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

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?

3

4

100ms

2mV

Translation of cortical phase models across levels

6

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

8

0

p/2

3p/2

p

A0 msec

Electrical:Spatial

summation

Chemical:LTP/LTD

Zero-Lag Synchronization

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Electrical:Spatial

summation

Chemical:LTP/LTD

10

“…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.

11

= dw - a sin - 2b sin (2) + 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?

14

15

16

Theoretical hypothesis

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

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Operational hypothesis

18

=f ( )

19

20

Zero-lag?

21

Phase preference?

Phase locked?

22

23

24 Adapted from Molotchnikoff & Shumikhina, 2000

26Tognoli & Kelso, (submitted)

27

E1: AE1: amplitude at location 1fE1:frequency at location 1E1: phase at location 1

E2: AE2: amplitude at

location 1fE2: frequency at location

1E2: phase at location 1

S1: AS1: amplitude at location 1fS1:frequency at location 1S1: phase at location 1

S2: AS2: amplitude at

location 1fS2: frequency at location

1S2: phase at location 1

E1=0.95*S1+p*S2E2=0.95*S2+p*S1

Tognoli & Kelso, (submitted)

28Tognoli & Kelso, (submitted)

Two coupled oscillations

29

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.