The memory storehouse

Retrieval, monitoring, and control processes: a 7 tesla FMRI approach to memory accuracy

MEMORY RESEARCH HAS BEEN GUIDED BY TWO POWERFUL METAPHORS: the storehouse (computer) and the correspondence metaphor. The latter emphasizes the dependability of retrieved mnemonic information and draws upon ideas about the state dependency and reconstructive character of episodic memory. We used a new movie to unveil the neural correlates connected with retrieval, monitoring, and control processes, and memory accuracy (MAC), according to the paradigm of Koriat and Goldsmith (1996a,b). During functional magnetic resonance imaging, subjects performed a memory task which required (after an initial learning phase) rating true and false statements [retrieval phase (RP)], making confidence judgments in the respective statement [monitoring phase (MP)], and deciding for either venturing (volunteering) the respective answer or withholding the response [control phase (CP)]. Imaging data pointed to common and unique neural correlates. Activations in brain regions related to RP and MAC were observed in the precuneus, middle temporal gyrus, and left hippocampus. MP was associated with activation in the left anterior and posterior cingulate cortex along with bilateral medial temporal regions. If an answer was volunteered (as opposed to being withheld) during the CP, temporal, and frontal as well as middle and posterior cingulate areas and the precuneus revealed activations. Increased bilateral hippocampal activity was found during withholding compared to volunteering answers. The left caudate activation detected during withholding compared to venturing an answer supports the involvement of the left caudate in inhibiting unwanted responses. Contrary to expectations, we did not evidence prefrontal activations during withholding (as opposed to volunteering) answers. This may reflect our design specifications, but alternative interpretations are put forth.

A rapprochement between emotion and cognition: amygdala, emotion, and self-relevance in episodic-autobiographical memory

Lindquist et al. remark that not all fear instances lead to heightened amygdalar activity and, instead, point to roles of the amygdala in detecting "motivationally salient "or "emotionally impactful" stimuli. By reviewing research on the amygdala's functions in episodic-autobiographical memory, we further emphasize the involvement of the amygdala in coding the subjective relevance and extracting the biological and social significance of the stimuli.

Autobiographical memory: a biocultural relais between subject and environment

Autobiographical memory is described as integrated part of a number of memory systems which serve different functions in human information processing. These systems are regarded to be build-up onto each other both phylo- and ontogenetically and are named 'procedural memory', 'priming', 'perceptual memory', 'semantic memory (or knowledge system)' and episodic-autobiographical memory (EAM)'. Of these, EAM requires an established self and autonoetic consciousness and processes events or personal episodes. On the brain level, EAM is based on the synchronous activation of cognitive fact-processing and emotional, evaluating structures (e.g., hippocampal formation, amygdaloid body). Retrieval from EAM requires the activation of fronto-temporal areas and of limbic regions, particularly of the right hemisphere. Damage to these structures or their functional disengagement due to traumatic, stressful events selectively blocks the retrieval of EAM, though that of facts remains unimpaired ('mnestic block syndrome'). Consequently, both brain tissue damage and an altered hormonal status can have the same consequences, namely severe retrograde amnesia, which is either named organic or dissociative amnesia.

Neuronal mechanisms mediating drug-induced cognition enhancement: cognitive activity as a necessary intervening variable

The conceptual foundations of a research aimed at the determination of potential neuronal, neuropharmacological, and behavioral/cognitive mechanisms mediating drug-induced cognition enhancement are discussed. The available evidence justifies a focus on attentional processes as a target for drug-induced cognition enhancement. Neuropharmacological mechanisms that may mediate drug-induced enhancement of attentional functions are proposed to interact necessarily with attention-associated neuronal activity. The elements of a transsynaptic approach to increase the excitability of basal forebrain cholinergic neurons and hence, attentional functions are discussed. Experimental tests of this hypothesis require the demonstration of interactions between cognition-induced increases in the activity of cortical cholinergic afferents and the effects of putative cognition enhancers. The available data illustrate that the effects of benzodiazepine receptor (BZR) agonists and inverse agonists on cortical acetylcholine (ACh) efflux interact with the state of activity in this system. The feasibility, potential heuristic power, and the experimental and conceptual problems of studies attempting to simultaneously assess drug effects on behavioral/cognitive abilities, ACh efflux, and neuronal activity have been revealed by an experiment intended to correlate performance in a task measuring sustained attention with medial prefrontal ACh efflux and medial prefrontal single-unit activity. The rational development of a psychopharmacology of cognition enhancers requires a union among behavioral/cognitive pharmacology, neuropharmacological and electrophysiological approaches.