Verbal and non-verbal intelligence changes in the teenage brain.

Intelligence quotient (IQ) is a standardized measure of human intellectual capacity that takes into account a wide range of cognitive skills. IQ is generally considered to be stable across the lifespan, with scores at one time point used to predict educational achievement and employment prospects in later years. Neuroimaging allows us to test whether unexpected longitudinal fluctuations in measured IQ are related to brain development. Here we show that verbal and non-verbal IQ can rise or fall in the teenage years, with these changes in performance validated by their close correlation with changes in local brain structure. A combination of structural and functional imaging showed that verbal IQ changed with grey matter in a region that was activated by speech, whereas non-verbal IQ changed with grey matter in a region that was activated by finger movements. By using longitudinal assessments of the same individuals, we obviated the many sources of variation in brain structure that confound cross-sectional studies. This allowed us to dissociate neural markers for the two types of IQ and to show that general verbal and non-verbal abilities are closely linked to the sensorimotor skills involved in learning. More generally, our results emphasize the possibility that an individual's intellectual capacity relative to their peers can decrease or increase in the teenage years. This would be encouraging to those whose intellectual potential may improve, and would be a warning that early achievers may not maintain their potential.

Multiple routes from occipital to temporal cortices during reading.

Contemporary models of the neural system that supports reading propose that activity in a ventral occipitotemporal area (vOT) drives activity in higher-order language areas, for example, those in the posterior superior temporal sulcus (pSTS) and anterior superior temporal sulcus (aSTS). We used fMRI with dynamic causal modeling (DCM) to investigate evidence for other routes from visual cortex to the left temporal lobe language areas. First we identified activations in posterior inferior occipital (iO) and vOT areas that were more activated for silent reading than listening to words and sentences; and in pSTS and aSTS areas that were commonly activated for reading relative to false-fonts and listening to words relative to reversed words. Second, in three different DCM analyses, we tested whether visual processing of words modulates activity from the following: (1) iO→vOT, iO→pSTS, both, or neither; (2) vOT→pSTS, iO→pSTS, both or neither; and (3) pSTS→aSTS, vOT→aSTS, both, or neither. We found that reading words increased connectivity (1) from iO to both pSTS and vOT; (2) to pSTS from both iO and vOT; and (3) to aSTS from both vOT and pSTS. These results highlight three potential processing streams in the occipitotemporal cortex: iO→pSTS→aSTS; iO→vOT→aSTS; and iO→vOT→pSTS→aSTS. We discuss these results in terms of cognitive models of reading and propose that efficient reading relies on the integrity of all these pathways.

The right posterior paravermis and the control of language interference.

Auditory and written language in humans' comprehension necessitates attention to the message of interest and suppression of interference from distracting sources. Investigating the brain areas associated with the control of interference is challenging because it is inevitable that activation of the brain regions that control interference co-occurs with activation related to interference per se. To isolate the mechanisms that control verbal interference, we used a combination of structural and functional imaging techniques in Italian and German participants who spoke English as a second language. First, we searched structural MRI images of Italian participants for brain regions in which brain structure correlated with the ability to suppress interference from the unattended dominant language (Italian) while processing heard sentences in their weaker language (English). This revealed an area in the posterior paravermis of the right cerebellum in which gray matter density was higher in individuals who were better at controlling verbal interference. Second, we found functional activation in the same region when our German participants made semantic decisions on written English words in the presence of interference from unrelated words in their dominant language (German). This combination of structural and functional imaging therefore highlights the contribution of the right posterior paravermis to the control of verbal interference. We suggest that the importance of this region for language processing has previously been missed because most fMRI studies limit the field of view to increase sensitivity, with the lower part of the cerebellum being the region most likely to be excluded.

Auditory short-term memory capacity correlates with gray matter density in the left posterior STS in cognitively normal and dyslexic adults.

A central feature of auditory STM is its item-limited processing capacity. We investigated whether auditory STM capacity correlated with regional gray and white matter in the structural MRI images from 74 healthy adults, 40 of whom had a prior diagnosis of developmental dyslexia whereas 34 had no history of any cognitive impairment. Using whole-brain statistics, we identified a region in the left posterior STS where gray matter density was positively correlated with forward digit span, backward digit span, and performance on a "spoonerisms" task that required both auditory STM and phoneme manipulation. Across tasks and participant groups, the correlation was highly significant even when variance related to reading and auditory nonword repetition was factored out. Although the dyslexics had poorer phonological skills, the effect of auditory STM capacity in the left STS was the same as in the cognitively normal group. We also illustrate that the anatomical location of this effect is in proximity to a lesion site recently associated with reduced auditory STM capacity in patients with stroke damage. This result, therefore, indicates that gray matter density in the posterior STS predicts auditory STM capacity in the healthy and damaged brain. In conclusion, we suggest that our present findings are consistent with the view that there is an overlap between the mechanisms that support language processing and auditory STM.

Neuronal activation for semantically reversible sentences.

