the disease.   Most of these articles from the review looked at bilinguals who had a longterm experience with the second language, however the researchers wanted to look into those who learned languages in the short-term and found there was increased white matter in those that took a Chinese course for 9 months compared to those who didn’t.  Another study took monolingual English speakers and taught them pseudowords and they found that the more successful learners had more focused activation in the phonological processing center while the less successful learners had a more diffuse network.  For more successful learners, they had more white matter volume and density compared to slower, less successful learners.  Overall, the papers I have read so far have given me much insight into the studies that have been and are currently being conducted to answer the questions that I and many others have asked.