Neurocognitive networks in higher-level visual perception

The ability to accurately perceive and respond to our visual environment is critical for optimising primate behaviour. A number of related cognitive functions, such as visual learning and longer-term memory, also depend upon an accurate percept of objects and their location within the visual environment. Understanding how the healthy brain supports higher-order visual perception is, therefore, a key goal for cognitive neuroscientist. A substantial body of research involving both humans and animals highlights a role for regions within the extrastriate cortex in visual perception, with many of these regions apparently exhibiting a high degree of functional specialisation for the processing of particular categories of complex stimuli (e.g. faces versus scenes). More recently, studies have found that patients with damage to structures within the medial temporal lobe, such as the hippocampus and perirhinal cortex, can also present with impairments in higher-level perception. More specifically, damage to perirhinal cortex has been linked to impairments in perception for complex objects and faces, whereas hippocampal damage has been linked to impairments in scene perception. Multiple regions distributed across the extrastriate cortex and medial temporal lobe may make individual category-sensitive contributions to visual perception, but it remains unclear how these regions interact with one another, and to what extent their ability to interact underpins successful visual perception. These issues are addressed here via a series of novel experiments involving a combination of behavioural paradigms and magnetic resonance imaging techniques in healthy human participants. These experiments aim to: a) investigate the functional and structural connections that support the category-sensitive contributions of the perirhinal cortex and hippocampus to higher-level visual perception; b) demonstrate that inter-individual variation in the structural properties of white matter pathways providing inputs/outputs to the perirhinal cortex or hippocampus is an important factor underpinning the contributions of these regions to successful higher-level perceptions

Structural connections support emotional connections: uncinate fasciculus microstructure is related to the ability to decode facial emotion expressions

The Uncinate Fasciculus (UF) is an association fibre tract connecting regions in the frontal and anterior temporal lobes. UF disruption is seen in several disorders associated with impaired social behaviour, but its functional role is unclear. Here we set out to test the hypothesis that the UF is important for facial expression processing, an ability fundamental to adaptive social behaviour. In two separate experiments in healthy adults, we used high-angular resolution diffusion-weighted imaging (HARDI) and constrained spherical deconvolution (CSD) tractography to virtually dissect the UF, plus a control tract (the corticospinal tract (CST)), and quantify, via tissue fractional anisotropy (FAT), individual differences in tract microstructure. In Experiment 1, participants completed the Reading the Mind in the Eyes Task (RMET), a well-validated assay of facial expression decoding. In Experiment 2, a different set of participants completed the RMET, plus an odd-emotion-out task of facial emotion discrimination. In both experiments, participants also completed a control odd-identity-out facial identity discrimination task. In Experiment 1, FAT of the right-, but not the left-hemisphere, UF was significantly correlated with performance on the RMET task, specifically for emotional, but not neutral expressions. UF FAT was not significantly correlated with facial identity discrimination performance. In Experiment 2, FA of the right-, but not left-hemisphere, UF was again significantly correlated with performance on emotional items from the RMET, together with performance on the facial emotion discrimination task. Again, no significant association was found between UF FAT and facial identity discrimination performance. Our findings highlight the contribution of right-hemisphere UF microstructure to inter-individual variability in the ability to decode facial emotion expressions, and may explain why disruption of this pathway affects social behaviour

The effectiveness of virtual reality interventions for improvement of neurocognitive performance post-traumatic brain injury: a systematic review

Objective: To evaluate current evidence for the effectiveness of virtual reality (VR) interventions in improving neurocognitive performance in individuals who have sustained a traumatic brain injury (TBI). Methods: A systematic literature search across multiple databases (PubMed, EMBASE, Web of Science) for articles of relevance. Studies were evaluated according to study design, patient cohort, VR intervention, neurocognitive parameters assessed, and outcome. VR interventions were evaluated qualitatively with respect to methodology and extent of immersion and quantitatively with respect to intervention duration. Outcomes: Our search yielded 324 articles, of which only 13 studies including 132 patients with TBI met inclusion criteria. A wide range of VR interventions and cognitive outcome measures is reported. Cognitive measures included learning and memory, attention, executive function, community skills, problem solving, route learning, and attitudes about driving. Several studies (n = 10) reported statistically significant improvements in outcome, and 2 studies demonstrated successful translation to real-life performance. Conclusions: VR interventions hold significant potential for improving neurocognitive performance in patients with TBI. While there is some evidence for translation of gains to activities of daily living, further studies are required to confirm the validity of cognitive measures and reliable translation to real-life performance

Distinct contributions of the fornix and inferior longitudinal fasciculus to episodic and semantic autobiographical memory

