Social perception gaze patterns, symptom severity and resting brain function measured using Arterial Spin Labelling

Autistic spectrum disorder (ASD) is characterised by qualitative alterations in reciprocal social interactions. Some recent studies show alterations in gaze patterns during social perception and rest-functional abnormalities in the ‘social brain network’. This study investigated: i) social perception gaze patterns in children with ASD and controls, ii) the relationship between autism clinical severity and social perception gaze patterns, iii) the relationship between resting cerebral blood flow (rCBF) and social perception gaze patterns. Methods: Nine children with ASD and 9 children with typical development were studied. Eye-tracking was used to detect gaze patterns during presentation of stimuli depicting social scenes. Autism clinical severity was established using the Autism Diagnostic Interview Revised (ADI-R). Arterial spin labelling MRI was used to quantify rCBF. Results: The ASD group looked less at social regions and more at non-social regions than controls. No significant correlation was found between ASD clinical severity and social perception gaze patterns. In the ASD group, gaze behaviour was related to rCBF in the temporal lobe regions at trend level. Positive correlations were found between temporal rCBF and gaze to the face region, while negative correlations were found between temporal rCBF and gaze to non-social regions. Conclusions: These preliminary results suggest that social perception gaze patterns are altered in children with ASD, and could be related to temporal rCBF.

Correntes permanentes em anéis mesoscópicos

Correntes permanentes em anéis mesoscópicos imersos num campo magnético constante foram pela primeira vez observadas experimentalmente em 1990, apresentando intensidades entre uma a duas ordens de grandeza superiores aos valores previstos teoricamente, uma discrepância que permanece por resolver. Neste trabalho apresenta-se um estudo em que se considera um modelo com uma impureza e interações repulsivas entre os eletrões do anel. Através da transformação de Jordan-Wigner obtém-se o hamiltoneano XXZ para cadeias de spin 1/2, com um defeito de troca e condições de fronteira “torcidas”. Utilizando o algoritmo do Grupo de Renormalização da Matriz Densidade (DMRG) estudamos os coeficientes de Fourier da corrente permanente e do respetivo peso de Drude em função da intensidade das interações e do tamanho do anel. Observamos que a amplitude da corrente permanente e o valor do peso de Drude são sempre diminuídos pelas interações.