Thesis (M.A.)--University of Toronto, 2004. / Includes bibliographical references (leaves [33]-40).

Thesis (Ph. D. in Psychology)--Vanderbilt University, Dec. 2008. / Title from title screen. Includes bibliographical references.

This thesis investigated the role of the anterior temporal lobes (ATLs) in conceptual knowledge and name relearning by studying people with semantic dementia (SD). People with SD have atrophy focussed on the ATLs and they exhibit a pan-modal semantic impairment (e.g., Hodges, Patterson, Oxbury, & Funnell, 1992). Recent evidence suggests that modality-invariant concept representations are built up in the ATLs and that these modality-invariant representations are crucial for abstracting away from the surface features of items in order to generalise conceptual information based on their core semantic similarity (e.g., Lambon Ralph & Patterson, 2008). In order to test this, two of the studies described in this thesis (Chapters 2 and 3) assessed semantic generalisation in people with SD. These studies showed that people with SD are less able to generalise conceptual information on the basis of the deeper semantic structure of concepts but instead are increasingly influenced by the superficial similarity of the items. These studies support the hypothesis that the modality-invariant representations formed in the ATLs are crucial for semantic-based generalisation. Previous SD relearning studies have reported relatively good learning but a lack of generalisation to untrained items, tasks, and/or contexts (i.e., under-generalisation). This has been interpreted based on the Complementary Learning Systems (CLS) (McClelland, McNaughton, & O'Reilly, 1995) to suggest that the neocortical semantic system no longer makes a meaningful contribution to relearning but instead relearning is primarily dependent upon the sparse representational medial temporal lobe (MTL) learning system. The studies described in two of the thesis chapters (Chapters 4 and 5) investigated the role of the underlying systems further and found that the neocortical semantic system does still contribute to relearning in SD (although its contribution is disordered and based on the degraded concept representations in the ATL) but there is a shift in the division of labour such that the MTL system takes over more of the work. Finally, in order to clarify the outcomes of relearning in SD, Chapter 6 reviewed all of the previous SD relearning studies and confirmed that people with SD are able to relearn the specific information that they study but that this relearning is rigid. The review and a subsequent re-analysis of the data from Chapters 4 and 5 also showed that relearning in SD can have negative side-effects as well as positive effects.

Cigarette smoking is an addictive behavior. There are two learned emotional responses to smoking that may be particularly important for promoting addiction to smoking: the pleasure obtained from the airway sensory effects of smoking (airway sensory pleasure) and the urge to smoke that is elicited by environmental smoking cues (cue-induced urge). The ventromedial prefrontal cortex (VMPFC) has been implicated in a variety of learned emotional and motivational responses to drug-associated sensory cues. This project set out to address the role of the VMPFC and related areas in airway sensory pleasure and cue-induced urge, as well as the role of this region in promoting smoking behavior in real life, by examining the effects of focal lesions within the VMPFC and related areas in human cigarette smokers. It was found that lesions of the VMPFC itself were associated with a marked impairment of cue-induced urge in the laboratory, which was paralleled by a reported reduction in the difficulty of abstaining from smoking in real life. At the same time, VMPFC lesions led to a relative sparing of airway sensory pleasure in the laboratory, which was paralleled by no change in the enjoyment from smoking in real life. In addition, it was found that VMPFC lesions were not associated with changes in real-life measures of smoking dependence. It was found that lesions of the insula, a region that is functionally related to the VMPFC, were associated with an ability to quit smoking easily, immediately, without relapses and without a lasting urge to smoke. However, among patients with insula lesions who continued to smoke after lesion onset, there were no appreciable impairments of airway sensory pleasure or cue-induced urge. The results suggest that, while VMPFC lesions may disrupt cue-induced urges, they do not disrupt dependence upon smoking. This may be because VMPFC lesions spare more implicit motivational processes, such as "habits" and "incentive salience," that can drive smoking behavior in the absence of a conscious desire to smoke. The results also suggest that the insula functions in psychological processes that may contribute to the difficulty of quitting smoking.

