Biomedical subjects

Nancy J Minshew

Publications and source records attributed to Nancy J Minshew.

At least 19 recordsLinked to original sources

PubMed2007

Spatial working memory deficits in autism.

Previous studies have reported working memory deficits in autism, but this finding has been inconsistent. One possibility is that deficits in this domain may be present only when working memory load exceeds some limited capacity. High-functioning individuals with autism performed the CANTAB computerized test of spatial working memory. Individuals with autism made more errors than a matched group of typically developing controls on this task, and were less likely to consistently use a specific organized search strategy to complete the task. Overall, these results demonstrate reduced spatial working memory abilities in autism, and extend previous findings by demonstrating that these deficits are significant when tasks impose heavier demands on working memory.

Adolescent↗

PubMed2006

Abnormal brain size effect on the thalamus in autism.

This study was conducted to examine the volume of the thalamus in autism and to investigate the effect of brain size on this structure in an attempt to replicate, in a larger sample, findings from a previous study reporting the existence of a relationship between brain volume and thalamus in healthy controls but not in individuals with autism. Additionally, the relationships between thalamic volumes and clinical features were examined. Volumetric measurements of the right and left thalamic nuclei were performed on MRI scans obtained from 40 high-functioning individuals with autism (age range: 8-45 years) and 41 healthy controls (age range: 9-43 years). No differences were observed between the two groups for unadjusted thalamic volumes. However, the expected linear relationship between TBV and thalamic volume was not observed in individuals with autism. Furthermore, no correlations were observed between thalamic volumes and clinical features. Findings from this larger study are consistent with the previous report of an abnormal brain size effect on the thalamus in autism and support the possibility of abnormal connections between cortical and subcortical structures in this disorder.

Adolescent↗

PubMed2006

Volumetric alterations of the orbitofrontal cortex in autism.

Recent evidence has implicated the orbitofrontal cortex (OFC) in the pathophysiology of social deficits in autism. An MRI-based morphometric study of the OFC was conducted involving 11 children with autism (age range 8.1-12.7 years) and 18 healthy, age-matched controls (age range 8.9-12.8 years). Decreased grey matter volume in the right lateral OFC in the patient group was found, and correlations were observed between social deficits and white, but not grey, matter structures of the OFC. These findings support the role of OFC in autism and warrant further investigations of this structure using structural and functional methodologies.

Autistic Disorder↗

PubMed2006

Sentence comprehension in autism: thinking in pictures with decreased functional connectivity.

Comprehending high-imagery sentences like The number eight when rotated 90 degrees looks like a pair of eyeglasses involves the participation and integration of several cortical regions. The linguistic content must be processed to determine what is to be mentally imaged, and then the mental image must be evaluated and related to the sentence. A theory of cortical underconnectivity in autism predicts that the interregional collaboration required between linguistic and imaginal processing in this task would be underserved in autism. This functional MRI study examined brain activation in 12 participants with autism and 13 age- and IQ-matched control participants while they processed sentences with either high- or low-imagery content. The analysis of functional connectivity among cortical regions showed that the language and spatial centres in the participants with autism were not as well synchronized as in controls. In addition to the functional connectivity differences, there was also a group difference in activation. In the processing of low-imagery sentences (e.g. Addition, subtraction and multiplication are all math skills), the use of imagery is not essential to comprehension. Nevertheless, the autism group activated parietal and occipital brain regions associated with imagery for comprehending both the low and high-imagery sentences, suggesting that they were using mental imagery in both conditions. In contrast, the control group showed imagery-related activation primarily in the high-imagery condition. The findings provide further evidence of underintegration of language and imagery in autism (and hence expand the understanding of underconnectivity) but also show that people with autism are more reliant on visualization to support language comprehension.

Adult↗

PubMed2006

Functional and anatomical cortical underconnectivity in autism: evidence from an FMRI study of an executive function task and corpus callosum morphometry.

