Time dynamics of stimulus- and event-related gamma band activity: contrast-VEPs and the visual P300 in man

• Published in: Clinical neurophysiology Vol. 112; no. 12; pp. 2241 - 2249
• Main Authors: Sannita, Walter G, Bandini, Fabio, Beelke, Manolo, De Carli, Fabrizio, Carozzo, Simone, Gesino, Diana, Mazzella, Luca, Ogliastro, Carla, Narici, Livio
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.12.2001; Elsevier Science
• Subjects: Adult; Behavioral psychophysiology; Biological and medical sciences; Contrast Sensitivity - physiology; Contrast stimulation; Electroencephalography; Electrophysiology; Event-Related Potentials, P300; Evoked Potentials, Visual; Fundamental and applied biological sciences. Psychology; Gamma band activity; Healthy humans; Humans; Onset/offset visual evoked potentials; Oscillatory visual response; Oscillometry; Phase-locking to the stimulus; Photic Stimulation - methods; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Time Factors; Visual P300; Onset/offset visual evoked potentials; Visual P300; Oscillatory visual response; Healthy humans; Gamma band activity; Contrast stimulation; Phase-locking to the stimulus; Human; Gamma rhythm; Central nervous system; Electrophysiology; Visual evoked potential; Cognition; P300 potential; Synchronization; Contrast; Selective attention; Visual stimulus; Oscillation; Information processing; Event evoked potential; Brain (vertebrata)
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/S1388-2457(01)00700-3

Objectives: To investigate the time dynamics and phase relationship with the stimulus of the onset/offset visual evoked potentials (VEPs), P300 and gamma band oscillatory responses to visual (contrast) stimulation. Gamma band oscillatory activity mediates in sensory and cognitive operations, with a role in stimulus-related cortical synchronization, but is reportedly reduced in the time window of the P300 response. Methods: Ten healthy volunteers were studied. VEPs and P300 were obtained in a stimulus condition combining standard contrast stimulation and a visual odd-ball paradigm. Visual stimuli were gratings with a sinusoidal luminance profile (9.0° central retina; 1.3 cycles/degree; 70% contrast) that were presented monocularly in onset/offset mode, with vertical orientation (frequent stimulus; 80%) or with a 15° rotation to the right (infrequent, target stimulus). The total signal activity (temporal spectral evolution), the activity phase-locked to the stimulus onset (rectified integrated average), and the ‘locking index’ (ratio of the activity phase-locked to the stimulus to the total signal activity) were computed over time and across frequencies on the signals recorded at occipital (visual responses) and central locations (P300). Results: Oscillatory activity centered around ∼20.0–35.0 Hz and phase-locked to the stimulus was recorded at occipital locations with time dynamics anticipating the conventional VEPs. Phase-locking was higher after frequent than in response to target stimuli and after the stimulus offset compared to onset, while the phase-locking of the VEP frequency components was higher after the stimulus onset. The low frequency components of the P300 recorded at Cz (below ∼8.0–10.0 Hz) were almost totally phase-locked to the stimulus, while the gamma band activity at the P300 location did not vary over time in amplitude or phase-locking and was mostly non-locked to the target stimulus. Conclusions: These observations add to the evidence of a role of the gamma band oscillatory responses (centered at ∼20.0–35.0 Hz) in visual information processing and suggest that the increment in gamma band activity during cognitive operations also depends on task characteristics, vigilance or selective attention, and brain functional state. The visual P300 appears to reflect low frequency synchronization mechanisms.