Cosyne 2009 Workshops
March 2-3, 2009
Snow Bird, Utah
Workshop Title
The consequences of brain rhythms in the organization of neuronal computation
Organizer(s)
Kai Miller, University of Washington
Thilo Womelsdorf, University of Western Ontario
Abstract
Some of the first neurophysiological experiments measured changes in cortical brain rhythms of awake behaving animals. Yet, nearly 150 years later, the role that these rhythms play in brain function is not well understood. In fact, there has been much debate about whether the rhythms themselves reflect an active role in the cortex at all, or whether they instead reflect emergent synchrony in the cortex which is not somehow requisite for cortical computation. An active, functional role of rhythms at local and large-scale levels of neuronal computation has been suggested by recent experimental findings. Complementary insights from theoretical neuroscientists demonstrate how the various rhythms could play an important organizational role in cortical information processing. This workshop will bring together these experimentalists and theoreticians, and present them in a common setting, where the interaction between brain rhythms and the timing of neuronal activity for both single unit recordings and interactions between non-local neuronal populations can be examined.
The discussion will span several spatial scales and functional domains: Locally, at the scale of microcircuit, empirical work suggest the involvement of interneurons to generate synchronous rhythms in the cortex. Theoretical work from Paul Tiesinga and Nancy Kopell utilize and expand these insights to delineate detailed microcircuit architectures supporting effective neuronal computations on the basis of dynamic synchronization at various frequencies. Empirical support for these theoretically suggested relevance of synchronization for efficient neuronal coding and computation will be discussed by Tim Blanche based on data from cortical recordings in behaving animals. These insights are complemented by inter-areal cortical recordings in humans and animals by Bijan Pesaran, Markus Siegel, and Florian Mohrmann, discussing data demonstrating the functional relevance of synchronization for diverse functional domains including sensory-motor integration, attentive processing and memory formation. How such functional inter-areal, large scale interaction patterns arise and which computational advantages they confer will be discussed from a theoretical perspectives by Gustavo Deco and Michael Breakspear.
Speakers
Morning session (8:00 – 11:00AM)
8:00-8:15 Kai Miller and Thilo Womelsdorf “Introduction to the workshop”
8:15-8:45 David McCormick (Yale) "[title to be announced]."
8:45-9:15 Tim Blanche (UC Berkeley) "The functional role of spike timing precision to the phase of local field potentials in primary visual cortex."
9:15-9:45 Jacob Reimer & Nicholas Hatsopoulos (Chicago) "Beta oscillations and the timing of early sensorimotor activity in primary motor cortex."
9:45-10:00 Break
10:00-10:30 Bijan Pesaran (NYU) "Frontal-Parietal coupling and its relation to behavior as revealed by spike to local field potential (LFP) interactions."
10:30-11:00 Markus Siegel (MIT) "Neuronal dynamics during active visual motion processing in humans."
Afternoon session (4:30 – 7:30PM)
4:30-5:00 Florian Mormann (Caltech) "Brain oscillations and single neuron activity in the human medial temporal lobe during perception and memory."
5:00-5:30 Paul Tiesinga (UNC Chapel Hill) "The role of neural coherence in visual stimulus selection and attention: model studies at the local circuit level."
5:30-6:00 Nancy Kopell (Boston University) "Period concatenation underlies interaction between gamma and beta rhythms in neocortex."
6:00-6:15 Break
6:15-6:45 Gustavo Deco (Universitat Pompeu Fabra – Barcelona, Spain) "Computational role and dynamic range of neuronal synchronization during selective attentional processing in mult-layer models of cortical information processing."
6:45-7:15 Michael Breakspear (Sydney, Australia) "Bistability, super-diffusivity and nonlinearity in large scale brain rhythms."
7:15-7:30 Closing Discussion
Speaker Abstracts
Tim Blanche
The functional role of spike timing precision to the phase of local field potentials in primary visual cortex.
Irrespective of the functional role and dominant frequency of specific cortical oscillations, all are a manifestation of coherent activity in populations of neurons, and accordingly modulate the firing probability of individual neurons. My talk will focus on the interplay between spike timing and the phase of local field potentials (LFP) in different frequency bands, drawing upon data from multi-neuron recordings made in the primary visual cortex of anaesthetized cats and awake, free-viewing monkeys. Individual neurons show varying degrees of phase locking to the LFP in all of the classically defined EEG bands, independent of the visual stimulus. Neurons also exhibit remarkably high response reliability and spike timing precision, but only for stimuli that evoke periods of coherent large scale cortical activity. When ongoing stimulus-independent cortical dynamics dominate, as is the case with white noise, response variability is high. In contrast, highly reproducible responses are seen with both naturalistic stimuli and immediately following saccades, the latter accompanied by broadband LFP phase resetting. Complementary studies in humans reveal comparable phenomena in the occipital EEG. The functional implications of these findings are twofold: first, existing studies of neuronal response reliability that have ignored intrinsic cortical dynamics have underestimated the level of spike timing precision; second, under real world viewing conditions, saccadic phase resetting may be a mechanism for enabling precise temporal coding of information across large populations of neurons.
Jacob Reimer and Nicholas Hatsopoulos
Beta oscillations and the timing of early sensorimotor activity in primary motor cortex.
