Brain asymmetry for language in dyslexic children

Studies of brain asymmetry in dyslexia have yielded mixed results both with respect to patterns of asymmetry and their cognitive correlates. This paper assessed language lateralisation inferred from dichotic listening with forced attention in a clinical group of young dyslexic subjects. As a whole the dyslexic group showed a deviant asymmetry pattern compared to a control group. Subdivision into two subgroups by receptive language abilities yielded differential patterns within the dyslexia group. Both subgroups exhibited a weaker response pattern to right ear stimuli than the control group. In addition, the subgroup with no language impairment showed bilateral language representation, whereas the subgroup with impaired receptive language abilities showed reversed dominance patterns.     

Familial resemblance for cognitive abilities in families with P-type dyslexic, L-type dyslexic, or normal reading boys

P-type dyslexic, L-type dyslexic, and normal reading boys, and their parents were administered a number of cognitive tasks. The P- and L-type dyslexic boys showed impaired performances on tasks representing a verbal/memory dimension. In addition, L-type dyslexics performed worse on a figure-rotation task, a result that supported the notion of a visuospatial deficit in this type of reading disturbance. The parents of P- and L-type dyslexics exhibited lowered performances on verbal/memory tasks, but they showed no evidence of impaired visuospatial functioning. Indices of familial resemblance revealed differential familial resemblances in the three types of families. In the families of P-type dyslexics, a high father-son effect was found for the visuospatial dimension. In the families of L-type dyslexics, moderately high single-parent/child effects were found for both fathers and mothers and for both the verbal/memory dimension and the visuospatial dimension. In the families of normal readers, only small single-parent/child effects were found.     

Familial resemblance for cognitive abilities in families with P-type dyslexic,L-type dyslexic,or normal reading boys

Abstract

P-type dyslexic, L-type dyslexic, and normal reading boys, and their parents were administered a number of cognitive tasks. The P-and L-type dyslexic boys showed impaired performances on tasks representing a verbal/memory dimension. In addition, L-type dyslexics performed worse on a figure-rotation task, a result that supported the notion of a visuospatial deficit in this type of reading disturbance. The parents of P-and L-type dyslexics exhibited lowered performances on verbal/ memory tasks, but they showed no evidence of impaired visuospatial functioning. Indices of familial resemblance revealed differential familial resemblances in the three types of families. In the families of P-type dyslexics, a high father-son effect was found for the visuospatial dimension. In the families of L-type dyslexics, moderately high single-parent/child effects were found for both fathers and mothers and for both the verbal/memory dimension and the visuospatial dimension. In the families of normal readers, only small single-parent/child effects were found.     

Cognitive mode and asymmetry in cerebral functioning

Male graduate students from the fields of sculpture, psychology, and law were used to test the assumption that an individual's cognitive mode (verbal-analytic vs. spatial-holistic) is related to actual laterality in cerebral functioning. A measure of asymmetry of cognitive mode for each student, based on relative performance on three verbal-analytic tests compared to three spatial-holistic tests, successfully discriminated occupational groups. Laterality in cerebral functioning was indexed by relative reaction times to discriminate visual stimuli presented unilaterally to the left or right hemisphere. Reaction times to discriminate faces were less for the right hemisphere, while letters were discriminated faster by the left hemisphere. However, measures of cerebral laterality were not related to occupational group membership nor to asymmetry of cognitive mode. Asymmetry in performance on tests of cognitive mode may reflect an individual's general approach to problem solving, but is not closely related to laterality in cerebral functioning.     

Altered hemispheric asymmetry during word processing in dyslexic children: an event-related potential study

The present event-related potential study aimed at finding neurophysiological correlates of inadequate reading performances in developmental dyslexia. By using the same set of words in different linguistic tasks, we found variations of cortical asymmetry between dyslexic individuals and controls starting with the N420, a component supposed to index the phonological processing during reading. Whereas in controls this component was left lateralized, in disabled readers it was more distributed across hemispheres. The observed lack of lateralization in dyslexic individuals was also found in the later slow negative wave that developed in the 700 to 1500-ms time interval. We postulate that the altered asymmetry is related to an impairment of the grapheme-phoneme conversion mechanism. The findings would therefore support the hypothesis of a phonological deficit underlying this learning disability.     

