The role of the dentate gyrus and adult neurogenesis in hippocampal-basal ganglia associated behaviour

The ability of the brain to continually generate new neurons throughout life is one of the most intensely researched areas of modern neuroscience. While great advancements in understanding the biochemical mechanisms of adult neurogenesis have been made, there remain significant obstacles and gaps in connecting neurogenesis with behavioural and cognitive processes such as learning and memory. The purpose of the thesis was to examine by review and laboratory experimentation the role of the dentate gyrus and of adult neurogenesis within the hippocampus in the performance of cognitive tasks dependent on the hippocampal formation and hippocampal-basal ganglia interactions. Advancement in understanding the role of neurogenesis in these processes may assist in improving treatments for common brain injury and cognitive diseases that affect this region of the brain. Mild chronic stress reduced the acquisition rate of a stimulus-response task (p=0.043), but facilitated the acquisition of a discrimination between a small and a large reward (p=0.027). In locomotor activity assays, chronic stress did not shift the dose-response to methamphetamine. Analysis of 2,5-bromodeoxyuridine incorporation showed that, overall, chronic mild stress did not effect survival of neuronal progenitors . However, learning of the tasks had a positive influence on cell survival in stressed animals (p=0.038). Microinjections of colchicine produced significant lesions of the dentate gyrus and surrounding CA1-CA3 and neocortex. Damage to these regions impaired hippocampal-dependent reference memory (p=0.054) while preserving hippocampal independent simple discrimination learning. In a delay discounting procedure, the lesions did not induce impulsive-like behaviour when delay associated with a large reward was introduced. The experiments uphold a current theory that learning acts as a buffer to mitigate the negative effects of stress on neurogenesis

Effective Monitoring of Freeloading User in the Presence of Active User in Cognitive Radio Networks

In cognitive networks, primary and secondary users (PUs and SUs) share the radio resource according to fair regulations. The goal of this paper is to introduce a new method to detect an unfair user (freeloader) that hides its radio signal under the noise floor in the presence of an active (either primary or secondary) user. The performance of the proposed technique is evaluated by theoretical analysis and computer simulations. The probability of detection is expressed, for constant false-alarm rates, as a function of both the active signal power and the background noise variance. The results show the effectiveness of the new monitoring algorithm in several operating cases

A Software Radio Implementation for Spectrum Hole Sensing in Cognitive Mobile Networks

This paper presents a software radio implementation for spectrum hole sensing in cognitive mobile networks. We propose a multi-channel spectrum sensing method for spectrum hole detection, exploiting Fast Fourier Transform (FFT) filter bank (FFTFB). Our method tests multiple frequency bands at the same time, detecting multiple spectrum holes at once. We modify a recently introduced two-dwell sensing method, implementing the second stage under a software radio approach (i.e. using a digital reprogrammable hardware). In particular, a filter bank implementation varying the length of the FFT is deeply investigated. FFTs with a small number of coefficients, that can be computed with fast and low complexity algorithms (multiplication free), are exploited and their performance discussed in terms of required complexity. The obtained results have evidenced the efficiency of such an approach for cognitive mobile networks

A Fast Unambiguous Acquisition Algorithm for BOC-Modulated Signals

This paper proposes a fast unambiguous acquisition technique for BOC-modulated signals. We remove the ambiguities (side-peaks) of the BOC autocorrelation function, exploiting a reduced-complexity (real and symmetric) filter composed of only 7 non-zero samples. The proposed scheme is applicable to both generic sine and cosine-phased BOC signals. Theoretical and simulation results show that the proposed method removes the ambiguities in the acquisition problem, without requiring any auxiliary signal in the receiver.Peer reviewe

Advanced Techniques on Multirate Signal Processing for Digital Information Processing

Multirate signal processing has become a key topic enabling efficient techniques for digital information processing in a variety of applications such as digital transceivers s for wireless as well as satellite communication systems, digital broadcasting, high performance audio and video, multimedia services, and signal compression. In the wireless communications arena, multirate signal processing techniques provide effective means to implement flexible receiver channelisation filtering and sampling rate conversion for software and cognitive radio digital frontends. As far as multimedia signal processing is concerned, recent techniques relying on multirate filter banks have resulted in improved subband coding techniques reflected in the JPEG-2000 multimedia standard, as well as on some modern audio compression formats such as MP3, AAC3 and ATRAC3plus, to cite but a few