Oscillations in the beta (10-45Hz) frequency range are commonly observed throughout the motor system. As in other cortical areas, oscillations measured in the local field potential (LFP) of primary motor cortex (MI) are also reflected in periodic variations in the spiking probability of MI single units. These phenomena have typically been studied with respect to the cortical motor output (i.e. with respect to various features of behavior), and their effects on incoming sensory information in motor cortex have been relatively unexplored. We simultaneously recorded multiple single units and LFPs in MI in two monkeys (Macaca Mulatta) during continuous, self-paced movements to serially presented targets. Motivated by recent work in a variety of sensory areas, we examine the effect of phase-locked beta oscillations on temporally-precise responses to visual target events in MI. We find that beta oscillations temporally structure this event-related spiking, and that the information available in both single-unit and ensemble spiking varies with the phase of the oscillation. We propose that beta oscillations serve an important role in structuring early sensorimotor processing in MI.
Markus Siegel
Neuronal dynamics during active visual motion processing in humans.
In a series of experiments, we combined MEG and distributed source-reconstruction to investigate the role of oscillatory population activity at key processing stages along the human sensory-motor axis during active processing of visual motion. We have previously shown that oscillatory population activity, within distinct frequency ranges and cortical regions, reflects the strength of visual motion, predicts the accuracy of behavioral motion detection, and reflects the planning of a motor choice. It has also been proposed that oscillatory neuronal synchronization within and between cortical areas mediates the selection of attended stimuli for enhanced processing. Here, we focus on the question if, and at which processing stages, visuospatial attention modulates oscillatory synchronization in the human brain. We find that attention modulates local oscillatory population activity, in a spatially selective fashion, from early visual cortex up to parietal and prefrontal association cortex. However, the spectral signatures and stimulus dependencies of attentional effects differ markedly between these processing stages. Furthermore, spatial attention selectively modulates oscillatory synchronization between early visual, parietal, and prefrontal cortex in a stimulus independent fashion. Our data indicate that regionally and spectrally specific synchronization within most stages of the human dorsal visual pathway may mediate the enhanced processing of attended visual stimuli. Furthermore, attentional selection may be controlled by the synchronization between frontal-parietal and early visual cortex.
Florian Mormann
Brain oscillations and single neuron activity in the human medial temporal lobe during perception and memory.
This talk will address findings from electrophysiological recordings from the human medial temporal lobe (MTL), comprising both clinical depth electrodes and microwires. Recent research has indicated that the hippocampus and the entorhinal cortex in humans exhibit two independent rhythms of oscillatory activity in the theta range, which in turn modulates the amplitude of activity in the gamma range. The processing of visual stimuli in a continuous word recognition task causes a broad-band phase reset of ongoing theta activity in both structures. Single-neurons in the human MTL encode explicit and invariant representations of visual objects. The latencies of these explicit representations are substantially longer that those of a stimulus-related phase reset, indicating a role of this phase reset in the generation of these single-neuron responses. We observed a highly significant correlation between the latency and the selectivity of these neurons: the longer the latency the greater the selectivity. Particularly, parahippocampal neurons were found to respond significantly earlier and less selectively than those in the other three regions. These findings provide direct evidence for hierarchical processing of sensory information at the interface between the visual pathway and the limbic system, by which increasingly refined and specific representations of stimulus identity are generated over time along the anatomic pathways of the medial temporal lobe.
Nancy Kopell
Period concatenation underlies interaction between gamma and beta rhythms in neocortex.
The neocortex generates rhythmic electrical activity over a large frequency range, and can simultaneously express different rhythms. These rhythms can also undergo transitions to other frequencies. We describe recordings from in vitro preparations of rat somatosensory cortex showing that two frequencies (gamma-40 Hz and beta2 - 25 Hz), co-expressed in superficial and deep cortical laminae with low temporal interaction, can combine to generate a third frequency (beta 1- 15 hz) with strong temporal interaction among laminae. The process occurs via period concatenation, with basic rhythm-generating microcircuits underlying gamma and beta2 rhythms forming the building blocks of the beta1 rhythm by a process of addition. The mean ratio of both sets of adjacent frequency components was the same, approximately the golden mean, with implications for interactions of the rhythms.
Paul Tiesinga
The role of neural coherence in visual stimulus selection and attention: model studies at the local circuit level.
When cued appropriately, our visual system effortlessly detects a target among many distracters. For example, consider the problem of finding a friend among a crowd of people at a train station. We do not yet understand at the neural level how stimulus selection happens, but experiments suggest that it must involve feature-selective neurons in the visual cortex, whose response is modulated by the task at hand. At the population level, it also requires a rerouting of information flow between different cortical areas, which is associated with coherence changes in various frequency bands. A fundamental problem in neuroscience is to link response modulation at the single neuron level to that at the population level, which requires understanding the properties of the local cortical circuit and the development of new analysis methods. I will report on our recent efforts to make this link. We explore the hypothesis that interneuron diversity and interneuron-generated brain rhythms play a critical role in selective attention. Because of advances in molecular biology, this hypothesis currently is the focus of a major experimental effort.
Michael Breakspear
Bistability, super-diffusivity and nonlinearity in large scale brain rhythms.
It is widely assumed that the brain is a complex system par-excellence and should hence exhibit all the hallmarks of a self organising system, such as nonlinearity, coherency and non-diffusivity. Surprisingly, at least at the very large-scale of neocortical dynamics, there is actually little empirical evidence to support this, and hence most computational and methodological frameworks have proceeded quite adequately from a purely linear/diffusive perspective. In this talk, I will review some recent evidence that shows that whilst these simple assumptions hold true at some temporal scales, there is strong evidence for bistability and super-diffusivity in key brain rhythms. Bistability is manifest as non-classic bursting between high and low coherent modes in the alpha rhythm, whereas the beta rhythm exhibits irregular extremal amplitude events due to super-diffusivity. Whilst there is a good conceptual framework for understanding bistability in cortical dynamics, the implications of the extremal events challenges existing computational tools.
