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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Autism is a syndrome with multiple etiologies, as is made clear both by the evidence of neurobiological research and by the catalog of disorders that present with autistic behaviors. What remains unclear are the specific neuropathological mechanisms that produce autistic behaviors; for example, is there a common neuroanatomic pathology for all cases of autism, or can autistic behaviors emerge from different pathological sequences within the brain? Although it is premature to generalize, neuropathological studies appear to have identified common abnormalities in the cerebellum and limbic system of at least five autistic subjects. These subjects, with variable levels of mental retardation, demonstrated marked Purkinje cell loss in the cerebellar hemispheres, together with retained fetal neuronal circuitry in cerebellar nuclei and increased neuronal packing in specific regions of the limbic system, amygdala, and hippocampus. The architecture of the cerebral cortex was not affected. Although our knowledge of brain functioning is incomplete, alterations of the kind noted in the cerebellum and limbic system could reasonably produce autistic behaviors. For more detail, readers are directed to a review of cerebellar contributions to higher functions by Schmahmann (1991). Neuroimaging studies allow less resolution of brain structure than do neuroanatomic studies, and the reported findings from neuroimaging are somewhat contradictory. However, a number of investigators have reported structural abnormalities in ventricle size and cerebral hemispheric asymmetry using CT. MRI, which offers greater resolution, has uncovered some consistent findings, along with a variety of nonspecific abnormalities. Common abnormalities include reduced volume of cerebellar hemispheres and vermal lobules--findings not inconsistent with the above-mentioned neuropathological defects. It is also interesting to note that individuals with fragile X syndrome have similar cerebellar findings. PET and NMR studies of autism are at a preliminary stage, but these methodologies allow insight into the functioning of the brain, rather than simply brain anatomy. Recent PET studies indicating decreased association between paired regions of the brains of autistic subjects are of interest, particularly if they can be confirmed and refined by additional studies. Neurophysiological studies also offer insight into brain function, but are subject to numerous methodological criticisms. Nevertheless, recent reports of diminished P300 waves and absent NC components in autistic subjects seem to indicate fundamental defects in attention and secondary processing, which could help explain the self-stimulatory behaviors often seen in autism. The disturbances in brain development associated with autism can be produced in a number of ways, and at different times during development of the nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The neurobiology and genetics of infantile autism. 846 65

Abnormal or borderline electroencephalograms are commonly observed in cases of gross mental retardation. However, fewer studies have focused on the use of event-related responses to aid in the differential diagnosis of developmental cognitive disorders. Fetal alcohol syndrome (FAS) and Down syndrome represent the most common known causes of mental retardation in the Western world. Although Down syndrome is easily diagnosed with a chromosome assay, FAS can be more difficult to diagnose since the diagnostic features are more subjectively based. The present study is the first to characterize auditory event-related potentials (ERPs) in children with FAS and contrast them to subjects with Down syndrome and controls. A passive auditory "oddball-plus-noise" paradigm was utilized to elicit ERPs. Parietal P300 latencies in response to the noise-burst stimuli for the FAS children were significantly longer, as were the P300s from all cortical sites in Down syndrome subjects in response to the both the infrequent tone and noise-burst stimuli when compared with the controls. Frontal P300s in Down syndrome children were significantly larger in amplitude compared to the controls and FAS children in response to the infrequent tone. A discriminant function analysis also revealed that these children could be correctly classified as being either Down syndrome, FAS, or normal controls using measures of latency and amplitude of the P300. These data suggest that an evaluation of ERP characteristics may provide a better understanding of the differences between FAS and Down syndrome children, and prove to be an aid in the early identification of children with FAS. These results demonstrate neurophysiological differences between FAS and Down syndrome, and suggest that P300 amplitude and latency data collected from a passive ERP task may be helpful in the discrimination of developmental cognitive disorders.
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PMID:Auditory event-related potentials in fetal alcohol syndrome and Down's syndrome children. 865 59

Event-related potentials (ERPs) in response to a stimulus change in the visual color modality were recorded in normal subjects and children with mental retardation (MR) under selective attention conditions with auditory stimuli. The paradigm included the presentation of a standard (blue color screen, B) or deviant (red, R, or greenish blue color screen, GB) visual stimulus, and a target or non-target tone burst stimulus. In Experiment 1, negativity of the subtracted waveform in response to visual stimuli with a latency of 250-280 ms was clearly observed in the ERPs of normal adults. These potentials prominently appeared at posterior sites in one condition, for which the deviant was GB, but were frontal site-dominant for the other condition. A P300 response to visual deviance was not observed in the GB-B paradigm and the subtracted negativity for this paradigm seemed to be more evident than that for the R-B paradigm. The subtracted negativities could be detected in the range of 180-400 ms after the stimulus onset in control children for the GB-B paradigm. The grand average waves of subtracted ERPs in normal children showed a similar distribution to that in normal adults. Similar subtracted potentials could be recorded with the same paradigm in children with MR, however, the negativities were different in waveform and spatial distribution than in controls. Therefore, the subtracted negativity of the present visual modality represented the analogue of the auditory mismatch negativity (MMN), and so-called 'visual MMN' was detectable in children and even in MR patients when the selective attention was directed to other stimuli.
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PMID:Mismatch negativity of the color modality during a selective attention task to auditory stimuli in children with mental retardation. 1242 18

In order to objectively evaluate visual perception of patients with mental retardation (MR), the P300 event-related potentials (ERPs) for visual oddball tasks were recorded in 26 patients and 13 age-matched healthy volunteers. The latency and amplitude of visual P300 in response to the Japanese ideogram stimuli (a pair of familiar Kanji characters or unfamiliar Kanji characters) and a pair of meaningless complicated figures were measured. In almost all MR patients visual P300 was observed, however, the peak latency was significantly prolonged compared to control subjects. There was no significant difference of P300 latency among the three tasks. The distribution pattern of P300 in MR patients was different from that in the controls and the amplitudes in the frontal region was larger in MR patients. The latency decreased with age even in both groups. The developmental change of P300 latency corresponded to developmental age rather than the chronological age. These findings suggest that MR patients have impairment in processing of visual perception. Assessment of P300 latencies to the visual stimuli may be useful as an objective indicator of mental deficit.
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PMID:[Visual perception of Kanji characters and complicated figures. II. Visual P300 event-related potentials in patients with mental retardation]. 1244 97

In order to evaluate visual perception, the P300 event-related potentials (ERPs) for visual oddball tasks were recorded in 11 patients with attention deficit/hyperactivity disorders (AD/HD), 12 with mental retardation (MR) and 14 age-matched healthy controls. With the aim of revealing trial-to-trial variabilities which are neglected by investigating averaged ERPs, single sweep P300s (ss-P300s) were assessed in addition to averaged P300. There were no significant differences of averaged P300 latency and amplitude between controls and AD/HD patients. AD/HD patients showed an increased variability in the amplitude of ss-P300s, while MR patient showed an increased variability in latency. These findings suggest that in AD/HD patients general attention is impaired to a larger extent than selective attention and visual perception.
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PMID:[Visual perception of Kanji characters and complicated figures. Part 3. Visual P300 event-related potentials in patients with attention deficit/hyperactivity disorders]. 1527 13