Memory Evocation Research Articles

Autobiographical Memory in Major Depression: A Comparison between First-Episode and Recurrent Patients

Autobiographical memory in depression is characterized by an increase in general memory evocation. The aim of this study is to compare autobiographical memory in patients with a first depressive episode and in recurrent patients before and after recovery, using Williams’ and Scott’s autobiographical memory test. Our results show an increase of the number of general memories only with positive cue words in both groups of patients during the depressive episode. After clinical improvement, this specificity remains in recurrent patients who, in addition, recall more general memories for negative words. By contrast, patients with a first depressive episode are no longer different from controls. These results show both an overgeneralization and a deficit in positive memory access during the depressive episode, whatever the number of previous episodes. Moreover, recurrence chronically modifies access to emotional memories.

Positive feedback circuits and memory

The concept of regulatory feedback circuit refers to oriented cyclic interactions between elements of a system. There are two classes of circuits, positive and negative, whose properties are in striking contrast. Positive circuits are a prerequisite for the occurrence of multiple steady states (multistationarity), and hence, they are involved in all processes showing hysteresis or memory. Endogenous or exogenous perturbations can lead the system to exhibit or to evoke one particular stable regime. The role of positive circuits in cell differentiation and in immunology is well documented. Negative circuits are involved in homeostatic regulation, with or without oscillations. The aim of this paper is to show: a) that positive circuits account for many features of memory stricto sensu (i.e., neural memory and mnesic evocation) as well as largo sensu (e.g. differentiation or immunological memory); and b) that simple combinations of positive and negative circuits provide powerful regulatory modules, which can also be associated in batteries. These entities have vast dynamical possibilities in the field of neurobiology, as well as in the fields of differentiation and immunology. Here we consider a universal minimal regulatory module, for which we suggest to adopt the term ‘logical regulon’, which can be considered as an atom of Jacob's integron. It comprises a positive and a negative circuit in its interaction matrix, and we recall the main results related to the simultaneous presence of these circuits. Finally, we give three applications of this type of interaction matrix. The first two deal with the coexistence of multiple stable steady states and periodicity in differentiation and in an immunological system showing hysteretic properties. The third deals with the dual problems of synchronization and desynchronization of a neural model for hippocampus memory evocation processes.

The secondary antibody response induced in tissue cultures.

The conditions for induction of memory cells (B-MC) and evocation of the secondary antibody (Ab) response in tissue cultures (TC) were estimated. (1) In vivo primed B-MC cells were isolated 6-150 d after priming and stimulated in TC with different doses of sheep red blood cell (SRBC) antigen. The Ab response has a strict time and dose dependence: only small doses (10(5)) evoke a secondary response, high doses (10(8), 10(9)) a state of immediate tolerance. (2) Antigen added to TC directly with B-MC rescued their Ab production for a long period. Addition of the antigen 1 or 2 d after setting the TC, follows the Ab-response decay, comparable with virgin cells (B-ICC). (3) Primed B-MC stimulated in TC responded preferentially with an IgM secondary response; the same cell suspension adoptively transferred into isologous recipients switched into IgG cells. (4) Virgin, immunocompetent, B-ICC were primarily stimulated in TC with a small dose of antigen (10(5) SRBC); after 7 d of cultivation the cells were transferred into isologous recipients, SCID mice and into TC. In all cases, the secondary response of IgM was determined, 10 times higher than in the primary controls.

Prosopagnosia: anatomic basis and behavioral mechanisms.

Critical analysis of postmortem and CT scan data indicates that prosopagnosia is associated with bilateral lesions of the central visual system. Those lesions are located in the mesial occipitotemporal region and are functionally symmetric. The prime factor in the appearance of prosopagnosia is the requirement to evoke the specific context of a given visual stimulus. The "ambiguity" of the stimulus (the frequency with which different members of a group are visually similar) is an adjuvant factor. But prosopagnosia is not specific to human faces. The phenomenon appears in relation to any visually "ambiguous" stimulus whose recognition depends on contextual memory evocation.