The brain activation of a group of high-functioning autistic participants was measured using functional magnetic resonance imaging during the performance of a Tower of London task, in comparison with a control group matched with respect to intelligent quotient, age, and gender. The 2 groups generally activated the same cortical areas to similar degrees. However, there were 3 indications of underconnectivity in the group with autism. First, the degree of synchronization (i.e., the functional connectivity or the correlation of the time series of the activation) between the frontal and parietal areas of activation was lower for the autistic than the control participants. Second, relevant parts of the corpus callosum, through which many of the bilaterally activated cortical areas communicate, were smaller in cross-sectional area in the autistic participants. Third, within the autism group but not within the control group, the size of the genu of the corpus callosum was correlated with frontal-parietal functional connectivity. These findings suggest that the neural basis of altered cognition in autism entails a lower degree of integration of information across certain cortical areas resulting from reduced intracortical connectivity. The results add support to a new theory of cortical underconnectivity in autism, which posits a deficit in integration of information at the neural and cognitive levels.

Adult↗

PubMed2006

Maturation of executive function in autism.

BACKGROUND: Executive dysfunction has been reported at different ages in autism. It is not clear however, when this impairment emerges or how its expression is affected by development. METHODS: 61 non-mentally retarded autism participants (AUT) and 61 age, gender, and IQ matched typically developing participants (CON) were assessed with two oculomotor executive function tasks, the oculomotor delayed response task (ODR) and the antisaccade task (AS), as well as a visually-guided saccade sensorimotor task (VGS). RESULTS: The AUT group demonstrated impairments in response inhibition and spatial working memory at all ages tested. Developmental improvements in speed of sensorimotor processing and voluntary response inhibition were similar in both groups indicating sparing of some attentional control of behavior. Developmental progression in the speed of initiating a cognitive plan and maintaining information on line over time, however, was impaired in the AUT group indicating abnormal development of working memory. CONCLUSIONS: These results indicate that while executive dysfunction is present throughout development, there is evidence for both typical and atypical developmental progression of executive functions in autism. The plasticity suggested by the developmental improvements may have implications regarding appropriate developmental epochs and types of interventions aimed at enhancing cognitive capacities in individuals with autism.

Adolescent↗

PubMed2006

An MRI study of minor physical anomalies in autism.

The objective of this investigation was to examine the existence of minor physical anomalies (MPA) in autism. The interorbital and interlens distances were measured on MRI scans obtained from a sample of 40 non-mentally retarded individuals with autism and 41 healthy controls. No differences were observed between the two groups on any measurements. However, when the analysis was conducted using a split median procedure, individuals with autism and either low FSIQ, PIQ, or VIQ had shorter interorbital distances when compared to controls. Hypotelorism is a MPA that may be present in a subgroup of individuals with autism. Additional research is warranted using large sample sizes with a wide range of intellectual functioning.

Adolescent↗

PubMed2006

The profile of memory function in children with autism.

A clinical memory test was administered to 38 high-functioning children with autism and 38 individually matched normal controls, 8-16 years of age. The resulting profile of memory abilities in the children with autism was characterized by relatively poor memory for complex visual and verbal information and spatial working memory with relatively intact associative learning ability, verbal working memory, and recognition memory. A stepwise discriminant function analysis of the subtests found that the Finger Windows subtest, a measure of spatial working memory, discriminated most accurately between the autism and normal control groups. A principal components analysis indicated that the factor structure of the subtests differed substantially between the children with autism and controls, suggesting differing organizations of memory ability.

Adolescent↗

PubMed2006

Neuropsychologic functioning in children with autism: further evidence for disordered complex information-processing.

A wide range of abilities was assessed in 56 high-functioning children with autism and 56 age- and IQ-matched controls. Stepwise discriminant analyses produced good group discrimination for sensory-perceptual, motor, complex language, and complex memory domains but lower agreement for the reasoning domain than previously obtained for adults. Group discrimination did not occur for attention, simple language, simple memory, and visuospatial domains. Findings provide additional support for a complex information-processing model for autism, previously based on adult data, demonstrating a pattern across domains of selective impairments on measures with high demands for integration of information and sparing when demands were low. Children as compared to adults with autism exhibited more prominent sensory-perceptual symptoms and less pronounced reasoning deficits reflecting brain maturation.

Adolescent↗

PubMed2006

An MRI study of increased cortical thickness in autism.

