Biomedical subjects

Eric Courchesne

Publications and source records attributed to Eric Courchesne.

28 records · Page 2Linked to original sources

PubMed2003

Linguistic theory and neuroimaging evidence: an fMRI study of Broca's area in lexical semantics.

There has been a long debate on the functional characterization of left inferior frontal cortex, including proposals regarding syntactic and lexico-semantic involvement. We studied nine right-handed adults, using functional magnetic resonance imaging (fMRI) during performance on a semantic decision task in which subjects had to determine whether noun-verb pairs were semantically associated. In comparison with a visuoperceptual control task, activation clusters were seen in left inferior frontal and middle temporal regions, as well as the bilateral superior frontal gyrus. In agreement with previous studies, our findings suggest that Broca's area is involved in semantic processing. Findings of lexico-semantic as well as syntactic processing in the inferior frontal lobe may be accounted for in terms of working memory demands.

Adult↗

PubMed2003

Abnormal variability and distribution of functional maps in autism: an FMRI study of visuomotor learning.

OBJECTIVE: Autism is a neurally based psychiatric disorder, but there is no consensus regarding the underlying neurofunctional abnormalities. Previous functional magnetic resonance imaging (fMRI) studies of simple movement suggested individually variable and scattered functional brain organization in autism. The authors examined whether such abnormalities generalize to multimodal processing (visually driven motor sequence learning). METHOD: Eight male autistic patients and eight comparison subjects matched with the patients on age, gender, and handedness were examined by using fMRI while they performed finger press movements prompted by visually presented repeating six-digit sequences. Hemodynamic responses to the six-digit sequences were statistically compared to responses to single-digit stimuli in one experiment and to regular six-digit sequences in another experiment. RESULTS: Both groups showed activations in bilateral premotor, superior parietal, and occipital cortices in both experiments. Task-by-group interactions showed that superior parietal activations were less pronounced in the autism group, whereas prefrontal cortex and more posterior parietal loci showed greater activation in the autism group than in the comparison group. The distances between Individual subjects' activation peaks and the groupwise peak were greater in the autism group than in the comparison group. CONCLUSIONS: The results support earlier findings of abnormal variability and scatter of functional maps in autism. They are consistent with evidence from other studies suggesting early-onset disturbances in the development of cerebello-thalamo-cortical pathways in autism.

Adolescent↗

PubMed2003

Differential effects of developmental cerebellar abnormality on cognitive and motor functions in the cerebellum: an fMRI study of autism.

OBJECTIVE: Recent years have seen a revolution in views regarding cerebellar function. New findings suggest that the cerebellum plays a role in multiple functional domains: cognitive, affective, and sensory as well as motor. These findings imply that developmental cerebellar pathology could play a role in certain nonmotor functional deficits, thereby calling for a broader investigation of the functional consequences of cerebellar pathology. Autism provides a useful model, since over 90% of autistic cerebella examined at autopsy have shown well-defined cerebellar anatomic abnormalities. The aim of the present study was to examine how such pathology ultimately impacts cognitive and motor function within the cerebellum. METHOD: Patterns of functional magnetic resonance imaging (fMRI) activation within anatomically defined cerebellar regions of interest were examined in eight autistic patients (ages 14-38 years) and eight matched healthy comparison subjects performing motor and attention tasks. For the motor task, subjects pressed a button at a comfortable pace, and activation was compared with a rest condition. For the attention task, visual stimuli were presented one at a time at fixation, and subjects pressed a button to every target. Activation was compared with passive visual stimulation. RESULTS: While performing these tasks, autistic individuals showed significantly greater cerebellar motor activation and significantly less cerebellar attention activation. CONCLUSIONS: These findings shed new light on the cerebellar role in attention deficits in autism and suggest that developmental cerebellar abnormality has differential functional implications for cognitive and motor systems.

Adolescent↗

PubMed2002

Transmission disequilibrium studies of the serotonin 5-HT2A receptor gene (HTR2A) in autism.

