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Terezinha Medeiros Gonçalves de Loureiro, Givago S Souza, Veronica da Silva, Thiago Costa, Dora Fix Ventura, Luiz Carlos L Silveira; SELECTIVE AMPLITUDE CHANGE OF THE VISUALLY EVOKED EEG BANDS AFTER FLICKER ADAPTATION. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5762.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effects of luminance flicker adaptation on the evoked electroencephalogram (EEG) α, β, and γ bands.
Eight healthy volunteers were tested (20.25 ± 1.5 years old). Stimuli were generated using Delphi 7 programming language and the ViSaGe system (Cambridge Research Systems, UK) graphical library and displayed in a high spatial, temporal, and chromatic resolution 21” CRT monitor (Mitsubishi, Japan). A test session was composed by an adaptation period (8 s) followed by a test period (2 s). The stimuli were a 2-dimensional Gaussian luminance mask followed by a same mean luminance (40 cd/m-2) achromatic sinusoidal grating. The Gaussian mask (2.5o standard deviation) was shown during the adaptation period, without flicker or with 5, 10, and 30 Hz flicker. The gratings (5o visual angle, 99% Michelson contrast) were shown during the test period, at 0.4, 2, and 10 cpd and 1 Hz. Session conditions comprised 12 combinations of adaptation and test. The electrophysiological recordings were done using a CED 1902 amplifier, Micro 1401-3 ADC, and Spike2 software (Cambridge Electronic Design, UK). EEG was recorded by surface electrodes placed at Fpz (ground), Fz (inactive), and Oz (active), amplified x30,000, sampled at 1 KHz, and filtered at 0.1-100 Hz. Recordings were performed during the test periods (400 sweeps of 500 ms for each condition). A short time fast Fourier transform was applied in the mean waveforms, using 30 ms window and 25 ms of overlap between consecutive windows. The mean amplitudes of the evoked α (6-12 Hz), β (13-26 Hz), and γ bands (27-40 Hz) were examined between 0 and 250 ms (evoked response) and between 250 and 500 ms (late period) during the test period for the 12 combinations.
Flicker adaptation at 5 Hz was associated with reduction of the α band amplitude for the 0.4 cpd grating. During the late period, mean α band amplitude for 0.4 cpd was higher at 10 and 30 Hz of flicker adaptation than at 5 Hz or without flicker adaptation. Moreover, mean γ band amplitude was higher at 5, 10, and 30 Hz of flicker adaptation during the late period of recordings for 0.4 cpd. At 2 and 10 cpd, there were no significant changes of the EEG band mean amplitudes associated with the flickering stimulus.
Adaptation to flicker affected the response to a spatial grating at the α and γ bands that was dependent on the stimulus spatial frequency and on the rate of flicker.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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