Navegando por Autor "Belchior, Hindiael"
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Apresentado em Evento Codificação de localização e identidade de objetos em populações neuronais do hipocampo e do córtex cingulado anterior(2010-09) Belchior, Hindiael; Barbosa, Flávio Freitas; Lemos, Nelson; Silva, Regina; Ribeiro, Sidarta Tollendal GomesDiversos estudos sugerem o envolvimento do hipocampo e do córtex cingulado anterior na aquisição de memórias episódicas. No entanto, pouco se sabe sobre o modo como estruturas codificam informações complexas acerca do contexto de um ambiente. O objetivo deste trabalho é avaliar como neurônios dessas estruturas respondem durante a exploração de dois conjuntos de objetos em uma arena familiar. Duas matrizes de microeletrodos foram cirurgicamente implantadas para registros crônicos da atividade de neurônios isolados e do potencial de campo local na sub-região CA1 do hipocampo dorsal direito e bilateralmente no córtex cingulado anterior de um rato Wistar macho (~300g). Após 10 dias de recuperação, o animal foi submetido a duas sessões de 10 minutos de exploração de um campo aberto circular intervaladas por 90 minutos numa caixa de dormir à qual o animal estava previamente habituado. No dia seguinte, quatro cópias do objeto A foram introduzidas no campo para a exploração da primeira sessão. Após 90 minutos na caixa de dormir, o animal foi re-exposto ao campo com quatro cópias do objeto B, das quais duas foram colocadas nos mesmos locais dos objetos A na primeira sessão de exploração. O comportamento foi continuamente monitorado por um sistema de vídeo que sincroniza a posição do animal ao registro de dados neurais. A atividade de 37 neurônios foi registrada em cada sessão experimental, dos quais 14 foram hipocampais e 23 corticais. Observamos um neurônio hipocampal que aumenta a taxa de disparos apenas para o objeto A em uma posição específica, o qual denominamos ‘neurônio item-posição’ (teste t; p<0,05). Este mesmo neurônio não responde a objetos A posicionados em diferentes locais, nem a um objeto B na posição onde estava A. Além disso, verificamos que o neurônio item-posição é fortemente modulado por oscilações teta hipocampais (6-10 Hz; teste de Rayleigh, p<0,01). Como esperado, os neurônios corticais não codificaram as diferentes localizações dos objetos. Por outro lado, ao compararmos diferentes itens (AxB) localizados em uma mesma posição entre as sessões, observamos que três neurônios hipocampais e dois neurônios corticais apresentaram diferenças de taxa de disparo de acordo com a identidade do objeto. Contudo, verificamos que os neurônios que codificam apenas a identidade do objeto não sofreram modulação por oscilações teta. Nossos resultados preliminares sugerem que o hipocampo e o córtex cingulado anterior estão envolvidos na formação de memórias episódicas e na identificação de objetos. Regidos por oscilações teta, neurônios hipocampais codificam identidade e posição do objeto. Além disso, tanto neurônios hipocampais como corticais codificam a identidade dos objetos. Assim, mesmo durante breves exposições a diferentes conjuntos de objetos, neurônios do hipocampo dorsal e cingulado anterior codificam respectivamente o local e a identidade de objetos em um campo aberto.Artigo Cross-modal responses in the primary visual cortex encode complex objects and correlate with tactile discrimination(2011-09-13) Vasconcelos, Nivaldo; Pantoja, Janaina; Belchior, Hindiael; Caixeta, Fábio Viegas; Faber, Jean; Freire, Marco Aurelio M.; Cota, Vinícius Rosa; Macedo, Edson Anibal de; Laplagne, Diego Andrés; Gomes, Herman Martins; Ribeiro, Sidarta Tollendal GomesCortical areas that directly receive sensory inputs from the thalamus were long thought to be exclusively dedicated to a single modality, originating separate labeled lines. In the past decade, however, several independent lines of research have demonstrated cross-modal responses in primary sensory areas. To investigate whether these responses represent behaviorally relevant information, we carried out neuronal recordings in the primary somatosensory cortex (S1) and primary visual cortex (V1) of rats as they performed whiskerbased tasks in the dark. During the free exploration of novel objects, V1 and S1 responses carried comparable amounts of information about object identity. During execution of an aperture tactile discrimination task, tactile recruitment was slower and less robust in V1 than in S1. However, V1 tactile responses correlated significantly with performance across sessions. Altogether, the results support the notion that primary sensory areas have a preference for a given modality but can engage in meaningful cross-modal processing depending on task demand.Apresentado em Evento Hippocampal Theta Oscillations and Cross-Frequency Coupling during Spatial Decision-Making(2014-09) Belchior, Hindiael; Souza, Bryan; Santos, Vítor Lopes dos; Ribeiro, Sidarta Tollendal Gomes; Tort, Adriano Bretanha LopesIntrodução The processing of spatial and mnemonic information is believed to depend on hippocampal theta oscillations (512 Hz). However, in rats both the power and frequency of the theta rhythm are