Brain Differences in the Prefrontal Cortex, Amygdala, and Hippocampus in Youth with Congenital Adrenal Hyperplasia

Context: Classical Congenital Adrenal Hyperplasia (CAH) due to 21-hydroxylase deficiency results in hormone imbalances present both prenatally and postnatally that may impact the developing brain. Objective: To characterize gray matter morphology in the prefrontal cortex and subregion volumes of the amygdala and hippocampus in youth with CAH, compared to controls. Design: A cross-sectional study of 27 CAH youth (16 female; 12.6 ± 3.4 year) and 35 typically developing, healthy controls (20 female; 13.0 ± 2.8 year) with 3-T magnetic resonance imaging scans. Brain volumes of interest included bilateral prefrontal cortex, and nine amygdala and six hippocampal subregions. Between-subject effects of group (CAH vs control) and sex, and their interaction (group-by-sex) on brain volumes were studied, while controlling for intracranial volume (ICV) and group differences in body mass index and bone age. Results: CAH youth had smaller ICV and increased cerebrospinal fluid volume compared to controls. In fully-adjusted models, CAH youth had smaller bilateral, superior and caudal middle frontal volumes, and smaller left lateral orbito-frontal volumes compared to controls. Medial temporal lobe analyses revealed the left hippocampus was smaller in fully-adjusted models. CAH youth also had significantly smaller lateral nucleus of the amygdala and hippocampal subiculum and CA1 subregions. Conclusions: This study replicates previous findings of smaller medial temporal lobe volumes in CAH patients, and suggests that lateral nucleus of the amygdala, as well as subiculum and subfield CA1 of the hippocampus are particularly affected within the medial temporal lobes in CAH youth

Ultra-high Field MRI Methods for Precise Anatomical and Spectroscopic Measurements in the Brain and Application to Neurological and Neuropsychiatric Diseases

Neurological and neuropsychiatric diseases and disorders are a major burden on society, impairing the health and functioning of millions of people every year. There is a need to define the biological bases of these diseases and identify potential biomarkers to improve diagnosis, monitoring, and treatment efficacy across multiple diseases. Magnetic resonance imaging (MRI) is a noninvasive imaging technique which facilitates detection of brain lesions and visualization of the brain overall. However, limitations in contrast and resolution at clinical field strengths may hinder investigation of the underlying biological mechanisms of these diseases. Ultra-high field MRI scanners, such as those at 7-Tesla, can enhance biomarker detection because they provide superior contrast, resolution, and signal-to-noise-ratio (SNR) in feasible scan times. Since ultra-high field systems come with their own unique set of technical challenges, especially as applied to brain imaging, technique optimization and development is often required. To address these concerns while leveraging the advantages of 7-Tesla MRI, we have designed and conducted studies to provide high-resolution imaging of small structures and high spectral resolution of metabolite concentrations in clinically feasible scan times. As a group, these studies provide support for the usefulness of ultra-high field MRI for revealing disease pathophysiology through the detection of biomarkers, which may be unclear or below the threshold of detectability at clinical field strengths. The purpose of this work was to investigate anatomical and spectroscopic biomarkers in the brain. Specifically, we analyzed limbic structure subfield volumes, including subfields of the hippocampus, amygdala, and thalamus, for diseases including major depressive disorder (MDD) and trigeminal neuralgia (TN). We found a significant reduction in the right CA2/3 subfield volume of the hippocampus in MDD patients compared to healthy controls. In TN, we found significant differences in subfield volumes between patients and controls, specifically in the nerve cross-sectional-area, in the basal and paralaminar subnuclei of the amygdala, and in the central lateral subnucleus and the inferior and lateral pulvinar subnuclei of the thalamus. We also developed a method for detecting gamma-Aminobutyric acid (GABA) with spectroscopic editing, with potential application to MDD. In summary, we have presented significant findings in biomarker detection and a novel method for spectroscopic signal editing of GABA at ultra-high field MRI

Brain Differences in the Prefrontal Cortex, Amygdala, and Hippocampus in Youth with Congenital Adrenal Hyperplasia

