No description available.

The electrical activity of the olfactory bulbs of many vertebrates is characterized by large amplitude regular bursts of waves. These waves, known as induced waves, appear with each inspiration of odourous air through the nostrils. The work described in this thesis establishes that the induced waves are detectable in a variety of species investigated, from amphibia to mammalia. The occurrence of the waves under similar experimental conditions leads to the conclusion that the mechanism of their genesis is similar in all animals. The group activity of the neurones in the various layers of the olfactory bulb was studied together with the amplitude of the induced wave signal. It was found that most cellular activity occurred in the external plexiform and mitral cell layers whereas the maximum of the induced wave activity was in the granular layer. A peak of cellular activity was observed in the external plexiform and mitral cell layers with both nostrils occluded. On opening the ipsilateral nostril the cellular activity was enhanced in these same layers and on opening the contralateral nostril it was decreased. With strong olfactory stimulation an increase in the cellular activity in the granule cell layer was observed. Recordings from single olfactory neurones were made and whereas these were easily observed in the external plexiform and mitral cell layers they were found only rarely in the granule cell layer. It is proposed that the granule cell layer is the site of integration of the inhibitory influence from the contralateral olfactory bulb and from higher centres of the brain. It is further postulated that the cells in the granule cell layer do not normally generate action potentials but that they are capable of doing so with strong olfactory stimulation. It is thought that these cells are the site of genesis of the induced wave activity which is probably generated at the dendrodendritic synaptic connections with the secondary neurones. Evidence in favour of these dendrodendritic synapses being the normal pathway between the mitral and granule cells is presented. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

No description available.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (M.A.)--Baylor University, 2007. / Includes bibliographical references (p. 34-38).

No description available.

There are some discrepancies in the literature regarding the response of the "induced waves" of the olfactory bulb to odorous stimuli. This work was designed to resolve the controversy by relating the different types of response to alertness of the animal and to concentration of the odour. The envelope of 40 Hz activity from the olfactory bulbs of unanaesthetised cats was recorded on a polygraph, and found to vary with respiration. The animal's nose projected into a stream of clean air to which odorant could be added at different fixed rates for about a minute at intervals. The amplitude of induced wave activity during the stimulus was compared to that shortly before it. Odour concentrations were varied within a 5 x 10⁶ -fold range and the logarithm taken. The alertness of the cat was estimated on a 5-point scale. The data for the middle alertness category were eliminated and those of the two extreme groups subjected to statistical analysis by multiple regression. The percentage change in integrated induced wave activity during stimulus as compared to that during control in a drowsy cat was found to be independent of stimulus concentration and could be in either direction but usually increased. In an aroused cat regression to a third order polynomial was statistically significant (p < 0.02) and accounted for 0.34 of the variability. This result appears surprisingly good in view of the enormous spontaneous variation in the signal and the unreliability of the stimulus, both as to its exact concentration and in the resemblance of its presentation parameters to a square wave. It would be worth while to repeat this study with more animals, more odours and a. better olfactometer design. The shape of the regression was predicted as follows. At low concentrations an alert cat would show an olfactory response in the form of a depression of induced waves. At intermediate concentrations an alarm response would sometimes increase alertness, augmenting the induced waves. At high concentrations the trigeminal-to-autonomic noxious vapour response would intervene, mechanically reducing access of air to olfactory receptors and/ or respiration. A drowsy cat on the other hand might be subject to alerting by any suprathreshold concentration, or could ignore the stimulus with or without perceiving it. Effects of non-olfactory stimuli and spontaneous variations were in fact far more obvious than most of the "olfactory responses". / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

The level of familiarity of a given stimulus plays an important role in memory processing. Indeed, the novelty/familiarity of learned material has been proven to affect the pattern of activations during recognition memory tasks. We used visually presented words to investigate the neural basis of recognition memory for relatively novel and familiar stimuli in schizophrenia. Subjects were 34 healthy volunteers and 19 schizophrenia spectrum patients. Two experimental cognitive conditions were used: 1 week and again 1 day prior to the PET imaging subjects had to thoroughly learn a list of 18 words (well-learned memory). Subjects were also asked to learn another set of 18 words presented 1 min before the PET experiment (novel memory). During the PET session, subjects had to recognize the list of 18 words among 22 new (distractor) words. Subjects also performed a control task (reading words). A nonparametric randomization test and a statistical t-mapping method were used to determine between- and within-group differences. In patients the recognition of novel material produced relatively less flow in several frontal areas, superior temporal gyrus, insular cortex, and parahippocampal areas, and relatively higher activity in parietal areas, visual cortex, and cerebellum, compared to controls. No significant differences in flow were seen when comparing well-learned memory activations between groups. These results suggest that different neural pathways are engaged during novel recognition memory in patients with schizophrenia compared to healthy individuals. During recognition of novel material, patients failed to activate frontal/limbic regions, recruiting a set of posterior perceptual brain regions instead.

No description available.

Body Dysmorphic Disorder (BDD) is a mental disorder where the patient is preoccupied with a misperceived deficit in their appearance. It is a common disorder (~2% prevalence worldwide), leaving the patients significantly disabled and distressed. Comorbid disorders such as social phobia, depression, and anxiety disorders appear frequently. Previous neuroimaging studies have found heterogeneous abnormalities in brain regions involved in visual and emotional processing when comparing BDD patients to healthy controls. Some of these areas are involved in limbic structures. The emotional limbic system (involved in emotion recognition, reward, social behaviour, and decision-making) and the memory hippocampal limbic system (involved in episodic memory, information about objects, faces, and spatial locations) have been stated as two separate neural systems. The aim of this systematic review was to analyse the neural correlates of BDD focusing on structural changes in limbic structures, and further investigate whether the emotional limbic circuit exclusively is affected or solely higher influenced than the rest of the limbic structures. Abnormalities in information processing due to aberrant WM connectivity was found, as well as that volumetric alterations in GM and WM tracts correlate with clinical symptomatology. The relationship between visual and emotional processing system abnormalities and BDD severity suggests an involvement of the emotional limbic system in BDD.