High-frequency brain activity: its possible role in attention, perception and language processing.

Coherent high-frequency neuronal activity has been proposed as a physiological indicator of perceptual and higher cognitive processes. Some of these processes can only be investigated in humans and the use of non-invasive recording techniques appears to be a prerequisite for investigating their physiological substrate in the healthy human brain. After addressing methodological issues in the non-invasive recording of high-frequency responses, we summarize studies indicating co-occurrence of neuronal synchrony of single cells exhibiting rhythmic activity at high frequencies, oscillations in the local field potential and dynamics in high frequencies recorded using high-resolution electroencephalography (EEG) and magnetoencephalography (MEG). We then review EEG and MEG studies of attention, perception, and language processing in humans indicating that dynamics in the high-frequency range > 20 Hz reflect specific cognitive processes. Types of high-frequency (HF) activity can be distinguished according to their latency after stimulus onset, stimulus-locking, cortical topography and frequency. There appears to be a systematic relationship between specific cognitive processes and types of HF activity. The findings are related to recent theories about the generation of HF activity and their possible role in binding of stimulus features. Dynamics of HF cortical activity reflecting higher cognitive processes can be accounted for based on the assumption that the elements of cognitive processing, e.g. visual objects and words, are organized in the brain as distributed neuronal assemblies with defined cortical topographies generating well-timed spatio-temporal activity patterns.