De acordo com Gray (1982) o sistema nervoso monitora o ambiente e o comportamento continuamente, sendo capaz de inibir o comportamento em curso quando se depara com novidades ou com discrepâncias entre expectativas geradas com base em memórias de regularidades passadas e a informação sensorial presente, de modo a explorar a fonte de novidade ou discrepância e, assim, obter informações que possibilitem gerar previsões melhores no futuro. O sistema septo-hipocampal compararia estímulos presentes com informações antecipadas (ou previstas). Tal sistema envolve um comparador, o subículo, que receberia informações do presente através de aferências neocorticais, via córtex entorrinal, e informações \"previstas\" geradas em um \"circuito gerador de previsões\". Gray (1982) propôs que esse circuito gerador de previsões inclui o subículo, os corpos mamilares, o tálamo anteroventral, o córtex cingulado e, novamente, o subículo. Destas estruturas, o tálamo anteroventral encontra-se em posição privilegiada, do ponto de vista hodológico e experimental, para investigar este postulado circuito gerador de previsões. O objetivo do presente trabalho foi investigar o efeito da lesão seletiva no tálamo anteroventral, pela aplicação tópica de ácido N-metil-D-aspártico (NMDA), sobre a habilidade de ratos extrapolarem a partir de padrões seriais de estímulos. Tampão fosfato foi aplicado em sujeitos controle. Ratos da linhagem Wistar, machos, foram treinados a correr em uma pista reta para receberem reforço ao seu final. Em cada sessão (uma sessão por dia), os animais correram 4 tentativas sucessivas, recebendo quantidades diferentes de sementes de girassol em cada tentativa. No padrão monotônico decrescente os sujeitos receberam 14, 7, 3 e 1 sementes de girassol, enquanto os sujeitos expostos ao padrão não-monotônico receberam 14, 3, 7 e 1 sementes de girassol. Os animais foram treinados ao longo de 31 sessões. No 32° dia do experimento, uma quinta tentativa, nunca antes experienciada pelos animais, foi adicionada à sessão. Como esperado, os tempos de corrida na quinta tentativa dos animais controle expostos ao padrão monotônico decrescente foram substancialmente maiores se comparados aos animais controle expostos ao padrão não-monotônico, indicando a ocorrência de extrapolação. Em contraste, os sujeitos lesados expostos ao padrão monotônico não exibiram esse aumento de latência na quinta corrida, indicando que esses animais não extrapolaram. Em conclusão, os resultados indicam que extrapolação a partir de padrões seriais de estímulos é prejudicada pela lesão seletiva do tálamo anteroventral / According to Gray (1982) the brain continuously monitors environment and behavior, being capable of inhibiting ongoing behaviors when facing novelty or detecting discrepancies involving predictions generated from memories of past regularities and the actual sensorial information, in order to explore the source of novelty and/or discrepancy, and thus to gather information for generating better predictions in the future. The septo-hippocampal system compares anticipated and present information. The comparator would be the subiculum. This brain structure would receive present information from neocortical afferents, via the entorhinal cortex, and expected information from a \"generator of predictions system\" including the subiculum, mammillary bodies, anteroventral thalamus, cingulate cortex and, again, the subiculum. The anteroventral thalamus is in a privileged position, both hodologically and experimentally, to allow investigation of this postulated generator of predictions system. This study investigated the effect of selective damage to the anteroventral thalamus, by topical application of N-Methyl-D-Aspartic acid (NMDA), on the ability of rats to extrapolate relying on serial stimulus patterns. Control subjects were injected with phosphate buffer. Male Wistar rats were trained to run through a straight alleyway to get rewarded. In each session (one session per day) the animal run four successive trials, one immediately after the other, receiving different amounts of sunflower seeds in each trial. While subjects exposed to the monotonic decremental schedule received 14, 7, 3, 1 sunflower seeds along trials, subjects exposed to the non-monotonic schedule received 14, 3, 7, 1 sunflower seeds. Subjects were trained along 31 sessions. Then, on the 32nd testing session, a fifth trial never experienced before by all subjects was included immediately after the fourth trial. As expected, running times on the fifth trial for Control subjects exposed to the monotonic schedule were significantly longer as compared to the corresponding scores of Control subjects exposed to the non-monotonic schedule, thus indicating the occurrence of extrapolation. In contrast, lesioned subjects exposed to the monotonic schedule did not exhibit this increase in running times on the fifth trial thus indicating that these subjects did not extrapolate. In conclusion, results indicate that extrapolation relying on serial stimulus patterns is disrupted following selective damage to the anteroventral thalamus

De acordo com Gray (1982) o sistema nervoso monitora o ambiente e o comportamento continuamente, sendo capaz de inibir o comportamento em curso quando se depara com novidades ou com discrepâncias entre expectativas geradas com base em memórias de regularidades passadas e a informação sensorial presente, de modo a explorar a fonte de novidade ou discrepância e, assim, obter informações que possibilitem gerar previsões melhores no futuro. O sistema septo-hipocampal compararia estímulos presentes com informações antecipadas (ou previstas). Tal sistema envolve um comparador, o subículo, que receberia informações do presente através de aferências neocorticais, via córtex entorrinal, e informações \"previstas\" geradas em um \"circuito gerador de previsões\". Gray (1982) propôs que esse circuito gerador de previsões inclui o subículo, os corpos mamilares, o tálamo anteroventral, o córtex cingulado e, novamente, o subículo. Destas estruturas, o tálamo anteroventral encontra-se em posição privilegiada, do ponto de vista hodológico e experimental, para investigar este postulado circuito gerador de previsões. O objetivo do presente trabalho foi investigar o efeito da lesão seletiva no tálamo anteroventral, pela aplicação tópica de ácido N-metil-D-aspártico (NMDA), sobre a habilidade de ratos extrapolarem a partir de padrões seriais de estímulos. Tampão fosfato foi aplicado em sujeitos controle. Ratos da linhagem Wistar, machos, foram treinados a correr em uma pista