modulated by locomotor activity, which is a major confounding factor when estimating its cognitive correlates. Previous studies have suggested that hippocampal theta oscillations and its modulation of higher frequency rhythms support decisionmaking processes. Objetivos In the present study, we investigated to what extent spatial decisionmaking modulates hippocampal theta oscillations when controlling for variations in locomotion speed. In addition, we measured how the amplitude of lowgamma (2550 Hz), high-gamma (6090 Hz), and highfrequency oscillations (>100 Hz) is modulated by the phase of theta oscillations (crossfrequency coupling). Métodos We recorded local field potentials from the CA1 region of 5 male Wistar rats while animals had to choose one arm to enter for reward (goal) in a fourarm radial maze. The animals were previously trained to achieve 70% of correct choices and four sessions were used to the analyses. We then analyzed intervals of intertrial period (DELAY), decisionmaking (DM), and running to reward (RUN). Trials with similar locomotion speed were used to compare theta power across intervals. We measured crossfrequency coupling within each interval and temporally triggered to the end of DM. Resultados e Conclusões We observed prominent theta oscillations and strong phase modulation of gamma amplitude during DM interval of the task, which occurred in the center of the maze before animals deliberately ran through an arm towards goal location. In speed-controlled analyses, theta power and frequency were higher during the decision period when compared to either an intertrial delay period (also at the maze center), or to the period of running towards goal location (p<0.05, twoway ANOVA followed by Tukey's post hoc test). Moreover, theta activity was higher during decision intervals preceding correct choices than during decision intervals preceding incorrect choices (p<0.05, Student's ttest). Altogether, our data support a cognitive function for the hippocampal theta rhythm in spatial decisionmaking.Artigo Increase in Hippocampal Theta Oscillations during Spatial Decision Making(2014-02) Belchior, Hindiael; Lopes-dos-Santos, Vitor; Tort, Adriano Bretanha Lopes; Ribeiro, Sidarta Tollendal GomesArtigo On High-Frequency Field Oscillations ( 100 Hz) and the Spectral Leakage of Spiking Activity(2013-01-23) Scheffer-Teixeira, Robson; Belchior, Hindiael; Leão, Richardson Naves; Ribeiro, Sidarta Tollendal Gomes; Tort, Adriano Bretanha LopesRecent reports converge to the idea that high-frequency oscillations in local field potentials (LFPs) represent multiunit activity. In particular, the amplitude of LFP activity above 100 Hz—commonly referred to as “high-gamma” or “epsilon” band—was found to correlate with firing rate. However, other studies suggest the existence of true LFP oscillations at this frequency range that are different from the well established ripple oscillations. Using multisite recordings of the hippocampus of freely moving rats, we show here that high-frequency LFP oscillations can represent either the spectral leakage of spiking activity or a genuine rhythm, depending on recording location. Both spike-leaked, spurious activity and true fast oscillations couple to theta phase; however, the two phenomena can be clearly distinguished by other key features, such as preferred coupling phase and spectral signatures. Our results argue against the idea that all high-frequency LFP activity stems from spike contamination and suggest avoiding defining brain rhythms solely based on frequency range.Artigo On information metrics for spatial coding(2018-04-01) Souza, Bryan C.; Pavão, Rodrigo; Belchior, Hindiael; Tort, Adriano Bretanha LopesThe hippocampal formation is involved in navigation, and its neuronal activity exhibits a variety of spatial correlates (e.g., place cells, grid cells). The quantification of the information encoded by spikes has been standard procedure to identify which cells have spatial correlates. For place cells, most of the established metrics derive from Shannon's mutual information (Shannon, 1948), and convey information rate in bits/s or bits/spike (Skaggs et al., 1993, 1996). Despite their widespread use, the performance of these metrics in relation to the original mutual information metric has never been investigated. In this work, using simulated and real data, we find that the current information metrics correlate less with the accuracy of spatial decoding than the original mutual information metric. We also find that the top informative cells may differ among metrics, and show a surrogate-based normalization that yields comparable spatial information estimates. Since different information metrics may identify different neuronal populations, we discuss current and alternative definitions of spatially informative cells, which affect the metric choice.Apresentado em Evento Processamento metamodal no córtex sensorial primario de ratos(2010-09) Caixeta, Fábio Viegas; Belchior, Hindiael; Laplagne, Diego Andrés; Freire, Marco; Nicolelis, Miguel; Ribeiro, Sidarta Tollendal GomesO modelo de processamento sensorial mais aceito atualmente afirma que os sentidos são processados