Hyperserotonemia in autism is one of the longest-standing biochemical findings in a psychiatric disorder. This well-replicated finding and subsequent studies of platelet serotonin receptors in autism indicate that the serotonin 2A receptor gene (HTR2A) on chromosome 13q is a primary candidate gene in autism. Converging data from recent genome screens also implicates the genomic region containing HTR2A. Based on these lines of evidence, the transmission/disequilibrium test (TDT) was used to assess transmission disequilibrium between autism and haplotypes of three polymorphisms, including the promoter -1438 G/A single nucleotide polymorphism (SNP) in perfect linkage disequilibrium with the 102 T/C SNP in previous studies, a newly identified SNP in intron 1 near exon 2, and the SNP responsible for the His452Tyr amino acid change in exon 3. Because expression studies have shown HTR2A to be polymorphically imprinted in the brain, secondary analyses were split into maternal and paternal transmissions. No evidence was found for unequal transmission of haplotypes; however, power analysis reveals low power to detect a parent-of-origin effect in this sample size.

Alleles↗

PubMed2002

Mutation screening and transmission disequilibrium study of ATP10C in autism.

Autism is a complex genetic disorder. Chromosome 15 is of particular interest in this disorder, because of previous reports of individuals with autism with chromosomal abnormalities in the 15q11-q13 region. Transmission disequilibrium between polymorphisms in this region and autism has been also been reported in some, but not all studies. Recently, a novel maternally expressed gene, ATP10C, was characterized and mapped to the chromosome 15q11-q13 region, 200 kb distal to UBE3A. It encodes a putative aminophospholipid translocase likely to be involved in the asymmetric distribution of proteins in the cell membrane. Preferential maternal expression has been demonstrated in fibroblasts and brain. Because of its physical location and imprinting pattern, ATP10C was considered to be a candidate gene for chromosome 15-associated autism. In an effort to find the genes responsible for autism in this chromosomal region, 1.5 kb of the 5' flanking region, as well as the coding and splicing regions of ATP10C, were screened for sequence variants. Several polymorphic markers including five nonsynonymous SNPs were identified. To investigate transmission disequilibrium between ATP10C and autism, a family-based association study was conducted for 14 markers in 115 autism trios. No significant transmission disequilibrium was found, suggesting ATP10C is unlikely to contribute strongly to susceptibility to autism in these families. However, due to limited power to detect genes of modest effect, the possible functional role of the nonsynonymous SNPs and the functional implications of the SNPs identified from 5' flanking region and intron 2 splicing region may be evaluated in further studies.

Adenosine Triphosphatases↗

PubMed2002

Cerebral lobes in autism: early hyperplasia and abnormal age effects.

Metabolic, functional, behavioral, and histologic studies suggest that the structure of the cerebrum may be abnormal in autism. In a previous cross-sectional study we found abnormal enlargement of cerebral cortex and cerebral white matter volumes in autistic 2- and 3-year-olds and abnormally slow rates of volume change across later ages. In the present study, we assessed whether these volume abnormalities are limited to particular cerebral regions or are pervasive throughout the cerebrum. We used magnetic resonance imaging (MRI) to quantify volumes of cerebral lobes (frontal, temporal, parietal, and occipital regions), using classic sulcal boundaries to define regions. We examined 38 boys with autism and 39 normal control boys between the ages of 2 and 11 years. Several regions showed signs of gray matter and white matter hyperplasia in 2- and 3-year-old patients (as much as 20% enlargement), but there appeared to be an anterior to posterior gradient in the degree of hyperplasia. The frontal lobe showed the greatest enlargement while the occipital lobe was not significantly different from normal. Gray and white matter differences were not found in the older children. By examining the relationships between regional volumes and subject age, we found that frontal, temporal, and parietal white matter volumes, as well as frontal and temporal gray matter volumes, changed at significantly slower rates in autism patients than in controls across the 2- to 11-year-age range. For example, frontal lobe white matter volume increased by about 45% from 2-4 years of age to 9-11.5 years, but by only 13% in autistic patients. Mechanisms that might account for early hyperplasia are discussed as they might relate to the regional differences in degree of abnormality. For instance, possible influences of neurotrophic factors, or of abnormal afferent activity from other affected brain regions are considered.

Aging↗

PubMed2002

Functional MRI of motor sequence acquisition: effects of learning stage and performance.

