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Emergence of spatially heterogeneous burst suppression in a neural field model of electrocortical activity.

Bojak I, Stoyanov ZV, Liley DT - Front Syst Neurosci (2015)

Bottom Line: Classically it is thought of as spatially synchronous, quasi-periodic bursts of high amplitude EEG separated by low amplitude activity.However, its characterization as a "global brain state" has been challenged by recent results obtained with intracranial electrocortigraphy.Simulations reveal heterogeneous bursting over the model cortex and complex spatiotemporal dynamics during simulated anesthetic action, and provide forward predictions of neuroimaging signals for subsequent empirical comparisons and more detailed characterization.

View Article: PubMed Central - PubMed

Affiliation: Systems Neuroscience Research Group, School of Systems Engineering, University of Reading Reading, UK.

ABSTRACT
Burst suppression in the electroencephalogram (EEG) is a well-described phenomenon that occurs during deep anesthesia, as well as in a variety of congenital and acquired brain insults. Classically it is thought of as spatially synchronous, quasi-periodic bursts of high amplitude EEG separated by low amplitude activity. However, its characterization as a "global brain state" has been challenged by recent results obtained with intracranial electrocortigraphy. Not only does it appear that burst suppression activity is highly asynchronous across cortex, but also that it may occur in isolated regions of circumscribed spatial extent. Here we outline a realistic neural field model for burst suppression by adding a slow process of synaptic resource depletion and recovery, which is able to reproduce qualitatively the empirically observed features during general anesthesia at the whole cortex level. Simulations reveal heterogeneous bursting over the model cortex and complex spatiotemporal dynamics during simulated anesthetic action, and provide forward predictions of neuroimaging signals for subsequent empirical comparisons and more detailed characterization. Because burst suppression corresponds to a dynamical end-point of brain activity, theoretically accounting for its spatiotemporal emergence will vitally contribute to efforts aimed at clarifying whether a common physiological trajectory is induced by the actions of general anesthetic agents. We have taken a first step in this direction by showing that a neural field model can qualitatively match recent experimental data that indicate spatial differentiation of burst suppression activity across cortex.

No MeSH data available.


Related in: MedlinePlus

(A) Snapshot of the he activity of the cortical surface at simulation time 54.94 s under the influence of 1 MAC isoflurane. Black arrows with labels “a,” “b,” and “c” point to the cortical locations of the time series shown in the other panel. Note the toroidal boundaries, e.g., the circular burst front that appears cut off around (x,y) = (44.8, 0) cm continues at x = (44.8, 51.2) cm. (B) Time series of he (blue) and Γee (green) taken from the three different positions marked as “a,” “b,” and “c” in the other panel. It is obvious that bursts are not generally synchronized in time at the different positions. Spatiotemporal correlations from propagating “burst waves” can occur, but are removed at larger distances by the interference from other emergent patterns. An animation of this simulation is provided as Movie 1 in the Supplementary Material.
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Figure 3: (A) Snapshot of the he activity of the cortical surface at simulation time 54.94 s under the influence of 1 MAC isoflurane. Black arrows with labels “a,” “b,” and “c” point to the cortical locations of the time series shown in the other panel. Note the toroidal boundaries, e.g., the circular burst front that appears cut off around (x,y) = (44.8, 0) cm continues at x = (44.8, 51.2) cm. (B) Time series of he (blue) and Γee (green) taken from the three different positions marked as “a,” “b,” and “c” in the other panel. It is obvious that bursts are not generally synchronized in time at the different positions. Spatiotemporal correlations from propagating “burst waves” can occur, but are removed at larger distances by the interference from other emergent patterns. An animation of this simulation is provided as Movie 1 in the Supplementary Material.

Mentions: The burst suppression phase shown in Movie 1 of the Supplementary Material makes obvious that one cannot expect global synchrony of the burst suppression across cortex. A multitude of transient spatiotemporal patterns emerge, travel across cortex, and dissolve. This is also shown in Figure 3, which shows time series from three well-separated locations on the simulated cortex at a specific point in time. There is little evidence of strong systematic correlations. While one might expect that the propagation of “burst waves” should lead to correlations with temporal delay at these distances, other burst features emerge across these spatial scales and interfere with the burst timing. Without observing spatiotemporal pattern globally, it hence will be difficult to find systematic correlations of the bursts at large distances. However, locally it may be possible to track the regular motion of burst patterns, e.g., at a point close to the one labeled “a” one might see bursting appear with a delay, characteristic for the “burst wave” passing through these two points sequentially. Overall, we expect stronger synchronization—or at least consistent phase differences from traveling patterns—at shorter distances, whereas at longer distances such correlations will be basically accidental. Thus, one would expect to see considerable spatial differentiation if one records from several spatial locations, as in Lewis et al. (2013). How many electrodes would be seen to burst at the same time would depend on the size and motion of the emerging spatiotemporal burst patterns.


