Damage precipitating cognitive decline in Alzheimer's disease (AD) begins long before behavioural alterations become clinically apparent. At this prodromal stage, communication between networks of neurons connecting different brain regions starts to break down; setting in motion a chain of events leading to clinical AD. A significant challenge facing Alzheimer's researchers today is finding a cheap, easy-to-perform test capable of detecting prodromal AD. Such a test would afford significant benefits to patients, including a chance of early intervention. Perhaps, more importantly, it would also aid development and testing of novel therapies aimed at combating AD before it causes irreversible damage. Since oscillations in electrical field activity are important for facilitating connectivity across the brain and have been seen to alter in AD, this work studied how oscillations and regional connectivity are affected in the AD brain. Specifically, local field oscillations were recorded from the hippocampus and prelimbic cortex (regions implicated in memory formation and maintenance) in a double transgenic AD model - the TASTPM mouse. Here, periods of predominant theta activity were assessed both spontaneously, under urethane anaesthesia and following electrical induction through dorsal periaqueductal gray (dPAG) stimulation. From these recordings, spectral power and connectivity between regions was assessed using both a traditional measure of functional connectivity (inter-region correlation) and through a novel information theoretic approach measuring effective connectivity (transfer entropy).Perhaps the most prominent finding from this study was the observation that young TASTPM mice, at an age prior to overt cognitive decline or plaque deposition, showed significant alterations in measures of both functional and effective connectivity. This suggests that such measures may be used as biomarkers predictive of prodromal AD and, as such, may be used to aid development of drugs targeted towards treatment of prodromal AD.This study also uncovered a number of interesting observations concerning hippocampal/prelimbic connectivity. Firstly, although spectral power and inter-regional correlation peaked at ∼ 3Hz, information flow between these structures was strongest at ∼6Hz. This suggests that low and high-band theta activity may fulfil separate functions. Secondly, at theta frequencies, information flowed predominantly from the prelimbic cortex to the hippocampus. However, during lower frequency activity, information flowed predominantly in the opposite direction. Suggesting that separate frequency bands may be important for routing information flow between these structures. Finally, the strength of information transfer was seen to oscillate at approximately double the frequency of its carrier signal, perhaps suggesting locking of information transfer to certain phases of an underlying oscillation. Therefore, oscillations may structure information transfer by temporal windowing and frequency-locked routing; processes which can be studied using measures of effective connectivity such as transfer entropy.

O estresse é muito presente na vida das pessoas, e grande parte deste é de origem social. O estresse contínuo induz a uma série de efeitos nocivos no organismo. Estes efeitos também podem ser observados no cérebro, principalmente no hipocampo, onde promove alterações na sua morfologia e função. Recentemente, demonstrou-se uma redução do tamanho dos telômeros em leucócitos de mulheres com alto grau de estresse. Os telômeros são seqüências repetitivas dos nucleotídeos TTAGGG, responsáveis por proteger as extremidades dos cromossomos, e sua manutenção e alongamento é mediado, principalmente, pela enzima telomerase. Telômeros e telomerase têm sido alvos de muitos estudos envolvendo o envelhecimento e morte celular. Assim, o presente trabalho estudou os efeitos do estresse psicossocial prolongado em um modelo animal de subjugação/submissão sobre a biologia telomérica do hipocampo. O modelo de subjugação consistiu em um pareamento dos animais experimentais com um camundongo agressivo por 30 minutos. Camundongos machos jovens adultos da linhagem C57BL/6J passaram por este modelo de estresse diariamente por 21 dias. Observou-se um aumento na temperatura corpórea basal em repouso no 21º dia, bem como diminuição na hipertermia reativa a um estresse agudo de manipulação, demonstrando a efetividade do modelo em indução de estresse. Os tamanhos dos telômeros, a expressão gênica da enzima telomerase e sua atividade protéica foram investigados no hipocampo dos camundongos que sofreram o estresse crônico e comparados com animais do grupo controle. Observou-se, após o período de indução do estresse, uma diminuição em aproximadamente 58% no tamanho relativo médio dos telômeros das células hipocampais nos camundongos submetidos ao estresse psicossocial, quando comparados ao grupo controle. A quantidade de RNAm relativo ao gene da telomerase, bem