Context: Classical Congenital Adrenal Hyperplasia (CAH) due to 21-hydroxylase deficiency results in hormone imbalances present both prenatally and postnatally that may impact the developing brain. Objective: To characterize gray matter morphology in the prefrontal cortex and subregion volumes of the amygdala and hippocampus in youth with CAH, compared to controls. Design: A cross-sectional study of 27 CAH youth (16 female; 12.6 ± 3.4 year) and 35 typically developing, healthy controls (20 female; 13.0 ± 2.8 year) with 3-T magnetic resonance imaging scans. Brain volumes of interest included bilateral prefrontal cortex, and nine amygdala and six hippocampal subregions. Between-subject effects of group (CAH vs control) and sex, and their interaction (group-by-sex) on brain volumes were studied, while controlling for intracranial volume (ICV) and group differences in body mass index and bone age. Results: CAH youth had smaller ICV and increased cerebrospinal fluid volume compared to controls. In fully-adjusted models, CAH youth had smaller bilateral, superior and caudal middle frontal volumes, and smaller left lateral orbito-frontal volumes compared to controls. Medial temporal lobe analyses revealed the left hippocampus was smaller in fully-adjusted models. CAH youth also had significantly smaller lateral nucleus of the amygdala and hippocampal subiculum and CA1 subregions. Conclusions: This study replicates previous findings of smaller medial temporal lobe volumes in CAH patients, and suggests that lateral nucleus of the amygdala, as well as subiculum and subfield CA1 of the hippocampus are particularly affected within the medial temporal lobes in CAH youth

Involvement of hippocampal subfields and anterior-posterior subregions in encoding and retrieval of item, spatial, and associative memories: Longitudinal versus transverse axis

The functional role of the hippocampal formation in episodic memory has been studied using functional magnetic resonance imaging (fMRI) for many years. The hippocampus can be segmented into three major anteroposterior sections, called head, body and tail, and into the Cornu Ammonis (CA), dentate gyrus (DG), and subiculum (Sub) subfields based on its transverse axis. However, the exact role of these subregions and subfields in memory processes is less understood. In the present study we combined ultra-high resolution structural Magnetic Resonance Imaging (MRI) at 4.7 T with an event-related high-resolution fMRI paradigm based on the ‘Designs’ subtest of the Wechsler Memory Scale to investigate how the hippocampal subfields and longitudinal subregions are involved in encoding and retrieval of item, spatial, and associative memories. Our results showed that during memory encoding, regardless of the type of memory being learned, all subregions and all subfields were active. During the retrieval phase, on the other hand, we observed an anterior to posterior gradient in hippocampal activity for all subfields and all types of memory. Our findings also confirmed presence of an anterior to posterior gradient in hippocampal activity during spatial learning. Comparing subfield activities to each other revealed that the DG was more active than the CA1-3 and Sub during both encoding and retrieval. Finally, our results showed that for every subfield, encoding vs. retrieval activity differences were larger in the hippocampal head than in the hippocampal body and tail. Furthermore, these encoding vs. retrieval activity differences were similar in all subfields, highlighting the importance of studying both the longitudinal and transverse axis specialization simultaneously. Current findings further elucidate the structure–function relationship between the human hippocampus and episodic memory