reta para receberem reforço ao seu final. Em cada sessão (uma sessão por dia), os animais correram 4 tentativas sucessivas, recebendo quantidades diferentes de sementes de girassol em cada tentativa. No padrão monotônico decrescente os sujeitos receberam 14, 7, 3 e 1 sementes de girassol, enquanto os sujeitos expostos ao padrão não-monotônico receberam 14, 3, 7 e 1 sementes de girassol. Os animais foram treinados ao longo de 31 sessões. No 32° dia do experimento, uma quinta tentativa, nunca antes experienciada pelos animais, foi adicionada à sessão. Como esperado, os tempos de corrida na quinta tentativa dos animais controle expostos ao padrão monotônico decrescente foram substancialmente maiores se comparados aos animais controle expostos ao padrão não-monotônico, indicando a ocorrência de extrapolação. Em contraste, os sujeitos lesados expostos ao padrão monotônico não exibiram esse aumento de latência na quinta corrida, indicando que esses animais não extrapolaram. Em conclusão, os resultados indicam que extrapolação a partir de padrões seriais de estímulos é prejudicada pela lesão seletiva do tálamo anteroventral / According to Gray (1982) the brain continuously monitors environment and behavior, being capable of inhibiting ongoing behaviors when facing novelty or detecting discrepancies involving predictions generated from memories of past regularities and the actual sensorial information, in order to explore the source of novelty and/or discrepancy, and thus to gather information for generating better predictions in the future. The septo-hippocampal system compares anticipated and present information. The comparator would be the subiculum. This brain structure would receive present information from neocortical afferents, via the entorhinal cortex, and expected information from a \"generator of predictions system\" including the subiculum, mammillary bodies, anteroventral thalamus, cingulate cortex and, again, the subiculum. The anteroventral thalamus is in a privileged position, both hodologically and experimentally, to allow investigation of this postulated generator of predictions system. This study investigated the effect of selective damage to the anteroventral thalamus, by topical application of N-Methyl-D-Aspartic acid (NMDA), on the ability of rats to extrapolate relying on serial stimulus patterns. Control subjects were injected with phosphate buffer. Male Wistar rats were trained to run through a straight alleyway to get rewarded. In each session (one session per day) the animal run four successive trials, one immediately after the other, receiving different amounts of sunflower seeds in each trial. While subjects exposed to the monotonic decremental schedule received 14, 7, 3, 1 sunflower seeds along trials, subjects exposed to the non-monotonic schedule received 14, 3, 7, 1 sunflower seeds. Subjects were trained along 31 sessions. Then, on the 32nd testing session, a fifth trial never experienced before by all subjects was included immediately after the fourth trial. As expected, running times on the fifth trial for Control subjects exposed to the monotonic schedule were significantly longer as compared to the corresponding scores of Control subjects exposed to the non-monotonic schedule, thus indicating the occurrence of extrapolation. In contrast, lesioned subjects exposed to the monotonic schedule did not exhibit this increase in running times on the fifth trial thus indicating that these subjects did not extrapolate. In conclusion, results indicate that extrapolation relying on serial stimulus patterns is disrupted following selective damage to the anteroventral thalamus

The anterior thalamic nuclei (ATN) are a critical part of an extended hippocampal system that supports key elements of episodic memory. Damage or disconnection of the ATN is a component of clinical conditions associated with severe anterograde amnesisa such as the Korsakoff’s syndrome, thalamic stroke, and neurodegenerative disorders. Previous studies have demonstrated that the ATN and hippocampus are often interdependent, and that ATN damage can result in ‘covert pathology’ in ostensibly healthy distal regions of the extended hippocampal system. Adult male rats with neurotoxic bilateral ATN lesions or sham surgery were post-operatively housed in an enriched environment or standard housing after a lesion-induced spatial working memory deficit had been established. These rats were retested on cross-maze and then trained in radial-arm maze spatial memory tasks. Other enriched rats received pseudo-training only after the enrichment period. The detailed neuromorphology of neurons was subsequently examined in the hippocampal CA1. Soma characteristics were also examined in the retrosplenial granular b cortex and the prelimbic cortex. In Experiment 1, ATN lesions produced clear deficits in both the cross-maze and radial-arm maze tasks and reduced hippocampal CA1 dendritic complexity, length, and spine density, while increasing the average diameter of the dendrites. Post-operative enrichment reversed the ATN lesion-induced deficits in the cross-maze and radial-arm maze, and returned CA1 basal and apical spine density to a level comparable to that of sham standard housed trained rats. The sham enriched rats exhibited improved radial-arm maze performance and increased CA1 branching complexity and spine density in both basal and apical arbors compared to sham standard housed rats. The neuromorphological changes observed in the enriched ATN and sham rats may be in part responsible for the spatial working memory improvements observed. Experiment 2 provided support for this contention by demonstrating that the CA1 spine changes were explicitly relevant to spatial learning and memory, because trained enriched sham and ATN rats had increased spines, particularly in the basal tree when compared to closely comparable pseudo-trained enriched rats. Interestingly, spatial memory training increased the numbers of both thin and mushroom spines, whereas enrichment was only associated with an increase in thin spines. In Experiment 3, ATN lesions increased cell body size in layer II of the retrosplenial granular b cortex, whereas enrichment decreased cell body size in layer V of this region. Neither ATN lesions nor enrichment had any effect on cell body morphology in the prelimbic cortex. The current research provides some of the strongest evidence to date of ATN and hippocampal interdependence within the extended hippocampal system, and provides the first evidence of neuromorphological correlates of recovery after ATN lesions.