como sua atividade enzimática, mostraram-se similares entre os grupos controle e experimental. Estes resultados sugerem que o estresse psicossocial prolongado reduz o tamanho dos telômeros do hipocampo de camundongos e que esta redução não parece ser devido a alterações gênicas ou enzimáticas da telomerase. Com este estudo procuramos entender melhor os mecanismos celulares e genômicos cerebrais modulados pelo estresse psicológico prolongado, de natureza social. Uma vez que muitos distúrbios psiquiátricos e neurodegenerativos são provenientes do estresse crônico, nossos resultados fornecem mais subsídios para se evidenciar a importância do ambiente social na saúde mental dos indivíduos. / Stressor stimuli are part of the daily life and the major part is derived from the social context. Long term stress can be very harmful, and induce several noxious events in the organism. These effects can also be perceived in the central nervous system, particularly in the hippocampus, in which morphological and functional damages may be observed. Recently a correlation of perceived stress and telomere length was demonstrated in leukocytes of stressed women. Telomeres, which are in tanden repeats of the nucleotides TTAGGG, are responsible to protect the extremities of the chromosomes, and it´s maintenance and elongation is mainly mediated by the enzyme telomerase. Telomeres and telomerase have been the targets of many studies in the last years, concerning aging and cell death. In this regard, the present study has investigated the effects of prolonged psychosocial defeat stress model in the telomeric biology of the hippocampus. Male C57Bl/6J young adult mice were submitted to a 21 days of psychosocial stress. We observed a raise in body temperature, as well as a decrease in reactive hyperthermia to the handling stress, demonstrating the effectiveness of this stress model. The telomere length, the transcript levels of telomerase mRNA, and the activity of the enzyme telomerase were also investigated in the hippocampus of psychosocially stressed mouse. A decrease of 58% in average telomere length was observed in the hippocampal cells of stressed mice when compared to control group. Levels of telomerase mRNA and telomerase activity were similar between control and defeat groups. In this study, we intend to better understand the cellular and genomic mechanisms promoted by long term psychological stress, with social nature, in brain. Since many psychiatric and neurodegenerative disorders have chronic stress underlying them, our results reinforce the importance of the social environment on individual mental health.

Homeostatic plasticity is important in neurobiology for stabilising neuronal networks in the face of Hebbian forms of synaptic plasticity that are thought to mediate memory storage. Impairment of homeostatic plasticity has also been implicated in neurological diseases such as Rett syndrome and fragile X syndrome. Homeostatic plasticity can be achieved through scaling of the strength of synaptic connections between neurones or by changes in intrinsic excitability. While homeostatic plasticity has been studied mainly using in vitro preparations, it is for the most part not known whether changes of neural activity in vivo induce homeostatic changes. The molecular pathway responsible for homeostatic plasticity still remains unclear. In this thesis, I have used stereotaxic surgery to over express Kir2.1, an inwardly rectifying potassium channel, in vivo in the brains of adult mice. I show that the expression of Kir2.1 through adeno-associated virus (AAV) does not cause any adverse effects in the dentate gyrus nor the CA1 of the mouse hippocampus. I go on to use slice patch clamp methods to measure the change in electrical properties of granule cells in the dentate gyrus and pyramidal cells in CA1 caused by expression of Kir2.1. I show that the excitability of neurones expressing Kir2.1 was reduced compared to control neurones. By 2 weeks after virus injection the neurones showed homeostatic plasticity in response to Kir2.1 over expression. Interestingly, the mechanism of adaptation was different in different types of cells; dentate gyrus granule cells adapted through change in their intrinsic excitability, whereas CA1 pyramidal cells adapted by modifying the strength of their synaptic inputs. To establish whether induction of homeostatic plasticity is associated with changes in gene expression I used fluorescent activated cell sorting (FACs) to isolate pure population of neurones infected with viruses. I then sequenced RNA extracted from neurones expressing Kir2.1 and control neurones. Analysis of the RNAseq data revealed molecular candidates involved in homeostatic plasticity. In summary, I show that Kir2.1 over expression causes change in excitability and subsequent homeostatic plasticity in vivo. The mechanism of adaptation differs between cell types. RNAseq results identify novel candidates for future investigation.

