The apolipoprotein E ε4 (ApoE ε4) allele not only represents the strongest single genetic risk factor for sporadic Alzheimer's disease, but also imposes independent effects on brain function in healthy individuals where it has been shown to promote subtle memory deficits and altered intrinsic functional brain network connectivity. Based on previous work showing a potential relevance of the default mode network (DMN) functional connectivity for episodic memory function, we hypothesized that the ApoE ε4 genotype would affect memory performance via modulation of the DMN. We assessed 63 healthy individuals (50-80 years old), of which 20 carried the ε4 allele. All participants underwent resting-state functional magnetic resonance imaging (fMRI), high-resolution 3D anatomical MRI imaging and neuropsychological assessment. Functional connectivity analysis of resting-state activity was performed with a predefined seed region located in the left posterior cingulate cortex (PCC), a core region of the DMN. ApoE ε4 carriers performed significantly poorer than non-carriers in wordlist recognition and cued recall. Furthermore, ε4 carriers showed increased connectivity relative to ε4 non-carriers between the PCC seed region and left-hemispheric middle temporal gyrus (MTG). There was a positive correlation between recognition memory scores and resting-state connectivity in the left MTG in ε4 carriers. These results can be interpreted as compensatory mechanisms strengthening the cross-links between DMN core areas and cortical areas involved in memory processing.

O artigo pretende introduzir o questionamento acerca dos sintomas marcados pelo real, a partir da análise do sintoma fóbico do caso clínico de Freud, o “Pequeno Hans”. Por um lado, o sintoma como formação de compromisso (Freud), e como formação do inconsciente (Lacan), vem no lugar de algo que não pode ser sabido pelo sujeito, isto que é recalcado e endereçado ao Outro. Por outro, a fobia traz a particularidade de ser marcada por um real, carente de interdição paterna, sem visar um deciframento por parte do sujeito.

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