Recent electrophysiological studies have shown that electrical brain stimulation (EBS) can produce lasting increases in synaptic efficacy, defined as the quantitative relationship between pre- and postsynaptic activity. However, the behavioural significance of this long-term potentiation (LTP) has yet to be demonstrated clearly. The principal objective of this thesis was to determine whether increased synaptic efficacy, produced by high-frequency EBS, enhances behavioural responses to a fixed amount of presynaptic activity. Following identification of EBS parameters capable of monitoring synaptic efficacy for long periods without producing LTP, a paradigm was developed in which a single-pulse of EBS in the perforant path (PP) acquired stimulus control over the temporal pattern of operant responses. In this paradigm, postsynaptic evoked potentials in the dentate gyrus (DG) produced by the PP EBS were used to monitor synaptic efficacy on every trial of conditioning and also to measure one component of the neural activity generated by the EBS stimulus controlling the operant responses. In Experiment 3, high-frequency stimulation of the PP produced- LTP at the PP-DG synaptic interface and facilitated subsequent acquisition of stimulus control by the single pulse PP EBS. This effect could not have been due to sensitization or to the stimulus properties of the high-frequency trains. The final experiment confirmed the importance of the EBS-evoked activity in the DG to the stimulus control by the PP EBS. The rate of acquisition was directly related to the magnitude of the evoked potentials and two-stage bilateral lesions of the PP in a specific sequence reduced the probability of behavioural responses to the EBS. Taken together, these results indicate that the behavioural consequence of excitatory neural activity can be enhanced by an increase in synaptic efficacy. As such, they provide considerable support for the validity of LTP as a model of neural changes subserving learning and for physiological theories of memory based on modifications in the- strength of synaptic connections. / Arts, Faculty of / Psychology, Department of / Graduate

Orientador: Elenice Aparecida de Moraes Ferrari / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-06T20:47:31Z (GMT). No. of bitstreams: 1 Siqueira_LuisOtavio_D.pdf: 1043861 bytes, checksum: 39ebfc094cde948f0af9f82213528298 (MD5) Previous issue date: 2006 / Resumo: O comportamento exploratório garante a inspeção, a localização, a identificação e a avaliação precisa de eventos ambientais. A exploração também é abordada como sendo relacionada com a curiosidade do animal direcionada a novos estímulos. Os comportamentos reflexos que precedem as reações exploratórias, caracterizando-se, portanto, como comportamentos pré-exploratórios e também têm importante função adaptativa. Poucos estudos analisaram a influência da hora do dia sobre respostas incondicionadas e condicionadas ao som. Dessa forma, o presente estudo investigou a variação circadiana da amplitude da resposta aversiva ao som em pombos. Experimento I usou um equipamento de registro automatizado da amplitude da resposta acústica, formado por uma câmara experimental, com uma célula de carga acoplada ao piso e interface dos sinais a um microcomputador utilizado para controle, armazenamento e análise dos dados. O Experimento II analisou a sensibilização da resposta em diferentes horários do dia usando: (a) linha de base com apresentação de 5 estímulos acústicos com intervalo entre sons de 3Os; (b) treino, iniciado 5 min após o último som, com dois choques elétricos, intervalo entre choques de 5 min e (c) teste, iniciado 10 min após o último choque, com 40 estímulos acústicos. Os animais dos grupos controles permaneceram na caixa experimental sem estimulação. O Experimento 111 usou intervalos (a) entre o término da linha de base e o início do treino, (b) entre os dois choques e (c) entre o último choque e o teste foram de 1 mino O Experimento IV investigou o condicionamento clássico de traço, utilizando grupos: Experimental, com três associações som-choque; Randômico, com 3 choques e 3 sons casualizados e Controle, expostos à caixa experimental.Em todos os experimentos usou-se fotoperíodo esqueleto com pulsos de luz (15 min) às 6h (ZTOO) e às 18h (ZT12) e sub-grupos em cada horário de teste: ZT02, ZT06, ZT10, ZT14, ZT18 e ZT22. De um modo geral, os dados mostraram que tanto a sensibilização quanto o condicionamento clássico aversivo resultaram em alterações da amplitude da resposta ao som que variaram em função do horário de teste, com amplitudes máximas na transição dia-noite e mínimas na transição noite-dia. O conjunto desses dados indica a modulação do aprendizado aversivo pelo sistema temporizador circadiano / Abstract: Exploratory behavior allows the inspection, localization, identification and the correct evaluation of the environmental events. The exploration also is related with curiosity related to new stimuli. The reflex behaviors that preceed the exploratory reactions are characterized as pre- exploratory and also have an important adaptative function. There are few studies that analyse the influence of time of the day on this response. Thus, the present study investigated the circadian variation of response to aversive sounds in pigeons. Experiment I, used a new equipment especially designed for automatic recording of response of acoustic response amplitude. The system is composed by an experimental chamber, with a load cell under the floor and a computer interface for contrai, storage and data analysis. Experiment 11 analyzed the sensitization of sound response in different times of the day. The experimental protocol used: (a) baseline with 5 acoustic stimulus presentation with inter-stimulus-interval between sounds of the 30s; (b) training, starting 5 min afier the last sound, with apresentation of two electric shocks with interval between electric shocks of the 5 min and (c) test, starting 10 min afier the last shock, with 40 acoustic stimuli. The Control Group animais received no stimulation. Experiment 11I, used 1 min time intervals between (a) the end of the baseline and the trainning, (b) the two electric shocks and (c) the last electric shock and test. Experiment IV investigated the trace fear conditioning, using 2 groups: Experimental, with 3 sound shock associations; Random, with 3 shocks and 3 sounds in the random arder and Contrai, only exposed to experimental chamber. Ali the experiments used a skeleton photoperiod with 2 light pulses (15 min) to 6h (ZTOO) and 18h (ZT12) and sub-groups for each time of test: ZT02, ZT06, ZT10, ZT14, ZT18 and ZT22. In a general, the data showed that both sensitization and classical fear conditioning resulted in increases of the amplitude of sound responses with variations depending on the time of the test. Taken together, the data indicated a modulation of aversive leaming by the circadian pacemaker / Doutorado / Fisiologia / Doutor em Biologia Funcional e Molecular