Chronically elevated brain glucocorticoid (GC) levels impair cognition. Age-related cognitive deficits or "sickness" behaviour is often associated with neuroinflammation. In rodents, raised GC levels prior to lipopolysaccharide (LPS) administration potentiate neuroinflammation although GC suppresses neuroinflammation if administered after LPS. 11β-hydroxysteroid dehydrogenase-1 (11β-HSD1) reductase activity can increase intracellular GC levels, including in the brain, without alteration in circulating levels. Deficiency/pharmacological inhibition of 11β-HSD1 is protective against age related cognitive impairment in both rodent and humans. However, the underlying mechanism remains unclear. 11β-HSD1 reductase activity is coupled to hexose-6-phosphate dehydrogenase activity, itself dependent on cellular energy status. Processes affected by deficiency/inhibition of 11β- HSD1 (e.g. acute inflammation, angiogenesis) are associated with increased glycolysis. Additionally, compared to C57BL/6J controls, adipose tissue of 11β-HSD1 deficient mice shows increased expression of glycolytic and oxidative metabolism genes in a rodent model of obesity, characterised by low-grade chronic inflammation. I hypothesised that 11β-HSD1 has a role in regulation of cellular energetics basally and following inflammation. 11β-HSD1 expression in the brain will be up-regulated during systemic inflammation. Following inflammation, 11β-HSD1 deficiency will attenuate the pro-inflammatory response and subsequently alter energy substrate uptake and/or utilisation in the key areas of brain (i.e. hypothalamus and the hippocampus) that sense and respond to inflammation and energy balance. To test my hypothesis, global 11β-HSD1 KO mice, primary macrophages in vitro and murine models of inflammations were utilised. 11β-HSD1 mRNA and protein expression were confirmed in the hypothalamus and the hippocampus of C57BL/6J mice. In the absence of inflammation, expression of inflammatory markers is low or negligible in the brains of Hsd11b1-/- mice similar to C57BL/6J controls. However, compared to C57BL/6J, Hsd11b1-/- mice show altered mRNA levels of metabolic transporters and enzymes in the hypothalamus and the hippocampus. Overall, the mRNA profiling suggests reduced dependence on glucose in the brains of Hsd11b1-/- mice, either through increased lactate availability (in the whole brain and hippocampus) or through increased glycolysis and mitochondrial number/function (in the hypothalamus). Primary macrophages were utilised to investigate the role of 11β-HSD1 in cellular energetics in vitro. In these cell based assays, glycolysis was found to be the predominant glucose metabolising pathway in C57BL/6J primary macrophages, consistent with the literature. Preliminary data suggested reduced glycolytic activity in Hsd11b1-/- compared to C57BL/6J primary macrophages. However, initial attempts to utilise these cell based assays on primary microglia were unsuccessful. Moreover, Hsd11b1 mRNAs in the brain (down-regulation with inflammation, discussed later) was found to be differentially regulated in comparison to Hsd11b1 mRNA levels in the macrophages (up-regulation with inflammation) hence further investigation was not pursued. To identify a model of peripheral inflammation where 11β-HSD1 is regulated in the brain in vivo, Staph. aureus induced acute lung inflammation and the K/BxN serum transfer induced model of arthritis were utilised. Increased expression of inflammatory markers in the brain was associated with reduced Hsd11b1 mRNA levels in the hippocampus of control mice in these models. Comparison of Hsd11b1-/- and C57BL/6J mice showed increased levels of mRNAs encoding metabolic transporters in the hypothalamus and the hippocampus of Hsd11b1-/- mice following inflammation in the K/BxN serum transfer model of arthritis suggesting increased energy substrate availability. Additionally, increased levels of mRNA encoding metabolic enzymes suggested increased glycolytic capacity and mitochondrial oxidative phosphorylation activity in the hippocampus but not the hypothalamus of Hsd11b1- /-, compared to C57BL/6J mice, following K/BxN serum induced arthritis. Overall, these data suggest that the reduction in expression of 11β-HSD1 could be a potential mechanism to increase energy substrate availability, glycolytic capacity and mitochondrial activity in the hippocampus to provide metabolic support for neuronal metabolism and function following peripheral inflammation. The role of 11β-HSD1 in the pro-inflammatory response and cellular energetics in the hippocampus was further investigated in a well characterised sterile peritonitis model of systemic inflammation in which a low to moderate dose of LPS was used. Mice were administered LPS or vehicle (0.9% saline) by a single i.p. injection and culled 3h, 6h or 9h post injection. Inflammation resulted in significant