Is Gamma-Band Activity in the Local Field Potential of V1 Cortex a "Clock" or Filtered Noise?

Abstract

Gamma-band (25–90Hz) peaks in local field potential (LFP) power spectra are present throughout the cerebral cortex and have been related to perception, attention, memory, and disorders e.g. schizophrenia and autism. It has been theorized gamma oscillations provide a `clock' for precise temporal encoding and `binding' of signals about stimulus features across brain regions. For gamma to function as a `clock' it must be autocoherent: phase and frequency conserved over a period of time. We computed phase and frequency trajectories of gamma-band bursts, using time-frequency analysis of LFPs recorded in macaque primary visual cortex (V1) during visual stimulation. The data were compared with simulations of random networks and clock signals in noise. Gamma-band bursts in LFP data were statistically indistinguishable from those found in filtered broadband noise. Therefore, V1 LFP data did not contain `clock'-like gamma-band signals. We consider possible functions for stochastic gamma-band activity, such as a synchronizing pulse signal.

On the Universal Mechanism Underlying Conscious Systems and the Foundations for a Theory of Consciousness

“…Such a moment of disorder creates the prerequisites for a stimulus to induce a reorganization of the background activity and to prompt the emergence of the subsequent attractor (Freeman, 2004(Freeman, , 2009). These results imply that noise plays a fundamental role in the functioning of the brain, which has been confirmed by investigations of other groups (Kitajo, Doesburg, Yamanaka, Nozaki, Ward, & Yamamoto, 2007;Burns, Xing, Shelley, & Shapley, 2010;Burns, Xing, & Shapley, 2011).…”

Intersubject variability and induced gamma in the visual cortex: DCM with empirical Bayes and neural fields

“…The spectral profile of this response generally has one or more spectral peaks, including a peak in the gamma region (when the parameters are set to their prior means). The origin of this gamma activity is an active area of research and could be due to random membrane depolarizations of individual units due to noisy inputs [Brunel and Wang, 2003; Burns et al, 2011]. In our framework, this random activity is described by the spectral density of endogenous neuronal fluctuations $g_u(k,\omega )=U(k,\omega )U{false(k,\omega false)}^{*}$ that produce observed (cross spectral) responses at sensors l and m according to the following likelihood model: $\begin{array}{c}{g}_{{}_{lm}}^i(\omega )={\Gamma }_i({\theta }^{false(1false)})+g_n(\omega )+{\varepsilon }^{false(1false)}\\ {\Gamma }_i({\theta }^{false(1false)})={\displaystyle {\sum }_k{T}_l(k,\omega )g_u(k,\omega )T_m{false(k,\omega false)}^{†}}\\ \\ T_r(k,\omega )=L_r(k,\phi )Q\cdot T(k,\omega ,{\theta }^{false(1false)})\\ g_n(\omega )={\alpha }_n+{\beta }_n/\omega \\ g_u(\omega )={\alpha }_u+{\beta }_u/\omega \\ \\ Re({\varepsilon }^{false(1false)})\sim \mathcal{N}(0,\Sigma (\omega ,\lambda )) \end{array}$…”

“…In this (single source ‐ single sensor) setup, Eq. (2) models gamma rhythms as the bandpass‐filtered output of the cortical circuit depicted in Figure 1, whose input is a mixture of white and pink noise; compare [Burns et al, 2011]. …”

For things needing your attention: the role of neocortical gamma in sensory perception

“…This fluctuation means that gamma oscillations will neither be coherent across time, if stimulus contrast changes rapidly, nor in space, if contrast varies across the visual field. Further, the temporal dynamics of gamma oscillations recorded in awake and anesthetized macaque V1 are stochastic in nature, indicating that gamma cannot serve as a 'clock' signal for an external observer [63,64]. Although these observations appear to restrict the utility of gamma as a mechanism for binding stimuli from different regions of the visual field into coherent percepts, they do not undermine the potential utility of gamma as a mechanism for gain control within a local representation, for example, a neocortical column.…”