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Irregular spiking of pyramidal neurons organizes as scale-invariant neuronal avalanches in the awake state.

Bellay T, Klaus A, Seshadri S, Plenz D - Elife (2015)

Bottom Line: As the animal transitions from the anesthetized to awake state, spontaneous single neuron firing increases in irregularity and assembles into scale-invariant avalanches at the group level.In vitro spike avalanches emerged naturally yet required balanced excitation and inhibition.This demonstrates that neuronal avalanches are linked to the global physiological state of wakefulness and that cortical resting activity organizes as avalanches from firing of local PN groups to global population activity.

View Article: PubMed Central - PubMed

Affiliation: Section on Critical Brain Dynamics, National Institute of Mental Health, Bethesda, United States.

ABSTRACT
Spontaneous fluctuations in neuronal activity emerge at many spatial and temporal scales in cortex. Population measures found these fluctuations to organize as scale-invariant neuronal avalanches, suggesting cortical dynamics to be critical. Macroscopic dynamics, though, depend on physiological states and are ambiguous as to their cellular composition, spatiotemporal origin, and contributions from synaptic input or action potential (AP) output. Here, we study spontaneous firing in pyramidal neurons (PNs) from rat superficial cortical layers in vivo and in vitro using 2-photon imaging. As the animal transitions from the anesthetized to awake state, spontaneous single neuron firing increases in irregularity and assembles into scale-invariant avalanches at the group level. In vitro spike avalanches emerged naturally yet required balanced excitation and inhibition. This demonstrates that neuronal avalanches are linked to the global physiological state of wakefulness and that cortical resting activity organizes as avalanches from firing of local PN groups to global population activity.

No MeSH data available.


Related in: MedlinePlus

Single AP detection in YC2.60-expressing neurons at physiological temperature and performance of the OOPSI deconvolution algorithm.(A) Using whole-cell patch recording of YC2.60-expressing PNs in cortical slice cultures, we confirmed that YC2.60 reliably resolved spontaneous single AP firing at physiological temperature (∼32°C), in line with previous reports (Yamada et al., 2011). Gray: Individual trials: Black: Average. Inset: Zoomed view of bar graph from 1 AP subpanel. Note the decay in ΔR/R by ∼2/3 within 1–2 s. Responses from single PN. (B) Peak and integral of instantaneous rate λ as well as peak ΔR/R linearly increase with the number of spontaneous APs/250 ms (n = 7 neurons). (C) Single movie data showing that the minimum reconstruction error of the deconvolution was found at decay time τ = 1.5 s (n = 39 ROIs).DOI:http://dx.doi.org/10.7554/eLife.07224.004
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fig1s1: Single AP detection in YC2.60-expressing neurons at physiological temperature and performance of the OOPSI deconvolution algorithm.(A) Using whole-cell patch recording of YC2.60-expressing PNs in cortical slice cultures, we confirmed that YC2.60 reliably resolved spontaneous single AP firing at physiological temperature (∼32°C), in line with previous reports (Yamada et al., 2011). Gray: Individual trials: Black: Average. Inset: Zoomed view of bar graph from 1 AP subpanel. Note the decay in ΔR/R by ∼2/3 within 1–2 s. Responses from single PN. (B) Peak and integral of instantaneous rate λ as well as peak ΔR/R linearly increase with the number of spontaneous APs/250 ms (n = 7 neurons). (C) Single movie data showing that the minimum reconstruction error of the deconvolution was found at decay time τ = 1.5 s (n = 39 ROIs).DOI:http://dx.doi.org/10.7554/eLife.07224.004