Neural networks of motor control are well understood and the motor domain therefore lends itself to the study of learning. Neuroimaging of motor learning has demonstrated fronto-parietal, subcortical, and cerebellar involvement. However, there is conflicting evidence on the specific functional contributions of individual regions and their relative importance for early and advanced stages of learning. Using functional MRI (fMRI), we examined hemodynamic effects in seven right-handed men during brief episodes of explicit learning of novel six-digit sequences (experiments 1 and 2) and during prolonged learning of an eight-digit sequence (experiment 3), all performed with the dominant hand. Brief episodes of new learning were predominantly associated with bilateral activations in premotor and supplementary motor areas, superior and inferior parietal cortices, and anterior cerebellum. In experiment 2, which included a control condition matched for complexity of motor execution, we also found unexpectedly strong activation in the bilateral inferior frontal lobes. In experiment 3, analysis of task by learning stage interactions showed greater involvement of the bilateral superior parietal lobes, the right middle frontal gyrus, and the left caudate nucleus during early stages, whereas left occipito-temporal and superior frontal cortex as well as the bilateral parahippocampal region were more activated during late learning stages. Analysis of task by performance interactions (based on each subject's response times and accuracy during each scan) showed effects in bilateral fronto-polar, right hippocampal, and anterior cerebellar regions associated with high levels of performance, as well as inverse effects in bilateral occipito-parietal regions. We conclude that superior parietal and occipital regions are most intensely involved in visually driven explicit digit sequence learning during early stages and low performance, whereas later stages of acquisition and higher levels of performance are characterized by stronger recruitment of prefrontal and mediotemporal regions.

Adult↗

PubMed2002

Cerebellar abnormalities in infants and toddlers with Williams syndrome.

One commonly observed neuroanatomical abnormality in adults with Williams syndrome is an enlarged cerebellum relative to a small cerebrum. Our study is the first to examine neuroanatomy in young children with Williams syndrome. Clinical brain MRI was examined in nine young children with Williams syndrome (mean age 21 months, range 7 to 43 months) relative to nine age- and sex-matched normally developing control children (mean age 29 months, range 20 to 42 months), and two children with undiagnosed developmental disorders (6 and 41 months). Two neuroradiologists who were blinded to participant classification, hypotheses, and regions of interest for the study, sorted the brain scans into two groups on the basis of six neuroanatomical criteria. The raters placed more of the MR scans from children with Williams syndrome into a separate group when they analyzed features of the cerebellum, but not when they analyzed other brain regions. Based on their written comments, the raters focused on the large size of the cerebellum in the children with Williams syndrome. The results lead us to suggest that abnormal cerebellar enlargement is evident in those with Williams syndrome at an early age. Our results are discussed relative to the cognitive delays observed in Williams syndrome versus other disorders such as autism, leading us to suggest that the cerebellum may play a role in cognition.

Autistic Disorder↗

PubMed2002

The neurobiological basis of autism from a developmental perspective.

Autism is a neurobiological disorder that is diagnosed through careful behavioral assessment in early childhood. In this paper, we review recent studies that have attempted to reveal the underlying causes of autism using a variety of techniques. Particular emphasis is placed on techniques that have been used by a number of different laboratories, including structural magnetic resonance imaging and postmortem studies of neuroanatomy. Neurobiological and neuropsychological data from individuals across a wide age range are examined from a neurodevelopmental perspective. We discuss how these recent advances have led us to develop a growth dysregulation hypothesis of autism. Finally, we discuss how this hypothesis may lead to new innovations in autism research.

Autistic Disorder↗

PubMedDate not supplied

Brain overgrowth in autism during a critical time in development: implications for frontal pyramidal neuron and interneuron development and connectivity.

While abnormalities in head circumference in autism have been observed for decades, it is only recently that scientists have begun to focus in on the developmental origins of such a phenomenon. In this article we review past and present literature on abnormalities in head circumference, as well as recent developmental MRI studies of brain growth in this disorder. We hypothesize that brain growth abnormalities are greatest in frontal lobes, particularly affecting large neurons such as pyramidal cells, and speculate how this abnormality might affect neurofunctional circuitry in autism. The relationship to clinical characteristics and other disorders of macrencephaly are discussed.

Age Factors↗