Age-related alterations in functional connectivity along the longitudinal axis of the hippocampus and its subfields.

Hippocampal circuit alterations that differentially affect hippocampal subfields are associated with age-related memory decline. Additionally, functional organization along the longitudinal axis of the hippocampus has revealed distinctions between anterior and posterior (A-P) connectivity. Here, we examined the functional connectivity (FC) differences between young and older adults at high-resolution within the medial temporal lobe network (entorhinal, perirhinal, and parahippocampal cortices), allowing us to explore how hippocampal subfield connectivity across the longitudinal axis of the hippocampus changes with age. Overall, we found reliably greater connectivity for younger adults than older adults between the hippocampus and parahippocampal cortex (PHC) and perirhinal cortex (PRC). This drop in functional connectivity was more pronounced in the anterior regions of the hippocampus than the posterior ones, consistent for each of the hippocampal subfields. Further, intra-hippocampal connectivity also reflected an age-related decrease in functional connectivity within the anterior hippocampus in older adults that was offset by an increase in posterior hippocampal functional connectivity. Interestingly, the anterior-posterior dysfunction in older adults between hippocampus and PHC was predictive of lure discrimination performance on the Mnemonic similarity task (MST), suggesting a role in memory performance. While age-related dysfunction within the hippocampal subfields has been well-documented, these results suggest that the age-related dysfunction in hippocampal connectivity across the longitudinal axis may also contribute significantly to memory decline in older adults.

Predicted and remembered emotion: tomorrow's vividness trumps yesterday's accuracy.

People rely on predicted and remembered emotion to guide important decisions. But how much can they trust their mental representations of emotion to be accurate, and how much do they trust them? In this investigation, participants (N = 957) reported their predicted, experienced, and remembered emotional response to the outcome of the 2016 U.S. presidential election. They also reported how accurate and vivid they perceived their predictions and memories to be, and the importance of the election. Participants remembered their emotional responses more accurately than they predicted them. But, strikingly, they perceived their predictions to be more accurate than their memories. This perception was explained by the greater importance and vividness of anticipated versus remembered experience. We also assessed whether individuals with Highly Superior Autobiographical Memory for personal and public events (N = 33) showed superior ability to predict or remember their emotional responses to events. They did not and, even for this group, predicting emotion was a more intense experience than remembering emotion. These findings reveal asymmetries in the phenomenological experience of predicting and remembering emotion. The vividness of predicted emotion serves as a powerful subjective signal of accuracy even when predictions turn out to be wrong.

Response bias, recollection, and familiarity in individuals with Highly Superior Autobiographical Memory (HSAM).

The current study focused on individuals with Highly Superior Autobiographical Memory (HSAM) and had two main objectives: 1) investigate whether HSAMs have increased recollection performance compared to controls, and 2) investigate whether HSAMs have a reliably different response bias than controls. While previous lab-based recognition tests have shown that HSAMs have normal memory performance, these tests were based on a mixture of both recollection and familiarity. Here, we employed recognition tests specifically designed to separate recollected responses from those based on familiarity. Additionally, we were interested in how HSAMs make their memory decisions. Several studies have shown a great deal of variability between individuals in their response bias. Here, individuals with HSAM and age- matched controls completed a remember/know and a source memory test. HSAMs behaved like controls in both overall and recollection-based memory discrimination. However, HSAMs showed a significantly more liberal response bias, endorsing more items as "old" than controls. These findings contribute to our understanding of how memory processes - especially those related to decision-making - function in those with superior memory abilities and may help elucidate how other (non-HSAM) memory experts make decisions.

Cross-task and cross-manipulation stability in shifting the decision criterion.

In recognition memory experiments participants must discriminate between old and new items, a judgment influenced by response bias. Research has shown substantial individual differences in the extent to which people will strategically adjust their response bias to diagnostic cues such as the prior probability of an old item. Despite this significant between subject variability, shifts in bias have been found to be relatively predictive within individuals across memory tests. Experiment 1 sought to determine whether this predictability extends beyond memory. Results revealed that the amount a subject shifted response bias in a recognition memory task was significantly predictive of shifting in a visual perception task, suggesting that shifting can generalise outside of a specific testing domain. Experiment 2 sought to determine how predictive shifting would be across two manipulations well known to induce shifts in bias: a probability manipulation and a response payoff manipulation. A modest positive relationship between these two methods was observed, suggesting that shifting behaviour is relatively predictive across different manipulations of shifting. Overall, results from both experiments suggest that response bias shifting, like response bias setting, is a relatively stable behaviour within individuals despite changes in test domain and test manipulation.

Structural foundations of resting-state and task-based functional connectivity in the human brain.

Magnetic resonance imaging enables the noninvasive mapping of both anatomical white matter connectivity and dynamic patterns of neural activity in the human brain. We examine the relationship between the structural properties of white matter streamlines (structural connectivity) and the functional properties of correlations in neural activity (functional connectivity) within 84 healthy human subjects both at rest and during the performance of attention- and memory-demanding tasks. We show that structural properties, including the length, number, and spatial location of white matter streamlines, are indicative of and can be inferred from the strength of resting-state and task-based functional correlations between brain regions. These results, which are both representative of the entire set of subjects and consistently observed within individual subjects, uncover robust links between structural and functional connectivity in the human brain.

