Autism spectrum disorders (ASDs) represent a heterogeneous group of neurodevelopmental disorders characterised by deficits in social interaction and communication, and by restricted and stereotyped behaviour. The diagnosis of autism is based on behavioural observation of the subject as research has not yet identified specific markers. Today, several studies show that disturbances in sensory processing are a crucial feature of autism. Indeed, around 90% of individuals diagnosed with autism show atypical responses to various sensory stimuli. These sensory abnormalities (described as hyper- or hypo-reactivity to sensory stimulation) are currently recognised as diagnostic criteria for autism. Among the sensory defects, tactile abnormalities represent a very common finding impacting the life of autistic individuals. It has been shown how abnormal responses to tactile stimuli not only correlate with the diagnosis of autism but also predict its severity. Indeed hypo-responsiveness to tactile stimuli is associated with greater severity of the main symptoms of autism. To date, the neural substrates of these behaviours are still poorly understood. Over the years, the use of genetically modified animal models has enabled a major step forward in the study of the aetiology of autism spectrum disorders. Interestingly, several animal models that carry autism-related mutations also show deficits of a sensory nature. This is the case with the Shank3b-/- and Cntnap2-/- mouse models, strains in which the expression of the gene in question is suppressed. The SHANK3 gene encodes for a crucial protein in the structure of the postsynaptic density of glutamatergic synapses. In humans, haploinsufficiency of SHANK3 causes the Phelan-McDermid syndrome, a neurodevelopmental disorder characterised by ASD-like behaviour, developmental delay, intellectual disability and absent or severely delayed speech. Individuals with Phelan-McDermid syndrome often show dysfunctions in somatosensory processing, including disturbances in tactile sensitivity. CNTNAP2 codes for CASPR2, a transmembrane protein of the neurexin superfamily involved in neuron-glia interactions and clustering of potassium channels in myelinated axons. Missense mutation in CNTNAP2 is causative of cortical dysplasia-focal epilepsy syndrome (CDFE), a rare disorder characterized by epileptic seizures, language regression, intellectual disability, and autism. Following these findings, mice lacking the Shank3b isoform (Shank3b-/-) and Cntnap2 gene (Cntnap2-/-) show autistic-like behaviours. In this study, we used an interdisciplinary approach (behavioural, molecular, and imaging techniques) to study the neuronal substrates of whisker-mediated behaviours in genetic mouse models of ASD. We performed two behavioural tests, namely the textured novel object recognition test (tNORT) and the whisker nuisance test (WN) to have in-depth insight in whisker dependent behaviours. Following behavioural assessment, through a molecular approach, we investigated the neural underpinnings of this aberrant behaviour. We evaluated neuronal activation in key brain areas involved in the processing of sensory stimuli via c-fos mRNA in situ hybridization. Finally, using a seed-based approach in resting-state functional magnetic resonance imaging (rsfMRI) we probed the functional connectivity phenotype of these mutant mice. The contribution of the peripheral nervous system to sensory processing was also assessed via RT-qPCR at the level of the trigeminal ganglion. Sensory abnormalities that characterize ASDs represent a symptom of primary relevance in the life of autistic individuals. Scientific research has only recently addressed this important aspect and animal models represent a useful preclinical tool to investigate the causal role of genetic mutations in the aetiology of ASDs. In such context, the complementary approach used in this work represents a crucial step to the understanding of sensory-related deficits which characterize ASD.

The last decade has seen an increasing interest in bio-mathematical modelling and scientific computing, resulting in new applications to relevant physiological phenomena and to a better understanding of the origin of various diseases. A topic of great interest to several degenerative diseases is filtration across microvessel walls. The role of the microvessel wall is to let oxygen and nutrients contained in the blood stream to reach the interstitium, and ultimately the surrounding cells, while blocking macromolecules. An understanding of these processes is important in preventing and curing neuro-degenerative diseases, as well as for exploring possible mechanisms to make drug delivery more efficient. This work presents a one-dimensional, time dependent mathematical model describing transport of blood plasma and macromolecules across blood vessel walls. The model takes into account the heterogeneous microvessel wall composition, in order to accurately describe trans-vascular flow. This results in a multi-layered domain, accounting for variable physical properties across the layers forming the micro-vascular wall. In particular, the glycocalyx and endothelium, accounted for in many biological studies, are represented in our model. This micro-structural, yet simplified description of the vascular wall, allows us to simulate the effect of glycocalyx damage and of other pathologies, such as hypertension, hemorrhage and hypovolemia, both in steady and time-dependent states. Due to the simplicity, and thus efficiency of the proposed model, simulations are fast and provide results which are in line with published experimental studies. Furthermore, the simulation tool may be useful for practical applications in physiological and medical studies, by evaluating the possible consequences of pathological conditions.