Mentions: To identify the relationship between AP firing and neuronal avalanches, which are primarily found in superficial layers of cortex (Stewart and Plenz, 2006; Petermann et al., 2009), we expressed the genetically encoded calcium indicator (GECI) YC2.60 (Yamada et al., 2011) in layer 2/3 (L2/3) PNs of rats using in utero electroporation at embryonic day 15.5 ± 0.5 (Saito, 2006). Labeled mature neurons distributed throughout dorsolateral frontal and sensorimotor cortex. They exhibited PN morphology (Figure 1A), and their synaptic transmission was blocked by glutamate receptor antagonists (data not shown). To record ongoing AP activity in local PN groups, we performed 2-photon imaging (2-PI) of YC2.60-expressing PNs in head-restrained rats (Figure 1A,B; depth = 270 ± 50 µm; cortical area = 0.15 ± 0.05 mm2; 10–15 min per recording). Recordings were done under anesthesia (AN; 1–2% isoflurane), during wakening (WK; 5–20 min at 0% isoflurane), and in the awake state (AW; after >20 min at 0% isoflurane). Intracellular calcium transients produced fluorescence changes in visually identified somatic ROIs (Figure 1B), which were converted into ratiometric time courses (ΔR/R) and then deconvolved to obtain an instantaneous firing rate estimate, λ, for each neuron (Vogelstein et al., 2010) (see ‘Materials and methods’; Figure 1C,D). In control experiments, we showed (1) YC2.60 reliably and linearly reported AP activity at physiological temperature from single APs to AP bursts up to 28 Hz (Figure 1—figure supplement 1A,B) and (2) λ linearly recovered spike trains at different temporal resolutions (Figure 1—figure supplement 2). We first recorded at a temporal resolution of Δt = 250 ms (n = 6 rats; 38 recordings; 15–30 active PNs/recording; >1 AP/min). Neuronal activity was stationary in λ and in the average crosscorrelation, R, between ROIs (Figure 1E,F, respectively). Neurons fired on average more during AW compared to WK and AN (ANOVA, F(2,35) = 23.05, p < 0.001; probability density function (PDF) shown in Figure 1G). Under all three conditions, though, neurons fired irregular APs interspaced by relatively long periods of quiescence. This was quantified by three measures. First, λ distributed exponentially for single neurons [log-likelihood ratio (LLR) comparison between power law vs exponential, >98% of ROIs in favor of exponential distribution, p < 0.05; Figure 2A, single distributions and average for one PN group; Figure 2B, averages over all PN groups]. Second, neurons tended to not fire at all within Δt (Figure 2A,B, left; arrow). The corresponding probability of quiescence, Pq (λ < minimal λ threshold, λthr, set to 0.5), was highest for AN and WK (Figure 2B, inset; ANOVA, F(2,35) = 23.05, p = 0.002). Both of these characteristics remained true for higher temporal resolutions despite the expected increase in λ fluctuations (Figure 2B, right; additional n = 6 rats; n = 19 recordings; Δt = 167 and 88 ms during AW; LLR in favor of exponential, p < 0.05) and Pq (ANOVA, F(2,28) = 31.46, p < 0.001). Third, the normalized duration of quiescent times, IBInorm, between firing (i.e., λ < λthr = 0.5) also distributed exponentially for all conditions (Figure 2A, right; Figure 2C; LLR: >98% of ROIs with p < 0.05). The corresponding CV was larger than 1 for all conditions, was significantly higher for AW than WK and AN (Figure 2C, left; inset, AW: 1.5 ± 0.2; WK: 1.2 ± 0.1; AN: 1.2 ± 0.1; mean ± SD, F(2,35) = 25.66, p < 0.001), and increased further with temporal resolution (AW, Figure 2C, right; Δt = 167 ms, 1.9 ± 0.4; Δt = 88 ms, 2.1 ± 0.3, mean ± SD; F(2,28) = 15.48, p < 0.001). This irregularity was also robust to minimal AP activity: increasing λthr smoothly reduced the average firing rate λavg (data not shown), yet maintained a CV larger than 1 for all conditions and Δt (Figure 2—figure supplement 1). CV values for single units (n = 26; average firing rate = 1.3 Hz; range: 0.1–6.2 Hz) recorded with chronic microelectrode arrays from superficial layers in the AW rat (Figure 1—figure supplement 2) compared favorably with λ results from our imaging analysis and ranged between 1.6 ± 0.4 (Δt = 0.033 ms) and 1.3 ± 0.3 (resampled at Δt = 250 ms), respectively.10.7554/eLife.07224.003Figure 1.Imaging of ongoing spiking activity in groups of L2/3 PNs in the awake (AW) rat.


