Grating stimuli do bias our concepts on cortical gamma synchronization: a study in capuchin monkey V1

• Autor(a) principal: Rocha, Kátia Simone de Araújo Nóbrega
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFRN
• Texto Completo: https://repositorio.ufrn.br/jspui/handle/123456789/24605
• topic: CNPQ::OUTROS::CIENCIAS: NEUROCIÊNCIAS; Gama; Sincronização; V1; Percepção visual; Macaco-prego

Cortical gamma oscillations (30 - 90 Hz) have been implicated in various cognitive processes, such as perceptual binding and attention. So far, most evidence in support of this hypothesis is based on studies that used artificial and simplified stimuli, such as moving gratings and bars. Recently, experimental work using natural images led to conflicting conclusions. In a paradigm that required human subjects to maintain fixation, electrocorticogram signals (ECoG) showed gamma for grating stimuli but not for static images or pink noise (Hermes et al., 2015). On the contrary, analysis of ECoG in the early visual cortex of macaque monkeys revealed strong gamma components for free viewing of natural scenes (Brunet et al., 2015). Here, we aim to clarify these discrepancies using a paradigm that allowed direct comparisons between fixation vs. free viewing conditions, for both simplified stimuli (moving and static gratings) and natural scenes (static and moving images). Recordings of spiking activity and local field potentials (LFPs) were obtained from the central and the peripheral representations of V1. Our results show that in capuchins (N= 3 monkeys), as previously described in macaques and humans, gamma is characteristically strong when stimulus parameters, such as size, orientation, and speed are set at to optimal values. Comparisons between fixation vs. free viewing conditions and gratings vs. natural stimuli revealed that gamma is always high for optimal grating stimuli, regardless of viewing condition (N= 93 recording sites, 2 monkeys). However, gamma is surprisingly absent during free viewing of natural images and movies. Similar negative findings were also obtained when the monkeys were exposed to real-world scenes, such as objects and other animals in the laboratory. The present results suggest that strong, narrow-band, gamma responses in V1 are primarily associated with the selective activation of cell populations sharing similar response properties. Therefore, gamma may be seen as a resonance phenomenon of the underlying cortical connectivity. Overall, our results belittle the importance of gamma as a critical cortical mechanism for vision.