Anomalous cerebral lateralization and Down syndrome

Computerized physical and cognitive training improves the functional architecture of the brain in adults with Down syndrome: A network science EEG study

Understanding the neuroplastic capacity of people with Down syndrome (PwDS) can potentially reveal the causal relationship between aberrant brain organization and phenotypic characteristics. We used resting-state EEG recordings to identify how a neuroplasticity-triggering training protocol relates to changes in the functional connectivity of the brain's intrinsic cortical networks. Brain activity of 12 PwDS before and after a 10-week protocol of combined physical and cognitive training was statistically compared to quantify changes in directed functional connectivity in conjunction with psychosomatometric assessments. PwDS showed increased connectivity within the left hemisphere and from left-to-right hemisphere, as well as increased physical and cognitive performance. Our findings reveal a strong adaptive neuroplastic reorganization as a result of the training that leads to a less-random network with a more pronounced hierarchical organization. Our results go beyond previous findings by indicating a transition to a healthier, more efficient, and flexible network architecture, with improved integration and segregation abilities in the brain of PwDS. Resting-state electrophysiological brain activity is used here for the first time to display meaningful relationships to underlying Down syndrome processes and outcomes of importance in a translational inquiry. This trial is registered with ClinicalTrials.gov Identifier NCT04390321.

Lexical decision performance using the divided visual field technique following training in adults with intellectual disabilities with and without Down syndrome

Studies of brain lateralization in individuals with non-specific intellectual disability and Down syndrome suggest atypical brain lateralization to speech perception. According to the biological dissociation model, the right hemisphere (RH) mediates speech perception and the left hemisphere (LH) mediates motor control in Down syndrome. The current study aimed to test, for the first time, brain lateralization in both non-specific intellectual disability and Down syndrome, compared to individuals with typical development. Furthermore, bilateral word presentation was utilized to assess interhemispheric communication. Twenty adults with non-specific intellectual disability, 14 adults with Down syndrome, and 30 adults with typical development participated in the study. Participants in the non-specific intellectual disability and Down syndrome groups were trained to perform the task prior to the experiment. The results showed that whereas hemispheric lateralization did not differ between individuals with non-specific intellectual disability and typical development, individuals with DS showed reduced brain lateralization in comparison to adults with typical development. All three groups showed no significant difference between words presented to the LH and bilaterally. Our results also show that individuals with intellectual disabilities can benefit from training programmes and that they may perform equally as fast as their typically developing peers.

Visual filtering and covert orienting in persons with Down syndrome

A forced-choice reaction time (RT) task was used to examine the efficiency of visual filtering (the inhibition of processing of irrelevant stimuli) and covert orienting (shifts of visual attention independent of eye movement) components of attention in persons with Down syndrome ( n = 20) and children of average intelligence ( n = 20) matched for mental age (MA) (average MA = approximately 5.4 years). Conditions varied with regard to presence or absence of distractors, and the validity (valid, invalid, or neutral) of location cues. Contrary to expectations, persons with Down syndrome and MA-matched children of average intelligence at approximately age 5 showed similar patterns of performance on a task that required filtering distracting stimuli and searching for relevant information in the visual field. Both groups responded more efficiently to a target preceded by a valid cue as compared to a target preceded by an invalid or neutral cue. In addition, performance was more efficient with a target that was presented without irrelevant information as compared to one that was flanked on either side by extraneous, nontarget information and therefore necessitated filtering for efficient performance. These two findings indicate that: (1) disengaging from the location of an incorrect cue, and then searching for, locating, and responding to a target requires more time and attention than simply locating and responding to a target that has been validly cued; and (2) processing and responding to a target flanked by extraneous information entails filtering, and therefore requires more time and resources than simply responding to a target without distractors. In general, the development of visual reflexive, covert orienting, and filtering are intact in persons with Down syndrome relative to their level of functioning at an MA level of approximately 5 years, a period that is critical in the development of attentional processes.

Infants with Down syndrome and their interactions with objects: development of exploratory actions after reaching onset

During infant development, objects and their functions are learned by means of active exploration. Factors that may influence exploration include reaching and grasping ability, object properties and the presence of developmental disorders. We assessed the development of exploratory actions in 16 typically-developing (TD) infants and 9 infants with Down syndrome (DS) after reaching onset. Infants with DS reached for and explored objects less frequently than TD infants, especially small objects. Over time, the amount of reaches increased in both groups, with no changes in the amount of exploration in the DS group. Pre-grasping actions were different across objects, but less efficient in generating action-relevant information in the DS group. These infants also performed fewer behaviors requiring complex motor skills. The results suggest that perceptual-motor abilities determine different exploratory behaviors in TD and DS infants. The reduced amount and complexity of exploratory actions may impact developmental outcome in DS.

