493 research outputs found
Neural synchrony in cortical networks : history, concept and current status
Following the discovery of context-dependent synchronization of oscillatory neuronal responses in the visual system, the role of neural synchrony in cortical networks has been expanded to provide a general mechanism for the coordination of distributed neural activity patterns. In the current paper, we present an update of the status of this hypothesis through summarizing recent results from our laboratory that suggest important new insights regarding the mechanisms, function and relevance of this phenomenon. In the first part, we present recent results derived from animal experiments and mathematical simulations that provide novel explanations and mechanisms for zero and nero-zero phase lag synchronization. In the second part, we shall discuss the role of neural synchrony for expectancy during perceptual organization and its role in conscious experience. This will be followed by evidence that indicates that in addition to supporting conscious cognition, neural synchrony is abnormal in major brain disorders, such as schizophrenia and autism spectrum disorders. We conclude this paper with suggestions for further research as well as with critical issues that need to be addressed in future studies
Neural synchrony in cortical networks : history, concept and current status
Following the discovery of context-dependent synchronization of oscillatory neuronal responses in the visual system, the role of neural synchrony in cortical networks has been expanded to provide a general mechanism for the coordination of distributed neural activity patterns. In the current paper, we present an update of the status of this hypothesis through summarizing recent results from our laboratory that suggest important new insights regarding the mechanisms, function and relevance of this phenomenon. In the first part, we present recent results derived from animal experiments and mathematical simulations that provide novel explanations and mechanisms for zero and nero-zero phase lag synchronization. In the second part, we shall discuss the role of neural synchrony for expectancy during perceptual organization and its role in conscious experience. This will be followed by evidence that indicates that in addition to supporting conscious cognition, neural synchrony is abnormal in major brain disorders, such as schizophrenia and autism spectrum disorders. We conclude this paper with suggestions for further research as well as with critical issues that need to be addressed in future studies
LFP beta amplitude is predictive of mesoscopic spatio-temporal phase patterns
Beta oscillations observed in motor cortical local field potentials (LFPs)
recorded on separate electrodes of a multi-electrode array have been shown to
exhibit non-zero phase shifts that organize into a planar wave propagation.
Here, we generalize this concept by introducing additional classes of patterns
that fully describe the spatial organization of beta oscillations. During a
delayed reach-to-grasp task in monkey primary motor and dorsal premotor
cortices we distinguish planar, synchronized, random, circular, and radial
phase patterns. We observe that specific patterns correlate with the beta
amplitude (envelope). In particular, wave propagation accelerates with growing
amplitude, and culminates at maximum amplitude in a synchronized pattern.
Furthermore, the occurrence probability of a particular pattern is modulated
with behavioral epochs: Planar waves and synchronized patterns are more present
during movement preparation where beta amplitudes are large, whereas random
phase patterns are dominant during movement execution where beta amplitudes are
small
Investigating the role of fast-spiking interneurons in neocortical dynamics
PhD ThesisFast-spiking interneurons are the largest interneuronal population in neocortex. It is
well documented that this population is crucial in many functions of the neocortex by
subserving all aspects of neural computation, like gain control, and by enabling
dynamic phenomena, like the generation of high frequency oscillations. Fast-spiking
interneurons, which represent mainly the parvalbumin-expressing, soma-targeting
basket cells, are also implicated in pathological dynamics, like the propagation of
seizures or the impaired coordination of activity in schizophrenia. In the present thesis,
I investigate the role of fast-spiking interneurons in such dynamic phenomena by using
computational and experimental techniques.
First, I introduce a neural mass model of the neocortical microcircuit featuring divisive
inhibition, a gain control mechanism, which is thought to be delivered mainly by the
soma-targeting interneurons. Its dynamics were analysed at the onset of chaos and
during the phenomena of entrainment and long-range synchronization. It is
demonstrated that the mechanism of divisive inhibition reduces the sensitivity of the
network to parameter changes and enhances the stability and
exibility of oscillations.
Next, in vitro electrophysiology was used to investigate the propagation of activity in
the network of electrically coupled fast-spiking interneurons. Experimental evidence
suggests that these interneurons and their gap junctions are involved in the propagation
of seizures. Using multi-electrode array recordings and optogenetics, I investigated the
possibility of such propagating activity under the conditions of raised extracellular K+
concentration which applies during seizures. Propagated activity was recorded and the
involvement of gap junctions was con rmed by pharmacological manipulations.
Finally, the interaction between two oscillations was investigated. Two oscillations with di erent frequencies were induced in cortical slices by directly activating the pyramidal
cells using optogenetics. Their interaction suggested the possibility of a coincidence
detection mechanism at the circuit level. Pharmacological manipulations were used to
explore the role of the inhibitory interneurons during this phenomenon. The results,
however, showed that the observed phenomenon was not a result of synaptic activity.
Nevertheless, the experiments provided some insights about the excitability of the
tissue through scattered light while using optogenetics.
This investigation provides new insights into the role of fast-spiking interneurons in the
neocortex. In particular, it is suggested that the gain control mechanism is important
for the physiological oscillatory dynamics of the network and that the gap junctions
between these interneurons can potentially contribute to the inhibitory restraint during
a seizure.Wellcome Trust
Entropy-based parametric estimation of spike train statistics
We consider the evolution of a network of neurons, focusing on the asymptotic
behavior of spikes dynamics instead of membrane potential dynamics. The spike
response is not sought as a deterministic response in this context, but as a
conditional probability : "Reading out the code" consists of inferring such a
probability. This probability is computed from empirical raster plots, by using
the framework of thermodynamic formalism in ergodic theory. This gives us a
parametric statistical model where the probability has the form of a Gibbs
distribution. In this respect, this approach generalizes the seminal and
profound work of Schneidman and collaborators. A minimal presentation of the
formalism is reviewed here, while a general algorithmic estimation method is
proposed yielding fast convergent implementations. It is also made explicit how
several spike observables (entropy, rate, synchronizations, correlations) are
given in closed-form from the parametric estimation. This paradigm does not
only allow us to estimate the spike statistics, given a design choice, but also
to compare different models, thus answering comparative questions about the
neural code such as : "are correlations (or time synchrony or a given set of
spike patterns, ..) significant with respect to rate coding only ?" A numerical
validation of the method is proposed and the perspectives regarding spike-train
code analysis are also discussed.Comment: 37 pages, 8 figures, submitte
- …