Contribution of Cerebellar Sensorimotor Adaptation to Hippocampal Spatial Memory

Complementing its primary role in motor control, cerebellar learning has also a bottom-up influence on cognitive functions, where high-level representations build up from elementary sensorimotor memories. In this paper we examine the cerebellar contribution to both procedural and declarative components of spatial cognition. To do so, we model a functional interplay between the cerebellum and the hippocampal formation during goal-oriented navigation. We reinterpret and complete existing genetic behavioural observations by means of quantitative accounts that cross-link synaptic plasticity mechanisms, single cell and population coding properties, and behavioural responses. In contrast to earlier hypotheses positing only a purely procedural impact of cerebellar adaptation deficits, our results suggest a cerebellar involvement in high-level aspects of behaviour. In particular, we propose that cerebellar learning mechanisms may influence hippocampal place fields, by contributing to the path integration process. Our simulations predict differences in place-cell discharge properties between normal mice and L7-PKCI mutant mice lacking long-term depression at cerebellar parallel fibre-Purkinje cell synapses. On the behavioural level, these results suggest that, by influencing the accuracy of hippocampal spatial codes, cerebellar deficits may impact the exploration-exploitation balance during spatial navigation

Stochastic neural network dynamics: synchronisation and control

Biological brains exhibit many interesting and complex behaviours. Understanding of the mechanisms behind brain behaviours is critical for continuing advancement in fields of research such as artificial intelligence and medicine. In particular, synchronisation of neuronal firing is associated with both improvements to and degeneration of the brain’s performance; increased synchronisation can lead to enhanced information-processing or neurological disorders such as epilepsy and Parkinson’s disease. As a result, it is desirable to research under which conditions synchronisation arises in neural networks and the possibility of controlling its prevalence. Stochastic ensembles of FitzHugh-Nagumo elements are used to model neural networks for numerical simulations and bifurcation analysis. The FitzHugh-Nagumo model is employed because of its realistic representation of the flow of sodium and potassium ions in addition to its advantageous property of allowing phase plane dynamics to be observed. Network characteristics such as connectivity, configuration and size are explored to determine their influences on global synchronisation generation in their respective systems. Oscillations in the mean-field are used to detect the presence of synchronisation over a range of coupling strength values. To ensure simulation efficiency, coupling strengths between neurons that are identical and fixed with time are investigated initially. Such networks where the interaction strengths are fixed are referred to as homogeneously coupled. The capacity of controlling and altering behaviours produced by homogeneously coupled networks is assessed through the application of weak and strong delayed feedback independently with various time delays. To imitate learning, the coupling strengths later deviate from one another and evolve with time in networks that are referred to as heterogeneously coupled. The intensity of coupling strength fluctuations and the rate at which coupling strengths converge to a desired mean value are studied to determine their impact upon synchronisation performance. The stochastic delay differential equations governing the numerically simulated networks are then converted into a finite set of deterministic cumulant equations by virtue of the Gaussian approximation method. Cumulant equations for maximal and sub-maximal connectivity are used to generate two-parameter bifurcation diagrams on the noise intensity and coupling strength plane, which provides qualitative agreement with numerical simulations. Analysis of artificial brain networks, in respect to biological brain networks, are discussed in light of recent research in sleep theor

Functional Implications of Synaptic Spike Timing Dependent Plasticity and Anti-Hebbian Membrane Potential Dependent Plasticity

A central hypothesis of neuroscience is that the change of the strength of synaptic connections between neurons is the basis for learning in the animal brain. However, the rules underlying the activity dependent change as well as their functional consequences are not well understood. This thesis develops and investigates several different quantitative models of synaptic plasticity. In the first part, the Contribution Dynamics model of Spike Timing Dependent Plasticity (STDP) is presented. It is shown to provide a better fit to experimental data than previous models. Additionally, investigation of the response properties of the model synapse to oscillatory neuronal activity shows that synapses are sensitive to theta oscillations (4-10 Hz), which are known to boost learning in behavioral experiments. In the second part, a novel Membrane Potential Dependent Plasticity (MPDP) rule is developed, which can be used to train neurons to fire precisely timed output activity. Previously, this could only be achieved with artificial supervised learning rules, whereas MPDP is a local activity dependent mechanism that is supported by experimental results

The role of the anterior thalamic nuclei for properties of episodic memory: what, when, where

Amnesia impairs episodic memory in humans, and can occur following damage to the medial diencephalon. This thesis examines the importance of the anterior thalamic nuclei, a diencephalic structure, for different elements (what, when, where) of episodic memory (or episodic-like memory) in rats. The overall goal was to understand why this region is so critical for normal memory in humans. An initial series of experiments investigated the ability of rats with anterior thalamic lesions to recognise objects and odours with a variety of delays. These experiments found that anterior thalamic lesions spare item recognition (what). This same ability was further explored with the use of the immediate early gene zif268, and the results again indicated that this thalamic nucleus does not have a direct role in recognition. A related series of studies explored the effects of anterior thalamic lesions on temporal order judgments (when) for objects. Two different discrimination procedures were tested, between-block recency and within-block recency. Lesions to the anterior thalamic nuclei selectively impaired performance on within-block recency but spared between-block recency. The ability of rats with anterior thalamic damage to discriminate between two locations (where) in both complex and simple environments was also tested. Anterior thalamic lesions significantly impaired place learning compared with control animals, despite the finding that rats with anterior thalamic lesions could sometimes discriminate between the two locations (i.e., could perform significantly above chance). In addition, the effects of anterior thalamic damage on biconditional learning (what-where conjunction) were examined. The rats were trained on both item-place and item-context associations. Lesions to the anterior thalamic nuclei disrupted acquisition of the former, but not the latter. The results suggest that the contributions of the rodent anterior thalamic nuclei to episodic memory, as part of the extended-hippocampal system, primarily reflect the involvement of these nuclei in allocentric spatial learning

The role of PTEN in synaptic and cognitive function and in social behavior

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología Molecular. Fecha de lectura: 10-07-2017Esta tesis tiene embargado el acceso al texto completo hasta el 10-01-201

LASER Tech Briefs, Spring 1994

Topics in this Laser Tech Brief include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Mechanics, Fabrication Technology, and books and reports