Abstract
Linking the structural connectivity of brain circuits to their cooperative dynamics and emergent functions is a central aim of neuroscience research. Graph theory has recently been applied to study the structure-function relationship of networks, where dynamical similarity of different nodes has been turned into a “static” functional connection. However, the capability of the brain to adapt, learn and process external stimuli requires a constant dynamical functional rewiring between circuitries and cell assemblies. Hence, we must capture the changes of network functional connectivity over time. Multi-electrode array data present a unique challenge within this framework. We study the dynamics of gamma oscillations in acute slices of the somatosensory cortex from juvenile mice recorded by planar multi-electrode arrays. Bursts of gamma oscillatory activity lasting a few hundred milliseconds could be initiated only by brief trains of electrical stimulations applied at the deepest cortical layers and simultaneously delivered at multiple locations. Local field potentials were used to study the spatio-temporal properties and the instantaneous synchronization profile of the gamma oscillatory activity, combined with current source density (CSD) analysis. Pair-wise differences in the oscillation phase were used to determine the presence of instantaneous synchronization between the different sites of the circuitry during the oscillatory period. Despite variation in the duration of the oscillatory response over successive trials, they showed a constant average power, suggesting that the rate of expenditure of energy during the gamma bursts is consistent across repeated stimulations. Within each gamma burst, the functional connectivity map reflected the columnar organization of the neocortex. Over successive trials, an apparently random rearrangement of the functional connectivity was observed, with a more stable columnar than horizontal organization. This work reveals new features of evoked gamma oscillations in developing cortex.
Highlights
In the last decade, the connectome approach is providing more and more information on the wiring of the nervous system at different spatial scales of investigation, while multi-channel electrical and optical recordings provide a massive amount of data on brain activity dynamics recorded from multiple sites (Friston, 2005; Lebedev and Nicolelis, 2006; Homma et al, 2009; Sporns, 2011)
We focus on the dynamic aspect of transient coupling using a non-linear measure of functional connectivity
The electrical activity in the somatosensory cortical area was evoked and measured using multi-electrode arrays (MEAs) with 60 electrode terminals arranged in an 8 × 8 grid and with an inter-electrode distance of 100 or 200 μm with its top aligned at about 150 μm below the cortical surface
Summary
The connectome approach is providing more and more information on the wiring of the nervous system at different spatial scales of investigation, while multi-channel electrical and optical recordings provide a massive amount of data on brain activity dynamics recorded from multiple sites (Friston, 2005; Lebedev and Nicolelis, 2006; Homma et al, 2009; Sporns, 2011). There is a need for new theoretical and experimental tools to bridge these different levels (scale) of investigations (Stevenson et al, 2008; Rubinov and Sporns, 2010; Feldt et al, 2011; Bastos et al, 2012). By studying the dynamics of gamma oscillatory activity, a main brain rhythm (Buzsáki, 2006; Fries, 2009), we concentrate on establishing a clear and general set of tools that minimizes assumptions about network structure. Oscillations are seen in-vivo in local field potential and/or EEG signals, in peripheral structures (olfactory bulb), in sensory and motor cortices, in the hippocampus and in the thalamus
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