reduction in burrowing activity both in Hsd11b1-/- and C57BL/6J mice suggesting sickness behaviour.. The number of circulating immune cells, as a measure of peripheral inflammation, did not differ between genotypes. Similarly, plasma corticosterone levels were elevated following inflammation but no genotype difference was observed. However, levels of plasma 11-dehydrocorticosterone, the inert substrate for 11β- HSD1, were significantly elevated in the Hsd11b1-/-, compared to C57BL/6J mice, following inflammation. Levels of mRNA encoding inflammatory markers were lower in the hippocampus of Hsd11b1-/-, compared to C57BL/6J mice, following inflammation. Also, Hsd11b1 mRNA levels were reduced in the hippocampus of C57BL/6J mice following inflammation, consistent with the finding above. Principal component analysis on levels of mRNA encoding metabolite transporters and enzymes revealed a distinct metabolic response in the hippocampus of Hsd11b1-/-, compared to C57BL/6J mice, 6h post LPS. At the same time point in the hippocampus, levels of mRNAs encoding metabolite transporters and enzymes suggested an attenuated switch to aerobic glycolysis with maintenance of mitochondrial function/activity. Quantification of hippocampal energy metabolites using targeted metabolomics in the Hsd11b1-/- compared to C57BL/6J mice 6h post LPS showed correspondence with the mRNA results. Overall, these results suggest that reduced expression of 11β-HSD1 could be a potential mechanism to reduce the pro-inflammatory response and provide better metabolic support for neuronal function and metabolism in the hippocampus, following systemic inflammation. In summary, the current work provides evidence for neuroprotection with 11β-HSD1 deficiency, following systemic inflammation. The suggestive neuroprotection is at least in part mediated via an attenuated pro-inflammatory responses and increased energy substrate uptake and/or utilisation providing better metabolic support for neuronal function following inflammation. It argues for the development of tissue specific small molecule inhibitors of 11β-HSD1 that can cross the blood brain barrier as therapeutic agents against the adverse cognitive effects of systemic inflammation and/or inflammaging.

Les représentations mentales, en particulier les représentations spatiales, sont étroitement associées à l'activation coordonnée de groupes de cellules dans l'hippocampe. Nous avons entrepris l'étude des propriétés et activités spontanées du réseau hippocampique (et plus particulièrement de la région CA3) afin de mieux en comprendre le fonctionnement, dans les situations normales et pathologiques. En effet, certaines pathologies neurodégénératives telle que la maladie de Parkinson serait potentiellement associées à des troubles cognitifs hippocampo-dépendants. Ainsi dans la première partie de ma thèse, nous avons caractérisé la dynamique temporelle des signaux excitateurs et inhibiteurs spontanés de l'hippocampe par une approche électrophysiologique in vitro sur tranches d'hippocampe mais aussi chez l'animal anesthésié grâce des enregistrements multi-unitaires multi-sites. Ces travaux nous a permis de mettre en évidence que les caractéristiques de la dynamique du réseau CA3 remplissent quelques critères essentiels au concept d'assemblées cellulaires. De plus, cette étude a mis en évidence les caractéristiques fonctionnelles de l'hippocampe chez l'animal normal. Ces résultats peuvent donc être utiles pour de futures études sur les pathologies hippocampo-dépendantes touchant le codage ou la mémoire spatiale telle que la maladie de Parkinson. Ainsi, dans la deuxième partie de ma thèse, nous avons étudié les altérations fonctionnelles du circuit hippocampique chez un modèle rat de la maladie de Parkinson. La maladie de Parkinson est une maladie neurologique qui affecte le système nerveux central et entraine des symptômes essentiellement moteurs. La cause est une dégénérescence des neurones dopaminergiques mais aussi noradrénergiques et sérotoninergiques. Cependant, en dehors des troubles moteurs, cette pathologie est aussi caractérisée par des troubles cognitifs notamment des déficits spatiaux. Notre projet a donc consisté à analyser les mécanismes par lesquels les déplétions monoaminergiques entraîneraient des troubles de l'apprentissage spatial. Ce travail a été réalisé chez le rongeur à l'aide d'une étude associant une approche comportementale et des enregistrements électrophysiologiques chez l'animal anesthésié mais aussi chez l'animal éveillé en comportement. Nous avons ainsi pu mettre en évidence des dysfonctionnements hippocampiques causés par des lésions contrôlées des différents systèmes mono-aminergiques (plus particulièrement dopaminergique et noradrenergique) impliqués dans la maladie de Parkinson. / Mental representations, especially spatial ones are closely related to correlated