zero-lag synchronization in neural populations: where are the strong evidences? the human brain and...
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Zero-lag synchronization in neural populations: where are the strong
evidences?
The Human
Brain and Behavior
Laboratory
Emmanuelle Tognoli
02/01/2008Journal Club
http://www.ccs.fau.edu/hbbl.html
Synchronization at the microscopic level?
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4
100ms
2mV
Translation of cortical phase models across levels
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Syn-chronos
0
p/2
3p/2
p 0
p/2
3p/2
p0
p/2
p
3p/24p/3
50 msec
67 msecA B C
0 msec
Hypotheses about phase relationships in neural cell assemblies at
macroscopic level
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0
p/2
3p/2
p
A
0 msec
Electrical:Spatial
summation
Chemical:LTP/LTD
Zero-Lag Synchronization
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Electrical:Spatial
summation
Chemical:LTP/LTD
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“…my evidence in the past 18 years for sustained synchrony (never antiphasic), for spatial phase gradients in intracranial EEGs
from high-density arrays, and for phase cones with phase velocities corresponding to intracortical axonal propagation
velocities as evidence for state transitions.”
Walter Freeman
"However, there is an important discrepancy between the EEG phase patterns (x) and the phase patterns of the model j. The values of (x) [real EEG] seldom exceed ±20°, or about 5 percent of the mean cycle duration of the ensemble average. The values for ji [modeled EEG] range from +70° phase lead to –160° phase lag from the ensemble average”
Freeman WJ., (1980). Use of Spatial Deconvolution to Compensate for Distortion of EEG by Volume Conduction. IEEE Transactions On Biomedical Engineering, Vol. Bme-27, No. 8.
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f = dw - a sinf - 2b sin (2f) + QxtExtended HKB model
Hypotheses about phase relationships in neural cell assemblies at
macroscopic level
Only zero lag Everything… but no antiphase
(Near) inphase and
(near) antiphase
Have we really seen the phase that everybody is talking about?
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Theoretical hypothesis
• Mutual influence depends mechanistically on the phase (Markram: synchrony causes synaptic change)
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Operational hypothesis
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=f ( )
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Zero-lag?
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Phase preference?
Phase locked?
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24 Adapted from Molotchnikoff & Shumikhina, 2000
26Tognoli & Kelso, (submitted)
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E1: AE1: amplitude at location 1fE1:frequency at location 1fE1: phase at location 1
E2: AE2: amplitude at
location 1fE2: frequency at location
1fE2: phase at location 1
S1: AS1: amplitude at location 1fS1:frequency at location 1fS1: phase at location 1
S2: AS2: amplitude at
location 1fS2: frequency at location
1fS2: phase at location 1
E1=0.95*S1+p*S2
E2=0.95*S2+p*S1
Tognoli & Kelso, (submitted)
28Tognoli & Kelso, (submitted)
Two coupled oscillations
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Tognoli & Kelso, (submitted)Two uncoupled oscillations
Conclusions:We found no solid evidence to
support the preference for zero-lag synchronization in large-scale neural
cell assemblies.
Because inphase, antiphase, and other phases are differently affected by spurious synchrony, more studies are needed to characterize the real
distribution of relative phase in coordinated brain states.