Learning a specific skill during childhood may partly determine the functional organization of the adult brain. This hypothesis led us to study oral language processing in illiterate subjects who, for social reasons, had never entered school and had no knowledge of reading or writing. In a brain activation study using PET and statistical parametric mapping, we compared word and pseudoword repetition in literate and illiterate subjects. Our study confirms behavioural evidence of different phonological processing in illiterate subjects. During repetition of real words, the two groups performed similarly and activated similar areas of the brain. In contrast, illiterate subjects had more difficulty repeating pseudowords correctly and did not activate the same neural structures as literates. These results are consistent with the hypothesis that learning the written form of language (orthography) interacts with the function of oral language. Our results indicate that learning to read and write during childhood influences the functional organization of the adult human brain.

Illiterates represent a significant proportion of the world's population. Written language not only plays a role in mediating cognition, but also extends our knowledge of the world. Two major reasons for illiteracy can be distinguished, social (e.g., absence of schools), and personal (e.g., learning difficulties). Without written language, our knowledge of the external world is partially limited by immediate sensory information and concrete environmental conditions. Literacy is significantly associated with virtually all neuropsychological measures, even though the correlation between education and neuropsychological test scores depends on the specific test. The impact of literacy is reflected in different spheres of cognitive functioning. Learning to read reinforces and modifies certain fundamental abilities, such as verbal and visual memory, phonological awareness, and visuospatial and visuomotor skills. Functional imaging studies are now demonstrating that literacy and education influence the pathways used by the brain for problem-solving. The existence of partially specific neuronal networks as a probable consequence of the literacy level supports the hypothesis that education impacts not only the individual's day-to-day strategies, but also the brain networks. A review of the issues related to dementia in illiterates is presented, emphasizing that the association between the education level and age-related cognitive changes and education remains controversial. The analysis of the impact of illiteracy on neuropsychological test performance represents a crucial approach to understanding human cognition and its brain organization under normal and abnormal conditions.

Research from JAMA — Neurobehavioral Effects of Dental Amalgam in Children — A Randomized Clinical Trial — ContextDental (silver) amalgam is a widely used restorative material containing 50% elemental mercury that emits small amounts of mercury vapor. No randomized clinical trials have determined whether there are significant health risks associated with this low-level mercury exposure.ObjectiveTo assess the safety of dental amalgam restorations in children.DesignA randomized clinical trial in which children requiring dental restorative treatment were randomized to either amalgam for posterior restorations or resin composite instead of amalgam. Enrollment commenced February 1997, with annual follow-up for 7 years concluding in July 2005.Setting and ParticipantsA total of 507 children in Lisbon, Portugal, aged 8 to 10 years with at least 1 carious lesion on a permanent tooth, no previous exposure to amalgam, urinary mercury level <10 μg/L, blood lead level <15 μg/dL, Comprehensive Test of Nonverbal Intelligence IQ ≥67, and with no interfering health conditions.InterventionRoutine, standard-of-care dental treatment, with one group receiving amalgam restorations for posterior lesions (n = 253) and the other group receiving resin composite restorations instead of amalgam (n = 254).Main Outcome MeasuresNeurobehavioral assessments of memory, attention/concentration, and motor/visuomotor domains, as well as nerve conduction velocities.ResultsDuring the 7-year trial period, children had a mean of 18.7 tooth surfaces (median, 16) restored in the amalgam group and 21.3 (median, 18) restored in the composite group. Baseline mean creatinine-adjusted urinary mercury levels were 1.8 μg/g in the amalgam group and 1.9 μg/g in the composite group, but during follow-up were 1.0 to 1.5 μg/g higher in the amalgam group than in the composite group (P<.001). There were no statistically significant differences in measures of memory, attention, visuomotor function, or nerve conduction velocities (average z scores were very similar, near zero) for the amalgam and composite groups over all 7 years of follow-up, with no statistically significant differences observed at any time point (P values from .29 to .91). Starting at 5 years after initial treatment, the need for additional restorative treatment was approximately 50% higher in the composite group.ConclusionsIn this study, children who received dental restorative treatment with amalgam did not, on average, have statistically significant differences in neurobehavioral assessments or in nerve conduction velocity when compared with children who received resin composite materials without amalgam. These findings, combined with the trend of higher treatment need later among those receiving composite, suggest that amalgam should remain a viable dental restorative option for children.Trial Registrationclinicaltrials.gov Identifier: NCT00066118

Learning to read and write generates new rules within the language processing systems. These new rules significantly change the manner in which some operations are performed. This finding was studied, by comparing the performance of literate and illiterate persons in several tasks. It was found that illiterate individuals (1) had difficulties in repeating pseudowords, (2) were worse at memorizing pairs of phonologically related words compared to pairs of semantically related words, and (3) were unable to generate words according to a formal criterion. Illiterate persons use strategies that are good for semantic processing, but inadequate for phonological analysis, while literate individuals are able to use several parallel running strategies. (JINS, 1997, 3, 444–450.)

Previous behavioral and functional neuroimaging data indicate that certain aspects of phonological processing may not be acquired spontaneously, but are modulated by learning an alphabetic written language, that is, learning to read and write. It appears that learning an alphabetic written language modifies the auditory-verbal (spoken) language processing competence in a nontrivial way. We have previously suggested, based on behavioral and functional neuroimaging data, that auditory-verbal and written language interact not only during certain language tasks, but that learning and developing alphabetic written language capacities significantly modulates the spoken language system. Specifically, the acquisition of alphabetic orthographic knowledge has a modulatory influence on sublexical phonological processing and the awareness of sublexical phonological structure. We have suggested that developing an orthographic representation system for an alphabetic written language, and integrating a phonemegrapheme correspondence with an existing infrastructure for auditory-verbal language processing, will result in a modified language network. Specifically, we suggest that the parallel interactive processing characteristics of the underlying language-processing brain network differ in literate and illiterate subjects. Therefore, the pattern of interactions between the regions of a suitably defined large-scale functional-anatomical network for language processing will differ between literate and illiterate subjects during certain language tasks. In order to investigate this hypothesis further, we analyzed the observed covariance structure in a PET data set from a simple auditory-verbal repetition paradigm in literate and illiterate subjects, with a network approach based on structural equation modeling (SEM). Based on a simple network model for language processing, the results of the present network analysis indicate that the network interactions during word and pseudoword repetition in the illiterate group differ, while there were no significant differences in the literate group. The differences between the two tasks in the illiterate group may reflect differences in attentional modulation of the language network, executive aspects of verbal working memory and the articulatory organization of verbal output. There were no significant differences between the literate and illiterate group during word repetition. In contrast, the network interactions differed between the literate and illiterate group during pseudoword repetition. In addition to differences similar to those observed in the illiterate group between word and pseudoword repetition, there were differences related to the interactions of the phonological loop between the groups. In particular, these differences related to the interaction between Broca's area and the inferior parietal cortex as well as the posterior-midinsula bridge between Wernicke's and Broca's area. In conclusion, the results of this network analysis are consistent with our previously presented results and support the hypothesis that learning to read and write during childhood influences the functional architecture of the adult human brain. In particular, the basic auditory-verbal language network in the human brain is modified as a consequence of acquiring orthographic language skills.