activity in cellular assembly in the hippocampus. In this work, we analyzed the properties and the spontaneous activity of the hippocampal network in order to unravel its functioning in normal and pathological conditions. Several neurodegenerative disorders such as Parkinson's disease seems to be also associated to cognitive disorder related to hippocampus dysfunction. We first characterized the temporal dynamic properties of spontaneous excitatory and inhibitory signal. We then studied the functional alteration of the hippocampal network in a rat model of Parkinson's disease using behavioral and electrophysiological investigations. Our work showed that controlled lesion of the various monoaminergic systems induced hippocampus dysfunction related to spatial disorientation.In the first part of my thesis, we characterized the temporal dynamic of excitatory and inhibitory signals with electrophysiological recordings in vivo on hippocampal slices but also in anesthetized animals with multi-units multi-sites recordings. These studies allowed us to highlight that dynamic of CA3 network meets the criteria of cells assembly concept. Moreover, we characterize the functional properties of hippocampus in physiological conditions. These results could be useful for further studies on hippocampo-dependant pathologies in the context of spatial coding and memory.Thus, in the second part of my work, we studied the functional alterations of hippocampal network in the context of Parkinson disease. This pathology is a neurodegenerative disease which affects the central nervous system and leads essentially to motor symptoms. The cause is the degeneration of dopamine neurons but also of noradrenalin and serotonin neurons. Nevertheless, this pathology is also associated to cognitive disorders notably a form of spatial disorientation. Our project consisted to analyze the mechanisms by which monoamines depletions led to spatial learning impairments. This work was realized on rats with a study combinating behavioral approach with electrophysiological recordings in anesthetized animals but also in awake animals. We showed that some monoamines depletions (and notably dopamine and noradrenalin depletions) led to spatial impairments in behavioral tasks correlated to a change in firing and coding of neurons of hippocampus.

Recent improvements in high performance fluorescent sensors and scientific CMOS cameras enable optical imaging of neural networks at a much larger scale. Our lab has demonstrated the ability of wide-field calcium-imaging (using GCaMP6f) to capture the concurrent dynamic activity from hundreds to thousands of neurons over millimeters of brain tissue in behaving mice. The expansiveness of the neuronal network captured by the system requires innovation in data analysis methods. This thesis explores data analysis techniques to extract dynamics of hippocampal neural network containing a large number of individual neurons recorded using GCaMP6, while mice were learning a classical eye puff conditioning behavior. GCaMP6 fluorescence signals in each neuron is first considered one dimension, and each dataset thus contains hundreds to thousands dimensions. To understand the network structure, we first performed dimension reduction technique to examine the low-dimension evolution of the neural trajectory using Gaussian Process Factor Analysis, which smooths across dimensions, while extracting the low dimension representation. Because of the slow time course of GCaMP6 signals, the Factor Analysis was biased to the long lasting decay phase of the signal that does not represent neural activities. We found that it is critical to first estimate the spike train inference prior to application of dimension reduction, such as using the Fast Nonnegative Deconvolution method. While the low-dimension presentation described intriguing features in the neural trajectories that paralleled the learning behavior of the animal, to further quantify the network changes we directly examined the network in the high dimension space. We calculated the changes in the distance of the network trajectory over time in the high dimension space without any filtering, and compared across different phases of the behavioral states. We found that the speed of the trajectory in the high dimension space is significantly higher when animal learned the task, and the trajectory travelled much further away from baseline during the delay phase of the conditioning behavior. Together, these results demonstrate that dimension reduction analysis technique and the network trajectory within the non-reduced high dimension space can capture evolving features of neural networks recorded using calcium imaging. While this thesis concerns the hippocampal dynamics during learning, such data analysis techniques are expected to be broadly applicable to other behaviorally relevant networks.