Structurally-constrained relationships between cognitive states in the human brain.

The anatomical connectivity of the human brain supports diverse patterns of correlated neural activity that are thought to underlie cognitive function. In a manner sensitive to underlying structural brain architecture, we examine the extent to which such patterns of correlated activity systematically vary across cognitive states. Anatomical white matter connectivity is compared with functional correlations in neural activity measured via blood oxygen level dependent (BOLD) signals. Functional connectivity is separately measured at rest, during an attention task, and during a memory task. We assess these structural and functional measures within previously-identified resting-state functional networks, denoted task-positive and task-negative networks, that have been independently shown to be strongly anticorrelated at rest but also involve regions of the brain that routinely increase and decrease in activity during task-driven processes. We find that the density of anatomical connections within and between task-positive and task-negative networks is differentially related to strong, task-dependent correlations in neural activity. The space mapped out by the observed structure-function relationships is used to define a quantitative measure of separation between resting, attention, and memory states. We find that the degree of separation between states is related to both general measures of behavioral performance and relative differences in task-specific measures of attention versus memory performance. These findings suggest that the observed separation between cognitive states reflects underlying organizational principles of human brain structure and function.

Individual differences in shifting decision criterion: a recognition memory study.

An ability to flexibly shift a decision criterion can be advantageous. For example, a known change in the base rate of targets and distractors on a recognition memory test will lead optimal decision makers to shift their criterion accordingly. In the present study, 95 individuals participated in two recognition memory tests that included periodic changes in the base rate probability that the test stimulus had been presented during the study session. The results reveal a wide variability in the tendency to shift decision criterion in response to this probability information, with some appropriately shifting and others not shifting at all. However, participants were highly reliable in their tendency to shift criterion across tests. The goal of the present study was to explain what factors account for these individual differences. To accomplish this, over 50 variables were assessed for each individual (e.g., personality, cognitive style, state of mind). Using a regression model that incorporated different sets of factors, over 50% of the variance was accounted for. The results of the analysis describe the total, direct, and mediating effects on criterion shifting from factors that include memory strength, strategy, and inherent characteristics such as a fun-seeking personality, a negative affect, and military rank. The results are discussed with respect to understanding why participants rarely chose an optimal decision-making strategy and provide greater insight into the underlying mechanisms of recognition memory.

Modulation of associative learning in the hippocampal-striatal circuit based on item-set similarity.

Mounting evidence suggests that the medial temporal lobe (MTL) and striatal learning systems support different forms of learning, which can be competitive or cooperative depending on task demands. We have previously shown how activity in these regions can be modulated in a conditional visuomotor associative learning task based on the consistency of response mappings or reward feedback (Mattfeld & Stark, 2015). Here, we examined the shift in learning towards the MTL and away from the striatum by placing strong demands on pattern separation, a process of orthogonalizing similar inputs into distinct representations. Mnemonically, pattern separation processes have been shown to rely heavily on processing in the hippocampus. Therefore, we predicted modulation of hippocampal activity by pattern separation demands, but no such modulation of striatal activity. Using a variant of the conditional visuomotor associative learning task that we have used previously, we presented participants with two blocked conditions: items with high and low perceptual overlap during functional magnetic resonance imaging (fMRI). As predicted, we observed learning-related activity in the hippocampus, which was greater in the high than the low overlap condition, particularly in the dentate gyrus. In contrast, the associative striatum also showed learning related activity, but it was not modulated by overlap condition. Using functional connectivity analyses, we showed that the correlation between the hippocampus and dentate gyrus with the associative striatum was differentially modulated by high vs. low overlap, suggesting that the coordination between these regions was affected when pattern separation demands were high. These findings contribute to a growing literature that suggests that the hippocampus and striatal network both contribute to the learning of arbitrary associations that are computationally distinct and can be altered by task demands.

The posterior parietal cortex: comparing remember/know and source memory tests of recollection and familiarity.

Numerous neuroimaging studies have shown a dissociation within the left posterior parietal cortex (PPC) between recollection and familiarity, with dorsal regions routinely active during familiarity and ventral regions active during recollection. The two most common methods for separating the neural correlates of these retrieval states are the remember/know paradigm and tests probing source memory. While relatively converging results have been found using these methods, the literature is lacking an adequate and direct comparison of the two procedures. We directly compared these two methodologies and found differences in both the magnitude and extent of activation within the left PPC. During familiarity, dorsal PPC regions were more strongly activated by the source test, while the remember/know test led to stronger recollection-related activations within the ventral regions of the PPC. This modulation of PPC activity is particularly important because it suggests that the neural correlates of familiarity and recollection depend on how they are operationalized. Previous assumptions that remember/know and source memory tests are functionally equivalent should therefore be re-evaluated. Additionally, any theories attempting to explain the functional role of the PPC during memory retrieval must take these differences into account.