Autobiographical memory (AM) is multifaceted, incorporating the vivid retrieval of contextual detail (episodic AM), together with semantic knowledge that infuses meaning and coherence into past events (semantic AM). While neuropsychological evidence highlights a role for the hippocampus and anterior temporal lobe (ATL) in episodic and semantic AM, respectively, it is unclear whether these constitute dissociable large-scale AM networks. We used high angular resolution diffusion-weighted imaging and constrained spherical deconvolution-based tractography to assess white matter microstructure in 27 healthy young adult participants who were asked to recall past experiences using word cues. Inter-individual variation in the microstructure of the fornix (the main hippocampal input/output pathway) related to the amount of episodic, but not semantic, detail in AMs e independent of memory age. Conversely, microstructure of the inferior longitudinal fasciculus, linking occipitotemporal regions with ATL, correlated with semantic, but not episodic, AMs. Further, these significant correlations remained when controlling for hippocampal and ATL grey matter volume, respectively. This striking correlational double dissociation supports the view that distinct, large-scale distributed brain circuits underpin context and concepts in AM

Dissociable roles of the inferior longitudinal fasciculus and fornix in face and place perception

We tested a novel hypothesis, generated from representational accounts of medial temporal lobe (MTL) function, that the major white matter tracts converging on perirhinal cortex (PrC) and hippocampus (HC) would be differentially involved in face and scene perception, respectively. Diffusion tensor imaging was applied in healthy participants alongside an odd-one-out paradigm sensitive to PrC and HC lesions in animals and humans. Microstructure of inferior longitudinal fasciculus (ILF, connecting occipital and ventro-anterior temporal lobe, including PrC) and fornix (the main HC input/output pathway) correlated with accuracy on odd-one-out judgements involving faces and scenes, respectively. Similarly, blood oxygen level-dependent (BOLD) response in PrC and HC, elicited during oddity judgements, was correlated with face and scene oddity performance, respectively. We also observed associations between ILF and fornix microstructure and category-selective BOLD response in PrC and HC, respectively. These striking three-way associations highlight functionally dissociable, structurally instantiated MTL neurocognitive networks for complex face and scene perception

The effect of a cognitive inhibition task on gait performance during self-paced treadmill walking

Gait analysis can be used to predict health status in the elderly (1). Gait is no longer postulated as a totally automated motor task. It requires multiple executive function processes to utilise safe and efficient gait (2). With advanced age, executive function declines, which is linked to an increase in gait variability and fall-risk. Dual-task paradigms have been introduced to explore the automaticity of gait by challenging inhibition and/or attention (i.e. executive function). The utility of using dual-tasking has become more evident (2). However, the great variability of the dual-tasking paradigms limits its use in clinical gait assessment. There is also a lack of evidence for the consistency of dual-task effects upon gait performance. This may be due to the limited number of consecutive strides included during over-ground walking and effects of treadmill’s speed on gait patterns (3). The aim of this study was, therefore, to explore the effect of an inhibition response task on gait performance during selfpaced treadmill walking and the consistency of gait measurements between days

Does engaging working memory task during walking reduce knee adduction moment? Exploratory study

Alterations in knee adduction moment (KAM) has been suggested as a surrogate measure of medial compartment (1). It has two peaks; the first peak has been correlated with the progress of knee osteoarthritis (OA) that is more common in elderly population (2). Individuals with OA suffer to the limit of functional mobility including walking. Walking involves cognitive processes related to planning and performing actions. With advancing age, reduction in the cognitive functions related to walking has been noted (3). As OA is an age-related condition, it is therefore, necessary to consider OA gait assessment whilst individuals performing additional cognitively engaging tasks. There is, to the best of our knowledge, no published research examining the effects of concurrent cognitive tasks during walking on KAM. The aim of this study is to explore whether introducing cognitively engaging task during walking would affect the first peak of the KAM in healthy individuals

Subiculum – BNST structural connectivity in humans and macaques

Invasive tract-tracing studies in rodents implicate a direct connection between the subiculum and bed nucleus of the stria terminalis (BNST) as a key component of neural pathways mediating hippocampal regulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. A clear characterisation of the connections linking the subiculum and BNST in humans and non-human primates is lacking. To address this, we first delineated the projections from the subiculum to the BNST using anterograde tracers injected into macaque monkeys, revealing evidence for a monosynaptic subiculum-BNST projection involving the fornix. Second, we used in vivo diffusion MRI tractography in macaques and humans to demonstrate substantial subiculum complex connectivity to the BNST in both species. This connection was primarily carried by the fornix, with additional connectivity via the amygdala, consistent with rodent anatomy. Third, utilising the twin-based nature of our human sample, we found that microstructural properties of these tracts were moderately heritable (h2 ∼ 0.5). In a final analysis, we found no evidence of any significant association between subiculum complex-BNST tract microstructure and indices of perceived stress/dispositional negativity and alcohol use, derived from principal component analysis decomposition of self-report data. Our findings address a key translational gap in our knowledge of the neurocircuitry regulating stress