Background: Most of the neurocognitive research in Posttraumatic Stress Disorder (PTSD) thus far focused on impairment in learning and memory, neglecting the impact of PTSD on executive functioning processes. Therefore, this study specifically aims to investigate the impact of PTSD on frontal lobe executive functioning. Given the high prevalence rate for traumatic event exposure in South Africa, this study provides important findings on the role intact executive functioning plays in all areas of daily functioning, including the maintenance of good mental and physical health. Methods: Executive functions were assessed using an Executive Functioning Battery consisting of the three subtests of the Delis Kaplan Executive Functioning System (e.g., Trail Making Test, Colour-Word Interference Test, and Tower Test), as well as the Executive Functioning Index. The study sample consisted of 88 adult South African citizens who were divided into two groups (PTSD+; n = 44; PTSD–; n = 44) with different levels of trauma exposure. Results: PTSD was linked with impairment in executive functioning domains such as attention, cognitive flexibility, inhibition, working memory, and planning. Important gender differences were also reported in terms of empathy and organisation. In addition, education also appeared to affect frontal lobe executive functioning differently. Conclusions: The data suggest that overall, PTSD impaired executive functioning processes. It is therefore critical that assessment of executive functioning form part of a comprehensive treatment plan for individuals diagnosed with PTSD. / Mini Dissertation (MA)--University of Pretoria, 2019. / Psychology / MA / Unrestricted

One of the few areas in the brain that still exhibits experience-dependent neuroplasticity in adulthood is found in the medial temporal lobe (MTL) system. Within the MTL, this plasticity has been observed in the hippocampus in both humans and animal models. Rodent model studies focusing on the effect of aerobic exercise have shown a positive increase of neuroplasticity in the dentate gyrus subregion of the hippocampus. Another area in the MTL, the entorhinal cortex (EC), serves as a primary input to the hippocampus, and studies on environmental enrichment have reported greater EC volume in rodents supplied with toys and running wheels. Previous work in our lab working with healthy young adults showed a positive correlation between right EC volume, and aerobic fitness (VO2 max). In this thesis, I examined two aims, first whether aerobic fitness predicts changes in thickness or volume of the MTL as well as performance in an MTL dependent task in healthy young adults. Additionally, whether the brain morphology measures of the MTL can predict performance on the memory task. The second aim looks at the longitudinal effect a 12-week exercise intervention has on thickness or volume in the MTL and performance on an MTL dependent task in the same population. Results indicate that there is a positive baseline correlation between aerobic fitness and thickness of the EC on the left hemisphere but there are no longitudinal changes in morphology after the exercise intervention. These data extend previous work on the effects aerobic exercise has on MTL structure and offer interesting venues to combat neurodegenerative diseases that affect the MTL memory system like Alzheimer’s disease.

The question of how we form memories has fascinated scientists for decades. The hippocampus and surrounding medial-temporal-lobe (MTL) structures are critical for both memory and spatial navigation, yet we do not fully understand the neuronal representations used to support these behaviors. Much research has examined how the MTL neurally represents spatial information, such as with “place cells” that represent an animal’s current location or “head-direction cells” that code for an animal’s current heading. In addition to attending to current spatial locations, navigating to remote destinations is a common part of daily life. In this dissertation I investigate how the human MTL represents the relevant information in a goal-directed spatial-memory task. Specifically, I analyze single-neuron and local field potential (LFP) data from neurosurgical patients with respect to their spatial navigation and memory behavior, with a focus on probing the link between neuronal firing, oscillations, and memory. In Chapter 2, I find that the firing rates of many MTL neurons during navigation significantly change depending on the position of the current spatial target. In addition, I observe neurons whose firing rates during navigation are tuned to specific heading directions in the environment, and others whose activity changes depending on the timing within the trial. By showing that neurons in our task represent remote locations rather than the subject’s own position, my results suggest that the human MTL can represent remote spatial information according to task demands. In Chapter 3, I find that during encoding the left hippocampus exhibits greater low theta power for subsequently recalled items compared to unrecalled items. I also find that high frequency activity and neuronal firing in the hippocampus distinguish between item-filled compared to empty chests. Finally, I find that MTL cells’ firing rates and the differential timing of spikes relative to low frequency oscillations in the LFP distinguish between subsequent recall conditions. These results provide evidence for a distinct processing state during the encoding of successful spatial memory in the human MTL. Overall, in this thesis I show new aspects of the neural code for spatial memories, and how the human MTL supports these representations.

No description available.

