Biology subjects

Knights, E.

Publications and source records attributed to Knights, E..

7 recordsLinked to original sources

bioRxiv2023

Neural Evidence of Functional Compensation for Fluid Intelligence in Healthy Ageing

Functional compensation is a common notion in the neuroscience of healthy ageing, whereby older adults are proposed to recruit additional brain activity to compensate for reduced cognitive function. However, whether this additional brain activity in older participants actually helps their cognitive performance remains debated. We examined brain activity and cognitive performance in a human lifespan sample (N=223) while they performed a problem-solving task (based on Cattells test of fluid intelligence) during functional magnetic resonance imaging (fMRI). Whole-brain univariate analysis revealed that activity in bilateral cuneal cortex for hard vs. easy problems increased both with age and with performance, even when adjusting for an estimate of age-related differences in cerebrovascular reactivity. Multivariate Bayesian decoding further demonstrated that age increased the likelihood that activation patterns in this cuneal region provided non-redundant information about the two task conditions, beyond that of the multiple-demand network generally activated in this task. This constitutes some of the strongest evidence yet for functional compensation in healthy ageing, at least in this brain region during visual problem-solving.

neuroscience↗

bioRxiv2023

Behavioral and neuroimaging correlates of attentional biases to angry faces in individuals in remission from depression: a population-derived study

BackgroundDepressed individuals show attentional biases in the processing of emotional stimuli, such as negative face expressions. Some of these biases persist in previously depressed individuals, but their mechanisms remain largely unknown. MethodsA population-derived cohort (n = 134, 68 females; 21 - 92 years) was recruited by Cam-CAN. Functional MRI was acquired during a gender discrimination task, which used angry and neutral faces. Drift diffusion modelling (DDM) was used to investigate the latent components of the decision process, focusing on the effect of emotional valence. DDM parameters were correlated with activity in brain regions. Results14% of participants reported a history of depression in remission. The best fitting DDM specified a different drift rate for angry and neutral faces. A slower drift rate for angry faces predicted depression in remission (OR 0.092, p = 0.048). This effect persisted after accounting for current depression symptoms and drift rate for neutral faces. Participants with a slower drift rate for angry faces demonstrated increased activations in the bilateral insula, bilateral inferior frontal gyrus and bilateral parietal cortex when viewing angry relative to neutral faces. ConclusionsOur results suggest a persistent attentional bias in the processing of angry faces in individuals with depression in remission, over and above their current depressive symptoms. The imaging findings suggest that the slowing is associated with changes in areas involved in emotional regulation and evidence accumulation. Attentional biases in the processing of emotional information may reflect a trait, rather than state, in individuals with depression.

neuroscience↗

bioRxiv2021

A morphometric double dissociation: cortical thickness is more related to aging; surface area is more related to cognition

The thickness and surface area of cortex are genetically distinct aspects of brain structure, and may be affected differently by age. However, their potential to differentially predict age and cognitive abilities has been largely overlooked, likely because they are typically aggregated into the commonly used measure of volume. In a large sample of healthy adults (N=647, aged 18-88), we investigated the brain-age and brain-cognition relationships of thickness, surface area, and volume, plus five additional morphological shape metrics. Cortical thickness was the metric most strongly associated with age cross-sectionally, as well as exhibiting the steepest longitudinal change over time (subsample N=261, aged 25-84). In contrast, surface area was the best single predictor of age-residualized cognitive abilities (fluid intelligence), and changes in surface area were most strongly associated with cognitive change over time. These findings were replicated in an independent dataset (N=1345, aged 18-93). Our results suggest that cortical thickness and surface area make complementary contributions the age-brain-cognition triangle, and highlight the importance of considering these volumetric components separately.

neuroscience↗

bioRxiv2021

Ageing and the ipsilateral M1 BOLD response: a connectivity study

Young people exhibit a negative BOLD response in ipsilateral primary motor cortex (M1) when making unilateral movements, such as button presses. This negative BOLD response becomes more positive as people age. Here we investigated why this occurs, in terms of the underlying effective connectivity and haemodynamics. We applied dynamic causal modelling (DCM) to task fMRI data from 635 participants aged 18-88 from the Cam-CAN dataset, who performed a cued button pressing task with their right hand. We found that connectivity from contralateral supplementary motor area (SMA) and dorsal premotor cortex (PMd) to ipsilateral M1 became more positive with age, explaining 44% of the variability across people in ipsilateral M1 responses. Neurovascular and haemodynamic parameters in the model were not able to explain the age-related shift to positive BOLD. Our results add to a body of evidence implicating neural, rather than vascular factors as the predominant cause of negative BOLD - while emphasising the importance of inter-hemispheric connectivity. This study provides a foundation for investigating the clinical and lifestyle factors that determine the sign and amplitude of the M1 BOLD response, which could serve as a proxy for neural and vascular health, via the underlying neurovascular mechanisms.

neuroscience↗

bioRxiv2021

Does Hemispheric Asymmetry Reduction in Older Adults (HAROLD) in motor cortex reflect compensation?

