Impaired Olfactory Identification in Asperger's Syndrome

Y. Suzuki, H.D. Critchley, A. Rowe, P. Howlin, and D. G.M. Murphy, The Journal of Neuropsychiatry and Clinical Neurosciences; Winter 2003; 15, 1, 105 - 107.

The authors measured odor detection threshold and odor identification in 12 males with Asperger's Syndrome and 12 matched control subjects. Relative to control subjects, Asperger's Syndrome subjects were not impaired at odor detection but were significantly impaired at olfactory identification. We report normal odor detection, but impaired olfactory identification, in people with AS. Medial temporal lobe structures are implicated in odor detection, whereas orbitofrontal cortex is implicated in olfactory identification, therefore, our results suggest that AS is associated with orbitofrontal, but not medial temporal lobe, dysfunction.

Brain Anatomy and Sensorimotor Gating in Asperger's Syndrome

M. Grainne and Mc Alonan et al., Brain (2002), 127, 1594 - 1606.

There are few studies on brain anatomy of Asperger's Syndrome, and no focal anatomical abnormality has been reliably reported from brain imaging studies of autism, although there is increasing evidence for differences in limbic circuits. These brain regions are important in sensorimotor gating, and impaired 'gating' may partly explain the failure of people with autistic with autistic disorders to inhibit repetitive thoughts and actions. Thus, we compared brain anatomy and sensorimotor gating in healthy people with Asperger's Syndrome and controls. We included 21 adults with Asperger's Syndrome and 24 controls. All had normal IQ and were aged 18 - 49 years. We studied brain anatomy using quantitative MRI, and sensorimotor gating using prepulse inhibition of startle in a subset of 12 individuals with Asperger's Syndrome and 14 controls. We found significant age-related differences in volume of cerebral hemispheres and caudate nuclei (controls, but not people with Asperger's Syndrome, had age-related reductions in volume). Also, people with Asperger's Syndrome had significantly less grey matter in fronto-striatal and cerebellar regions than controls, and widespread differences in white matter. Moreover, sensorimotor gating was significantly impaired in Asperger's Syndrome. People with Asperger's Syndrome most likely have generalised alterations in brain development, but this is associated with significant differences from controls in the anatomy and function of specific brain regions implicated in behaviours characterising the disorder. We hypothesize that Asperger's Syndrome is associated with abnormalities in fronto-striatal pathways resulting in defective sensorimotor gating, and consequently characteristic difficulties inhibiting repetitive thoughts, speech and actions.

We found that, compared with controls, people with Asperger's Syndrome have age-related differences in brain anatomy, structural abnormalities in fronto-striatal systems and the cerebellum, and impaired sensorimotor gating. We suggest that Asperger's Syndrome probably arises from a generalised abnormality in brain development (causing widespread white matter abnormalities). This neurodevelopmental abnormality may, in turn, be modulated by environmental factors such as social isolation. Some regions are more affected than others, ad our findings support the hypothesis that a proportion of autistic symptomatology may be explained by frontostriatal disorder.

Deficient auditory processing in Children with Asperger's Syndrome, as indexed by event-related Potentials

E. Jansson-Verkasalo, R. Ceponiene, M. Kielinen, K. Suominen, V. Jantti, S. Liisa Linna, I. Moilanen, R. Naatanen, Neuroscience Letters, 338 (2003), 197 - 200.

Asperger Syndrome (AS) is characterised by normal language development but deficient understanding and use of the intonation and prosody of speech. While individuals with AS report difficulties in auditory perception, there are no studies addressing auditory processing at the sensory level. In this study, event-related potentials (ERP) were recorded for syllables and tones in children with AS and in their control counterparts. Children with AS displayed abnormalities in transient sound-feature encoding, as indexed by the obligatory ERP'S, and in sound discrimination, as indexed by the mismatch negativity. These deficits were more severe for the tone stimuli than for the syllables. These results indicate that auditory sensory processing is deficient in children with AS, and that these deficits might be implicated in the perceptual problems encountered by children with AS.

Sensory Processing Issues Associated with Asperger’s Syndrome: A Preliminary Investigation

Dunn, W., Smith-Myles, B., and Orr, S, The American Journal of Occupational Therapy, 56, pp 97-102.

The purpose of this study was to identify the sensory processing patterns of children with Asperger’s Syndrome. Researchers compared the performance of 42 children with Asperger’s Syndrome and 42 children without disabilities on section and factor scores of the Sensory Profile. As reported by parents on the Sensory Profile, the children with Asperger’s Syndrome were significantly different from children without disabilities on 22 of 23 items. This result was obtained with good power estimates (.997-1.00) and large effect sizes (02 = .267 - .732). Both groups of children performed the same on modulation of visual input affecting emotional responses and activity level. This study provides initial evidence that clear differences exist in the sensory processing patterns of children with Asperger’s Syndrome when compared with peers without disabilities.

The children in Asperger’s (1944) study displayed a range of hyposensitivities and hypersensitivities to taste, tactile, and auditory stimuli. In taste, he found them to have very specific likes and dislikes. For example, many preferred very sour or strongly spiced foods. Similarly, the children had a strong dislike for certain fabrics or an aversion to specific daily life activities containing strong tactile sensory input, such as cutting fingernails. The children displayed extreme levels of noise sensitivity; at times, they were hypersensitive to noise in certain environments and appeared to be hyposensitive to the same noises in other environments. Further, the children manifested a lack of respect or understanding for other people and their space. Asperger reported that they leaned on total strangers who touched them as if they were pieces of furniture.

Group performance (raw) scores reveal that the confidence intervals for the two groups are quite separate from each other, making differentiation between performance of children with and without Asperger’s Syndrome clear. That is, children with Asperger’s Syndrome consistently have lower scores (i.e., always displays the behaviour = 1) than children without disabilities. As reported by the parents, the children with Asperger’s Syndrome demonstrated a significantly different pattern of sensory processing from their peers without disabilities according to the Sensory Profile, suggesting a sensory processing correlate in Asperger’s Syndrome that needs to be included in the diagnosis.