Workshop 4: Rhythms and Oscillations
On the central role of theta in decoding speech
Theta gamma coordination in setting of psychomimetics and other modulatory interventions
Theta-gamma nested oscillations in speech perception
The role of oscillatory entrainment in auditory selective attention
The synaptic interaction of excitatory and inhibitory neurons (E- and I-cells) can generate oscillations, provided that the drive to the I-cells is low enough, so that they don't get ahead of the E-cells but merely respond to them. If the drive to the I-cells is high, and inhibitory synapses are strong, the E-cells are suppressed altogether. We think about the transition from rhythmicity (low drive to the I-cells) to suppression of the E-cells (high drive to the I-cells). In work with Nancy Kopell several years ago, we suggested that this transition, if it is abrupt, could be exploited to allow the network to toggle between rhythmic activity and suppression, and that this could be useful in attentional selection. In contrast with the earlier work, here we assume that synchronization of the I-cells is always enforced by gap junctions. We find that in this case, the transition from rhythmicity to suppression is much more abrupt when the I-cells have a type 2 phase response (excitation early in the phase retards them) than when they have a type 1 phase response (excitation always accelerates them). We demonstrate this with simulations and explain it using a one-dimensional map.
Neuronal communication between cortical areas heavily relies on oscillatory, periodic mechanisms whose precise timing critically determines the flow of information. Yet little is known about the perceptual and psychological consequences of such periodic neuronal dynamics at the rapid time scale of the oscillatory cycle: what perceptual changes accompany the drastic changes of neuronal activity observed between opposite phases of the cycle? I will show several experimental examples of these perceptual consequences in the visual domain. To summarize, visual perception and attention seem to wax and wane intermittently at frequencies in the theta (~7Hz) and alpha (~10Hz) range, possibly reflecting the underlying periodic neuronal processes. Based on spiking neural network simulations, I will argue that similar perceptual cycles can also exist at higher frequencies (gamma range), and that our perceptual experience may be the result of cross-frequency interactions between these different rhythms
Electrophysiological recordings from neurons in the hippocampal and entorhinal cortices of freely moving rodents provide detailed information regarding the neural representations of spatial location and orientation, and indicate a functional role for neural coding with respect to the theta rhythm of the local field potential. I will describe some of these experiments and the computational mechanisms they imply. These emphasise the roles of environmental boundaries in self-localization, via boundary vector cell firing, and temporal oscillations in the theta band in path integration, via grid cell firing. Both types of information are combined in the firing of place cells. I will describe the implications of these findings for the mechanisms supporting human spatial memory, and provide examples of electrophysiological and functional neuroimaging experiments designed to test these implications.
Oscillations and grid cells in entorhinal cortex
Large-Scale Synchronous Beta Rhythms
Collective oscillations in networks of spiking neurons: Mechanisms and input dependence