OBJECTIVE: The purpose of this study was to examine cortical thickness in autism in light of the postmortem evidence of cortical abnormalities of the disorder. METHOD: Magnetic resonance imaging (MRI) scans were acquired from 17 children with autism and 14 healthy comparison subjects, and sulcal and gyral thickness were measured for the total brain and for all lobes. RESULTS: Increases in total cerebral sulcal and gyral thickness were observed in children with autism relative to comparison subjects. Similar findings were noted in the temporal and parietal lobes but not in the frontal and occipital lobes. CONCLUSIONS: These preliminary findings indicate that increased cortical thickness may contribute to the increased gray matter volume and total brain size that have been observed in autism and may also be related to anomalies in cortical connectivity.

Autistic Disorder↗

PubMed2006

Magnetic resonance imaging study of the orbitofrontal cortex in autism.

The orbitofrontal cortex is involved in multiple psychologic functions, such as emotional and cognitive processing, learning, and social behavior. These functions are variably impaired in individuals with autism. The present study examined the size of the orbitofrontal cortex, and its medial and lateral subdivisions, using magnetic resonance imaging (MRI) scans obtained from 40 non-mentally retarded individuals with autism and 41 healthy controls. No differences were observed between the two groups on any of the orbitofrontal cortex measurements. However, when compared with controls, a smaller right lateral orbitofrontal cortex was observed in children and adolescents with autism, whereas a larger right lateral orbitofrontal cortex was found in adult patients. Interestingly, a positive relationship was found in the patient group between circumscribed interests and all orbitofrontal cortex structures. The present study suggests the absence of global volumetric abnormalities in the orbitofrontal cortex in autism and indicates that the functional disturbances in this structure might not be related to anatomic alterations.

Adolescent↗

PubMed2005

Oculomotor studies of cerebellar function in autism.

Histopathological, neuroimaging and genetic findings indicate cerebellar abnormalities in autism, but the extent of neurophysiological dysfunction associated with those findings has not been systematically examined. Suppression of intrusive saccades (square wave jerks) and the ability to sustain eccentric gaze, two phenomena requiring intact cerebellar function, were examined in 52 high-functioning individuals with autism and 52 age- and IQ-matched healthy subjects during visual fixation of static central and peripheral targets. Rates of intrusive saccades were not increased in autism during visual fixation, and foveopetal ocular drift was also not increased when subjects held an eccentric gaze. The absence of gross disturbances of visual fixation associated with cerebellar disease in individuals with autism, such as increased square wave jerk rates and foveopetal drift when holding eccentric gaze, indicates that the functional integrity of cerebellar--brainstem networks devoted to oculomotor control is preserved in autism despite reported anatomic variations. However, increased amplitude of intrusive saccades and reduced latency of target refixation after intrusive saccades were observed in individuals with autism, especially when subjects maintained fixation of remembered target locations without sensory guidance. The atypical metrics of intrusive saccades that were observed may be attributable to faulty functional connectivity in cortico-cerebellar networks.

Adolescent↗

PubMed2005

The application of short forms of the Wechsler Intelligence scales in adults and children with high functioning autism.

We evaluated the predictive accuracy of short forms of the Wechsler intelligence scales for individuals with high functioning autism. Several short forms were derived from participants who had received the full procedure. Stepwise multiple regression analyses were performed to determine the strength of association between the subtests included in the short form and IQ scores based upon the full test. These analyses were performed for all participants, and also for autism participants with atypical subtest profiles. In all analyses the percentages of explained variance were typically in the .8-.9 range. It was concluded that short forms may be used with good predictive accuracy in individuals with high functioning autism, even when the subtest profile is atypical.

Adolescent↗

PubMed2005

Verbal and spatial working memory in autism.

Verbal and spatial working memory were examined in high-functioning children, adolescents, and adults with autism compared to age and cognitive-matched controls. No deficit was found in verbal working memory in the individuals with autism using an N-back letter task and standardized measures. The distinction between the N-back task and others used previously to infer a working memory deficit in autism is that this task does not involve a complex cognitive demand. Deficits were found in spatial working memory. Understanding the basis for the dissociation between intact verbal working memory and impaired spatial working memory and the breakdown that occurs in verbal working memory as information processing demands are increased will likely provide valuable insights into the neural basis of autism.

