Biology subjects

Rugg, M.

Publications and source records attributed to Rugg, M..

9 recordsLinked to original sources

bioRxiv2026

Brain Structure-Function Association as a Compensatory Factor in Cognitive Aging

Functional activity in response to increasing task difficulty (BOLD-modulation) in regions of the default mode network (DMN/task-negative) and multiple demand network (MDN/task-positive) shows age-related decline, which is associated with reduced cognitive performance. While BOLD-modulation in the DMN begins to decline in middle-age, white matter structural connectivity declines earlier in MDN regions. We conjecture that to maintain executive function (EF) performance with aging, altered BOLD-modulation in DMN during task engagement serves as a compensatory reaction to structural decline in MDN. To test this possibility, functionally-guided tractography was applied in 160 healthy adults aged 20-94 to locate white matter connecting MDN and/or DMN regions that were active during a distance judgement paradigm. Specifically, analyses examined the effects of 1) age on white matter tracts (fractional anisotropy; FA); 2) structure-function association between FA and BOLD-modulation; and 3) age, positive/negative BOLD-modulation, and quadratic FA on EF. Age-related decline was found in one MDN tract (U-shaped tract) and a significant structure-function association was found in inferior fronto-occipital fasciculus (IFOF). Additionally, an interaction effect between quadratic frontal-insular (U-shaped) tract FA, age, and positive/negative BOLD-modulation was found for inhibition performance, supporting the hypothesis of compensatory functional activity effects on executive function for older adults with altered white matter microstructure.

neuroscience↗

bioRxiv2026

Encoding-related fMRI BOLD activity predicts subsequent memory for studied scenes, but not subsequent identification of perceptually similar lures.

Pattern separation is widely regarded as a hippocampally mediated process that reduces interference between memories of similar experiences. Performance on the Mnemonic Similarity Task (MST), where the requirement is to discriminate between studied items (targets) and perceptually similar lures, is commonly held to depend on pattern separation. Specifically, it has been proposed that similar lure identification is supported by a recall-to-reject strategy, whereby lures are identified as a result of the retrieval of the corresponding studied item. According to this proposal, therefore, the encoding operations that support successful target recollection and successful lure identification should be closely similar, since both mnemonic judgments depend upon subsequent recollection of the study item. Here, using fMRI, we examined this prediction. In samples of cognitively healthy young and older adults, we employed a three-choice MST (target/lure/new) with scene and object images as test items. Using ROI-based univariate and multivoxel analyses, we assessed whether encoding-related activity was predictive of the identification of target and similar lure items on the subsequent memory test. The activity elicited by scene images predicted memory performance for subsequently presented targets but not for corresponding similar lures, contrary to the recall-to-reject hypothesis. No effects could be identified for either class of object test items. The magnitude of the encoding effects for the scene targets was age-invariant, and, moreover, the univariate scene SMEs demonstrated a robust, age-invariant association with the target-lure discriminability metric. HighlightsO_LIEncoding fMRI activity predicted scene recognition but not lure discrimination. C_LIO_LIEncoding-related fMRI effects showed no age-related differences. C_LIO_LIEncoding fMRI effects for scenes predicted mnemonic discrimination performance. C_LIO_LINo encoding-related fMRI effects were detected for objects. C_LI

neuroscience↗

bioRxiv2025

Retrieval-related eye movements are predictive of memory precision

Eye movements are predictive of successful episodic memory encoding and retrieval, but it is unclear whether they reflect the precision of retrieved memory content. Here, we examined relationships between eye fixations, memory precision and fMRI BOLD activity. At study, participants were presented with object images, each placed at a random location on an invisible circle. At test, both studied and new images were presented. Participants were instructed to make a covert recognition memory judgment to each image, recall and then signal its studied location, guessing if necessary. Simultaneous fMRI and eye-tracking data were acquired during the test phase. For correctly recognized images, the trial-wise angular distance between the studied and reported locations was fitted to a two-component mixture model. Based on the model-derived parameters, correctly recognized images were categorized as those associated with successful location retrieval (location hits) or guesses. Location hits were further divided into high- and low precision trials. At retrieval, fixations predicted both successful retrieval and the precision of the retrieved location memory. Additionally, across-trial fixation patterns were more similar for location hits than for guesses, and for high- than for low-precision trials. The association between retrieval success and eye fixation precision was evident across almost the entire recall phase, whereas memory precision effects emerged around 1-1.5s after image onset. Fixation precision and fixation pattern similarity each predicted trial-wise memory precision independently of hippocampal BOLD activity, which also predicted precision. These findings suggest that eye fixations during retrieval track the fidelity of mnemonic content.

