Implicit procedural learning in fragile X and Down syndrome

The validity of learning potential for predicting educational adjustment in preschoolers with Down syndrome: A longitudinal study

Learning Potential tests aim to assess cognitive functioning using mediation strategies by observing subsequent changes in learning patterns. In this study, this methodology was applied with the Preschool Learning Potential and Abilities Scale and two additional tests, the Kaufman Brief Intelligence Test and the Battery of Aptitudes for School Learning I, to a total of 58 children with Down Syndrome, at four and six years of age. The results demonstrate improvements in general intelligence, learning potential, and school aptitudes between the two timepoints. There was a significant, positive relationship between the variables measured in the different tests, as well as on the predictive variables of school aptitudes, in these children at six years of age. There is evidence that supports the use of this dynamic evaluation methodology, opening new fields of action in child evaluation processes.

Acquisition of Reading and Intellectual Development Disorder

We propose a review of the literature of the studies investigating reading acquisition in intellectual deficiency (ID), with particular focus on the explanatory factors for reading difficulties. Indeed, we explore the role of intellectual efficiency, perceptual abilities, oral language development, phonological processing and memory. The study of reading acquisition in ID is a challenge because of a high degree of heterogeneity in the results which, together with other variables influencing learning and development. This review has allowed us to understand that there are multiple reasons why individuals with ID have difficulty learning to read. More specifically, there is a link between reading skills and certain cognitive skills, such as perception, oral language, phonological processing and working memory.

Evidence of stable individual differences in implicit learning

There is a fundamental psychological and neuropsychological distinction between explicit and implicit memory, and it has been proposed that whereas there are stable trait individual differences in explicit memory ability, there are not such differences across people for implicit learning. There is, however, little evidence about whether or not there are stable trait differences in implicit learning. Here we performed a test-retest reliability study with healthy young adults in which they performed four implicit learning tasks (artificial grammar learning, probabilistic classification, serial response, and implicit category learning) twice, about a week apart. We found medium (by Cohen's guidelines) test-retest reliability for three of the tasks: probabilistic classification, serial response, and implicit category learning, suggesting that differences in implicit learning ability are more stable than originally thought. In addition, implicit learning on all tasks was unrelated to explicit measures: we did not find any correlation between implicit learning measures and independent measures of IQ, working memory, or explicit learning ability. These findings indicate that implicit learning, like explicit learning, varies reliably across individuals.

Distributional Cues to Language Learning in Children With Intellectual Disabilities

Purpose

In typical development, distributional cues-patterns in input-are related to language acquisition processes. Statistical and implicit learning refer to the utilization of such cues. In children with intellectual disability, much less is known about the extent to which distributional cues are harnessed in mechanisms of language learning.

Method

This tutorial presents what is known about the process of language learning in children with language impairments associated with different sources of intellectual disability: Williams syndrome, autism spectrum disorder, Down syndrome, and fragile X syndrome.

Results

A broad view is taken on distributional cues relevant to language learning, including statistical learning (e.g., transitional probabilities) and other patterns that support lexical acquisition (e.g., sensitivities to sound patterns, cross-situational word learning) or relate to syntactic development (e.g., nonadjacent dependencies).

Conclusions

Critical gaps in the literature are highlighted. Research in this area is especially limited for Down syndrome and fragile X syndrome. Future directions for taking learning theories into account in interventions for children with intellectual disability are discussed, with a focus on the importance of language input.

Memory profiles in Down syndrome across development: a review of memory abilities through the lifespan

Down syndrome (DS) is associated with a variety of cognitive impairments, notably memory impairments. Due to the high prevalence rates of early-onset dementia associated with DS, it is imperative to understand the comprehensive development of memory impairments beginning in childhood and into adulthood, as this may help researchers identify precursors of dementia at earlier stages of development and pinpoint targets for memory intervention. The current paper provides a systematic, developmentally focused review of the nature of memory difficulties in DS across the lifespan. Specifically, this review summarizes what is known about long-term, short-term, and working memory abilities (distinguishing between verbal and nonverbal modalities) in DS, compared to both mental age-matched typically developing peers and individuals with other forms of intellectual disability (ID) at three developmental stages (i.e., preschool, adolescence, and adulthood). Additionally, this review examines the degree of impairment reported relative to typically developing mental age-matched peers in the existing literature by examining effect size data across memory domains as a function of age. With few exceptions, memory abilities were impaired across the lifespan compared to mental age-matched typically developing peers. Relative to other groups with ID, research findings are mixed. Our review of the literature identified a scarcity of memory studies in early childhood, particularly for STM and WM. In adulthood, research was limited in the LTM and WM domains and very little research has compared memory abilities in older adults with DS to those with typical development. Looking to the future, longitudinal studies could provide a better understanding of the developmental trajectory of memory abilities in DS, and the possible associations between memory abilities and real-world functioning. This research could ultimately inform interventions to improve independence and overall quality of life for those with DS and their families.