Probing brain function with pharmacological MRI

Lo sviluppo di tecniche di risonanza magnetica funzionale (fMRI) ha rivoluzionato le ricerca neuroscientifica clinica, determinando la possibilit\ue0 di investigare le dinamiche spazio-temporali dell\u2019attivit\ue0 cerebrale in maniera non invasiva e con grande accuratezza. Sebbene la tecnica sia stata originariamente sviluppata in ambito clinico, essa ha il potenziale di poter essere utilizzata in ambito preclinico come efficace strumento investigativo e traslazionale. Tuttavia, l\u2019implementazione preclinica di questi metodi \ue8 complicata da una serie di costrizioni sperimentali, in primis l\u2019utilizzo di anestetici, che minano fortemente il potenziale traslazionale di queste tecniche. Il recente sviluppo di tecniche di "MRI farmacologico" (phMRI) offre la possibilit\ue0 di superare alcune delle limitazioni sperimentali correlate all\u2019implementazione di approcci fMRI classici in animali da laboratorio. La tecnica si basa sull'utilizzo di metodi fMRI per mappare alterazioni di attivit\ue0 cerebrale prodotte dalla somministrazione di sostanze psicoattive. Studi preliminari hanno evidenziato la capacit\ue0 di generare robusti e specifici segnali phMRI anche in condizioni di anestesia, ed ha dimostrato la possibilit\ue0 di stimolare selettivamente diversi sistemi di neurotrasmettitori. Sfruttando la conservazione di circuiti cerebrali tra specie, tecniche phMRI offrono quindi l\u2019opportunit\ue0 di ampliare in maniera significativa il repertorio di stimolazione neuronale a disposizione in ambito preclinico, consentendo di indagare selettivamente specifici aspetti della funzione cerebrale in diversi stati di precondizionamento neuronale. In tale contesto, le attivit\ue0 di ricerca di questa tesi sono state finalizzate ad ampliare il campo di applicazione di metodi phMRI preclinici in due diversi ambiti sperimentali: a) come modalit\ue0 di indagine traslazionale, qualora applicata a modelli di malattia clinicamente rilevanti, b) pi\uf9 in generale come piattaforma investigativa per l'indagine della funzione cerebrale e della sua topologia funzionale in contesti sperimentali diversi. In un primo gruppo di studi, tecniche phMRI sono state impiegate per mappare i circuiti neuronali attivati da antagonisti del recettore del glutammato NMDA nel cervello del ratto (Sezione 4.1). Tali composti, grazie alle loro propriet\ue0 psicotogeniche, sono ampiamente sfruttati come modelli sperimentali di schizofrenia in animali ed in volontari allo scopo di valutare e validare nuovi trattamenti per la malattia. I risultati di questa ricerca hanno evidenziato uno specifico circuito corticolimbo- talamico che risulta essere attivato da antagonisti NMDAR sia nell'uomo che in Riassunto XII specie precliniche, e che \ue8 risultato essere modulabile da meccanismi antipsicotici diversi (Sezione 4.2). Il potenziale traslazionale dei metodi phMRI \ue8 stato ulteriormente avvalorato da un secondo gruppo di studi, in cui un approccio multi-parametrico \u201cphMRI-based\u201d \ue8 stato impiegato per indagare molteplici aspetti della funzione cerebrale in un modello murino di dipendenza da cocaina. Questa linea di investigazione ha evidenziato multiple alterazioni della funzione cerebrale basale e reattiva nel cervello di roditori esposti alla cocaina strettamente connesse a quelle osservate in analoghi studi di imaging su pazienti cocaina-dipendenti (Sezione 4.2). In una terza linea d\u2019 investigazione, l'uso combinato di avanzate strategie di targeting neuro-genetico (pharmaco-genetic silencing) e phMRI si \ue8 dimostrato efficace nello stabilire correlazioni dirette tra cellule, circuito e comportamento in linee di topo geneticamente modificate. Questi studi hanno portato all\u2019identificazione di una nuova e circoscritta popolazione neuroni nell'amigdala, in grado di controllare qualitativamente la risposta comportamentale alla paura attraverso il reclutamento di circuiti colinergici corticali (Sezione 4.3) Infine, l'approccio phMRI si \ue8 dimostrato uno strumento potente e versatile per l\u2019implementazione di misure di connettivit\ue0 funzionale nel cervello di roditori. Questo aspetto ha permesso l\u2019esplorazione di nuovi approcci statistici per l\u2019analisi della topologia funzionale del cervello basati sulla rappresentazione di misure di connettivit\ue0 in termini di reti complesse (Sezione 4.4). Complessivamente, i risultati di questo lavoro avvalorano il potenziale traslazionale di metodi phMRI nell\u2019ambito di diverse aree delle neuroscienze e della psicofarmacologia. La combinazione di phMRI e tecniche di manipolazione genetica avanzate definisce una nuova, potente piattaforma tecnologica per lo studio delle basi circuitali del comportamento in animali da laboratorio.The development of functional Magnetic Resonance Imaging (fMRI) has heralded a revolution in neuroscience, providing clinicians with a method to non-invasively investigate the spatio-temporal patterns of neuro-functional activity. Although primarily developed for human investigations, there exists significant scope for the application of fMRI in pre-clinical species as a translational and investigational platform across different areas of neuroscience and psychiatry research. However, the realization of this potential is hampered by a number of experimental constraints which make the application of fMRI methods to animal models less than straightforward. As a result, most fMRI research in laboratory species has been reduced to the employment of basic somato-sensory stimulation paradigms, thus greatly limiting the translational potential of the technique. An interesting approach to overcome some of these limitations has been dubbed \u201cpharmacological MRI\u201d (phMRI) and relies on the use of fMRI to map patterns of brain activity induced by psychoactive drugs. The approach has demonstrated the ability to elicit reliable fMRI signals even under anaesthesia, and to enable selective stimulation of different neurotransmitter systems. Building upon the homology between brain circuits in humans and laboratory animals, phMRI techniques thus offer the opportunity of significantly expanding the stimulation repertoire available to preclinical fMRI research, by allowing to selectively probe specific aspects of brain function under different preconditioning states. Within this framework, the research presented herein was aimed to broaden the scope of application of preclinical phMRI both as a translational technique, when applied to clinically-relevant disease models, and more generally as a versatile platform for the pre-clinical investigation of brain activity and its functional topology as a function of behavioural, pharmacological or genetic preconditioning. In a first group of studies, we developed a phMRI assay to map the circuitry activated by NMDAR antagonists in the rat brain. These psychotogenic compounds are widely exploited to model schizophrenia symptoms and to provide experimental models that may prove useful in the development of novel treatments for the disorder. The results of this research highlighted a conserved cortico-limbo-thalamic circuit that is activated by NMDAR antagonists both in humans and preclinical species, which can be modulated by existing and novel antipsychotic drugs (Section 4.1). The translational potential of phMRI measurements was further corroborated by a second group of studies, where a multi-parametric phMRI-based approach was applied to investigate multiple facets of brain function in a rodent cocaine selfSummary X administration model, a behavioural paradigm of established construct-validity for research of drug addiction. This line of investigation revealed specific basal and reactive functional alterations in the brain of cocaine-exposed rodents closely related to those observed in analogous neuroimaging studies in humans (Section 4.2). In a third line of investigation, the combined use of advanced neuro-genetic targeting strategies (i.e. pharmacogenetic silencing) and phMRI has proven successful in establishing direct correlations between cells, circuit and complex behaviours in genetically engineered mouse lines. These studies (Section 4.3) have led to the identification of a novel cell population in the amygdala that controls the behavioural response to fear through the recruitment of cholinergic circuits. Finally, the phMRI approach has proven a powerful tool to explore functional connectivity in rodents, and to map a variety of different neurotransmitter pathways by performing measures of correlated responses in spatially remote brain areas. This has provided a useful playground to explore novel statistical methods of analysis of functional connectivity represented in terms of complex networks (Section 4.4). Collectively, the results of this work strongly corroborate the translational use of phMRI approaches, and pave the way to the integrated implementation of phMRI and advance genetic manipulation as a novel powerful platform for basic neurobiological research