Differences in hemispheric asymmetry between dyslexic and normal children on a lateralised lexical decision task

The present experiment was conducted in order to further investigate the relationship between deficits in left hemisphere processing and phonetic decoding in dyslexic children. We administered a lateralised lexical decision task that manipulated wordness, length, and word regularity of grapheme-phoneme conversion. Right-handed male dyslexic children and normal control children were presented with words and pronounceable nonwords. Although there were no overall differences in hemispheric asymmetry between the groups, they did differ in laterality effects in accuracy when responding to nonwords and to phonetically regular words, with the normal children showing the right visual field advantage/ sensitivity (left hemisphere dominance/sensitivity), while the dyslexics failed to show any visual field advantage or sensitivity for these stimuli. Further, group differences were observed in left but not right hemisphere functioning. The results suggest that deficits in left hemisphere processing are apparent only when the dyslexics are attempting to utilise the rules of phonics. Support for the use of this paradigm for use with dyslexic children is also discussed.     

Cognitive deficits in the families of patients with schizophrenia

PURPOSE OF REVIEW: Studies of first-degree relatives of patients with schizophrenia over the past 25 years have reported a number of cognitive deficits, primarily in the domains of memory and executive function. Nevertheless, due to a number of methodological issues, such as including different types of relatives and not controlling for possible psychopathology, it is not yet clear that these findings can fully support a conclusion of heritability of cognitive dysfunction associated with a schizophrenia genotype. RECENT FINDINGS: Several recent meta-analyses have shown that the most consistent deficit shown by relatives is impaired performance on 'maintenance plus' frontal-lobe tasks requiring increased effort and higher central executive processing. Studies of multiplex families (multiple diagnoses in one family) also report that family members tend to have more difficulty on executive function tasks. Another interesting trend is research on subgroups of patients and relatives displaying distinct cognitive syndromes, particularly a subgroup with a generalized cognitive deficit. SUMMARY: As methodological designs improve, this field of study holds promise not only for understanding the neurobiological mechanisms of schizophrenia and the associated cognitive deficits, but also for possibly describing endophenotypes that may lead to identifying at-risk patients and relatives.     

Cognitive and behavioral profile of Perry syndrome in two families

ObjectivePerry syndrome (PS) is a rare neurodegenerative disorder with autosomal dominant inheritance caused by point mutations in DCTN1 and characterized by parkinsonism, hypoventilation, weight loss, and psychiatric symptoms. Even though behavioral manifestation is a main feature of PS, detailed neuropsychological assessment was not performed in this cohort. In this study, the neuropsychological profile of individuals from one Polish and one Colombian family are presented.MethodsDetailed clinical and neuropsychological data were obtained from Polish and Colombian families. Clinical and neuropsychological examinations on the proband from the Polish family were performed 6 times over 11 years. Each of 3 individuals from the Colombian family received a clinical and neuropsychological assessment.ResultsThe neurologic examination showed severe parkinsonism, levodopa-induced motor fluctuations, and dyskinesias in all cases. Respiratory insufficiency was observed in 2 patients and weight loss in 1 individual. Neuropsychological assessment revealed predominant deterioration of working memory and learning capacity in the Polish patient. He also demonstrated compulsive behaviors, such as excessive shopping and eating, but only in the “on” phase. In the Colombian family, attentional deficits were present in 2 out of 3 cases. Out of 4 reported cases apathy and depressed mood were present in 2 individuals. Two cases demonstrated impulsivity and one had episodes of hypomania.ConclusionsBoth of these families revealed relatively similar neurologic and neuropsychological profiles. The Polish patient's behavioral and neuropsychological profile was mostly compatible with a behavioral variant of frontotemporal dementia. Of note, not only depression and apathy, but also impulsivity can occur in PS.     

Lexical decision performances in P-type dyslexic,L-type dyslexic,and normal reading boys

Abstract

Lexical decision performances in P-type dyslexic, L-type dyslexic, and normal reading boys were investigated using three-letter and four-letter words (familiar words) and nonwords presented in the central visual field. For words, P-type dyslexics displayed significantly longer latencies for four-letter than for three-letter word decisions, whereas L-type dyslexics and normal readers did not. For nonwords, all subject groups showed significantly larger mean latencies for four-letter than for three-letter nonword decisions. In general, the error data corresponded to the latency data. L-type dyslexics, however, made more errors during four-letter words than during three-letter words, although they had similar latencies in both conditions. The results are discussed with reference to the hypothesis that P-type dyslexics would use a sequential processing mode for reading familiar words, whereas L-type dyslexics would employ a parallel processing mode for reading familiar words.     

Vertical saccades in dyslexic children

Vertical saccades have never been studied in dyslexic children. We examined vertical visually guided saccades in fifty-six dyslexic children (mean age: 10.5 ± 2.56 years old) and fifty-six age matched non dyslexic children (mean age: 10.3 ± 1.74 years old). Binocular eye movements were recorded using an infrared video-oculography system (mobileEBT®, e(ye)BRAIN). Dyslexic children showed significantly longer latency than the non dyslexic group, also the occurrence of anticipatory and express saccades was more important in dyslexic than in non dyslexic children. The gain and the mean velocity values were significantly smaller in dyslexic than in non dyslexic children. Finally, the up–down asymmetry reported in normal population for the gain and the velocity of vertical saccades was observed in dyslexic children and interestingly, dyslexic children also reported an up–down asymmetry for the mean latency. Taken together all these findings suggested impairment in cortical areas responsible of vertical saccades performance and also at peripheral level of the extra-ocular oblique muscles; moreover, a visuo-attentionnal bias could explain the up–down asymmetry reported for the vertical saccade triggering.     

