Abnormal Waveform of the Human Pattern VEP: Contribution from Gamma Oscillatory Components

Abstract

The human gamma oscillatory response mediating in cortical visual information processing further proved independent of the VEPs. It can contribute to VEP waveform distortion, and its observation in substitution of VEPs should be regarded as an indication of impaired visual pathway function.

‘Gamma’ band oscillatory response to chromatic stimuli in volunteers and patients with idiopathic Parkinson’s disease

“…The observation adds to the evidence suggesting partly distinct origins of the gamma-band and low-frequency VEP response components (Narici et al, 2003; Sannita, 2000; Sannita, 2005; Sannita et al, 1999, 2007), and indicates mechanisms of generation of the gamma response common to the subsystems that process contrast and colors. A functional role of gamma activity(ies) in processes such as the phase coding and bottom-up synchronization of neuronal activation, seems plausible (Adjamian et al, 2004; Bressler 1990; Bringuier et al, 1997; Cardin, Palmer, & Contreras, 2005; Engel et al, 1992a, 1992b; Fries et al, 2002; Gray, 1999; Hall et al, 2005; Jefferys et al, 1996; Liang, Bressler, Buffalo, Desimone, & Fries, 2005; Rodriguez, Kallenbach, Singer, & Munk, 2004; Sannita, 2000; Singer, 1993).…”

“…The cortical source equivalents of gamma response shared the macro-topography, but had different orientation than those of the VEP low-frequency components in a neuromagnetic study on humans (Narici, Carozzo, Lopez, Ogliastro, & Sannita, 2003). Oscillatory gamma responses were observed in the absence of recognizable VEP in a significant percentage of patients with retinal diseases or brain damage involving the visual system (Sannita, Carozzo, Fioretto, Garbarino, & Martinoli, 2007; Sannita et al, 1995). Recording instead of VEPs, phase-locking to stimulus and the factor structure suggest an origin of the gamma response partly independent from the mechanisms generating the VEP low-frequency components (Carozzo et al, 2004; Sannita et al, 1999).…”

Neuronal Functional Diversity and Collective Behaviors

“…In this respect, according to prevailing hypotheses, gamma activity is a class of elementary signal with multiple functional correlates and a role in the short-term synchronization of neuronal aggregates in spatiotemporal patterns of cortical coordinated activation. The occurrence of gamma response in the visually impaired instead of the broad-band visual responses [104] adds to the evidence that bottom-up synchronization is essential, but not necessarily sufficient, for higher brain processes to become operative. The functional diversity and hierarchy of brain signals with different dominant frequencies, e.g., [83,88,105], further suggests more complex interaction, still to a large extent unexplored.…”

Functional examinations of visual channels: physiological basis

“…У человека общий гамма-ответ почти полностью синхронизирован по фазе со стимулом и имеет более короткую латентность, чем низкочастотные (обычные) компоненты ЗВП. Осцилляторные гамма-ответы наблюдались даже в отсутствие идентифицируемых ЗВП-сигналов у многих пациентов с заболеваниями сетчатки, включающими также более высокие уровни зрительной системы [48]. Эти факты предполагают, что гамма-компонент частично независим от низкочастотных компонентов ЗВП [48].…”

“…Осцилляторные гамма-ответы наблюдались даже в отсутствие идентифицируемых ЗВП-сигналов у многих пациентов с заболеваниями сетчатки, включающими также более высокие уровни зрительной системы [48]. Эти факты предполагают, что гамма-компонент частично независим от низкочастотных компонентов ЗВП [48]. Различие гамма-ответов на ахроматические и цветные стимулы указывает на разный вклад в них Р-и М-путей [47].…”