Irregular spiking of pyramidal neurons organizes as scale-invariant neuronal avalanches in the awake state.

Bellay T, Klaus A, Seshadri S, Plenz D - Elife (2015)

Single AP detection in YC2.60-expressing neurons at physiological temperature and performance of the OOPSI deconvolution algorithm.(A) Using whole-cell patch recording of YC2.60-expressing PNs in cortical slice cultures, we confirmed that YC2.60 reliably resolved spontaneous single AP firing at physiological temperature (∼32°C), in line with previous reports (Yamada et al., 2011). Gray: Individual trials: Black: Average. Inset: Zoomed view of bar graph from 1 AP subpanel. Note the decay in ΔR/R by ∼2/3 within 1–2 s. Responses from single PN. (B) Peak and integral of instantaneous rate λ as well as peak ΔR/R linearly increase with the number of spontaneous APs/250 ms (n = 7 neurons). (C) Single movie data showing that the minimum reconstruction error of the deconvolution was found at decay time τ = 1.5 s (n = 39 ROIs).DOI:http://dx.doi.org/10.7554/eLife.07224.004
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4492006&req=5

fig1s1: Single AP detection in YC2.60-expressing neurons at physiological temperature and performance of the OOPSI deconvolution algorithm.(A) Using whole-cell patch recording of YC2.60-expressing PNs in cortical slice cultures, we confirmed that YC2.60 reliably resolved spontaneous single AP firing at physiological temperature (∼32°C), in line with previous reports (Yamada et al., 2011). Gray: Individual trials: Black: Average. Inset: Zoomed view of bar graph from 1 AP subpanel. Note the decay in ΔR/R by ∼2/3 within 1–2 s. Responses from single PN. (B) Peak and integral of instantaneous rate λ as well as peak ΔR/R linearly increase with the number of spontaneous APs/250 ms (n = 7 neurons). (C) Single movie data showing that the minimum reconstruction error of the deconvolution was found at decay time τ = 1.5 s (n = 39 ROIs).DOI:http://dx.doi.org/10.7554/eLife.07224.004
Mentions: To identify the relationship between AP firing and neuronal avalanches, which are primarily found in superficial layers of cortex (Stewart and Plenz, 2006; Petermann et al., 2009), we expressed the genetically encoded calcium indicator (GECI) YC2.60 (Yamada et al., 2011) in layer 2/3 (L2/3) PNs of rats using in utero electroporation at embryonic day 15.5 ± 0.5 (Saito, 2006). Labeled mature neurons distributed throughout dorsolateral frontal and sensorimotor cortex. They exhibited PN morphology (Figure 1A), and their synaptic transmission was blocked by glutamate receptor antagonists (data not shown). To record ongoing AP activity in local PN groups, we performed 2-photon imaging (2-PI) of YC2.60-expressing PNs in head-restrained rats (Figure 1A,B; depth = 270 ± 50 µm; cortical area = 0.15 ± 0.05 mm2; 10–15 min per recording). Recordings were done under anesthesia (AN; 1–2% isoflurane), during wakening (WK; 5–20 min at 0% isoflurane), and in the awake state (AW; after >20 min at 0% isoflurane). Intracellular calcium transients produced fluorescence changes in visually identified somatic ROIs (Figure 1B), which were converted into ratiometric time courses (ΔR/R) and then deconvolved to obtain an instantaneous firing rate estimate, λ, for each neuron (Vogelstein et al., 2010) (see ‘Materials and methods’; Figure 1C,D). In control experiments, we showed (1) YC2.60 reliably and linearly reported AP activity at physiological temperature from single APs to AP bursts up to 28 Hz (Figure 1—figure supplement 1A,B) and (2) λ linearly recovered spike trains at different temporal resolutions (Figure 1—figure supplement 2). We first recorded at a temporal resolution of Δt = 250 ms (n = 6 rats; 38 recordings; 15–30 active PNs/recording; >1 AP/min). Neuronal activity was stationary in λ and in the average crosscorrelation, R, between ROIs (Figure 1E,F, respectively). Neurons fired on average more during AW compared to WK and AN (ANOVA, F(2,35) = 23.05, p < 0.001; probability density function (PDF) shown in Figure 1G). Under all three conditions, though, neurons fired irregular APs interspaced by relatively long periods of quiescence. This was quantified by three measures. First, λ distributed exponentially for single neurons [log-likelihood ratio (LLR) comparison between power law vs exponential, >98% of ROIs in favor of exponential distribution, p < 0.05; Figure 2A, single distributions and average for one PN group; Figure 2B, averages over all PN groups]. Second, neurons tended to not fire at all within Δt (Figure 2A,B, left; arrow). The corresponding probability of quiescence, Pq (λ < minimal λ threshold, λthr, set to 0.5), was highest for AN and WK (Figure 2B, inset; ANOVA, F(2,35) = 23.05, p = 0.002). Both of these characteristics remained true for higher temporal resolutions despite the expected increase in λ fluctuations (Figure 2B, right; additional n = 6 rats; n = 19 recordings; Δt = 167 and 88 ms during AW; LLR in favor of exponential, p < 0.05) and Pq (ANOVA, F(2,28) = 31.46, p < 0.001). Third, the normalized duration of quiescent times, IBInorm, between firing (i.e., λ < λthr = 0.5) also distributed exponentially for all conditions (Figure 2A, right; Figure 2C; LLR: >98% of ROIs with p < 0.05). The corresponding CV was larger than 1 for all conditions, was significantly higher for AW than WK and AN (Figure 2C, left; inset, AW: 1.5 ± 0.2; WK: 1.2 ± 0.1; AN: 1.2 ± 0.1; mean ± SD, F(2,35) = 25.66, p < 0.001), and increased further with temporal resolution (AW, Figure 2C, right; Δt = 167 ms, 1.9 ± 0.4; Δt = 88 ms, 2.1 ± 0.3, mean ± SD; F(2,28) = 15.48, p < 0.001). This irregularity was also robust to minimal AP activity: increasing λthr smoothly reduced the average firing rate λavg (data not shown), yet maintained a CV larger than 1 for all conditions and Δt (Figure 2—figure supplement 1). CV values for single units (n = 26; average firing rate = 1.3 Hz; range: 0.1–6.2 Hz) recorded with chronic microelectrode arrays from superficial layers in the AW rat (Figure 1—figure supplement 2) compared favorably with λ results from our imaging analysis and ranged between 1.6 ± 0.4 (Δt = 0.033 ms) and 1.3 ± 0.3 (resampled at Δt = 250 ms), respectively.10.7554/eLife.07224.003Figure 1.Imaging of ongoing spiking activity in groups of L2/3 PNs in the awake (AW) rat.