Resting-state fMRI (rsfMRI) is widely used to map brain network organization in health and disease. However, the neural underpinnings and significance of interregional coupling as assessed with rsfMRI remain unclear. Neocortical Excitatory/Inhibitory (E/I) balance critically affects local and long-range information processing and as such can conceivably bias large-scale interareal functional connectivity and fMRI coupling. This notion would be consistent with the concomitant presence of neocortical E/I imbalance and atypical rsfMRI connectivity in multiple brain disorders, such as autism, or schizophrenia. Here, we combine chemogenetic manipulations, rsfMRI, electrophysiology in the mouse to causally probe how alteration in regional neocortical E/I balance affects interareal neural and rsfMRI coupling. We used DREADD-based chemogenetics to remotely alter the E/I balance of the mouse medial prefrontal cortex (PFC) by increasing pyramidal neuron excitability (↑Excitation), or by reducing the activity of fast spiking parvalbumin positive (PV+) inhibitory interneurons (↓Inhibition). For each of the employed manipulations, we recorded both locally elicited fMRI network activity, as well as large scale functional connectivity as measured with rsfMRI. To uncover the neural rhythms associated with our manipulations, we carried out corresponding in-vivo multielectrode electrophysiology in a sperate cohort of animals. Chemogenetic activation of pyramidal neurons (↑Excitation) or inhibition of PV+ interneurons (↓Inhibition) resulted in increased neural firing and evoked-BOLD activity in the targeted area. Both manipulations also produced socio-behavioral impairments in a three-chamber social-interaction test. However, the two manipulations were associated with different spectral signatures as probed with local-field potential measurements (LFP). Specifically, ↑Excitation produced largely decreased broad-band oscillatory power, while ↓Inhibition led to a robust increase in local oscillatory activity. Notwithstanding these spectral differences, both manipulations produced analogous patterns of fMRI hypoconnectivity in the mouse default mode network. To understand how these different local spectral activity may produce converging patterns of rsfMRI dysconnectivity, we turned to multielectrode electrophysiology and measured interareal coupling between the manipulated region (PFC) and its anatomical targets (retrosplenial cortex). These investigations revealed that fMRI hypoconnectivity produced by ↑Excitation or ↓Inhibition was associated with dissociable LFP coherency signatures. Specifically, chemogenetic activation of pyramidal neurons (↑Excitation) produced decreased coherence in slow-δ range (0.1-4 Hz), while inhibition of PV+ activity (↓Inhibition) produced a composite response, comprising reductions in slow frequency coherence along with a largely increased coherence in theta to beta bands. By relating fMRI changes to corresponding LFP coherency differences, we found that neural coupling in slow (0.1-4 Hz), but not faster frequency bands, significantly predicted the fMRI connectivity changes produced by all the employed manipulations. These results suggest that large-scale fMRI connectivity is primarily supported by electrophysiological coherence in infraslow/slow rhythms, and it is disproportionately less sensitive to high frequency coupling. Importantly, this relationship also held when recordings obtained upon chemogenetic silencing of the PFC (i.e. producing a reduced ↓Excitation) were included. Collectively, our results shed light on the general principles underlying macro-scale fMRI network organization in the mammalian brain with a number of important implications for the interpretation of rsfMRI connectivity in health and disease. First, they suggest that the relationship between interareal neural activity and fMRI connectivity is critically biased by local Excitatory/Inhibitory ratio. Second, our findings also support a simple framework whereby interareal patterns of hyper- and hypo-connectivity observed in brain disorders may counterintuitively reflect reduced or increased neural excitability of afferent systems, respectively. Third, these observations point at a possible unifying mechanistic link between E/I imbalance and connectivity disruption in brain disorders, suggesting that these two phenotypes may be the result of a unique etiopathological insult. Future extensions of this framework may offer opportunities to model the local contribution of regional E/I balance in affecting fMRI connectivity, and to physiologically decode fMRI dysconnectivity in human disorders

