Biology subjects

Stevens, W. D.

Publications and source records attributed to Stevens, W. D..

6 recordsLinked to original sources

bioRxiv2024

Atypical scene-selectivity in the retrosplenial complex in individuals with autism spectrum disorder

A small behavioral literature on individuals with autism spectrum disorder (ASD) has shown that they can be impaired when navigating using map-based strategies (i.e., memory-guided navigation), but not during visually guided navigation. Meanwhile, there is neuroimaging evidence in typically developing (TD) individuals demonstrating that the retrosplenial complex (RSC) is part of a memory-guided navigation system, while the occipital place area (OPA) is part of a visually-guided navigation system. A key identifying feature of the RSC and OPA is that they respond significantly more to pictures of places compared to faces or objects - i.e., they demonstrate scene-selectivity. Therefore, we predicted that scene-selectivity would be weaker in the RSC of individuals with ASD compared to a TD control group, while the OPA would not show such a difference between the groups. We used functional MRI to scan groups of ASD individuals and matched TD individuals while they viewed pictures of places and faces and performed a one-back task. As predicted, scene-selectivity was significantly lower in the RSC, but not OPA, in the ASD group compared to the TD group. These results suggest that impaired memory-guided navigation in individuals with ASD may, in part, be due to atypical functioning in the RSC. Lay summaryThe retrosplenial complex (RSC), a cortical region that is part of a neural system that supports our ability to form map-like mental representations of the environment and use them to navigate (i.e., memory-guided navigation), exhibits atypical responses to images of places in individuals with autism spectrum disorder (ASD). These results are a first step towards understanding the neural mechanisms responsible for understudied behavioral impairments in memory-guided navigation in individuals with ASD.

neuroscience↗

bioRxiv2022

Mixed Models Quantify Annual Volume Change; Linear Regression Determines Thalamic Volume as the Best Subcortical Structure Volume Predictor in Alzheimer's Disease and Aging

BackgroundThalamus-hippocampus-putamen and thalamus-cerebellar interconnections are dense. The extent this connectivity is paralleled by each structures volume impact on another is unquantified in Alzheimers disease (AD). Mixed model quantification of annual volume change in AD is scarce and absent inclusive of the cerebellum, hippocampus, putamen and lateral ventricles and thalamus. Among these structures, autopsy evidence of early-stage AD seems largely but not entirely restricted to the hippocampus and thalamus. ObjectiveVariation in annual volume related to time and baseline age was assessed for the hippocampus, putamen, cerebellum, lateral ventricles and thalamus. Which subcortical structures volume had the largest explanatory effect of volume variation in other subcortical structures was also determined. MethodThe intraclass correlation coefficient was used to assess test-retest reliability of structure automated segmentation. Linear regression (N = 45) determined which structures volume most impacted volume of other structures. Finally, mixed models (N = 36; 108 data points) quantified annual structure volume change from baseline to 24-months. ResultsHigh test-retest reliability was indicated by a mean ICC score of .989 (SD = .012). Thalamic volume consistently had the greatest explanatory effect of hippocampal, putamen, cerebellar and lateral ventricular volume. The group variable proxy for AD significantly contributed to the best-fitting hippocampal linear regression model, hippocampal and thalamic longitudinal mixed models, and approached significance in the longitudinal lateral ventricular mixed model. Mixed models determined time (1 year) had a negative effect on hippocampal, cerebellar and thalamic volume, no effect on putamen volume, and a positive effect on lateral ventricular volume. Baseline age had a negative effect on hippocampal and thalamic volume, no effect on cerebellar or putamen volume and a positive effect on lateral ventricular volume. InterpretationLinear regression determined thalamic volume as a virtual centralized index of hippocampal, cerebellar, putamen, and lateral ventricular volume. Relative to linear regression, longitudinal mixed models had greater sensitivity to detect contribution of early AD, or potential AD pathology (MCI), via the group variable not just to volume reduction in the hippocampus but also in the thalamus.