Semantically reversible sentences are prone to misinterpretation and take longer for typically developing children and adults to comprehend; they are also particularly problematic for those with language difficulties such as aphasia or Specific Language Impairment. In our study, we used fMRI to compare the processing of semantically reversible and nonreversible sentences in 41 healthy participants to identify how semantic reversibility influences neuronal activation. By including several linguistic and nonlinguistic conditions within our paradigm, we were also able to test whether the processing of semantically reversible sentences places additional load on sentence-specific processing, such as syntactic processing and syntactic-semantic integration, or on phonological working memory. Our results identified increased activation for reversible sentences in a region on the left temporal-parietal boundary, which was also activated when the same group of participants carried out an articulation task which involved saying "one, three" repeatedly. We conclude that the processing of semantically reversible sentences places additional demands on the subarticulation component of phonological working memory.

Contrasting effects of vocabulary knowledge on temporal and parietal brain structure across lifespan.

Using behavioral, structural, and functional imaging techniques, we demonstrate contrasting effects of vocabulary knowledge on temporal and parietal brain structure in 47 healthy volunteers who ranged in age from 7 to 73 years. In the left posterior supramarginal gyrus, vocabulary knowledge was positively correlated with gray matter density in teenagers but not adults. This region was not activated during auditory or visual sentence processing, and activation was unrelated to vocabulary skills. Its gray matter density may reflect the use of an explicit learning strategy that links new words to lexical or conceptual equivalents, as used in formal education and second language acquisition. By contrast, in left posterior temporal regions, gray matter as well as auditory and visual sentence activation correlated with vocabulary knowledge throughout lifespan. We propose that these effects reflect the acquisition of vocabulary through context, when new words are learnt within the context of semantically and syntactically related words.

Critical periods and catastrophic interference effects in the development of self-organizing feature maps.

The use of self-organizing feature maps (SOFM) in models of cognitive development has frequently been associated with explanations of critical or sensitive periods. By contrast, error-driven connectionist models of development have been linked with catastrophic interference between new knowledge and old knowledge. We introduce a set of simulations that systematically evaluate the conditions under which SOFMs demonstrate critical/sensitive periods in development versus those under which they display interference effects. We explored the relative contribution of network parameters (for example, whether learning rate and neighbourhood reduce across training), the representational resources available to the network, and the similarity between old and new knowledge in determining the functional plasticity of the maps. The SOFMs that achieved the best discrimination and topographic organization also exhibited sensitive periods in development while showing lower plasticity and hence limited interference. However, fast developing, coarser SOFMs also produced topologically organized representations, while permanently retaining their plasticity. We argue that the impact of map organization on behaviour must be interpreted in terms of the cognitive processes that the map is driving.

Bilingual children show an advantage in controlling verbal interference during spoken language comprehension.

Studies measuring inhibitory control in the visual modality have shown a bilingual advantage in both children and adults. However, there is a lack of developmental research on inhibitory control in the auditory modality. This study compared the comprehension of active and passive English sentences in 7-10 years old bilingual and monolingual children. The task was to identify the agent of a sentence in the presence of verbal interference. The target sentence was cued by the gender of the speaker. Children were instructed to focus on the sentence in the target voice and ignore the distractor sentence. Results indicate that bilinguals are more accurate than monolinguals in comprehending syntactically complex sentences in the presence of linguistic noise. This supports previous findings with adult participants (Filippi, Leech, Thomas, Green & Dick, 2012). We therefore conclude that the bilingual advantage in interference control begins early in life and is maintained throughout development.

The influence of reading ability on subsequent changes in verbal IQ in the teenage years.

Intelligence Quotient (IQ) is regularly used in both education and employment as a measure of cognitive ability. Although an individual's IQ is generally assumed to stay constant across the lifespan, a few studies have suggested that there may be substantial variation at the individual level. Motivated by previous reports that reading quality/quantity has a positive influence on vocabulary acquisition, we hypothesised that reading ability in the early teenage years might contribute to changes in verbal IQ (VIQ) over the next few years. We found that good readers were more likely to experience relative improvements in VIQ over time, with the reverse true for poor readers. These effects were largest when there was a discrepancy between Time 1 reading ability and Time 1 VIQ. In other words, VIQ increases tended to be greatest when reading ability was high relative to VIQ. Additional analyses supported these findings by showing that variance in VIQ change associated with Time 1 behaviour was also associated with independent measurements of brain structure. Our finding that reading in the early teenage years can predict a significant proportion of the variance in subsequent VIQ change has implications for targeted education in both home and school environments.

Structural MRI studies of language function in the undamaged brain.

In recent years, the demonstration that structural changes can occur in the human brain beyond those associated with development, ageing and neuropathology has revealed a new approach to studying the neural basis of behaviour. In this review paper, we focus on structural imaging studies of language that have utilised behavioural measures in order to investigate the neural correlates of language skills in the undamaged brain. We report studies that have used two different techniques: voxel-based morphometry of whole brain grey or white matter images and diffusion tensor imaging. At present, there are relatively few structural imaging studies of language. We group them into those that investigated (1) the perception of novel speech sounds, (2) the links between speech sounds and their meaning, (3) speech production, and (4) reading. We highlight the validity of the findings by comparing the results to those from functional imaging studies. Finally, we conclude by summarising the novel contribution of these studies to date and potential directions for future research.