Successfully acting largely depends on moving at the right time. Consider a member of an orchestra just few instants before starting to play her piece. She should be ready not only to launch the planned movements when appropriate, but also to stop them if required. Action initiation and control are characteristic features of many of our daily life actions. There is a large amount of evidence in monkeys and humans suggesting that the dorsal premotor cortex (PMD) and the supplementary motor areas (SMA) might be critically involved in these features. However, the distinctive role of these areas is still matter of controversy. The aim of the present thesis is to provide some preliminary steps toward a comprehension of whether and how the human dorsal precentral areas may selectively contribute to action initiation and control. In doing this we shall introduce and discuss a series of transcranial magnetic stimulation (TMS) experiments carried out with two different paradigms, namely dual-coil TMS and single pulse TMS paradigm. These experiments were primarily devoted to explore the structural and functional properties of PMD. They also allowed us to assess whether PMD and SMA may be differentially and selectively involved in action control. In more detail, we first investigated the structural connectivity between PMD and the ipsilateral orofacial M1, introducing a novel dual-coil TMS approach. Results displayed the existence of short-latency influences of the left PMD on the ipsilateral orofacial M1, measured by recording motor evoked potentials (MEPs) in the orofacial muscles. Then, taking advantage of this novel approach, we started to explore the functional PMD-M1 connectivity. We tested the short-latency effects of TMS, as measured by changes in orofacial MEPs, during a delayed motor task. The results showed an inhibitory activity in the PMD-M1 module during the SET-period. We also manipulated the duration of the SET-period, to establish whether the effects were time-locked to the start of the delay period or rather time-locked to the predicted GO-signal. Hence, the investigation of the PMD-M1 connectivity paved us the way to explore, first, the role of PMD in initiating action and, then, the differential role of PMD and SMA in controlling and inhibiting action. Indeed, we run a further study, in which we carried out two single pulse TMS experiments. We first stimulated PMD during a stop-signal task, then we contrasted the PMD stimulation with SMA stimulation when participants underwent the same stop-signal task. There are five chapters to come. In Chapter 1 we shall review some key studies exploring anatomical and functional properties of PMD and SMA in both monkeys and humans, with particular emphasis on their putative role in action initiation and control. In Chapter 2 we shall focus on the methodological aspects of our experimental studies. In particular, we shall introduce the so-called twin- or dual-coil TMS paradigm, discuss its main approaches present in the literature and propose a variant of them. In Chapter 3 we shall present and discuss our first dual-coil TMS study exploring, for the first time, the ipsilateral PMD-corticofacial system connectivity. In Chapter 4 we shall examine three dual-coil TMS studies investigating the functional connectivity between PMD and ipsilateral M1 during a motor delayed task. Finally, in Chapter 5 we shall scrutinize two single pulse TMS studies capitalizing on a stop-signal task in order to assess the role of PMD and SMA in action control. Results and future lines of research will be sketched in the Concluding remarks.

The honeybee, Apis mellifera, is an established model for the study of olfactory processing, olfactory learning and memory, and the related plasticity. The primary centre for olfactory processing in the bee brain, the antennal lobe, has a very important function in odour coding and odour discrimination. Nevertheless, both its structure and its function are plastic. In this thesis, I analysed the structural antennal lobe plasticity related to associative learning, and that related to a non-associative experience, i.e. prolonged odour exposure, in the adult honeybee. Subsequently, I analysed the functional modification taking place in the latter case within the output units of the antennal lobe, showing that parallel structural and functional changes occur. In the last part of the thesis, I focused on the effects of a common neonicotinoid pesticide, imidacloprid, on antennal lobe function and the discrimination abilities of honeybees. I demonstrated that both are strongly impaired in the acute treatment of the brain with such substance.