Where Bottom-up Meets Top-down: Neuronal Interactions during Perception and Imagery

Functional magnetic resonance imaging (fMRI) studies have identified category-selective regions in ventral occipito-temporal cortex that respond preferentially to faces and other objects. The extent to which these patterns of activation are modulated by bottom-up or top-down mechanisms is currently unknown. We combined fMRI and dynamic causal modelling to investigate neuronal interactions between occipito-temporal, parietal and frontal regions, during visual perception and visual imagery of faces, houses and chairs. Our results indicate that, during visual perception, category-selective patterns of activation in extrastriate cortex are mediated by content-sensitive forward connections from early visual areas. In contrast, during visual imagery, category-selective activation is mediated by content-sensitive backward connections from prefrontal cortex. Additionally, we report content-unrelated connectivity between parietal cortex and the category-selective regions, during both perception and imagery. Thus, our investigation revealed that neuronal interactions between occipito-temporal, parietal and frontal regions are task- and stimulus-dependent. Sensory representations of faces and objects are mediated by bottom-up mechanisms arising in early visual areas and top-down mechanisms arising in prefrontal cortex, during perception and imagery respectively. Additionally non-selective, top-down processes, originating in superior parietal areas, contribute to the generation of mental images, regardless of their content, and their maintenance in the ‘mind's eye

Detecting language activations with functional magnetic resonance imaging

This thesis investigates a number of factors that affect sensitivity to language activations in functional Magnetic Resonance Imaging (fMRI). In the first part, I investigate the impact of experimental design parameters on the ability to detect language activations. These parameters include stimulus rate, stimulus duration, stimulus amplitude, epoch length and stimulus ordering. Crucially, they may affect sensitivity in multiple ways that include neurophysiological, efficiency-mediated and BOLD saturation effects. I illustrate and discuss these effects by presenting biophysical simulations and fMRI studies of single word and pseudoword reading. In addition, I focus on the differential effects of the above parameters in Positron Emission Tomography and fMRI studies. In the second part, I investigate the impact of the analysis used to estimate effects of interest from the data. I compare event-related and epoch analyses and show that, even in the context of blocked design fMRI, an event-related model may provide greater sensitivity than an epoch model. I then address the notion that experimentally-induced effects may be detected not only as task-dependent changes in regional responses but also as changes in connectivity amongst functionally connected regions. These two complementary approaches are motivated by two fundamental principles of brain organisation: functional specialisation and functional integration. I present two fMRI studies investigating the neural correlates of reading words and pseudowords in terms of functional specialisation and functional integration. Furthermore, in both studies I address the issue of inter-subject variability, which may be a critical determinant of sensitivity. Men

Digging deeper in Shanghai:towards a ‘mechanism rich’ epidemiology

Background: There are very few close-up sociological or anthropological data informing epidemiological and psychiatric research design and/or contributing to our understanding of the relationship between mental health and specific forms of urban life. Furthermore, research on the relationships between urbanicity and mental disorder has paid little attention to the global diversity of urban experience, such as in cities in China, India and Brazil. Methods: Two innovative methods can be employed to unveil the diversified urban experience of migrants in China, i.e. an ethnography-informed sociological deep surveying instrument and an ecological momentary assessment with a smartphone app. This article introduces the design and pilot survey of these new instruments towards a 'mechanism-rich' epidemiology. Results: The ethnography-informed survey instrument enabled us to include some of the issues from the ethnography and successfully 'dig deeper' into respondents' social experience. The pilot of the smartphone app serves as 'proof of principle' that we can recruit respondents in Shanghai, and that we can receive and use the data. Conclusions: Both of these pilots have demonstrated good feasibility for studying mobility, urban life and mental health. Our next steps will be to extend the Shanghai sample, to use the app in Sao Paulo and Toronto and then hopefully in India and Africa.</p

Predicting clinical response in people at ultra-high risk of psychosis:A systematic and quantitative review

People at ultra-high risk (UHR) of psychosis have ~30% chance of developing the illness within two years. A range of pharmacological and psychosocial interventions are now available but there is great individual variation in clinical response. Here we examine the evidence for clinically applicable predictors of clinical response in people at UHR of psychosis. We report that currently there are no reliable predictive markers that can be used to optimise treatment. We argue that there is an urgent need for a better understanding of why some people at UHR of psychosis benefit from a certain treatment whereas others do not. This information will help clinicians make more-effective treatment decisions, and improve long-term clinical outcomes in this population.</p

Common Dysfunction of Large-Scale Neurocognitive Networks across Psychiatric Disorders