O estresse é muito presente na vida das pessoas, e grande parte deste é de origem social. O estresse contínuo induz a uma série de efeitos nocivos no organismo. Estes efeitos também podem ser observados no cérebro, principalmente no hipocampo, onde promove alterações na sua morfologia e função. Recentemente, demonstrou-se uma redução do tamanho dos telômeros em leucócitos de mulheres com alto grau de estresse. Os telômeros são seqüências repetitivas dos nucleotídeos TTAGGG, responsáveis por proteger as extremidades dos cromossomos, e sua manutenção e alongamento é mediado, principalmente, pela enzima telomerase. Telômeros e telomerase têm sido alvos de muitos estudos envolvendo o envelhecimento e morte celular. Assim, o presente trabalho estudou os efeitos do estresse psicossocial prolongado em um modelo animal de subjugação/submissão sobre a biologia telomérica do hipocampo. O modelo de subjugação consistiu em um pareamento dos animais experimentais com um camundongo agressivo por 30 minutos. Camundongos machos jovens adultos da linhagem C57BL/6J passaram por este modelo de estresse diariamente por 21 dias. Observou-se um aumento na temperatura corpórea basal em repouso no 21º dia, bem como diminuição na hipertermia reativa a um estresse agudo de manipulação, demonstrando a efetividade do modelo em indução de estresse. Os tamanhos dos telômeros, a expressão gênica da enzima telomerase e sua atividade protéica foram investigados no hipocampo dos camundongos que sofreram o estresse crônico e comparados com animais do grupo controle. Observou-se, após o período de indução do estresse, uma diminuição em aproximadamente 58% no tamanho relativo médio dos telômeros das células hipocampais nos camundongos submetidos ao estresse psicossocial, quando comparados ao grupo controle. A quantidade de RNAm relativo ao gene da telomerase, bem como sua atividade enzimática, mostraram-se similares entre os grupos controle e experimental. Estes resultados sugerem que o estresse psicossocial prolongado reduz o tamanho dos telômeros do hipocampo de camundongos e que esta redução não parece ser devido a alterações gênicas ou enzimáticas da telomerase. Com este estudo procuramos entender melhor os mecanismos celulares e genômicos cerebrais modulados pelo estresse psicológico prolongado, de natureza social. Uma vez que muitos distúrbios psiquiátricos e neurodegenerativos são provenientes do estresse crônico, nossos resultados fornecem mais subsídios para se evidenciar a importância do ambiente social na saúde mental dos indivíduos. / Stressor stimuli are part of the daily life and the major part is derived from the social context. Long term stress can be very harmful, and induce several noxious events in the organism. These effects can also be perceived in the central nervous system, particularly in the hippocampus, in which morphological and functional damages may be observed. Recently a correlation of perceived stress and telomere length was demonstrated in leukocytes of stressed women. Telomeres, which are in tanden repeats of the nucleotides TTAGGG, are responsible to protect the extremities of the chromosomes, and it´s maintenance and elongation is mainly mediated by the enzyme telomerase. Telomeres and telomerase have been the targets of many studies in the last years, concerning aging and cell death. In this regard, the present study has investigated the effects of prolonged psychosocial defeat stress model in the telomeric biology of the hippocampus. Male C57Bl/6J young adult mice were submitted to a 21 days of psychosocial stress. We observed a raise in body temperature, as well as a decrease in reactive hyperthermia to the handling stress, demonstrating the effectiveness of this stress model. The telomere length, the transcript levels of telomerase mRNA, and the activity of the enzyme telomerase were also investigated in the hippocampus of psychosocially stressed mouse. A decrease of 58% in average telomere length was observed in the hippocampal cells of stressed mice when compared to control group. Levels of telomerase mRNA and telomerase activity were similar between control and defeat groups. In this study, we intend to better understand the cellular and genomic mechanisms promoted by long term psychological stress, with social nature, in brain. Since many psychiatric and neurodegenerative disorders have chronic stress underlying them, our results reinforce the importance of the social environment on individual mental health.