De récentes études suggèrent que les problèmes d'ordre attentionnel observés dans le Trouble d'Attention et d'Hyperactivité (TAH) chez l'enfant pourraient être imputés à une dynamique inhibitrice déficitaire, processus qui seraient de toute évidence d'origine corticale préfrontale. Dans le but de tester, à la fois, la mécanique inhibitrice de ces enfants hyperactifs, le fonctionnement d'ordre frontal ainsi que les possibles associations entre ces deux activités complexes, trois tests ont été administrés à deux groupes d'enfants Cn=l8), soit un groupe d'enfants TAH, et un groupe témoin, sans diagnostic. Le Stroop Color-Word Test, en version informatisée, a été employé pour mesurer la performance inhibitrice dans une tâche attentionnelle classique, alors que le Wisconsin Card Sorting Test et le Sequential Matching Memory Task, en version informatisée, ont constitué le volet évaluatif frontal. Les résultats obtenus suggèrent un déficit significatif d'attention sélective ainsi que des performances inférieures au niveau de ·l'intensité et de la durée des processus inhibiteurs chez les enfants TAH. On retrouve également, chez ce dernier groupe, un taux significativement plus élevé d'erreurs frontales. Toutefois,aucune relation significative n'est observée entre ces deux processus déficitaire chez le groupe TAH. La discussion s'oriente autour de la spécificité des mesures employées ainsi que du fonctionnement cognitif particulier des enfants TAH. Diverses explications théoriques ainsi que certaines avenues de recherches futures sont avancées.

Chez les abeilles domestiques, les neurones à récepteurs olfactifs hébergés dans les antennes sont des neurones sensoriels primaires responsables de la détection des odeurs et des phéromones. L'information olfactive est ensuite acheminée par les nerfs antennaires jusqu'aux lobes antennaires qui constituent le premier étage d'intégration de l'information olfactive. Les abeilles butineuses sont exposées aux insecticides, notamment ceux de la classe des pyréthrinoïdes, qui sont utilisés pour la protection des plantes et la lutte contre les insectes considérés comme étant nuisibles.Nous avons caractérisé l'effet des pyréthrinoïdes sur les canaux sodiques activés par le potentiel (responsables des potentiels d'action) dans les deux premiers étages du système olfactif de l'abeille. Nos enregistrements électrophysiologiques en mode potentiel imposé dans les neurones à récepteurs olfactifs mis en culture révèlent que l'effet des pyréthrinoïdes de type I et II (notamment la tétraméthrine et la deltaméthrine) est amplifié par une intensification de l'activité électrique neuronale. Cette amplification survient notamment via le démasquage de canaux sodiques silencieux que nous avons également mis en évidence avec la toxine d'anémone de mer ATX-II. Le niveau maximal de canaux sodiques modifiés est atteint en quelques centaines de millisecondes. Dans les neurones centraux des lobes antennaires, cette amplification apparait très limitée voire absente avec les pyréthrinoïdes mais elle peut toutefois survenir en présence de l'alcaloïde végétal vératridine. Par ailleurs, dans ces neurones centraux, les pyréthrinoïdes semblent être à l’origine d’une accélération de l'inactivation lente des canaux sodiques auparavant décrite en présence de certains anesthésiques locaux. Les modifications différentielles observées dans les neurones périphériques et centraux pourraient être responsables des effets délétères des pyréthrinoïdes sur les capacités de perception, d'orientation et d'apprentissage de l'abeille domestique. / In domestic honeybees, the olfactory receptor neurons localized in the antennae are primary sensory neurons responsible for the detection of odor and pheromone compounds. The olfactory information is further conveyed to the antennal lobes by the antennal nerves. The antennal lobes are the first stage of integration of the olfactory information. Forager bees are exposed to insecticides, especially pyrethroids that are used for plant protection and eradication of pests.In the honeybee olfactory pathway, we investigated the effects of pyrethroids on the voltage-gated sodium channels (which underlie action potentials). Our patch-clamp recordings in the antennal olfactory receptor neurons maintained in cell culture reveal that the effects of type I and type II pyrethroids (e.g. tetramethrin and deltamethrin) are increased by an augmentation of neuronal electrical activity. The amplification of the effects of pyrethroids occurs as a result of the unmasking of silent sodium channels that we have also shown evidence for, with sea anemone toxin ATX-II. The maximal sodium channels modification takes place within few hundreds of milliseconds. In the central antennal lobe neurons, that amplification is rather limited or absent with pyrethroids but the plant alkaloid veratridine is able to induce such an amplification. Furthermore, in the latter cell type, pyrethroids cause an acceleration of the sodium channels slow inactivation. Such an effect has been previously reported for some local anesthetics. The differential actions of pyrethroids that we have observed in the peripheral and central neurons may be responsible for the impairment of learning performance, perception and disorientation exhibited by pyrethroid-exposed honeybees.