Dissociating state and item components of recognition memory using fMRI

Cognitive functions such as memory retrieval involve a combination of state- and item-related processes. State-related processes are sustained throughout a task (e.g., "retrieval mode" associated with ongoing goals), whereas item-related processes are transient and allied to individual stimuli (e.g., "retrieval success" associated with the recovery of information from memory). The present study employed a mixed "blocked and event-related" experimental design to identify neural mechanisms that support state- and item-related processes during a recognition memory task. Subjects alternated between blocks of fixation and recognition memory (discriminating between old and new words). Critically, event-related procedures were embedded within the recognition blocks, including the jittering of sequential trials. This design ensures that the temporal profiles of state- and item-related activity differ and consequently renders them separable; without this procedure item-related activity would summate to produce a state-like response. Results suggest three classes of brain region support recognition memory, exhibiting: (1) predominantly transient activity (including regions in medial parietal, lateral parietal, and anterior left frontal cortex) reflecting item-related processing associated with "retrieval success," (2) predominantly sustained activity (including decreased activity in bilateral parahippocampal cortex) reflecting state-related processing associated with "retrieval mode," (3) concurrent sustained and transient activity (including regions in left middle frontal gyrus, bilateral frontal operculum, and medial frontal gyrus), reflecting a combination of state- and item-related processing. The present findings support the idea that recognition memory tasks are dependent upon a combination of state- and item-related processes that have dissociable neural correlates identifiable using fMRI. Moreover, the mixed "blocked and event-related" design employed here provides a general procedure for separating state- and item-related processes

HLA class I expression on erythrocytes and platelets from patients with systemic lupus erythematosus, rheumatoid arthritis and from normal subjects

It has previously been shown, by a haemagglutination assay, that patients with systemic lupus erythematosus (SLE) express increased levels of HLA class I on erythrocytes compared with normal subjects and patients with rheumatoid arthritis (RA). A radioligand-binding assay, using monoclonal antibody W6/32, was devised to quantify HLA class I expression on erythrocytes and platelets. An increased number of class I molecules was expressed on erythrocytes from 45 patients with SLE (mean = 354 molecules per cell, median = 255 molecules, range = 30-1270 molecules per cell), compared with cells from 46 normal subjects (mean = 132, median = 78, range = 40-550) and 31 RA patients (mean = 132, median = 89, range = 26-497). The presence of HLA-B7 correlated with increased class I expression on erythrocytes from both normal subjects and patients with SLE. Levels of HLA class I in serum were measured. All subjects with HLA-A9 (A23, 24) showed higher levels of serum class I than their A9-negative counterparts, and there was no difference in levels between SLE patients and normal subjects. There were no correlations between class I levels in serum and on erythrocytes amongst SLE patients or normal subjects. Red cells were fractionated, according to their age in vivo, on Percoll gradients. Class I levels fell with increasing erythrocyte age in all individuals, but were higher in all fractions from SLE patients compared with age-matched fractions from normal subjects. HLA-B7-positive erythrocytes also expressed higher class I levels in each Percoll fraction, compared with their HLA-B7-negative counterparts, suggesting that enhanced B7 expression is not due to greater structural stability of this class I allotype. These data are compatible with the hypothesis that class I is expressed as an intrinsic protein of erythrocyte membranes and that expression is increased amongst patients with SLE