Improved correspondence of fMRI visual field localizer data after macroanatomical alignment

The study of the visual system and its role for human cognition in health and disease with fMRI often requires the use of localizer paradigms to define anatomical regions of interest (ROIs). However, the considerable degree of interindividual variability of the cerebral cortex represents an important confound, especially when analyzing visual localizer data on the group level. Cortex-based alignment (CBA) techniques lead to a reliable reduction of interindividual anatomical variability. Yet, the potential benefits of CBA has not been investigated for visual field localizer paradigms used to map specific parts of the visual field within retinotopically organized early visual areas. We evaluated CBA for an attention-enhanced visual field localizer mapping a homologous part of each visual quadrant in a cohort of 50 participants. After CBA, group ROIs showed markedly increased spatial consistency. CBA also led to an increase in the probability of activation overlap of up to forty percent. Furthermore, the size of group ROIs for the lower visual hemifield was larger than for the upper visual hemifield after CBA. This asymmetry, which mirrors previous findings from electrophysiological and fMRI studies, was not detectable before CBA. Our results confirm and extend the utility of CBA for the study of the visual system particularly in the context of group analyses. This method should be particularly important for the study of neuropsychiatric disorders with abnormally increased interindividual anatomical variability.

Evidence for two-stage binding by the 175-kD erythrocyte binding antigen of Plasmodium falciparum.

Plasmodium falciparum malaria merozoites invade human erythrocytes bearing sialic acid in a multistage process involving the sialic acid-dependent binding of a malaria molecule, the 175-kD erythrocyte binding antigen (EBA-175). We show here that after the initial interaction of EBA-175 with its sialic acid-containing erythrocyte determinant, endogenous proteases can cleave EBA-175 to 65-kD fragment(s), whose binding to erythrocytes is sialic acid independent. A 65-kD fragment was immunoprecipitated by antibodies against peptides between residues 354 and 1061 but not beyond residue 1062. Binding experiments utilizing combinations of native protein, expression-PCR-synthesized EBA-175 polypeptides, peptide synthesis, and antibodies, demonstrated that sialic acid-independent binding could be further mapped to a small (about 40-amino acid) homologous part of the dimorphic allelic region of EBA-175, residues 898-938 (Camp strain numbering). These data support a two-step binding hypothesis and are discussed in relation to the formation of a junction between the merozoite and the erythrocyte, and the finding that after the interaction of some viruses with specific cellular receptors, they undergo conformational changes or cleavage permitting membrane fusion with the host cell.