Preferência podal em lactentes com síndrome de Down: fatores extrínsecos e intrínsecos

Durante o processo de aquisição do chute em lactentes, a preferência podal pode ser influenciada de forma diferente pelos fatores extrínsecos e intrínsecos. O objetivo foi comparar a preferência podal e verificar a influência do peso adicional e do Reflexo Tônico Cervical Assimétrico (RTCA) na preferência podal entre lactentes com síndrome de Down e típicos. Participaram do estudo cinco lactentes com síndrome de Down e cinco típicos aos três e quatro meses de idade. O experimento foi subdividido em quatro condições experimentais: Treinamento, Linha de Base, Peso e Pós-Peso. Os lactentes com síndrome de Down apresentaram preferência à esquerda ou indefinida e os típicos, preferência à direita. O RTCA influenciou na preferência podal em ambos os grupos, indicando que o lado de rotação da cabeça orientou o chute do mesmo lado. Nos lactentes com síndrome de Down a correlação entre RTCA e chutes foi positiva, sendo forte aos três meses e moderada aos quatro meses. Para os lactentes típicos foi observada correlação positiva fraca aos três meses, e aos quatro meses a correlação não foi estatisticamente significativa. Lactentes com síndrome de Down apresentam preferência podal contrária aos lactentes típicos. O RTCA exerce influência na preferência podal por um período mais longo em lactentes com síndrome de Down em comparação aos lactentes típicos.

Reversal of handedness effects on bimanual coordination in adults with Down syndrome

BACKGROUND

Research on unimanual tasks suggested that motor asymmetries between hands may be reduced in people with Down syndrome. Our study examined handedness (as assessed by hand performance) and perceptual-motor integration effects on bimanual coordination.

METHODS

Adults with Down syndrome (13 non-right-handed, 22 right-handed), along with comparison groups of adults (16 non-right-handed, 21 right-handed) and children (15 non-right-handed, 22 right-handed) without Down syndrome, drummed with auditory, verbal and visual instructions.

RESULTS

In contrast to handedness effects in the children and adults without Down syndrome, right-handed participants with Down syndrome led more with the left hand, and had lower coordination stability than non-right-handed participants with Down syndrome.

CONCLUSIONS

The reversed handedness effect during bimanual coordination suggests a complex relationship between handedness and task requirements in adults with Down syndrome.

Atypical cerebral lateralisation in adults with compensated developmental dyslexia demonstrated using functional transcranial Doppler ultrasound

Functional transcranial Doppler ultrasound (fTCD) is a relatively new and non-invasive technique that assesses cerebral lateralisation through measurements of blood flow velocity in the middle cerebral arteries. In this study fTCD was used to compare functional asymmetry during a word generation task between a group of 30 dyslexic adults and a group of 30 non-dyslexic individuals. In light of previous evidence of atypical laterality in dyslexia, a reduced leftward asymmetry was predicted and confirmed. We know from previous research that most people with atypical language lateralisation have normal language and literacy skills: nevertheless, our results confirm that language laterality is reduced in those with dyslexia. Theoretical explanations for this apparent conundrum are discussed.

Abnormal fMRI activation pattern during story listening in individuals with Down syndrome

Down syndrome is characterized by disproportionately severe impairments of speech and language, yet little is known about the neural underpinnings of these deficits. We compared fMRI activation patterns during passive story listening in 9 young adults with Down syndrome and 9 approximately age-matched, typically developing controls. The typically developing group exhibited greater activation than did the Down syndrome group in classical receptive language areas (superior and middle temporal gyri) for forward > backward speech; the Down syndrome group exhibited greater activation in cingulate gyrus, superior and inferior parietal lobules, and precuneus for both forward speech > rest and backward speech > rest. The Down syndrome group showed almost no difference in activation patterns between the language (forward speech) and nonlanguage (backward speech) conditions.

Linguistic lateralization in adolescents with Down syndrome revealed by a dichotic monitoring test

Linguistic lateralization in 10 adolescents with Down syndrome (average age: 15.7 years), 15 adolescents with intellectual disabilities of unknown etiology (average age: 17.8 years), 2 groups of children without disabilities (11 children, average age: 4.7 years; 10 children, average age: 8.5 years), and 14 adolescents without disabilities (average age: 18.7 years) was examined, using a dichotic monitoring test (DMT). Different Japanese words with 2 consonant-vowel syllables were presented to each ear simultaneously. Participants pressed a button when they heard the target word. The younger children without disabilities and the adolescents with intellectual disabilities exhibited a right-ear advantage, whereas the adolescents with Down syndrome showed the reverse pattern, i.e., a left-ear advantage. These results suggest that there is atypical linguistic lateralization in adolescents with Down syndrome.