Cognitive aspects: sequencing, behavior, and executive functions

The question posed today is not whether the cerebellum plays a role in cognition, but instead, how the cerebellum contributes to cognitive processes, even in the developmental age. The central role of the cerebellum in many areas of human abilities, motor as well as cognitive, in childhood as well as in adulthood, is well established but cerebellar basic functioning is still not clear and is much debated. Of particular interest is the changing face of cerebellar influence on motor, higher cognitive, and behavioral functioning when adult and developmental lesions are compared. The idea that the cerebellum might play quite different roles during development and in adulthood has been proposed, and evidence from experimental and clinical literature has been provided, including for sequencing, behavioral aspects, and executive functions Still, more data are needed to fully understand the changes of cerebrocerebellar interactions within the segregated loops which connect cerebrum and cerebellum, not only between childhood and adulthood but also in health and disease.

Short-term motor learning through non-immersive virtual reality task in individuals with down syndrome

Background

Down syndrome (DS) has unique physical, motor and cognitive characteristics. Despite cognitive and motor difficulties, there is a possibility of intervention based on the knowledge of motor learning. However, it is important to study the motor learning process in individuals with DS during a virtual reality task to justify the use of virtual reality to organize intervention programs. The aim of this study was to analyze the motor learning process in individuals with DS during a virtual reality task.

Methods

A total of 40 individuals participated in this study, 20 of whom had DS (24 males and 8 females, mean age of 19 years, ranging between 14 and 30 yrs.) and 20 typically developing individuals (TD) who were matched by age and gender to the individuals with DS. To examine this issue, we used software that uses 3D images and reproduced a coincidence-timing task.

Results

The results showed that all individuals improved performance in the virtual task, but the individuals with DS that started the task with worse performance showed higher difference from the beginning. Besides that, they were able to retain and transfer the performance with increase of speed of the task.

Conclusion

Individuals with DS are able to learn movements from virtual tasks, even though the movement time was higher compared to the TD individuals. The results showed that individuals with DS who started with low performance improved coincidence- timing task with virtual objects, but were less accurate than typically developing individuals.

Trial registration

ClinicalTrials.gov Identifier: NCT02719600.

A note on motor skill acquisition in mild and moderate Down syndrome individuals

This study investigated the acquisition of a serial motor skill in individuals with Down syndrome with two levels of handicap, mild group (mean age = 14.5 years, SD = 2.3, 7 individuals) and moderate group (mean age = 15.2 years, SD = 3.2, 7 individuals). The task involved single-arm sequential movements to five. The measures to access performance were overall sequence error, reaction time, and total movement time. To evaluate action program, formation variability of sequencing and relative timing variability were considered. Although there was no clear practice effect, the results showed that the level of handicap led to different strategies to plan and control the actions. The moderate group presented a less stable action program expressed in the variability in sequencing and timing. Their longer reaction times also suggest a heavy demand on central processing in accord with the one-target advantage hypothesis and also due to memory deficits to select and plan movements.

Learning potential and cognitive abilities in preschool boys with fragile X and Down syndrome

BACKGROUND

Enhancing cognitive abilities is relevant when devising treatment plans.

AIMS

This study examined the performance of preschool boys with Down syndrome and fragile X syndrome in cognitive tasks (e.g., nonverbal reasoning and short-term memory), as well as in improving cognitive functions by means of a learning potential methodology.

METHODS AND PROCEDURES

The basic scales corresponding to the Skills and Learning Potential Preschool Scale were administered to children with Down syndrome and others with fragile X syndrome, matched for chronological age and nonverbal cognitive development level.

RESULTS

The fragile X syndrome group showed stronger performance on short-term memory tasks than the Down syndrome group prior to intervention, with no differences recorded in nonverbal reasoning tasks. In addition, both groups' cognitive performance improved significantly between pre- and post-intervention. However, learning potential relative to auditory memory was limited in both groups, and for rule-based categorization in Down syndrome children.

CONCLUSION

The scale offered the opportunity to assess young children's abilities and identify the degree of cognitive modifiability. Furthermore, factors that may potentially affect the children's performance before and during learning potential assessment are discussed.