Emergence of spatially heterogeneous burst suppression in a neural field model of electrocortical activity.

Bojak I, Stoyanov ZV, Liley DT - Front Syst Neurosci (2015)

(A) Snapshot of the he activity of the cortical surface at simulation time 54.94 s under the influence of 1 MAC isoflurane. Black arrows with labels “a,” “b,” and “c” point to the cortical locations of the time series shown in the other panel. Note the toroidal boundaries, e.g., the circular burst front that appears cut off around (x,y) = (44.8, 0) cm continues at x = (44.8, 51.2) cm. (B) Time series of he (blue) and Γee (green) taken from the three different positions marked as “a,” “b,” and “c” in the other panel. It is obvious that bursts are not generally synchronized in time at the different positions. Spatiotemporal correlations from propagating “burst waves” can occur, but are removed at larger distances by the interference from other emergent patterns. An animation of this simulation is provided as Movie 1 in the Supplementary Material.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4341547&req=5

Figure 3: (A) Snapshot of the he activity of the cortical surface at simulation time 54.94 s under the influence of 1 MAC isoflurane. Black arrows with labels “a,” “b,” and “c” point to the cortical locations of the time series shown in the other panel. Note the toroidal boundaries, e.g., the circular burst front that appears cut off around (x,y) = (44.8, 0) cm continues at x = (44.8, 51.2) cm. (B) Time series of he (blue) and Γee (green) taken from the three different positions marked as “a,” “b,” and “c” in the other panel. It is obvious that bursts are not generally synchronized in time at the different positions. Spatiotemporal correlations from propagating “burst waves” can occur, but are removed at larger distances by the interference from other emergent patterns. An animation of this simulation is provided as Movie 1 in the Supplementary Material.
Mentions: The burst suppression phase shown in Movie 1 of the Supplementary Material makes obvious that one cannot expect global synchrony of the burst suppression across cortex. A multitude of transient spatiotemporal patterns emerge, travel across cortex, and dissolve. This is also shown in Figure 3, which shows time series from three well-separated locations on the simulated cortex at a specific point in time. There is little evidence of strong systematic correlations. While one might expect that the propagation of “burst waves” should lead to correlations with temporal delay at these distances, other burst features emerge across these spatial scales and interfere with the burst timing. Without observing spatiotemporal pattern globally, it hence will be difficult to find systematic correlations of the bursts at large distances. However, locally it may be possible to track the regular motion of burst patterns, e.g., at a point close to the one labeled “a” one might see bursting appear with a delay, characteristic for the “burst wave” passing through these two points sequentially. Overall, we expect stronger synchronization—or at least consistent phase differences from traveling patterns—at shorter distances, whereas at longer distances such correlations will be basically accidental. Thus, one would expect to see considerable spatial differentiation if one records from several spatial locations, as in Lewis et al. (2013). How many electrodes would be seen to burst at the same time would depend on the size and motion of the emerging spatiotemporal burst patterns.

Bottom Line: Classically it is thought of as spatially synchronous, quasi-periodic bursts of high amplitude EEG separated by low amplitude activity.However, its characterization as a "global brain state" has been challenged by recent results obtained with intracranial electrocortigraphy.Simulations reveal heterogeneous bursting over the model cortex and complex spatiotemporal dynamics during simulated anesthetic action, and provide forward predictions of neuroimaging signals for subsequent empirical comparisons and more detailed characterization.

View Article: PubMed Central - PubMed

Affiliation: Systems Neuroscience Research Group, School of Systems Engineering, University of Reading Reading, UK.

ABSTRACT
Burst suppression in the electroencephalogram (EEG) is a well-described phenomenon that occurs during deep anesthesia, as well as in a variety of congenital and acquired brain insults. Classically it is thought of as spatially synchronous, quasi-periodic bursts of high amplitude EEG separated by low amplitude activity. However, its characterization as a "global brain state" has been challenged by recent results obtained with intracranial electrocortigraphy. Not only does it appear that burst suppression activity is highly asynchronous across cortex, but also that it may occur in isolated regions of circumscribed spatial extent. Here we outline a realistic neural field model for burst suppression by adding a slow process of synaptic resource depletion and recovery, which is able to reproduce qualitatively the empirically observed features during general anesthesia at the whole cortex level. Simulations reveal heterogeneous bursting over the model cortex and complex spatiotemporal dynamics during simulated anesthetic action, and provide forward predictions of neuroimaging signals for subsequent empirical comparisons and more detailed characterization. Because burst suppression corresponds to a dynamical end-point of brain activity, theoretically accounting for its spatiotemporal emergence will vitally contribute to efforts aimed at clarifying whether a common physiological trajectory is induced by the actions of general anesthetic agents. We have taken a first step in this direction by showing that a neural field model can qualitatively match recent experimental data that indicate spatial differentiation of burst suppression activity across cortex.

No MeSH data available.


Related in: MedlinePlus