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Previous issue date: 2017-08-31 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / 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. / As oscila??es corticais gama (30 - 90 Hz) t?m sido implicadas em
processos cognitivos como a liga??o perceptual e a aten??o. At? agora, a
maioria das evid?ncias que servem de suporte para esta hip?tese ?
baseada em e s t u d o s a p a r t i r do uso de e s t ? m u l o s s i m p l e s e
artificiais, como grades e barras luminosas. Recentemente, no entanto,
estudos experimentais utilizando imagens naturais levaram a conclus?es
conflitantes. Em um paradigma em humanos que requeria fixa??o mantida,
sinais eletrocorticogr?ficos (ECoG) mostraram gama para grades, mas n?o
p a r a imagens e s t ? t i c a s ou r u ? d o r o s a (Hermes e t a l . , 2 0 1 5 ) .
Contrariamente, a an?lise dos sinais ECoG no c?rtex visual de macacosreso
revelou fortes componentes gama para a livre observa??o de cenas
naturais (Brunet et al., 2015). Neste estudo, temos por objetivo esclarecer
essas discrep?ncias utilizando-se de um paradigma que permitiu
compara??es diretas entre uma condi??o de fixa??o vs. uma condi??o de
observa??o livre, tanto para est?mulos simplificados (grades m?veis e
e s t ? t i c a s ) q u a n t o p a r a c e n a s n a t u r a i s ( i m a g e n s e s t ? t i c a s e
em movimento). Registros de potenciais de a??o e de potenciais de campo
locais (LFPs) foram obtidos para a representa??o central e perif?rica de
V1. Nossos resultados demonstram que em macacos-capuchinhos (N = 3),
como descrito anteriormente para macacos-reso e humanos, a gama ?
caracteristicamente forte, sempre que os par?metros do est?mulo, como
tamanho, orienta??o e velocidade, s?o definidos para a ativa??o ?tima das
c?lulas. Compara??es entre condi??es de fixa??o e de livre observa??o e
grades vs. est?mulos naturais revelaram que a gama ? sempre forte para
grades de orienta??o ?tima, independentemente da condi??o de
visualiza??o (N = 93 s?tios de registro, 2 macacos). No entanto, a gama
est? surpreendentemente ausente durante a livre visualiza??o de imagens
e filmes naturais. Achados negativos semelhantes tamb?m foram obtidos
quando os macacos foram expostos a cenas do mundo real, como objetos
e outros animais no laborat?rio. Os presentes resultados sugerem que, no
c?rtex visual prim?rio, a atividade gama ? principalmente associada ?
ativa??o seletiva de popula??es neuronais que compartilham propriedades
de resposta similares. Portanto, a gama pode ser vista como um fen?meno
de resson?ncia da conectividade cortical subjacente. Em geral, nossos
resultados minimizam a import?ncia da gama como um mecanismo cortical
chave para a vis?o.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/24605 |
| Date | 31 August 2017 |
| Creators | Rocha, K?tia Simone de Ara?jo N?brega |
| Contributors | 45548927604, Schmidt, Kerstin Erika, 70024141437, Baron, Jerome Paul Armand Laurent, 01569268657, Maciel, S?rgio T?lio Neuenschwander |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM NEUROCI?NCIAS, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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