em paralelo, e que a atividade de córtices sensoriais específicos define a modalidade sensória percebida subjetivamente. Neste trabalho investigamos se neurônios nos córtices primários visual (V1) e somestésico (S1) podem responder a estímulos das modalidades sensoriais cruzadas. Seis ratos machos adultos da linhagem Long-Evans receberam implantes crônicos de múltiplos eletrodos para registro simultâneo de disparos de potencial de ação de neurônios individuais e de potenciais de campo local nos córtices V1 e S1. A posição dos eletrodos foi confirmada por análise histológica (coloração de Nissl e citocromo oxidase). Quatro ratos foram submetidos a uma sessão de estimulação visual sob anestesia (104 neurônios registrados em V1 e 143 em S1), e três ratos foram submetidos a uma sessão de estimulação tátil sob anestesia(61 neurônios registrados em V1 e 136 em S1). Durante a estimulação visual, 87% dos neurônios de V1 foram responsivos, enquanto 82% dos neurônios de S1 responderam à estimulação tátil. Nos mesmos registros,encontramos 23% dos neurônios de V1 responsivos a estímulos táteis e 22% dos neurônios de S1 responsivos a estímulos visuais. Analisando o potencial de campo local, encontramos um potencial de campo evocado em ambos os córtices com latência semelhante ao pico de disparo dos neurônios registrados, sendo a amplitude dessa resposta ~50% maior nos córtices isomodais. Nossos dados corroboram uma crescente série de evidências que indica a presença de processamento metamodal nos córtices sensoriais primários, o que desafia o paradigma do processamento sensorial unimodal e sugere a necessidade de uma reinterpretação do modelo de hierarquia cortical atualmente aceito.Artigo Theta-phase modulates different high-frequency oscillations in the CA1 region of the hippocampus during both waking and rapid-eye movement sleep.(2010-09) Teixeira, Robson Scheffer; Souza, Bryan C.; Belchior, Hindiael; Ribeiro, Sidarta Tollendal Gomes; Tort, Adriano Bretanha LopesRecent evidence suggests that not only the brain rhythms per se, but also the interactions among them are involved in the execution of cognitive tasks, mainly those requiring selective attention, information transmission and memory consolidation. However, still little is known about the general characteristics of cross-frequency coupling (CFC) in several brain regions. In the present work, we aimed to characterize phase-amplitude CFC in the CA1 region of rats (n=9) during different stages of the sleep-wake cycle: wake (WK), slow-wave sleep (SWS), and rapid-eye movement sleep (REM). Local field potentials were recorded using multielectrode arrays implanted in the dorsal hippocampus for chronic neural recordings. Electrode positioning was verified by histological analysis of cresyl-stained brain sections. Phase-amplitude coupling was assessed by means of the comodulogram analysis, a CFC tool we have recently developed. Our results show that (1) each sleep-wake state contains characteristic patterns of phase-amplitude CFC that are robust across all animals studied. (2) The CFC patterns obtained during WK and REM are similar and characterized by theta-phase (5 – 10 Hz) modulation of multiple higher frequencies; on the other hand, comodulograms from SWS period exhibited a distinct pattern, characterized by the modulation of very fast oscillations (> 100 Hz) by delta-phase (0 – 4 Hz), consistent with the occurrence of sharp wave-ripple complexes. All these patterns were stable across electrodes and days. Interestingly, during WK and REM, our results indicate that (3) theta-phase modulation comprises two non-overlapping, circumscribed higher frequency ranges: oscillations in the high-gamma (HG, 60 – 100 Hz) frequency range and oscillations between 120 – 160 Hz, which were defined as high-frequency oscillations (HFO). Moreover, (4) theta-phase preferentially modulated more HG or HFO depending on the spatial position of the electrode, with a clear switching between one and another as a function of electrode location, which was also stable across days. Further analyses indicated that (5) electrodes exhibiting HG or HFO modulation during WK and REM can also be differentiated by other electrophysiological features, such as power spectrum, phase-relations, and SWS comodulograms. We argue that the HFO we observed, though presenting overlapping frequency range with ripple oscillations, are distinct from the latter, which only appear in periods of rest and sleep associated to sharp-wave complexes. Therefore, while characterizing the patterns of rhythmic interactions in different cognitive states, the present work also reveals novel hippocampal oscillations that could only be detected by the use of the new CFC tools. We speculate that the different amplitude-modulated bands correspond to different biophysical processes occurring in CA1: HFO would result from entorhinal synaptic inputs to CA1, and HG from CA3 inputs.Artigo Undersampled Critical Branching Processes on Small-World and Random Networks Fail to Reproduce the Statistics of Spike Avalanches(2014-04-21) Ribeiro, Tiago; Ribeiro, Sidarta Tollendal Gomes; Belchior, Hindiael; Caixeta, Fábio; Copelli, Mauro