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Regular aerobic exercise has a wide range of positive effects on health and cognition. Exercise has been demonstrated to provide a particularly powerful and replicable method of triggering a wide range of structural changes within both human and animal brains. However, the details and mechanisms of these changes remain poorly understood. This thesis undertakes a comprehensive examination of the relationship between brain plasticity and aerobic exercise. A large, longitudinal experiment was conducted in which healthy but sedentary participants were scanned before and after six-weeks of monitored aerobic exercise. Increases in the volume of the anterior hippocampus were observed, as previously reported in an older cohort after a longer exercise intervention. Multimodal imaging methods allowed an in-depth exploration of the mechanisms underlying this volume change, which proved to be dominated by white matter changes rather than the vascular changes that have been previously reported. A surprising global change in the balance of CSF, blood, and brain tissue within the cranial cavity was also observed. Cross-sectional differences in memory and brain structure associated with fitness were also observed. The volume of the anterior hippocampus was shown to correlate with a measure of working memory. Higher cerebral blood volume throughout the brain was found to correlate with greater fitness and better working memory. Focal associations between fitness and magnetic susceptibility, a measure of iron content, were also observed in the basal ganglia. These findings demonstrate that aerobic fitness is associated with improved cognition and brain structure throughout the lifespan rather than simply acting to mitigate age related brain atrophy or accelerate brain development. Finally, a new pipeline was developed for analysing hippocampal morphometry using high-resolution, 7 Tesla scans. Striking variability in the convolution of the hippocampal surface is reported. This technique shows promise for imaging the precise nature of the change in hippocampal volume associated with aerobic exercise. This thesis adds to the evidence that aerobic exercise is a potent catalyst for behavioural and brain plasticity while also demonstrating that the mechanisms for those plastic changes are likely different than previously supposed. Future work will refine these measurement techniques, perhaps to a point where brain changes can be monitored on a single subject level. This work will provide an important tool to understand how best to utilize aerobic exercise to facilitate adaptive behavioural changes, mitigate the negative effects of ageing and disease on the brain, and maximize the benefits of active lifestyles.

In this study human color constancy was tested for two-dimensional (2D) and three-dimensional (3D) setups with real objects and lights. Four different illuminant changes, a natural selection task and a wide choice of target colors were used. We found that color constancy was better when the target color was learned as a 3D object in a cue-rich 3D scene than in a 2D setup. This improvement was independent of the target color and the illuminant change. We were not able to find any evidence that frequently experienced illuminant changes are better compensated for than unusual ones. Normalizing individual color constancy hit rates by the corresponding color memory hit rates yields a color constancy index, which is indicative of observers' true ability to compensate for illuminant changes.

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