Factor structure of the human gamma band oscillatory response to visual (contrast) stimulation

• Published in: Clinical Neurophysiology Vol. 115; no. 7; pp. 1669 - 1676
• Main Authors: Carozzo, Simone, De Carli, Fabrizio, Beelke, Manolo, Saturno, Moreno, Garbarino, Sergio, Martello, Cristina, Sannita, Walter G
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.07.2004; Elsevier BV; Elsevier Science
• Subjects: Adult; Biological and medical sciences; Contrast Sensitivity; Contrast Sensitivity - physiology; Contrast stimulation; Electroencephalography; Evoked Potentials, Visual; Eye and associated structures. Visual pathways and centers. Vision; Factor analysis; Factor Analysis, Statistical; Fourier Analysis; Fundamental and applied biological sciences. Psychology; Gamma band response; Healthy volunteers; Humans; Oscillatory potentials; Oscillometry; Pattern VEP; Photic Stimulation; Photic Stimulation - methods; Reaction Time; Reference Values; Vertebrates: nervous system and sense organs; Vision; Oscillatory potentials; Pattern VEP; Healthy volunteers; Factor analysis; Gamma band response; Vision; Contrast stimulation; Human; Visual cortex; Gamma rhythm; Central nervous system; Electrophysiology; Visual evoked potential pattern; Synchronization; Contrast; Encephalon; Time resolution; Visual stimulus; Visual pathway; Oscillation
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2004.02.025

Visual contrast stimulation evokes in man an oscillatory mass response at ∼20.0–35.0 Hz, consistent with stimulus-dependent synchronous oscillations in multiunit animal recordings from visual cortex, but shorter in duration and phase-locked to stimulus. A factor analysis was applied to characterize the signal structure under stimulus conditions inducing an oscillatory response and to identify possible subcomponents in normal volunteers. Contrast stimuli were gratings with a sinusoidal luminance profile (9.0°; 5.0 cycle/degree; 80% contrast; reversal 1.06 Hz). The amplitude spectrum of the signal was computed by Discrete Fourier Transform (DFT) and the oscillatory response was separated from the corresponding visually evoked potential (VEP) by DFT high-pass filter at 19.0 Hz. Nine consecutive waves were identified in all subjects (60 volunteers), with amplitudes/latencies consistent with normative studies. A factor analysis was computed 1- in the frequency domain, on the amplitude values of the signal components (2 Hz resolution), and 2- in the time domain, on the latencies/amplitudes of the averaged VEP and oscillatory responses. (1) Two non-overlapping factors accounted for the ∼2–20.0 and ∼20.0–40.0 Hz signal components, with separation of the ∼20.0–35.0 Hz oscillatory response from low frequency VEPs. (2) Two factors on latencies and one factor on amplitudes (independent of each other and from those of VEPs) accounted for the average ∼20.0–35.0 Hz oscillatory response. The factor structure further indicates an oscillatory structure and some independence from conventional VEPs of the human oscillatory response to contrast, with a separation between the oscillatory response early and late waves possibly reflecting functional differences.