Calculating hippocampal volume from Magnetic Resonance (MR) images is an essential task in many studies of neurocognition in healthy and diseased populations. The `gold standard' method involves hand tracing, which is accurate but laborious, requiring expertly trained researchers and significant amounts of time. As such, segmenting large datasets with the standard method is impractical. Current automated pipelines are inaccurate at hippocampal demarcation and volumetry. We developed a semi-automated hippocampal segmentation pipeline based on the Advanced Normalization Tools (ANTs) suite of programs to segment the hippocampus. We applied the semi-automated segmentation pipeline to 70 participant scans (26 female) from groups that included participants diagnosed with autism spectrum disorder, healthy older adults (mean age 74) and healthy younger controls. We found that hippocampal segmentations obtained with the semi-automated pipeline more closely matched the segmentations of an expert rater than those obtained using FreeSurfer or the segmentations of novice raters. Further, we found that the pipeline performed best when including manually- placed landmarks and when using a template generated from a heterogeneous sample (that included the full variability of group assignments) than a template generated from more homogeneous samples (using only individuals within a given age or with a specific neuropsychiatric diagnosis). Additionally, the semi-automated pipeline required much less time (5 minutes per brain) than manual segmentation (30-60 minutes per brain) or FreeSurfer (8 hours per brain).

Fear generalization, the generalization of fear to innocuous stimuli, is a characteristic component of pathological anxiety. For example, after returning from war, a person might begin to experience fear in response to the sound of fireworks, a stimulus typically regarded as safe. When excessive, “overgeneralization” serves as a core feature of fear and anxiety-related disorders, such as PTSD. The present collection of studies sought to investigate the neural correlates and temporal dynamics of fear generalization in humans. The first study sought to investigate the causal role of the ventromedial prefrontal cortex (vmPFC) and hippocampus in the generalization of fear. Contrary to hypotheses, individuals with focal damage to the vmPFC (N=8) or hippocampus (N=12) did not demonstrate significantly increased fear generalization relative to individuals with brain damage outside of these regions (N=16) or normal comparison participants (N=20). Potential explanations for this finding are explored. The second study sought to investigate the time course of fear generalization in humans. Participants (N = 107) completed a fear generalization task over the course of two sessions. Results indicate that fear generalization significantly increased as the duration of time between training and testing increased. This suggests that a stimulus may elicit a generalized fear response at one arbitrarily selected time point, but not another. This study establishes a novel paradigm that can be used in future work to investigate changes in the neural correlates of fear generalization over time. Fear generalization is found across an array of anxiety disorders, making it a compelling area of study. The present work highlights the dynamic nature of fear generalization in humans. Further, the present study leads to a number of questions for future research.

Research concerning the development of learning and memory suggests that there are multiple memory systems. These systems differ in complexity, underlying neural substrates, and consequently, their developmental emergence. Pavlovian conditioning, and specifically eyeblink conditioning (EBC), allows researchers to investigate both simple and complex forms of learning and memory early in development. Delay EBC, which is considered a relatively simple form of learning, involves the association of a conditioned stimulus (CS) with an unconditioned stimulus (US). Research from our laboratory suggests that the emergence of delay EBC is dependent on the development of sensory input to the pontine nucleus. Trace EBC, a more complex form of learning, involves the association of a CS with a US over a stimulus-free trace interval. Due to its relatively late emergence, the developmental time course of trace EBC has been traditionally regarded as independent of sensory system development. Rather, it is the involvement of late-developing structures such as the hippocampus which is considered the principle limiting factor in the emergence of trace EBC. The current collection of studies investigates the developmental emergence of delay and trace conditioning. We found that both delay and trace conditioning are facilitated by using an early-developing somatosensory CS. This suggests that the sensory system development plays a role in even late-developing trace EBC. Moreover, hippocampal CA1 neuronal activity shows increased responsiveness in even very young animals when trained with an early-developing somatosensory CS compared to those trained with a tone CS. Combined, these data suggest that both hippocampal and sensory system development may play key roles in the developmental emergence of learning.