Decaimento da frequência gama: estudo comparativo entre a retina, o núcleo geniculado lateral e o córtex

• Ano de defesa: 2018
• Autor(a) principal: Silva, Luana Dantas da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Rio Grande do Norte; Brasil; UFRN; PROGRAMA DE PÓS-GRADUAÇÃO EM NEUROCIÊNCIAS
• Palavras-chave em Português: Oscilações Gamma; Coerência neuronal; Sistema visual; Córtex cerebral; Retina
• Link de acesso: https://repositorio.ufrn.br/handle/123456789/45258

Gamma oscillations (30 to 90 Hz) has been implicated in cognitive processes such as visual binding (Singer, 1999; Uhlhaas et al., 2009) and attention (Fries, 2001; Gregoriou et al. Pesaran et al., 2002; Montgomery and Buzsáki, 2007; Lima et al., 2011). The communication through coherence hypothesis (CTC), proposed by Pascal Fries (Fries, 2005; Fries, 2009), identifies gamma as a key mechanism for stimulus encoding and control of the flow of information in cortical-cortical systems. Accordingly, experimental work on monkeys has suggested that the modulation of oscillation frequency may be fundamental for establishing coherence, and hence neural communication, for example between cortical areas V1 - V4, and V1 - V2 (Bosman et al, 2012; Roberts et al., 2013). Indeed, non-matching frequencies can be used as distinct channels for information transmission, as suggested between FEF and V4 (Gregoriou et al., 2009) and the hippocampus and the entorhinal cortex (Colgin et al, 2009). Thus, the oscillation frequency is likely a critical parameter for the modulation of gamma oscillations during attentional control. On the other hand, it is also known that gamma frequency depends on stimulus features, such as velocity (Gray et al., 1990; Lima et al., 2010); size (Gieselmann and Thiele, 2008), orientation and contrast (Ray & Mausell, 2015). The eccentricity position in the visual map seems as well determinant for the oscillation frequency, as higher frequencies are systematically seen for receptive fields at the central representation of the visual field as compared to the peripheral representation. Interestingly, gamma frequency is rarely stationary along the course of the responses. In general, oscillation frequency decreases continuously in the first hundreds of milliseconds after stimulus onset. This is a robust phenomenon, observable at different levels of the visual system, for a variety of species (cats, monkeys, humans, mice; see examples in CasteloBranco et al., 1998; Neuenschwander et al., 1999; Van Pelt et al., 2012; Storchi et al., 2017). Although remarkable, this decay in gamma frequency has been mostly ignored, and a possible functional role remains evasive (Fries et al., 2015). Here, we characterize the decay of gamma frequency for a variety of stimulus conditions. Comparisons are made for two systems known to show strong gamma oscillations: (1) the retinogeniculate system of the cat and (2) the primary visual cortex of the monkey. A robust finding is that both the retina and the cortex show pronounced decay in gamma frequency. This is striking since the cortical oscillations are known independent of the rhythms originated in the retina (CasteloBranco et al., 1998; Saleem et al., 2017). Overall, gamma frequency decay was observed for a variety of stimuli and appeared to be independent of the instantaneous firing of the cells. We discuss the possible meaning of a decay in frequency for the current ideas of the role of gamma in stimulus encoding and attentional control.