neuroscience↗

bioRxiv2025

The relationship between neural differentiation and exploratory eye movements in healthy young and older adults

Age-related neural dedifferentiation, characterized by lower selectivity of neural responses in the high-level sensory cortex, is thought to be a major contributor to age-related cognitive decline. However, the mechanisms that underlie dedifferentiation are poorly understood. Building on prior evidence that exploratory eye movements differ with age, we investigated the role that eye movement might play in age-related declines in neural selectivity. Healthy young and older adults of both sexes underwent fMRI with simultaneous eye-tracking as they viewed words paired with images of scenes and objects prior to a memory test. Consistent with numerous prior reports, multivoxel pattern similarity analysis (PSA) of the fMRI data revealed age-related neural dedifferentiation in scene-selective, but not object-selective cortex. Eye movements, operationalized as the number of gaze fixations made during stimulus viewing, were elevated in older adults. Analyses examining the relationship between trial-wise estimates of neural selectivity and fixation count revealed an age-invariant positive relationship in the object-selective lateral occipital complex. However, this association was found to be age-dependent in scene-selective cortex, such that there was a robust positive relationship between scene selectivity and fixation count in young, but not older adults. Lastly, scene-related selectivity in the parahippocampal place area predicted subsequent memory performance independently of age group and fixation counts at encoding. These findings suggest that age-related neural dedifferentiation in scene-selective cortex may relate to declines in the functional specialization of exploratory eye movements during scene viewing. Significance statementHealthy aging is associated with lower neural selectivity in brain regions responsive to distinct categories of perceptual stimuli. This phenomenon is most commonly observed in scene-selective cortex, although the underlying reasons remain unknown. Here, we report that trial-wise estimates of neural selectivity positively covary with the number of eye movements made during stimulus viewing. However, we also report an age-related breakdown in this relationship within scene-selective cortex, consistent with the notion that age differences in eye movements and neural selectivity reflect deficits in the extraction and binding of visual information into memory. The present findings highlight the complex interactions that occur between age, neural selectivity and eye movements, and provide novel insights into neural and behavioral mechanisms underlying cognitive aging.

neuroscience↗

bioRxiv2023

The effects of age on neural correlates of recollection: transient versus sustained fMRI effects

Prior fMRI findings in young adults indicate that recollection-sensitive neural regions dissociate according to the time courses of their respective recollection effects. Here, we examined whether such dissociations are also evident in older adults. Young and older participants encoded a series of word-object image pairs, judging which of the denoted objects was the smaller. At test, participants first judged whether a test word was old or new. For items judged old, they were required to recall the associated image and hold it in mind across a variable delay period. A post-delay cue denoted which of three judgments should be made on the retrieved image. Older adults demonstrated significantly lower associative memory performance than young adults. Replicating prior findings, transient recollection effects were identified in the left hippocampus, medial prefrontal cortex and posterior cingulate, while sustained effects were widespread across left lateral cortex and were also evident in the bilateral striatum. With the exception of those in the left insula, all effects were age-invariant. These findings add to the evidence that recollection-related BOLD effects in different neural regions can be temporally dissociated. Additionally, the findings suggest that both transient and sustained recollection effects are largely stable across much of the healthy adult lifespan.

neuroscience↗

bioRxiv2022

Cortical thickness, gray matter volume and cognitive performance: a cross-sectional study of the moderating effects of age on their inter-relationships

