Biology subjects

Richter, F. R.

Publications and source records attributed to Richter, F. R..

5 recordsLinked to original sources

bioRxiv2022

Reduced memory precision in older age is associated with functional and structural differences in the angular gyrus

Decreased fidelity of mnemonic representations plays a critical role in age-related episodic memory deficits, yet the brain mechanisms underlying such reductions remain unclear. Using functional and structural neuroimaging, we examined how changes in two key nodes of the posterior-medial network, the hippocampus and the angular gyrus, might underpin loss of memory precision in older age. Healthy young and older adults completed a memory task that involved reconstructing object features on a continuous scale. Investigation of BOLD activity during retrieval revealed an age-related reduction in activity reflecting successful recovery of object features in the hippocampus, whereas trial-wise modulation of BOLD signal by graded memory precision was diminished in the angular gyrus. Grey matter volume of the angular gyrus further predicted individual differences in memory precision in older age, beyond likelihood of successful retrieval. These findings provide converging evidence for a role of functional and structural integrity of the angular gyrus in constraining the fidelity of episodic remembering in older age, yielding new insights into parietal contributions to age-related episodic memory decline.

neuroscience↗

bioRxiv2021

Episodic memory precision and reality monitoring following stimulation of angular gyrus

The qualities of remembered experiences are often used to inform reality monitoring judgments, our ability to distinguish real and imagined events (Johnson & Raye, 1981). Previous experiments have tended to investigate only whether reality monitoring decisions are accurate or not, providing little insight into the extent to which reality monitoring may be affected by qualities of the underlying mnemonic representations. We used a continuous-response memory precision task to measure the quality of remembered experiences that underlie two different types of reality monitoring decisions: agency decisions that distinguish actions performed by participants and the experimenter, and perceptual decisions that distinguish perceived and imagined experiences. The data revealed memory precision to be associated with higher accuracy in both agency and perceptual reality monitoring decisions, with reduced precision linked with a tendency to misattribute self-generated experiences to external sources. We then sought to investigate the possible neurocognitive basis of these observed associations by applying brain stimulation to a region that has been implicated in precise recollection of personal events, left angular gyrus. Stimulation of angular gyrus selectively reduced the association between memory precision and self-referential reality monitoring decisions, relative to control site stimulation. Angular gyrus may, therefore, be important for the ability to imbue remembered experiences with a sense of self-agency, a key component of autonoetic consciousness that characterises episodic memory (Tulving, 1985).

neuroscience↗

bioRxiv2020

Hippocampal-cortical encoding activity predicts the precision of episodic memory

Our recollections of past experiences can vary both in the number of specific event details accessible from memory and the precision with which such details are reconstructed. Prior neuroimaging evidence suggests the success and precision of episodic recollection to rely on distinct neural substrates during memory retrieval. In contrast, the specific encoding mechanisms supporting later memory precision, and whether they differ from those underlying successful memory formation in general, are currently unknown. Here, we combined continuous measures of memory retrieval with model-based analyses of behavioural and neuroimaging data to tease apart the encoding correlates of successful memory formation and mnemonic precision. In the MRI scanner, participants encoded object-scene displays, and later reconstructed features of studied objects using a continuous scale. We observed overlapping encoding activity in inferior prefrontal and posterior perceptual regions to predict both which object features were later remembered versus forgotten, and the precision with which they were reconstructed from memory. In contrast, hippocampal encoding activity significantly predicted the precision, but not overall success, of subsequent memory retrieval. The current results identify a hippocampal-cortical encoding basis for episodic memory precision, and suggest a contribution of shared cortical encoding mechanisms to the formation of both accessible and precise memory representations.

neuroscience↗

bioRxiv2019

An EEG investigation of the trial-by-trial updating of complex knowledge structures

Memory schemas are higher-level knowledge structures that store an abstraction of multiple previous experiences. They allow us to retain a multitude of information without the cost of storing every detail. Schemas are believed to be relatively stable, but occasionally have to be updated to remain useful in the face of changing environmental conditions. Once a schema is consolidated, schema updating has been proposed to be the result of a prediction-error (PE) based learning mechanism, similar to the updating of less complex knowledge. However, for schema memory this hypothesis has been difficult to test because no sufficiently sensitive tools to track modifications to complex memory schemas existed so far. Current research on the updating of less complex beliefs and at much shorter time scales has identified the P3 as an electrophysiological correlate of PE-induced updating of beliefs. In this study, I recorded electroencephalography and continuous memory measures during the encoding of schema consistent vs. inconsistent material to test the behavioural and neural correlates of schema updating. I observed that PEs predicted the updating of a schema after a 24-hour delay, especially when participants were faced with inconsistent compared to consistent material. Moreover, the P3 amplitude tracked both the PE at the time of learning as well as the updating of the memory schema in the inconsistent condition. These results demonstrate that schema updating in the face of inconsistent information is driven by PE-based learning, and that similar neural mechanisms underlie the updating of consolidated long-term memory schemas and short-term belief structures.

neuroscience↗

bioRxiv2017

Decomposing parietal memory reactivation to predict consequences of remembering

Memory retrieval can strengthen, but also distort memories. Parietal cortex is a candidate region involved in retrieval-induced memory changes as it reflects retrieval success and represents retrieved content. Here, we conducted an fMRI experiment to test whether different forms of parietal reactivation predict distinct consequences of retrieval. Subjects studied associations between words and pictures of faces, scenes, or objects, and then repeatedly retrieved half of the pictures, reporting the vividness of the retrieved pictures ( retrieval practice). On the following day, subjects completed a recognition memory test for individual pictures. Critically, the test included lures highly similar to studied pictures. Behaviorally, retrieval practice increased both hit and false alarm rates to similar lures, confirming a causal influence of retrieval on subsequent memory. Using pattern similarity analyses, we measured two different levels of reactivation during retrieval practice: generic category-level reactivation and idiosyncratic item-level reactivation. Vivid remembering during retrieval practice was associated with stronger category- and item-level reactivation in parietal cortex. However, these measures differentially predicted subsequent recognition memory performance: whereas higher category-level reactivation tended to predict false alarms to lures, item-level reactivation predicted correct rejections. These findings indicate that parietal reactivation can be decomposed to tease apart distinct consequences of memory retrieval.

neuroscience↗