Linguistic profile of individuals with Down syndrome: comparing the linguistic performance of three developmental disorders

An increasing number of studies, addressing the linguistic abilities of individuals with Down syndrome (DS) suggest that they exhibit strengths and weaknesses within the linguistic domain. This article critically reviews the literature on the linguistic profile of individuals with DS, with particular emphasis on the expression and reception of vocabulary and grammar, including nonverbal linguistic expression during infant development. In doing so, attention is given to recent comparative studies of the linguistic abilities of individuals with DS, Specific Language Impairment (SLI), and Williams syndrome (WS). The possibility that deficits in one cognitive system may have consequences in another cognitive system, and that these consequences may define the nature of the impairment in each clinical syndrome is further discussed with suggestions for future research.

Interhemispheric transmission time in persons with Down syndrome

BACKGROUND

The study of cerebral specialization in persons with Down syndrome (DS) has revealed an anomalous pattern of organization. Specifically, persons with DS elicit a right cerebral hemisphere lateralization for receptive language and a left cerebral hemisphere lateralization for the production of simple and complex movements: a pattern quite different from the left hemisphere lateralization typically characterizing the aforementioned processes in the non-DS population. It is thought that the putative separation between speech perception and movement planning systems as well as the cost of interhemispheric integration impedes verbal-motor behaviours in persons with DS. Moreover, morphological anomalies of callosal structure may further amplify between-hemisphere communication difficulties in the DS population. In the present investigation, we employed a behavioural technique (i.e. the Poffenberger paradigm; Poffenberger) to determine whether global anomalies of callosal structure further amplify deficits in interhemispheric communication.

METHODS

Fourteen individuals with DS and 25 chronological age-matched and gender-equated participants without intellectual disability performed a visuomotor reaction time (RT) test with their left or right hand to visual stimuli appearing left or right of visual fixation. Typically it is reported that responses to visual stimuli appearing ipsilateral to the responding hand (i.e. the uncrossed condition) are faster than responses wherein visual stimuli and responding hand are contralaterally mapped (i.e. the crossed condition). The increased RT associated with the crossed condition is reported on the order of 4 ms and has been interpreted to reflect the physiological result of interhemispheric transmission.

RESULTS

Not surprisingly persons with DS exhibited slower and more variable RTs relative to control counterparts. In addition, a reliable RT advantage favouring the uncrossed conditions was observed among control participants but not persons with DS.

CONCLUSIONS

In keeping with the extant literature, RT performance of the DS group was slower and more variable than control counterparts. This finding has been interpreted to reflect an 'adaptive reaction' wherein the perceptual-motor abilities of persons with DS are not optimized to respond to externally paced stimuli. In terms of evaluating interhemispheric transmission via the Poffenberger paradigm, our results show the finite measures of explicit brain-behaviour relations characterizing so-called healthy controls are not always tenable in the DS population. Indeed, we believe such a finding underpins the aforementioned 'adaptive reaction' exemplifying preferred movement control in persons with DS.

Speech perception and motor control in children with Down syndrome

Twelve children with and without Down syndrome (DS) performed eight subtests of an apraxia battery to determine under what conditions children with DS had difficulty performing representational and nonrepresentational gestures. Participants with DS also completed a dichotic listening test. Participants with DS performed just as well as control participants on all aspects of the apraxia battery except a subtest in which they were required to pantomime tool use from verbal instruction. This suggests that children with DS have difficulty generating an action from memory following verbal instruction. Given the sufficient context or visual demonstration, children with DS performed similar to the other participants. As well, there was a great deal of within-group variability for dichotic listening ear advantage. Participants with a greater left ear advantage on the dichotic listening test committed more errors on an imitation test that also included a verbal component than participants with a greater right ear advantage.

Multimodal inhibition of return effects in adults with and without Down syndrome

Data from a previous study (Welsh & Elliott, 2001) has been reanalyzed to explore inhibition of return (IOR) effects in adults with and without Down syndrome (DS). Participants were required to react and move with either the left or right hand as quickly as possible to 1 of 2 target locations based on either a visual or a verbal cue. Although persons with DS demonstrated a different pattern of information processing capabilities, they demonstrated the same magnitude of IOR across all conditions of presentation as their peers without DS. This pattern of results provides further support for the multimodal and response-based nature of IOR. Moreover, the results indicate that the inhibitory processes that underlie IOR in the average population seem to be functional in persons with DS.

