Made available in DSpace on 2014-12-17T15:28:49Z (GMT). No. of bitstreams: 1 RobsonST_DISSERT.pdf: 350196 bytes, checksum: eaf6055553dc1f6cec39e0f754c20635 (MD5) Previous issue date: 2011-12-02 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Brain oscillation are not completely independent, but able to interact with each other through cross-frequency coupling (CFC) in at least four different ways: power-to-power, phase-to-phase, phase-to-frequency and phase-to-power. Recent evidence suggests that not only the rhythms per se, but also their interactions are involved in the execution of cognitive tasks, mainly those requiring selective attention, information flow and memory consolidation. It was recently proposed that fast gamma oscillations (60 150 Hz) convey spatial information from the medial entorhinal cortex to the CA1 region of the hippocampus by means of theta (4-12 Hz) phase coupling. Despite these findings, however, little is known about general characteristics of CFCs in several brain regions. In this work we recorded local field potentials using multielectrode arrays aimed at the CA1 region of the dorsal hippocampus for chronic recording. Cross-frequency coupling was evaluated by using comodulogram analysis, a CFC tool recently developted (Tort et al. 2008, Tort et al. 2010). All data analyses were performed using MATLAB (MathWorks Inc). Here we describe two functionally distinct oscillations within the fast gamma frequency range, both coupled to the theta rhythm during active exploration and REM sleep: an oscillation with peak activity at ~80 Hz, and a faster oscillation centered at ~140 Hz. The two oscillations are differentially modulated by the phase of theta depending on the CA1 layer; theta-80 Hz coupling is strongest at stratum lacunosum-moleculare, while theta-140 Hz coupling is strongest at stratum oriens-alveus. This laminar profile suggests that the ~80 Hz oscillation originates from entorhinal cortex inputs to deeper CA1 layers, while the ~140 Hz oscillation reflects CA1 activity in superficial layers. We further show that the ~140 Hz oscillation differs from sharp-wave associated ripple oscillations in several key characteristics. Our results demonstrate the existence of novel theta-associated high-frequency oscillations, and suggest a redefinition of fast gamma oscillations / As oscila??es cerebrais n?o s?o completamente independentes, mas capazes de interagir umas com as outras atrav?s de acoplamentos entre frequ?ncias (cross-frequency coupling, doravante CFC) em pelo menos quatro diferentes modalidades: amplitudeamplitude, fase-fase (coer?ncia), fase-frequ?ncia e fase-amplitude. Evid?ncias recentes sugerem que n?o somente os ritmos per se, mas tamb?m as intera??es entre eles est?o envolvidas na execu??o de tarefas cognitivas, principalmente aquelas que requerem aten??o seletiva, transmiss?o de informa??es e consolida??o de mem?rias. Estudos recentes prop?em que oscila??es gama alto (60 150 Hz) transferem informa??es espaciais do c?rtex entorrinal medial para a regi?o CA1 do hipocampo atrav?s do acoplamento com a fase de teta (4 12 Hz). Apesar destas descobertas, entretanto, pouco se sabe sobre as caracter?sticas gerais dos CFCs em diversas regi?es cerebrais. Neste trabalho, registramos potenciais de campo local usando matrizes de multieletrodos implantadas no hipocampo dorsal para registro neural cr?nico. O acoplamento fase-amplitude foi avaliado por meio da an?lise de comodulogramas, uma ferramenta de CFC desenvolvida recentemente (Tort et al. 2008, Tort et al. 2010). Todas as an?lises de dados foram realizadas em MATLAB (MathWorks Inc). Descrevemos duas oscila??es funcionalmente distintas dentro da faixa de frequ?ncia de gama, ambas acopladas ao ritmo teta durante explora??o ativa e sono REM: uma oscila??o com um pico de atividade em ~80 Hz e uma mais r?pida centrada em ~140 Hz. As duas oscila??es s?o diferencialmente moduladas pela fase de teta conforme a camada de CA1; o acoplamento teta-80 Hz ? mais forte no stratum lacunosum-moleculare, enquanto que o acoplamento teta-140 Hz ? mais forte no stratum oriens-alveus. Este perfil laminar sugere que a oscila??o de 80 Hz origina-se das entradas do c?rtex entorrinal para as camadas profundas de CA1, e que a oscila??o de 140 Hz reflete a atividade de CA1 em camadas superficiais. Ademais, n?s mostramos que a oscila??o de 140 Hz difere-se das oscila??es ripples associadas com sharp-waves em diversos aspectos chave. Nossos resultados demonstram a exist?ncia de novas oscila??es de alta frequ?ncia associadas ? teta e sugerem uma redefini??o das oscila??es gama alto