Amygdala responses to emotionally valenced stimuli in older and younger adults

ABSTRACT—As they age, adults experience less negative emotion, come to pay less attention to negative than to positive emotional stimuli, and become less likely to remember negative than positive emotional materials. This profile of findings suggests that, with age, the amygdala may show decreased reactivity to negative information while maintaining or increasing its reactivity to positive information. We used event-related functional magnetic resonance imaging to assess whether amygdala activation in response to positive and negative emotional pictures changes with age. Both older and younger adults showed greater activation in the amygdala for emotional than for neutral pictures; however, for older adults, seeing positive pictures led to greater amygdala activation than seeing negative pictures, whereas this was not the case for younger adults. Older adults experience less negative affect than younger adults in both cross-sectional and longitudinal studies (Carstensen, Pasupathi

A direct test of the unequal-variance signal detection model of recognition memory

Analyses of the receiver operating characteristic (ROC) almost invariably suggest that, on a recognition memory test, the standard deviation of memory strengths associated with the lures (sigma(lure)) is smaller than that of the targets (sigma(target)). Often, sigma(lure)/ sigma(target) approximately = 0.80. However, that conclusion is based on a model that assumes that the memory strength distributions are Gaussian in form. In two experiments, we investigated this issue in a more direct way by asking subjects to simply rate the memory strengths of targets and lures using a 20-point or a 99-point strength scale. The results showed that the standard deviation of the ratings made to the targets (S(target)) was, indeed, larger than the standard deviation of the ratings made to the lures (S(lure)). Moreover, across subjects, the ratio S(lure)/ S(target) correlated highly with the estimate of sigma(lure)/ sigma(target) obtained from ROC analysis, and both estimates were, on average, approximately equal to 0.80.</p

Spatial and temporal specificity of Ca2+signalling inChlamydomonas reinhardtiiin response to osmotic stress

Ca2+-dependent signalling processes enable plants to perceive and respond to diverse environmental stressors, such as osmotic stress. A clear understanding of the role of spatiotemporal Ca2+ signalling in green algal lineages is necessary in order to understand how the Ca2+ signalling machinery has evolved in land plants. We used single-cell imaging of Ca2+-responsive fluorescent dyes in the unicellular green alga Chlamydomonas reinhardtii to examine the specificity of spatial and temporal dynamics of Ca2+ elevations in the cytosol and flagella in response to salinity and osmotic stress. We found that salt stress induced a single Ca2+ elevation that was modulated by the strength of the stimulus and originated in the apex of the cell, spreading as a fast Ca2+ wave. By contrast, hypo-osmotic stress induced a series of repetitive Ca2+ elevations in the cytosol that were spatially uniform. Hypo-osmotic stimuli also induced Ca2+ elevations in the flagella that occurred independently from those in the cytosol. Our results indicate that the requirement for Ca2+ signalling in response to osmotic stress is conserved between land plants and green algae, but the distinct spatial and temporal dynamics of osmotic Ca2+ elevations in C. reinhardtii suggest important mechanistic differences between the two lineages

The limited usefulness of models based on recollection and familiarity.

A recent report concluded that magnetoencephalographic signals of neural activity associated with memory based on the recollection process are independent from signals associated with memory based on the familiarity process. These data can be interpreted equally well, however, as indications of memory aggregated from both processes and showing that signals associated with high-confidence recognition are dissociable from signals associated with low-confidence recognition. The usefulness of interpreting neural data according to psychological models based on recollection and familiarity is discussed

The limited usefulness of models based on recollection and familiarity.

A recent report concluded that magnetoencephalographic signals of neural activity associated with memory based on the recollection process are independent from signals associated with memory based on the familiarity process. These data can be interpreted equally well, however, as indications of memory aggregated from both processes and showing that signals associated with high-confidence recognition are dissociable from signals associated with low-confidence recognition. The usefulness of interpreting neural data according to psychological models based on recollection and familiarity is discussed

The roles of the hippocampus in recognition memory

Recognition is our awareness of prior experience and is thought to depend upon the recollection and familiarity processes. Recollection refers to remembering an experience with associated contextual details, whereas familiarity refers to a sense of awareness absent recollection. Some psychological models have proposed that when recollection is available, confidence in a recognition decision is categorically high. Other models propose that recollection and familiarity are both continuous processes and, therefore, differences in memory strength per se do not separate recollection from familiarity. Functional magnetic resonance imaging (fMRI) has been used extensively to examine the neural correlates of recollection and familiarity, yet interpretation of these data and how recognition is supported by the brain remain open debates. The two dual-process views make different interpretations about whether the fMRI results suggest a division of labor between medial temporal lobe (MTL) structures. The typical conclusion in these fMRI studies is that the hippocampus selectively subserves recollection. In this dissertation, Experiments 1 and 2 tested the hypotheses of both dual-process models (i.e., whether recollection is categorical or continuous). The results from both experiments showed that highly confident memory is not categorically based on recollection. Experiment 3 performed a meta-analysis on the relevant fMRI literature and considered the two model-based interpretations of the results. This analysis showed that although these studies intended to dissociate MTL activity on the basis of recognition processes, their interpretations dissociated activity on the basis of memory strength. Experiment 4, which scanned a source memory test during retrieval, took a new approach to compare correct source judgments (recollection) and incorrect source judgments (familiarity) while equating for old/new memory strength by including only high- confidence hits in the analysis. This approach avoided the complication from previous studies (identified in Experiment 3) that confounded recollection and familiarity with strong and weak memories. After equating for memory strength, activity in the hippocampus in association with high-confidence hits was greater than for forgotten items, regardless whether source judgments were correct (recollection succeeded) or incorrect (recollection failed). The conclusion in this dissertation, drawn from the results of the four experiments, is that the hippocampus serves a broader role than selectively supporting recollection. Two views are discussed about how this role may work. One view hypothesizes that the summation of MTL input associated with item identification, contextual information and arousal is mediated by the hippocampus. In this framework, the role of the hippocampus is to enhance the retrievability of salient experiences. Another view suggests that the hippocampus abstracts bits of information from prior experience. This role does not map onto specific recognition processes (i.e., recollection and familiarity) or measurements of memory strength. Further work is needed to examine the range of hippocampal sensitivity for memory strength. Taken as a whole, these developments elucidate a critical role for the hippocampus in recognition and not solely in recollectio