Speech production errors in adults with and without Down syndrome following verbal, written, and pictorial cues

Adults with Down syndrome and adults with developmental delays not related to Down syndrome were asked to read, repeat, and formulate speech from a picture following the presentation of 2- and 4-word and picture sequences. The speech sequences were produced either immediately after stimulus presentation or following a 5-sec response delay. Overall, participants with Down syndrome produced more memory errors than persons without Down syndrome. Participants with Down syndrome also committed more speech production errors than the other participants, but only when they were required to repeat what they had heard, or to formulate speech from pictures. The speech production performance of the two groups was equivalent in the read condition. These results are discussed with reference to Elliott, Weeks, and Elliott's (1987) model of cerebral specialization, and to verbal short-term memory in persons with Down syndrome.

Cerebral specialization and verbal-motor integration in adults with and without Down syndrome

Persons with Down syndrome (DS) tend to exhibit an atypical left ear-right hemisphere advantage (LEA) for the perception of speech sounds. In the present study, a recent adaptation of the dichotic listening procedure was employed to examine interhemispheric integration during the performance of a lateralized verbal-motor task. Although adults with DS (n = 13) demonstrated a right ear-left hemisphere advantage in the dichotic-motor task similar to their peers with (n = 14) and without undifferentiated developmental disabilities (n = 14), they showed an LEA in a free recall dichotic listening task. Based on a comparison of the laterality indices obtained from both dichotic listening procedures, it appears that the manifestation of lateral ear advantages in persons DS may dependent on the response requirements of the task.

Auditory information is beneficial for adults with Down syndrome in a continuous bimanual task

Much recent research using discrete unimanual tasks has indicated that individuals with Down syndrome (DS) have more difficulty performing verbal-motor tasks as compared to visual-motor tasks (see Perceptual-Motor Behavior in Down Syndrome, Human Kinetics, Champaign, IL, 2000, p. 305 for a review). In continuous tasks, however, individuals with DS perform better when movement is guided by auditory information compared to visual information (Downs Syndr.: Res. Prac. 4 (1996) 25; J. Sport Exercise Psy. 22 (2000) S90). The aim of the present study was to investigate if there are any differences for adults with DS between visual, auditory and verbal guidance in a continuous bimanual task. Ten adults with DS, 10 adults without DS and 10 typically developing children drew lines bimanually towards the body (down) and away from the body (up) following three different guidance conditions: visual (flashing line), auditory (high tone, low tone), and verbal ("up", "down"). All participants produced mostly in-phase movements and were close to the 1000 ms target time for all guidance conditions. The adults with DS, however, displayed greater variability in their movement time, movement amplitude and bimanual coordination than adults without DS. For all groups, the left hand was slower and more variable in producing the lateral movements than the right hand. The results regarding guidance information suggest that auditory information is beneficial for repetitive bimanual tasks for adults with DS. Possible mechanisms that cause these results will be discussed.

Cerebral specialization for speech production in persons with Down syndrome

The study of cerebral specialization in persons with Down syndrome (DS) has revealed an anomalous pattern of organization. Specifically, dichotic listening studies (e.g., Elliott & Weeks, 1993) have suggested a left ear/right hemisphere dominance for speech perception for persons with DS. In the current investigation, the cerebral dominance for speech production was examined using the mouth asymmetry technique. In right-handed, nonhandicapped subjects, mouth asymmetry methodology has shown that during speech, the right side of the mouth opens sooner and to a larger degree then the left side (Graves, Goodglass, & Landis, 1982). The phenomenon of right mouth asymmetry (RMA) is believed to reflect the direct access that the musculature on the right side of the face has to the left hemisphere's speech production systems. This direct access may facilitate the transfer of innervatory patterns to the muscles on the right side of the face. In the present study, the lateralization for speech production was investigated in 10 right-handed participants with DS and 10 nonhandicapped subjects. A RMA at the initiation and end of speech production occurred for subjects in both groups. Surprisingly, the degree of asymmetry between groups did not differ, suggesting that the lateralization of speech production is similar for persons with and persons without DS. These results support the biological dissociation model (Elliott, Weeks, & Elliott, 1987), which holds that persons with DS display a unique dissociation between speech perception (right hemisphere) and speech production (left hemisphere).