Beta activity: a carrier for visual attention.

The alpha (8-13 Hz), beta (15-25 Hz) and gamma (30-60 Hz) bands of the EEG have been long studied clinically because of their putative functional importance. Old experimental results indicate that repetitive stimulation of the visual pathway evokes synchronous responses at the cortical level with a gain that depends on frequency; oscillations within relevant bands are less damped at subsequent processing levels than others. Our current results show in the cat that cortico-geniculate feedback has a build-in potentiation mechanism that operates at around the beta frequency and activates thalamic cells thus lowering the threshold for visual information transmission. We have also shown that enhanced beta activity is propagated along this feedback pathway solely during attentive visual behavior. This activity consists of 300-1,000 ms bursts that correlate in time with gamma oscillatory events. Beta-bursting activity spreads to all investigated visual centers, including the lateral posterior and pulvinar complex and higher cortical areas. Other supporting data are discussed that are concerned with the enhanced beta activity during attentive-like behavior of various species, including humans. Finally, we put forward a general hypothesis which attributes the appearance of oscillations within the alpha, beta and gamma bands to different activation states of the visual system. According to this hypothesis, alpha activity characterizes idle arousal of the system, while beta bursts shift the system to an attention state that consequently allows for gamma synchronization and perception.