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bioRxiv2022

A neural mechanism of cognitive reserve: The case of bilingualism

Cognitive Reserve (CR) refers to the preservation of cognitive function in the face of age-or disease-related neuroanatomical decline. While bilingualism is known to contribute to CR, the extent to which, and what particular aspect of, second language experience contributes to CR are debated, and the underlying neural mechanism(s) unknown. Intrinsic functional connectivity reflects experience-dependent neuroplasticity that occurs across timescales ranging from minutes to decades, and may be a neural mechanism underlying CR. To test this hypothesis, we used voxel-based morphometry and resting-state functional connectivity analyses of MRI data to compare structural and functional brain integrity between bilingual and monolingual older adults, matched on cognitive performance using a rigorous propensity score matching technique, and across levels of second language proficiency measured as a continuous variable. Bilingualism, and degree of second language proficiency in particular, were associated with lower grey matter integrity in a hub of the default mode network - a region that is particularly vulnerable to decline in aging and dementia - but preserved functional network organization that resembled the young adult brain. Our findings confirm that lifelong bilingualism contributes to CR through experience-dependent maintenance of optimal functional network structure of the domain-general attentional control network across the lifespan.

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bioRxiv2021

Functional architecture of the aging brain

The intrinsic functional organization of the brain changes into older adulthood. Age differences are observed at multiple spatial scales, from global reductions in modularity and segregation of distributed brain systems, to network-specific patterns of dedifferentiation. Whether dedifferentiation reflects an inevitable, global shift in brain function with age, circumscribed, experience dependent changes, or both, is uncertain. We employed a multi-method strategy to interrogate dedifferentiation at multiple spatial scales. Multi-echo (ME) resting-state fMRI was collected in younger (n=181) and older (n=120) healthy adults. Cortical parcellation sensitive to individual variation was implemented for precision functional mapping of each participant, while preserving group-level parcel and network labels. ME-fMRI processing and gradient mapping identified global and macroscale network differences. Multivariate functional connectivity methods tested for microscale, edge-level differences. Older adults had lower BOLD signal dimensionality, consistent with global network dedifferentiation. Gradients were largely age-invariant. Edge-level analyses revealed discrete, network-specific dedifferentiation patterns in older adults. Visual and somatosensory regions were more integrated within the functional connectome; default and frontoparietal control network regions showed greater connectivity; and the dorsal attention network was more integrated with heteromodal regions. These findings highlight the importance of multi-scale, multi-method approaches to characterize the architecture of functional brain aging.

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bioRxiv2021

Medial occipital cortex participates in a cortical network for transsaccadic feature discrimination: an fMRI paradigm

Saccades change eye position and interrupt vision several times per second, necessitating neural mechanisms for continuous perception of object identity, orientation, and location. Neuroimaging studies suggest that occipital and parietal cortex play complementary roles for transsaccadic perception of intrinsic versus extrinsic spatial properties, e.g., dorsomedial occipital cortex (cuneus) is sensitive to changes in spatial frequency, whereas the supramarginal gyrus (SMG) is modulated by changes in object orientation. Based on this, we hypothesized that both structures would be recruited to simultaneously monitor identity and orientation across saccades. To test this, we merged two previous neuroimaging protocols: 21 participants viewed a 2D object and then, after sustained fixation or a saccade, judged whether the shape or orientation of the represented object changed. We, then, performed a bilateral region-of-interest analysis on identified cuneus and SMG sites. As hypothesized, cuneus showed both saccade and feature (i.e., orientation vs. shape change) modulations, and right SMG showed saccade-feature interactions. Further, the cuneus activity time course correlated with several other cortical saccade / visual areas, suggesting a functional network for feature discrimination. These results confirm the involvement of occipital / parietal cortex in transsaccadic vision and support complementary roles in spatial versus identity updating.

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bioRxiv2020

Parietal Mechanisms for Transsaccadic Spatial Frequency Perception: An fMRI Study

Posterior parietal cortex (PPC), specifically right supramarginal gyrus, is involved in transsaccadic memory of object orientation for both perception and action. Here, we investigated whether PPC is involved in transsaccadic memory of other features, namely spatial frequency. We employed a functional magnetic resonance imaging paradigm where participants briefly viewed a grating stimulus with a specific spatial frequency that later reappeared with the same or different frequency, after a saccade or continuous fixation. Post-saccadic frequency modulation activated a region in the right hemisphere spanning medial PPC (ventral precuneus) and posterior cingulate cortex. Importantly, the site of peak precuneus activation showed saccade-specific feature modulation (compared to fixation) and task-specific saccade modulation (compared to a saccade localizer task). Psychophysiological interaction analysis revealed functional connectivity between this precuneus site and the precentral gyrus (M1), lingual gyrus (V1/V2), and medial occipitotemporal sulcus. This differed from the transsaccadic orientation network, perhaps because spatial frequency signaled changes in object identity. Overall, this experiment supports a general role for PPC in transsaccadic vision, but suggests that different networks are employed for specific features.

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