Catherine Brandner

Somatosensory-motor bodily representation cortical thinning in Tourette: Effects of tic severity, age and gender

INTRODUCTION Tourette syndrome (TS) implicates the disinhibition of the cortico-striatal-thalamic-cortical circuitry (CSTC). Previous studies used a volumetric approach to investigate this circuitry with inconsistent findings. Cortical thickness may represent a more reliable measure than volume due to the low variability in the cytoarchitectural structure of the grey matter. METHODS 66 magnetic resonance imaging scans were acquired from 34 TS subjects (age range 10-25, mean 17.19+/-4.1) and 32 normal controls (NC) (age range 10-20, mean 16.33+/-3.56). Brain morphology was assessed using the fully automated CIVET pipeline at the Montreal Neurological Institute. RESULTS We report (1) significant cortical thinning in the fronto-parietal and somatosensory-motor cortices in TS relative to NC (p<.05); (2) TS boys showed thinner cortex relative to TS girls in the fronto-parietal cortical regions (p<.05); (3) significant decrease in the fronto-parietal mean cortical thickness in TS subjects with age relative to NC and in the pre-central cortex in TS boys relative to TS girls; (4) significant negative correlations between tic severity and the somatosensory-motor cortical thickness. CONCLUSIONS TS revealed important thinning in brain regions particularly involved in the somatosensory/motor bodily representations which may play an important role in tics. Our findings are in agreement with Leckman et al. (1991) hypothesis stating that facial tics would be associated with dysfunction in an orofacial subset of the motor circuit, eye blinking with the occulo-motor circuit, whereas lack of inhibition to a dysfunction in the prefrontal cortex. Gender and age differences may reflect differential etiological factors, which have significant clinical relevance in TS and should be considered in developing and using diagnostic and therapeutic interventions.

Allocentric spatial learning and memory deficits in Down syndrome

Studies have shown that persons with Down syndrome (DS) exhibit relatively poor language capacities, and impaired verbal and visuoperceptual memory, whereas their visuospatial memory capacities appear comparatively spared. Individuals with DS recall better where an object was previously seen than what object was previously seen. However, most of the evidence concerning preserved visuospatial memory comes from tabletop or computerized experiments which are biased toward testing egocentric (viewpoint-dependent) spatial representations. Accordingly, allocentric (viewpoint-independent) spatial learning and memory capacities may not be necessary to perform these tasks. Thus, in order to more fully characterize the spatial capacities of individuals with DS, allocentric processes underlying real-world navigation must also be investigated. We tested 20 participants with DS and 16 mental age-matched, typically developing (TD) children in a real-world, allocentric spatial (AS) memory task. During local cue (LC) trials, participants had to locate three rewards marked by local color cues, among 12 locations distributed in a 4 m × 4 m arena. During AS trials, participants had to locate the same three rewards, in absence of LCs, based on their relations to distal environmental cues. All TD participants chose rewarded locations in LC and AS trials at above chance level. In contrast, although all but one of the participants with DS exhibited a preference for the rewarded locations in LC trials, only 50% of participants with DS chose the rewarded locations at above chance level in AS trials. As a group, participants with DS performed worse than TD children on all measures of task performance. These findings demonstrate that individuals with DS are impaired at using an AS representation to learn and remember discrete locations in a controlled environment, suggesting persistent and pervasive deficits in hippocampus-dependent memory in DS.

Brain Morphology in Autism and Fragile X Syndrome Correlates With Social IQ: First Report From the Canadian-Swiss-Egyptian Neurodevelopmental Study

Fragile X syndrome shares most of the behavioral phenotypic similarities with autism. How are these similarities reflected in brain morphology? A total of 10 children with autism and 7 with fragile X underwent morphological (T1) 1.5-T magnetic resonance imaging (MRI). The authors found no significant difference in total brain volumes, regional volumes, gyrification index, sulcul depth, and cerebral cortical thickness. However, children with autism showed significant decrease in the medial prefrontal bilaterally and the left anterior cingulate cortices. Regression analysis revealed positive correlation between the medial prefrontal cortical thickness and the social IQ. The authors suggest that the difference between the 2 groups in the medial prefrontal and anterior cingulate cortices thickness may entail an altered social cognitive style. Functional MRI studies directly differentiating between social indifference (autism) and social avoidance (fragile X) are needed to further characterize the spectrum of social abnormalities between these 2 groups.

Improving Low Achievers’ Academic Performance at University by Changing the Social Value of Mastery Goals

Recent research has shown that, in a university context, mastery goals are highly valued and that students may endorse these goals either because they believe in their utility (i.e., social utility), in which case mastery goals are positively linked to achievement, or to create a positive image of themselves (i.e., social desirability), in which case mastery goals do not predict academic achievement. The present two experiments induced high versus neutral levels of mastery goals’ social utility and social desirability. Results confirmed that mastery goals predicted performance only when these goals were presented as socially useful but not presented as socially desirable, especially among low achievers, those who need mastery goals the most to succeed.