Adolescent↗

PubMed2005

Impaired memory for faces and social scenes in autism: clinical implications of memory dysfunction.

A clinical memory test, the Wechsler Memory Scale-III (WMS-III), was used to study the auditory and visual memory of 29 high-functioning adults with autism and 34 group-matched normal controls. The individuals with autism performed as well as the controls on immediate and delayed memory for word pairs and stories and on a verbal working memory task. The autism group was impaired on immediate and delayed recall of faces and of family scenes and had impaired spatial working memory. The integrity of verbal working memory and impaired spatial working memory is consistent with the findings of other studies and may reflect the greater computational demands of the spatial task. Most importantly, the deficits in memory for faces and common social scenes, complex visual/spatial stimuli, demonstrate the contribution of memory dysfunction in autism to deficits in real life function.

Adolescent↗

PubMed2004

Underdevelopment of the postural control system in autism.

OBJECTIVE: To determine if abnormalities exist in postural control in autism and if they are related to age. METHODS: Dynamic posturography was performed in 79 autistic individuals without mental retardation and 61 healthy volunteers between ages 5 and 52 years. Both the sensory organization and the movement coordination portions of the test were performed. RESULTS: The autistic subjects had reduced postural stability (p = 0.002). Examination of age effects revealed that the development of postural stability was delayed in the autistic subjects (p < 0.001) and failed to achieve adult levels (p = 0.004). Postural stability was reduced under all conditions but was clinically significant only when somatosensory input was disrupted alone or in combination with other sensory challenges (mean reduction in stability of 2.6 +/- 1.0 for the first three conditions without somatosensory disruption vs 6.7 +/- 2.7 for the last three conditions with somatosensory disruption), indicating problems with multimodality sensory integration. CONCLUSIONS: The evidence from this and studies of the motor system suggests more general involvement of neural circuitry beyond the neural systems for social behavior, communication, and reasoning, all of which share a high demand on neural integration of information.

Adolescent↗

PubMed2004

Functional connectivity in an fMRI working memory task in high-functioning autism.

An fMRI study was used to measure the brain activation of a group of adults with high-functioning autism compared to a Full Scale and Verbal IQ and age-matched control group during an n-back working memory task with letters. The behavioral results showed comparable performance, but the fMRI results suggested that the normal controls might use verbal codes to perform the task, while the adults with autism might use visual codes. The control group demonstrated more activation in the left than the right parietal regions, whereas the autism group showed more right lateralized activation in the prefrontal and parietal regions. The autism group also had more activation than the control group in the posterior regions including inferior temporal and occipital regions. The analysis of functional connectivity yielded similar patterns for the two groups with different hemispheric correlations. The temporal profile of the activity in the prefrontal regions was more correlated with the left parietal regions for the control group, whereas it was more correlated with the right parietal regions for the autism group.

Adult↗

PubMed2004

Pursuit eye movement deficits in autism.

Oculomotor studies provide a novel strategy for evaluating the functional integrity of multiple brain systems and cognitive processes in autism. The current study compared pursuit eye movements of 60 high-functioning individuals with autism and 94 intelligence quotient, age and gender matched healthy individuals using ramp and oscillating target tasks. Individuals with autism had normal pursuit latency, but reduced closed-loop pursuit gain when tracking both oscillating and ramp targets. This closed-loop deficit was similar for leftward and rightward pursuit, but the difference between individuals with autism and their age-matched peers was more apparent after mid-adolescence, suggesting reduced maturational achievement of the pursuit system in autism. Individuals with autism also had lower open-loop pursuit gain (initial 100 ms of pursuit) and less accurate initial catch-up saccades during a foveofugal step-ramp task, but these deficits were only seen when targets moved into the right visual field. Pursuit performance in both open- and closed-loop phases was correlated with manual praxis in individuals with autism. Bilateral disturbances in the ability to use internally generated extraretinal signals for closed-loop pursuit implicate frontostriatal or cerebellar circuitry. The hemifield specific deficit in open-loop pursuit demonstrates a lateralized disturbance in the left extrastriate areas that extract visual motion information, or in the transfer of visual motion information to the sensorimotor areas that transform visual information into appropriate oculomotor commands.

Adolescent↗