Human EEG responses to 1-100 Hz flicker: resonance phenomena in visual cortex and their potential correlation to cognitive phenomena

The individual properties of visual objects, like form or color; are repres ented in different areas in our visual cortex. In order to perceive one coh erent object, its features have to be bound together. This was found to be achieved in cat and monkey brains by temporal correlation of the firing rat es of neurons which code the same object. This firing rate is predominantly observed in the gamma frequency range (approx. 30-80 Hz, mainly around 40 Hz). In addition, it has been shown in humans that stimuli which flicker at gamma frequencies are processed faster by our brains than when they flicke r at different frequencies. These effects could be due to neural oscillator s, which preferably oscillate at certain frequencies, so-called resonance f requencies. It is also known that neurons in visual cortex respond to flick ering stimuli at the frequency of the flickering light. if neural oscillato rs exist with resonance frequencies, they should respond more strongly to s timulation with their resonance frequency. We performed an experiment, wher e ten human subjects were presented flickering light at frequencies from 1 to 100 Hz in 1-Hz steps. The event-related potentials exhibited steady-stat e oscillations at all frequencies up to at least 90 Hz. Interestingly, the steady-state potentials exhibited clear resonance phenomena around 10, 20, 40 and 80 Hz. This could be a potential neural basis for gamma oscillations in binding experiments. The pattern of results resembles that of multiunit activity and local field potentials in cat visual cortex.