In a sample comprising younger, middle-aged and older cognitively healthy adults (N = 375), we examined associations between mean cortical thickness, gray matter volume (GMV) and performance in four cognitive domains - memory, speed, fluency and crystallized intelligence. In almost all cases, the associations were moderated significantly by age, with the strongest associations in the older age group. An exception to this pattern was identified in a younger adult sub-group aged less than 23 yrs, when a negative association between cognitive performance and cortical thickness was identified. Other than for speed, all associations between structural metrics and performance in specific cognitive domains were fully mediated by mean cognitive ability. Cortical thickness and GMV explained unique fractions of the variance in mean cognitive ability, speed and fluency. In no case, however, did the amount of variance jointly explained by the two metrics exceed 7% of the total variance. These findings suggest that cortical thickness and GMV are distinct correlates of domain-general cognitive ability, that the strength and, for cortical thickness, the direction of these associations is moderated by age, and that these structural metrics offer only limited insights into the determinants of individual differences in cognitive performance across the adult lifespan.

neuroscience↗

bioRxiv2020

Effects of age on pre-stimulus neural activity predictive of successful memory encoding: an fMRI study

Pre-stimulus subsequent memory effects (SMEs) - differences in neural activity preceding the onset of study items that are predictive of later memory performance - have consistently been reported in young adults. The present fMRI experiment investigated potential age-related differences in pre-stimulus SMEs. During study, healthy young and older participants made one of two semantic judgments on images, with the judgment signaled by a preceding cue. In the test phase, participants first made an item recognition judgment and, for each item judged old, a source memory judgment. Age-invariant pre-stimulus SMEs were observed in left dorsomedial prefrontal cortex, left hippocampus, and right subgenual cortex. In each case, the effects reflected lower BOLD signal for later recognized items, regardless of source accuracy, than unrecognized items. A similar age-invariant pattern was observed in left orbitofrontal cortex, but the effect in this region was specific to items attracting a correct source response compared to unrecognized items. In contrast, the left angular gyrus and fusiform cortex demonstrated negative pre-stimulus SMEs that were exclusive to young participants. The findings indicate that age differences in pre-stimulus SMEs are regionally specific and suggest that pre-stimulus SMEs reflect multiple cognitive processes, only some of which are vulnerable to advancing age.

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bioRxiv2019

Gamma oscillations during episodic memory processing reveal reversal of information flow between the hippocampus and prefrontal cortex

A critical and emerging question in human episodic memory is how the hippocampus interacts with the prefrontal cortex during the encoding and retrieval of items and their contexts. In the present study, participants performed an episodic memory task (free recall) while intracranial electrodes were simultaneously inserted into the hippocampus and multiple prefrontal locations, allowing the quantification of relative onset times of gamma band activity in the cortex and the hippocampus in the same individual. We observed that in left anterior ventrolateral prefrontal cortex (aVLPFC) gamma band activity onset was significantly later than in the hippocampus during memory encoding, whereas its activity significantly preceded that in the hippocampus during memory retrieval. These findings provide direct evidence to support models of prefrontal-hippocampal interactions derived from studies of rodents, but suggest that in humans, it is the aVLPFC rather than medial prefrontal cortex that demonstrate these reciprocal interactions.

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bioRxiv2019

Intracranial EEG reveals bihemispheric parietal and extra parietal brain networks supporting mental arithmetic

Mathematical reasoning is central to everyday life. Lesion data and functional MRI studies suggest that even simple arithmetic involves the coordination of multiple spatially diverse brain regions, but to date, math processing has not been well characterized using direct brain recordings, especially outside of the parietal cortex. To address this, we utilized an unparalleled data set of 310 subjects implanted with intracranial electrodes to investigate the spatial and temporal dynamics of arithmetic reasoning. Our data support the importance of regions previously implicated in numerosity such as the superior parietal lobule and intraparietal sulcus. However, we also identify contributions to arithmetic processing from regions such as the entorhinal cortex and temporal pole. Using the excellent bihemispheric coverage afforded by our data set and the precise temporal resolution of intracranial recordings, we characterize in detail the spatial and temporal characteristics of an arithmetic processing network, quantifying subtle hemispheric differences for selected regions. We also examine how activity in these regions predicts arithmetic ability and look for gender differences in the pattern of network activation. Our findings further define the complex network of regions involved in human arithmetical reasoning.

neuroscience↗