Impaired parvocellular pathway in dyslexic children

Recent studies report that some children with dyslexia have impaired visual processing, specifically in the fast-processing magnocellular pathway. The objective was to study the effect of varying luminance and temporal and spatial frequency on the latency and amplitude of the visual evoked potentials (VEPs) in normal and dyslexic Egyptian children who speak Arabic (a right-left reading and writing system). VEPs were recorded in 52 dyslexic and 41 normal children in the fourth grade using a black and white checkerboard pattern with different checkerboard sizes and different rates of stimuli at high- and low-contrast media. The peak of the major positive wave component (P100) of each waveform and the trough of the previous major negative wave component were identified, and the peak-to-trough amplitude was measured. The latency and amplitude of VEPs in response to different experimental conditions showed significant shortening of P100 latency under high-contrast media and under low spatial frequency in children with dyslexia compared with normal readers. Furthermore, dyslexia children showed prolonged P100 latency in response to high spatial frequency stimulation compared with the low spatial frequency (P=0.003) and significantly higher N1-P1 amplitude under high-contrast media compared with low-contrast media (P=0.02), whilst no such changes were observed in normal readers. These results are suggestive of deficiency within the parvocellular pathway rather than the magnocellular pathway. As reading apparently places demands primarily on the ability to discriminate fine details, which is to say, on the parvocellular system, we suggested that deficiency in this system, at least in Arabic speaking children, could be a predisposing factor in dyslexia.     

Reduced interhemispheric coherence in dyslexic adults

Introduction

Developmental dyslexia has been associated with reduced interhemispheric neural connectivity in children. The present study investigated functional interhemispheric connectivity in male dyslexic adults.

Methods

A group of 19 dyslexic men were compared to a group of 15 controls on interhemispheric coherence of the dominant frequency in the power spectrum during a visuo-spatial attention task. The coherence between a left hemisphere central-parietal electrode and the respective right hemisphere electrode and surrounding sites was analysed.

Results

Compared to controls, the dyslexic group demonstrated reduced, and more diffuse, interhemispheric coherence of alpha activity in the central-parietal cortex. No group differences in interhemispheric coherence were found on frontal, temporal or central sites.

Conclusions

The deviant pattern of functional connectivity in dyslexics is suggestive of an altered development of neural circuitry that may lead to deficits in magnocellular processing.     

Attentional engagement deficits in dyslexic children

Reading acquisition requires, in addition to appropriate phonological abilities, accurate and rapid selection of sublexical orthographic units by attentional letter string parsing. Spatio-temporal distribution of attentional engagement onto 3-pseudoletter strings was studied in 28 dyslexic and 55 normally reading children by measuring attentional masking (AM). AM refers to an impaired identification of the first of two sequentially presented masked objects (O1 and O2). In the present study, O1 was always centrally displayed, whereas the location of O2 (central or lateral) and the O1-O2 interval were manipulated. Dyslexic children showed a larger AM at the shortest O1-O2 interval and a sluggish AM recovery at the longest O1-O2 interval, as well as an abnormal lateral AM. More importantly, these spatio-temporal deficits of attentional engagement were selectively present in dyslexics with poor phonological decoding skills. Our results suggest that an inefficient spatio-temporal distribution of attentional engagement - probably linked to a parietal lobule dysfunction - might selectively impair the letter string parsing mechanism during phonological decoding.     

Temporal envelope perception in dyslexic children

Speech intelligibility depends heavily on the accurate perception of auditory temporal envelope cues, that is the slower amplitude modulations present in the speech waveform. In a previous study, McAnally and Stein demonstrated that dyslexics may show impaired audibility (i.e. detectability) of these envelope cues. In the present psychophysical study, the ability to process temporal envelope cues was further investigated in dyslexic children by measuring detection thresholds of sinusoidal amplitude-modulation (SAM) and discrimination thresholds of SAM depth and SAM rate. Each threshold was measured at slow and fast SAM rates of 4 and 128 Hz, respectively. Overall, SAM thresholds were higher in dyslexics than in controls at both rates. The strongest deficit was observed at 4 Hz in the SAM detection task, but a deficit was also apparent at 128 Hz in the SAM discrimination tasks. Therefore, these results reveal that, in addition to reduced audibility of slow and fast envelope cues, some dyslexic children show poor encoding fidelity for these cues (as measured by the discrimination tasks). Overall, these findings are consistent with Tallal's hypothesis according to which the speech and reading deficits in some dyslexics may be caused by impaired temporal processes.     