Older adults tend to display greater brain activation in the non-dominant hemisphere during even basic sensorimotor responses. It is debated whether this Hemispheric Asymmetry Reduction in Older Adults (HAROLD) reflects a compensatory mechanism. Across two independent fMRI experiments involving an adult-lifespan human sample (N = 586 and N = 81; approximately half female) who performed right hand finger responses, we distinguished between these hypotheses using behavioural and multivariate Bayes (MVB) decoding approaches. Standard univariate analyses replicated a HAROLD pattern in motor cortex, but in- and out-of-scanner behavioural results both demonstrated evidence against a compensatory relationship, in that reaction time measures of task performance in older adults did not relate to ipsilateral motor activity. Likewise, MVB showed that this increased ipsilateral activity in older adults did not carry additional information, and if anything, combining ipsilateral with contralateral activity patterns reduced action decoding in older adults (at least in Experiment 1). These results contradict the hypothesis that HAROLD is compensatory, and instead suggest that the age-related, ipsilateral hyper-activation is non-specific, in line with alternative hypotheses about age-related reductions in neural efficiency/differentiation or inter-hemispheric inhibition. Significance StatementA key goal in the cognitive neuroscience of ageing is to provide a mechanistic explanation of how brain-behaviour relationships change with age. One interpretation of the common finding that task-based hemispheric activity becomes more symmetrical in older adults, is that this shift reflects a compensatory mechanism, with the non-dominant hemisphere needing to "help out" with computations normally performed by the dominant hemisphere. Contrary to this view, our behavioural and brain data indicate that the additional activity in ipsilateral motor cortex in older adults is not reflective of better task performance nor better neural representations of finger actions.

neuroscience↗

bioRxiv2020

Hand-selective visual regions represent how to grasp 3D tools for use: brain decoding during real actions

Most neuroimaging experiments that investigate how tools and their actions are represented in the brain use visual paradigms where tools or hands are displayed as 2D images and no real movements are performed. These studies discovered selective visual responses in occipito-temporal and parietal cortices for viewing pictures of hands or tools, which are assumed to reflect action processing, but this has rarely been directly investigated. Here, we examined the responses of independently visually defined category-selective brain areas when participants grasped 3D tools. Using real action fMRI and multi-voxel pattern analysis, we found that grasp typicality representations (i.e., whether a tool is being grasped appropriately for use) were decodable from hand-selective areas in occipito-temporal and parietal cortices, but not from tool-, object-, or body-selective areas, even if partially overlapping. Importantly, these effects were exclusive for actions with tools, but not for biomechanically matched actions with control nontools. In addition, decoding of grasp typicality was significantly higher in hand than tool-selective parietal regions. Notably, grasp typicality representations were automatically evoked even when there was no requirement for tool use and participants were naive to object category (tool vs non-tools). Finding a specificity for typical tool grasping in hand-, rather than tool-, selective regions challenges the long-standing assumption that brain activation for viewing tool images reflects sensorimotor processing linked to tool manipulation. Instead our results show that typicality representations for tool grasping are automatically evoked in visual regions specialised for representing the human hand, the brains primary tool for interacting with the world. Significance StatementThe unique ability of humans to manufacture and use tools is unsurpassed across the animal kingdom, with tool use considered a defining feature of our species. Most neuroscientific studies that investigate the brain mechanisms that support tool use, record brain activity while people simply view images of tools or hands and not when people perform actual hand movements with tools. Here we show that specific areas of the human visual system that preferentially process hands automatically encode how to appropriately grasp 3D tools, even when no actual tool use is required. These findings suggest that visual areas optimized for processing hands represent fundamental aspects of tool grasping in humans, such as which side they should be grasped for correct manipulation.

neuroscience↗

bioRxiv2020

Asymmetric thinning of the cerebral cortex across the adult lifespan is accelerated in Alzheimer's Disease

Normal aging and Alzheimers Disease (AD) are accompanied by large-scale alterations in brain organization that undermine brain function. Although hemispheric asymmetry is a global organizing feature of cortex thought to promote brain efficiency, current descriptions of cortical thinning in aging and AD have largely overlooked cortical asymmetry. Consequently, the foundational question of whether and where the cerebral hemispheres change at different rates in aging and AD remains open. First, applying vertex-wise data-driven clustering in a longitudinal discovery sample (aged 20-89; 2577 observations; 1851 longitudinal) we identified cortical regions exhibiting similar age-trajectories of asymmetry across the adult lifespan. Next, we sought replication in 4 independent longitudinal aging cohorts. We show that higher-order regions of cortex that exhibit pronounced asymmetry at age ~20 also show asymmetry change in aging. Results revealed that both leftward and rightward asymmetry is progressively lost on a similar time-scale across adult life. Hence, faster thinning of the (previously) thicker homotopic hemisphere is a feature of aging. This simple organizational principle showed high consistency across multiple aging cohorts in the Lifebrain consortium, and both the topological patterns and temporal dynamics of asymmetry-loss were markedly similar across replicating samples. Finally, we show that regions exhibiting gradual asymmetry-loss over healthy adult life exhibit faster asymmetry-change in AD. Overall, our results suggest a system-wide breakdown in the adaptive asymmetric organization of cortex across adult life which is further accelerated in AD, and may implicate thickness asymmetry as a viable marker for declining hemispheric specialization in aging and AD. SignificanceThe brain becomes progressively disorganized with age, and brain alterations accelerated in Alzheimers disease may occur gradually over the lifespan. Although hemispheric asymmetry aids efficient network organization, efforts to identify structural markers of age-related decline have largely overlooked cortical asymmetry. Here we show the hemisphere that is thicker when younger, thins faster. This leads to progressive system-wide loss of regional thickness asymmetry across life. In multiple aging cohorts, asymmetry-loss showed high reproducibility topologically across cortex and similar timing-of-change in aging. Asymmetry-change was further accelerated in AD. Our findings uncover a new principle of brain aging - thicker homotopic cortex thins faster - and suggest we may have unveiled a structural marker for a widely-hypothesized decline in hemispheric specialization in aging and AD.

neuroscience↗