Coherence and Comodulation: Phase Synchrony and Magnitude Synchrony David A. Kaiser, Ph.D. Sterman-Kaiser Imaging Labor

1. Coherence and Comodulation: Phase Synchrony and Magnitude SynchronyDavid A. Kaiser, Ph.D.Sterman-Kaiser Imaging Laboratory, Inc. • ISNR 16th Annual Conference - San Antonio, Texas • August 28-September 1, 2008 • Saturday Aug 30 9:10-9:30am

2. Anatomy is destiny – FreudAnatomy is merely a suggestion – Anatomy Functional connectivity and neuroplasticity

3. Neural recruitment into larger functional groups • Neurons fire around 80+ times a second intrinsically (and up to 800 times a second during seizure). • To process information of relevance to the organism, autorhythmicity is greatly suppressed and firing synchronized across neurons by means of inhibitory and excitatory influences. (Hopfield, 1999; Goldensohn & Purpura, 1963; Mountcastle, 1957; Casanova & Tillquist, 2008)

4. When autorhythmicity is suppressed in ~2,000,000 cortical minicolumns (6 cm2), it can be detected by scalp electrodes. Mountcastle, 1957; 1978; Cooper et al., 1965

5. Voltage rhythms correspond well with mental and physical behaviors

6. Certain rhythms are generated by inhibitory networks High information STATE Low information

7. Generation of spindles (7-14 Hz) • Length of inhibitory potential sets the frequency (which is mediated by GABA type A receptors) . The potential determines the time until another burst of spikes is generated by the TC neuron (Franks, 2008)

8. The more neurons recruited into a rhythm, the higher the spectral magnitude Spectral magnitude = proportion of neurons in the functional group (rhythm)

9. Time delay between brain areas recruited into the same function (rhythm) is indicated by phase

10. Detecting networks through timing and number Network organizes around event

11. Synchrony between sites as indicated by phase and magnitude relationships

12. Phase and Magnitude consistency Cross-spectral analysis Coherence is a phase consistency function Comodulation is a magnitude consistency function…between signals at a frequency across time Coh = average normalized cross-spectrum amplitude Comod = average normalized cross-product amplitude Coh ranges from 0.0 to 1.0 Comod ranges from -1.0 to 1.0 Comodulation

13. Shared information between EEG signals • Phase: • Mean consistency (coherence) • Mean difference (phase lag) • Magnitude • Mean consistency (comodulation) • Mean difference (asymmetry, unity)

14. Functional Connectivity from 5 to 35 years of age

15. Four possible connectivity parameters

16. Normalizing with Fisher z-transform (1921)

17. Similarity of Coh and Comod Kaiser, 2008 (n=43 children, 58 adults)

18. (Kaiser, 2008)n =101 • Sowell ER, Peterson BS, Thompson PM, Welcome SE, Henkenius AL, & Toga AW (2003). Mapping cortical change across the human life span. Nature Neuroscience, 6, 309-15. • We used magnetic resonance imaging and cortical matching algorithms to map gray matter density (GMD) in 176 normal individuals ranging in age from 7 to 87 years. We found a significant, nonlinear decline in GMD with age, which was most rapid between 7 and about 60 years, over dorsal frontal and parietal association cortices on both the lateral and interhemispheric surfaces. Age effects were inverted in the left posterior temporal region, where GMD gain continued up to age 30 and then rapidly declined. The trajectory of maturational and aging effects varied considerably over the cortex. Visual, auditory and limbic cortices, which are known to myelinate early, showed a more linear pattern of aging than the frontal and parietal neocortices, which continue myelination into adulthood. Our findings also indicate that the posterior temporal cortices, primarily in the left hemisphere, which typically support language functions, have a more protracted course of maturation than any other cortical region. Left posterior temporal lobe has longest maturation (Sowell et al., 2003)

19. Effect of age on connectivity • Comodulation increases with age • Coherence increase with age (5-35 y, n=101) Data are site-age correlations. (pink is significant)

20. Functional connectivity in childhood(5-20 years of age) • Structural changes • Functional changes

21. Functional connectivity in adulthood (20-35 years of age) • Structural changes • Functional changes

22. College students show frontal plasticity compared to older adults Coherence Comodulation

23. Role of myelin in cerebral connectivity Without myelin sheath, 2 mph With sheath, 260 mph Biggest 5 micron diameter “pipes” are posterior but big pipes continue frontally throughout life Corpus callosum cross-section

24. Functional connectivity in adulthood (20-35 years of age) • Red areas are last to myelinate • Functional changes

26. Global connectivity (alpha graphed)

27. Does phase and magnitude capture different aspects of neurophysiology? Scalp coherence may reflect RTN involvement in cortical rhythms and comodulation the more loosely organized corticocortical networks

28. Spectral parameters c.1994 • Absolute power • Power asymmetry (A-B) • Power ratio (A/B) • Relative power • Spectral entropy • Spectral Correlation Coefficient (SCC) • Coherence • Phase lag • Bicoherence • Spectral Correlation

29. Same spectral parameters, organized Bicoherence

30. Periodicity Table (Kaiser, in press)

32. “Chemistry” between periodicity types