Zero-lag synchronization in neural populations: where are the strong evidences?

1. The Human Brain and Behavior Laboratory Zero-lag synchronization in neural populations: where are the strong evidences? http://www.ccs.fau.edu/hbbl.html Emmanuelle Tognoli 02/01/2008 Journal Club

2. Synchronization at the microscopic level?

4. 2mV 100ms

5. Translation of cortical phase models across levels

6. p/2 p/2 p/2 p p 0 0 p 0 3p/2 3p/2 3p/2 Syn-chronos 4p/3 0 msec 67 msec 50 msec A C B

7. Hypotheses about phase relationships in neural cell assemblies at macroscopic level

8. p/2 p 0 3p/2 Zero-Lag Synchronization Electrical: Spatial summation Chemical: LTP/LTD 0 msec A

9. Chemical: LTP/LTD Electrical: Spatial summation

10. "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 Deconvolutionto Compensate for Distortion of EEG by Volume Conduction. IEEE Transactions On Biomedical Engineering, Vol. Bme-27, No. 8. “…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

11. f = dw - a sinf - 2b sin (2f) + Qxt Extended HKB model

12. Hypotheses about phase relationships in neural cell assemblies at macroscopic level (Near) inphase and (near) antiphase Everything… but no antiphase Only zero lag

13. Have we really seen the phase that everybody is talking about?

17. Theoretical hypothesis • Mutual influence depends mechanistically on the phase (Markram: synchrony causes synaptic change)

18. Operational hypothesis =f ( )

20. Zero-lag?

21. Phase preference? Phase locked?

24. Adapted from Molotchnikoff & Shumikhina, 2000

25. Tognoli & Kelso, (submitted)

26. E1=0.95*S1+p*S2 E2=0.95*S2+p*S1 E2: AE2: amplitude at location 1 fE2: frequency at location 1 fE2: phase at location 1 E1: AE1: amplitude at location 1 fE1:frequency at location 1 fE1: phase at location 1 S2: AS2: amplitude at location 1 fS2: frequency at location 1 fS2: phase at location 1 S1: AS1: amplitude at location 1 fS1:frequency at location 1 fS1: phase at location 1 Tognoli & Kelso, (submitted)

27. Two coupled oscillations Tognoli & Kelso, (submitted)

28. Two uncoupled oscillations Tognoli & Kelso, (submitted)

29. 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.