The Neural Correlates of Visual Hallucinations in Parkinson's Disease

Visual hallucinations are common in Parkinson’s disease (PD) and linked to worse outcomes: increased mortality, higher carer burden, cognitive decline, and worse quality of life. Recent functional studies have aided our understanding, showing large-scale brain network imbalance in PD hallucinations. Imbalance of different influences on visual perception also occurs, with impaired accumulation of feedforward signals from the eyes and visual parts of the brain. Whether feedback signals from higher brain control centres are also affected is unknown and the mechanisms driving network imbalance in PD hallucinations remain unclear. In this thesis I will clarify the computational and structural changes underlying PD hallucinations and link these to functional abnormalities and regional changes at the cellular level. To achieve this, I will employ behavioural testing, diffusion weighted imaging, structural and functional MRI in PD patients with and without hallucinations. I will quantify the use of prior knowledge during a visual learning task and show that PD with hallucinations over-rely on feedback signals. I will examine underlying structural connectivity changes at baseline and longitudinally and will show that posterior thalamic connections are affected early, with frontal connections remaining relatively preserved. I will show that PD hallucinations are associated with a subnetwork of reduced structural connectivity strength, affecting areas crucial for switching the brain between functional states. I will assess the role of the thalamus as a potential driver of network-level changes and show preferential medial thalamus involvement. I will utilise data from the Allen Institute transcription atlas and show how differences in regional gene expression in health contributes to the selective vulnerability of specific white matter connections in PD hallucinations. These findings reveal the structural correlates of visual hallucinations in PD, link these to functional and behavioural changes and provide insights into the cellular mechanisms that drive regional vulnerability, ultimately leading to hallucinations

Imaging the subthalamic nucleus in Parkinson’s disease

This thesis is comprised of a set of work that aims to visualize and quantify the anatomy, structural variability, and connectivity of the subthalamic nucleus (STN) with optimized neuroimaging methods. The study populations include both healthy cohorts and individuals living with Parkinson's disease (PD). PD was chosen specifically due to the involvement of the STN in the pathophysiology of the disease. Optimized neuroimaging methods were primarily obtained using ultra-high field (UHF) magnetic resonance imaging (MRI). An additional component of this thesis was to determine to what extent UHF-MRI can be used in a clinical setting, specifically for pre-operative planning of deep brain stimulation (DBS) of the STN for patients with advanced PD. The thesis collectively demonstrates that i, MRI research, and clinical applications must account for the different anatomical and structural changes that occur in the STN with both age and PD. ii, Anatomical connections involved in preparatory motor control, response inhibition, and decision-making may be compromised in PD. iii. The accuracy of visualizing and quantifying the STN strongly depends on the type of MR contrast and voxel size. iv, MRI at a field strength of 3 Tesla (T) can under certain circumstances be optimized to produce results similar to that of 7 T at the expense of increased acquisition time