Modulation of the Amplitude of Gamma-Band Oscillations by Stimulus Phase in Mouse Visual Cortex Neurons Improves Signal Encoding

Gamma band oscillations (25 - 70 Hz) play an important role in processing of information by neocortical neurons. In simple cells of the cat's visual cortex, it was previously shown that strength of gamma oscillations is modulated by the membrane potential oscillations at the temporal frequency of the stimulus. More recently, theoretical studies using a conductance-based neuronal model have shown that this coupling significantly improves visual stimulus encoding. Due to the availability of a broad range of genetic tools, mice had recently become an important experimental subject for research in various fields of neuroscience, including visual physiology. It has been suggested that gamma oscillations in the mouse visual cortex play a minor role in visual processing due to the lack of specialized neurons that take part in generating gamma oscillations. Here we show, using patch clamp recording from simple cells in the visual cortex of anesthetized mice, that the strength of gamma oscillations is modulated by the phase of stimulus-induced oscillations during visual stimulation with moving gratings. In addition, using patch clamp recording from mouse visual cortex neurons in slices, we demonstrated benefits of gamma activity modulation for encoding of slow sinusoidal signals into sequences of action potentials. Thus, the phenomenon of amplitude modulation of gamma oscillations by temporal frequency of stimulus, originally described in the visual system of cats, may represent a universal mechanism that improves encoding of visual information which is present even in animals with a relatively poorly developed visual system, such as mice.