Allocentric spatial learning and memory deficits in Down syndrome

Studies have shown that persons with Down syndrome (DS) exhibit relatively poor language capacities, and impaired verbal and visuoperceptual memory, whereas their visuospatial memory capacities appear comparatively spared. Individuals with DS recall better where an object was previously seen than what object was previously seen. However, most of the evidence concerning preserved visuospatial memory comes from tabletop or computerized experiments which are biased toward testing egocentric (viewpoint-dependent) spatial representations. Accordingly, allocentric (viewpoint-independent) spatial learning and memory capacities may not be necessary to perform these tasks. Thus, in order to more fully characterize the spatial capacities of individuals with DS, allocentric processes underlying real-world navigation must also be investigated. We tested 20 participants with DS and 16 mental age-matched, typically developing (TD) children in a real-world, allocentric spatial (AS) memory task. During local cue (LC) trials, participants had to locate three rewards marked by local color cues, among 12 locations distributed in a 4 m × 4 m arena. During AS trials, participants had to locate the same three rewards, in absence of LCs, based on their relations to distal environmental cues. All TD participants chose rewarded locations in LC and AS trials at above chance level. In contrast, although all but one of the participants with DS exhibited a preference for the rewarded locations in LC trials, only 50% of participants with DS chose the rewarded locations at above chance level in AS trials. As a group, participants with DS performed worse than TD children on all measures of task performance. These findings demonstrate that individuals with DS are impaired at using an AS representation to learn and remember discrete locations in a controlled environment, suggesting persistent and pervasive deficits in hippocampus-dependent memory in DS.

Symbolic sequence learning is associated with cognitive-affective profiles in female FMR1 premutation carriers

This study examines implicit sequence learning impairments that may indicate at-risk cerebellar profiles proposed to underlie some aspects of subtle cognitive and affective dysfunctions found among female fragile X mental retardation 1 (FMR1) premutation (PM)-carriers. A total of 34 female PM-carriers and 33 age- and intelligence-matched controls completed an implicit symbolically primed serial reaction time task (SRTT) previously shown to be sensitive to cerebellar involvement. Implicit learning scores indicated a preservation of learning in both groups; however, PM-carriers demonstrated poorer learning through significantly elevated response latencies overall and at each specific block within the symbolic SRTT. Group comparisons also revealed a core deficit in response inhibition, alongside elevated inattentive symptoms in female PM-carriers. Finally, strong and significant associations were observed between poor symbolic SRTT performance and executive, visuospatial and affective deficits in the PM-carrier group. These associations remained strong even after controlling motor speed, and were not observed in age- and intelligence quotient-matched participants. The findings implicate cerebellar non-motor networks subserving the implicit sequencing of responses in cognitive-affective phenotypes previously observed in female PM-carriers. We contend that symbolic SRTT performance may offer clinical utility in future pharmaceutical interventions in female PM-carriers.

Developmental molecular and functional cerebellar alterations induced by PCP4/PEP19 overexpression: implications for Down syndrome

PCP4/PEP19 is a modulator of Ca(2+)-CaM signaling. In the brain, it is expressed in a very specific pattern in postmitotic neurons. In particular, Pcp4 is highly expressed in the Purkinje cell, the sole output neuron of the cerebellum. PCP4, located on human chromosome 21, is present in three copies in individuals with Down syndrome (DS). In a previous study using a transgenic mouse model (TgPCP4) to evaluate the consequences of 3 copies of this gene, we found that PCP4 overexpression induces precocious neuronal differentiation during mouse embryogenesis. Here, we report combined analyses of the cerebellum at postnatal stages (P14 and adult) in which we identified age-related molecular, electrophysiological, and behavioral alterations in the TgPCP4 mouse. While Pcp4 overexpression at P14 induces an earlier neuronal maturation, at adult stage it induces increase in cerebellar CaMK2alpha and in cerebellar LTD, as well as learning impairments. We therefore propose that PCP4 contributes significantly to the development of Down syndrome phenotypes through molecular and functional changes.

Cognition in Down syndrome: a developmental cognitive neuroscience perspective

Down syndrome (DS) is the most common genetic form of intellectual disability. DS results in a characteristic profile of cognitive and neurological dysfunction. The predominant theory of the pattern of neural deficits in this syndrome suggests that DS affects 'late-developing' neural systems, including the function of the prefrontal cortex and hippocampus. In order to evaluate the validity of this theory, in this review, I highlight data addressing the neurological and cognitive phenotype in DS across development. In particular, I address the evidence suggesting that DS may impact late-developing neural systems and end with the conclusion that some cognitive difficulties in DS must result from poor communication between late-developing regions. Analogous to recent theories of cognitive processing in autism, cognitive deficits in DS may be substantially impacted by less efficient interregional communication. Finally, I discuss some ways in which understanding the impact of altered neurodevelopment in DS has the potential to inform our understanding of species-typical trajectories of cognitive development. WIREs Cogn Sci 2013, 4:307-317. doi: 10.1002/wcs.1221 For further resources related to this article, please visit the WIREs website.