Bottom Line: As the animal transitions from the anesthetized to awake state, spontaneous single neuron firing increases in irregularity and assembles into scale-invariant avalanches at the group level.In vitro spike avalanches emerged naturally yet required balanced excitation and inhibition.This demonstrates that neuronal avalanches are linked to the global physiological state of wakefulness and that cortical resting activity organizes as avalanches from firing of local PN groups to global population activity.

View Article: PubMed Central - PubMed

Affiliation: Section on Critical Brain Dynamics, National Institute of Mental Health, Bethesda, United States.

ABSTRACT
Spontaneous fluctuations in neuronal activity emerge at many spatial and temporal scales in cortex. Population measures found these fluctuations to organize as scale-invariant neuronal avalanches, suggesting cortical dynamics to be critical. Macroscopic dynamics, though, depend on physiological states and are ambiguous as to their cellular composition, spatiotemporal origin, and contributions from synaptic input or action potential (AP) output. Here, we study spontaneous firing in pyramidal neurons (PNs) from rat superficial cortical layers in vivo and in vitro using 2-photon imaging. As the animal transitions from the anesthetized to awake state, spontaneous single neuron firing increases in irregularity and assembles into scale-invariant avalanches at the group level. In vitro spike avalanches emerged naturally yet required balanced excitation and inhibition. This demonstrates that neuronal avalanches are linked to the global physiological state of wakefulness and that cortical resting activity organizes as avalanches from firing of local PN groups to global population activity.

No MeSH data available.


Related in: MedlinePlus