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PubMed1989

Study of the similar structure hypothesis with mentally retarded adults and nonretarded children of comparable mental age.

The similar structure hypothesis was tested by comparing the performance of mentally retarded adults and their nonretarded mental age peers on a series of Piagetian tasks. We controlled for variables that influence the testing of mentally retarded subjects and performance on Piagetian tasks. Statistical analysis revealed that five tests favored the developmental position whereas two tests favored the difference position. Qualitative analysis provided reason to question the validity of two of the seven tests. Nevertheless, the evidence still favored the developmental position 4:1. Corollaries challenged the use of vocabulary tests for matching and raised a caveat concerning the acquisition by mentally retarded adults of key concrete operations skills.

Adult↗
PubMed1988

Intrauterine radiation exposures and mental retardation.

Small head size and mental retardation have been known as effects of intrauterine exposure to ionizing radiation since the 1920s. In the 1950s, studies of Japanese atomic-bomb survivors revealed that at 4-17 wk of gestation, the greater the dose, the smaller the brain (and head size), and that beginning at 0.5 Gy (50 rad) in Hiroshima, mental retardation increased in frequency with increasing dose. No other excess of birth defects was observed. Otake and Schull (1984) pointed out that the period of susceptibility to mental retardation coincided with that for proliferation and migration of neuronal elements from near the cerebral ventricles to the cortex. Mental retardation could be the result of interference with this process. Their analysis indicated that exposures at 8-15 wk to 0.01-0.02 Gy (1-2 rad) doubled the frequency of severe mental retardation. This estimate was based on small numbers of mentally retarded atomic-bomb survivors. Although nuclear accidents have occurred recently, new cases will hopefully be too rare to provide further information about the risk of mental retardation. It may be possible, however, to learn about lesser impairment. New psychometric tests may be helpful in detecting subtle deficits in intelligence or neurodevelopmental function. One such test is PEERAMID, which is being used in schools to identify learning disabilities due, for example, to deficits in attention, short- or long-term memory, or in sequencing information. This and other tests could be applied in evaluating survivors of intrauterine exposure to various doses of ionizing radiation. The results could change our understanding of the safety of low-dose exposures.

Brain↗
PubMed1998

Cognitive representation of motion in individuals with mental retardation.

Participants with and without mental retardation were compared on their tendency to show the representational momentum effect when viewing a stimulus array that implied motion. The representational momentum effect occurs when, due to implied or apparent motion, an object is more likely to be remembered slightly shifted in the direction of motion rather than against the direction of motion. Participants with mental retardation showed the representational momentum effect as did participants without mental retardation, though the magnitude of the memory shift was smaller for participants with mental retardation. Results suggest that individuals with mental retardation cognitively process motion information in the same general way as do those without mental retardation, although less efficiently.

Adolescent↗
PubMed2006

Variants in the RAB3A gene are not associated with mental retardation in the Chinese population.

Mental retardation is a common form of cognitive impairment among children. The underlying causes of mental retardation are extremely heterogeneous, and include significant genetic factors. The coexistence of neuropathology and cognitive deficits supports the view that mental retardation is a disorder of brain development and plasticity. Rab3A, a member of the Rab small G protein family, is a key molecule in modulating basal neurotransmission and contributes to synaptic plasticity. The RAB3A gene is located on chromosome 19p13.11, near a region shown by a linkage study to be involved in the etiology of mental retardation. Because of both its function and chromosomal location, RAB3A is a potential candidate susceptibility gene for mental retardation. To investigate the possible genetic contribution of the RAB3A gene, we performed a case-control association study focused on the Han population of northwestern China using four common SNPs in the gene (rs7259012, rs17683539, rs2271882, and rs874628). Pairwise linkage disequilibrium analysis showed that the four SNPs were in linkage disequilibrium. However, there were no significant differences of either allele or genotype frequencies at any of the SNPs nor any significant differences in haplotype distributions between cases and controls. In conclusion, we have found no evidence for RAB3A conferring susceptibility on mental retardation in the Han Chinese population.

Adolescent↗
PubMed1978

National crisis in mental retardation research.

The incidence of mental retardation will be significantly reduced only when we have a greater understanding of the nonorganic form of mental retardation, the type that afflicts approximately 75 percent of persons labeled mentally retarded. Such an understanding requires an interdisciplinary research effort that includes a major contribution from the behavior sciences. The current level of support of mental retardation and behavior science research by the National Institute of Child Health and Human Development limits the nation's capability of achieving the goals of preventing and ameliorating mental retardation.

Child Development↗