Ageing makes us dyslexic

Background: Cross-linguistic studies on the production and comprehension of wh-questions and relative clauses, have revealed selective deficits in agrammatism with better performance observed in (a) subject questions and relative clauses compared to object ones; (b) object non-referential who questions compared to object referential questions; and (c) object what questions compared to object who questions. These selective deficits have been discussed within several neurolinguistic accounts (i.e., D-Linking Hypothesis, Derived Order Problem Hypothesis, and Relativised Minimality), which make different predictions. Limited research on wh-questions and relative clauses has been conducted in Greek agrammatism with inconclusive results, leaving open the question of which linguistic factors affect the agrammatic performance and which account best explains the attested patterns.

Aims: The aim of the present study is twofold: (a) to investigate the role of three linguistic factors (syntactic function, referentiality, and φ-features) in the production and comprehension of wh-questions and relative clauses in six agrammatic Greek-speaking participants; and (b) to examine which neurolinguistic account can explain the observed patterns.

Methods and Procedures: Two elicitation tasks (one for wh-questions and one for relative clauses) and two picture-pointing tasks (one for wh-questions and one for relative clauses) were used. All tasks targeted the following structures: referential and non-referential (who/what) questions, half with subject and half with object extraction, and relative clauses, half with subject and half with object dependencies.

Outcomes and Results: Referentiality had a greater impact οn the production and comprehension of wh-questions compared to the other two linguistic factors under investigation, i.e., syntactic function and φ-feature assignment. Syntactic function did not affect the production or comprehension of relative clauses given that no subject/object dissociations were attested.

Conclusion: With respect to wh-questions, the patterns observed in our data can be accounted for within the D-Linking Ηypothesis. The lack of subject/object dissociations attested in relative clauses is attributed to the case mismatch between the head of the relative clause and the relativisation site, and to the high proportion of complementiser omission observed in these structures.     

Immune and autoimmune diseases in dyslexic children

One hundred and five dyslexic and 105 control children were compared for frequency of immune diseases, autoimmune diseases, and non-right-handedness in the light of the Geschwind-Behan (1982) "testosterone hypothesis". The results showed significantly more immune- and autoimmune-diseases int he dyslexic group. There were no differences between the groups in the frequency of non-right-handedness. There were no interactions with gender, although there were more non-right-handed boys than girls in the total sample. Mothers of children who were dyslexic experienced significantly more negative life-events during pregnancy, they also experienced the pregnancy as more difficult, and they had more spontaneous abortions. In conclusion, the results support some aspects of the "testosterone hypothesis", but they also point to a more complex pattern of interaction between the factors that still remain unanswered.     

Ideogram reading in normal and dyslexic children

This study was concerned with the ideogram reading performances of groups of reading disabled and normal children. While adults with acquired alexia have associated defects in ideogram reading, all of the dyslexic children performed at normal adult levels. It was found that ideogram reading in control children is rather slow to develop, with only 7 and 8 year old subjects performing like normal adults; this is in contrast to other reading-related cognitive tasks in which normal performance develops earlier.     

Dichotic listening and spect in dyslexic children

Dichotic listening (DL) was evaluated in 36 children with: verbal dichotic listening test, alternating disyllable dichotic test and non-verbal dichotic listening test. Children were separated into two groups: experimental group with 18 dyslexic children and control group with 18 normal children. Both groups were comparable in gender, laterality and social-economic level. All dyslexic children underwent neuroimaging exam (SPECT). Our data showed that there was a statistical difference between both groups in all DL tests. Abnormal SPECT findings were seen in 50% of the dyslexic children, hypoperfusion of the left temporal lobe being the most frequent abnormality. We conclude that dyslexic children present an impairment of central neurologic processing that may be detected by DL tests, and by functional imaging exam, such as SPECT, as well.     

Diminished auditory mismatch fields in dyslexic adults

Electroencephalographic studies have demonstrated smaller auditory responses to infrequent deviances of speech and nonspeech sounds in dyslexic than normal-reading subjects. We used a whole-scalp neuromagnetometer to study selectively reactivity of the auditory cortices to sound deviances in 8 dyslexic and 11 normal-reading adults. Within a monotonous sequence of 50-millisecond 1000 Hz binaural tones, tones of 920 and 1080 Hz occurred with 7% probability each. Magnetic mismatch fields, elicited by the stimulus deviances, were diminished in the left hemisphere of the dyslexic subjects. The results indicate deficient change detection in the left auditory cortex of right-handed dyslexic adults.