A new study by scientists from Indian Institute of Science (IISc) has shown that hues of different colours generate large gamma oscillation in the primary visual cortex, the region of the brain that processes visual information. Reddish hues were seen to cause the strongest oscillations.
While monitoring the electrical activity of a brain, gamma oscillations or oscillation of neurons at frequency range around 30 to 80 hertz, are known to be a prominent signature of sensory stimulation, like seeing, touching and hearing. These oscillations are influenced by the properties of the stimulus and behavioural state. Gamma oscillations also play a purported role in natural vision, evidence for which is still lacking, and in cognitive functions, like paying attention.
Although gamma oscillations generated by the visual senses have been studied before, these studies were conducted using light from an achromatic (colourless) lens. In their new study, the scientists wanted to understand the response of the gamma oscillations, when different colours are presented in the field of view.
Tests conducted on monkeys have shown a dependence of the gamma oscillations to properties of the colour, like hue and saturation. Three adult female monkeys were shown flashing colours of different hue, saturation and luminance, while the gamma oscillations were recorded using probes implanted surgically.
“We show that gamma oscillations of extremely high magnitude (peak increase of ∼300-fold in some cases), far exceeding the gamma generated by optimally tuned achromatic gratings, are induced… by full-field color stimuli of different hues” say the authors about the result of the study.
They also noted that the gamma oscillations the strongest oscillations were recorded for long-wavelengths or reddish hues. The oscillations depended by the purity of the hue and increased with hue saturation. Interestingly, the luminance, or the intensity or brightness of the light did not appear to influence the oscillations. They also noted a strong correlation between L and M cone cell (types of photoreceptor cells in the eye) contrast produced by the stimuli. This, the author suggest gamma oscillations could be a marker of the specific mechanisms underlying this L-M cone contrast.
“These findings provide insights into the generation of gamma oscillations, as well as the processing of color along the visual pathway” say the authors about the importance of their work.