Neurophysiological mechanisms of audio-visual intersensory attention: Evidence from high-density surface EEG and human intracranial recordings

The spatio-temporal dynamics of audio-visual intersensory attention were investigated in a series of neurophysiological studies in cognitively healthy individuals. Four studies recorded electrophysiological (EEG) activity from high-density surface electrodes to investigate the broadband and band-specific mechanisms of attention in low and high-order cortices. A separate study recorded electro-cortico (ECoG) activity in two cognitively-healthy individuals to assess entrainment mechanisms at the earliest levels of auditory cortex during an audio-visual attention task. The results further established the role of the alpha (8 -- 14 Hz) frequency band as an active gating mechanism in early sensory cortex during intersensory attention. Further, the data revealed that oscillatory power in this frequency band can serve as a neurophysiological marker for behavioral outcome during high-demanding intersensory attentional deployments. In a rhythmic and predictable task, alpha-band power was modulated by the periodicity of a delta-band (1-3 Hz) frequency oscillation, thus further suggesting that higher frequency oscillations (> 8 Hz) influence sensory processing through power fluctuations, while slow oscillations (< 7 Hz) influence activity through phase-dependent mechanisms. In addition, the data also revealed that neuronal activity within the alpha-band is highly sensitive to the natural pharmacological agent L-Theanine. Finally, the data suggests that by allowing participants to voluntarily generate an attentional deployment, top-down attentional signals get reconfigured, which might give rise to a more endogenous (or less automatic) attentional set. Taken together, the present data firmly supports the 'early-model' of attention in that top-down attentional signals were found to have an effect on neural activity in early sensory areas and at relatively 'early' stages of stimulus processing.