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. Author manuscript; available in PMC: 2011 Mar 9.
Published in final edited form as: Neuron. 2010 Sep 9;67(5):885–896. doi: 10.1016/j.neuron.2010.08.004

Figure 4.

Figure 4

A stimulus whose contrast varies in space generates gamma rhythms at different frequencies in different neuronal assemblies. A) A grating of radius 1.56° (upper left) and a Gabor with a SD of 0.52° (upper right), both of 100% contrast at the center, along with the receptive fields of three sites at different distances from the stimulus center. The lower panels show the power spectra of the LFP (between 150-406 ms post stimulus onset) recorded from the three electrodes whose receptive fields are shown in the upper row. The black line shows the average LFP power during baseline. The LFPs show oscillations at different gamma frequencies depending on the distance between the receptive field center and the stimulus center for the Gabor stimulus (lower right), but not for the grating (lower left). B) Average population power spectra for different distances between the receptive field center and the stimulus center (binned at 0.2°), for the grating (left column) and Gabor (right column) stimulus, for Monkey 1 (upper row) and Monkey 2 (lower row). The five colored traces correspond to different distances, shown in the upper left panel. The black trace shows the power in the baseline period. See text for more details. C) Average gamma oscillation frequencies as a function of the distance between the receptive field and stimulus center for Monkey 1 (upper plot) and Monkey 2 (lower plot), for grating (open circles) and Gabor (closed circles) stimuli. Error bars are SEM and when not shown are smaller than the size of the symbols. The brown line indicates the estimated frequency by computing the effective contrast (the contrast within each of the receptive fields) for the Gabor stimuli and using the frequency versus contrast slopes shown in the inset of Figure 1F and I. The horizontal gray line shows the expected frequency for a grating stimulus, which should not vary with distance since the contrast remains constant. For Monkey 2 the frequency actually increases slightly, due to a decrease in the effective size of the stimulus. See text for more details.

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