Background Cognitive dysfunction is one of the most prominent characteristics of psychiatric disorders. At present, the neural correlates of cognitive dysfunction across psychiatric disorders are poorly understood. The aim of this study was to investigate functional connectivity and structural perturbations across psychiatric diagnoses in three neurocognitive networks of interest, including the default-mode (DMN), the frontoparietal (FPN) and the salience network (SN). Methods We performed meta-analyses of resting-state functional MRI (R-fMRI) whole-brain seed-based functional connectivity in 8,298 patients (involving 8 disorders) and 8,165 healthy controls and a voxel-based morphometry analysis of structural MRI data in 14,027 patients (involving 8 disorders) and healthy 14,504 controls. To aid the interpretation of the results, we examined neurocognitive function in 776 healthy participants from the Human Connectome Project. Results We found that the three neurocognitive networks of interest were characterized by shared alterations of functional connectivity architecture across psychiatric disorders. More specifically, hypoconnectivity was expressed between the DMN and ventral SN and between the SN and FPN, whereas hyperconnectivity was evident between the DMN and FPN and between the DMN and dorsal SN. This pattern of network alterations was associated with gray matter reductions in patients, and was localized in regions that subserve general cognitive performance. Conclusions This study is the first to provide meta-analytic evidence of common alterations of functional connectivity within and between neurocognitive networks. The findings suggest a shared mechanism of network interactions that may associate with the generalized cognitive deficits observed in psychiatric disorders

Impacts of extreme heat on mental health:Systematic review and qualitative investigation of the underpinning mechanisms

IntroductionWe are living on an increasingly hot planet, with negative impacts for the mental health of affected individuals and communities. A better understanding of the physiological, psychological, behavioral, and social mechanisms which underlie these impacts could inform the development of effective interventions. Here, we conducted a mixed-method study combining a systematic review and qualitative investigation to explore these mechanisms.MethodsAdhering to the PRISMA guidelines, we searched PubMed for publications related to extreme heat, mental health, and mechanisms. Peer-reviewed studies reporting original data on mechanisms explaining the impact of extreme heat on mental health were included. In addition, we conducted six focus groups on extreme heat and mental health with a total of 33 participants (n=21 people with lived experience, n=12 healthcare professionals). Transcripts were analyzed using thematic content analysis.ResultsOut of 241 articles identified by the literature search, four studies were eligible for inclusion. These provided limited evidence for activation of the hypothalamic-pituitary-adrenal axis, increased psychological stress, reduced exercise, and sleep disruption. The analysis of the focus groups expanded these findings by highlighting additional themes related to physical (e.g., fatigue), psychological (e.g., health anxiety), behavioral (e.g., reduced access to usual coping strategies), and social mechanisms (e.g., social isolation). ConclusionThere is a dearth of reliable data on the mechanisms underpinning the impacts of extreme heat on mental health. Our mixed-method approach identified a range of promising physiological, psychological, behavioral, and social mechanisms, and highlights the importance of including people with lived experience in the conversation

Neuroimaging distinction between neurological and psychiatric disorders

Background It is unclear to what extent the traditional distinction between neurological and psychiatric disorders reflects biological differences. Aims To examine neuroimaging evidence for the distinction between neurological and psychiatric disorders. Method We performed an activation likelihood estimation metaanalysis on voxelbased morphometry studies reporting decreased grey matter in 14 neurological and 10 psychiatric disorders, and compared the regional and networklevel alterations for these two classes of disease. In addition, we estimated neuroanatomical heterogeneity within and between the two classes. Results Basal ganglia, insula, sensorimotor and temporal cortex showed greater impairment in neurological disorders? whereas cingulate, medial frontal, superior frontal and occipital cortex showed greater impairment in psychiatric disorders. The two classes of disorders affected distinct functional networks. Similarity within classes was higher than between classes? furthermore, similarity within class was higher for neurological than psychiatric disorders. Conclusions From a neuroimaging perspective, neurological and psychiatric disorders represent two distinct classes of disorders.</p

Smartphone apps for mental health:systematic review of the literature and five recommendations for clinical translation

OBJECTIVES: Providing adequate access to mental health services is a global challenge. Smartphone apps offer a potentially cost-effective, available and accessible solution for monitoring, supporting and treating mental health conditions. This systematic review describes and evaluates the usage of smartphone apps across a wide range of mental health disorders in terms of clinical effectiveness, feasibility and acceptability.DESIGN: This is a systematic review of studies examining treatment, self-monitoring and multipurpose smartphone apps for mental health disorders.DATA SOURCES: Studies were identified through a comprehensive search of the Ovid and PubMed databases. Articles published up to 14 January 2024 were included based on predefined criteria.ELIGIBILITY CRITERIA: We included randomised controlled trials that compared mental health apps (single- or multipurpose) with treatment-as-usual or no treatment for clinical populations with mental health disorders. Studies were excluded if they focused on web-based interventions, combined apps with non-TAU treatments or targeted physical health apps.DATA EXTRACTION AND SYNTHESIS: Two independent reviewers screened and selected studies, with a third reviewer resolving inconsistencies. Extracted data included study details, participant characteristics, app information and outcome measures related to effectiveness, feasibility and acceptability. A risk-of-bias assessment for each study was conducted.RESULTS: Out of 4153 non-duplicate articles screened, 31 studies met full-text eligibility criteria. These included 6 studies on treatment apps, 4 on self-monitoring apps and 21 on multipurpose apps for a range of mental health disorders. Fifteen were identified as having between some and high concern on the risk-of-bias assessment. While smartphone apps were generally effective and acceptable, their feasibility appeared to decline over time.CONCLUSIONS: Smartphone apps are promising tools for mental healthcare, demonstrating effectiveness and acceptability. However, challenges such as reduced feasibility over time, potential biases and underrepresented demographics require further research. This review proposes five recommendations for improving clinical translation in future studies.</p