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

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slide1
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
anatomy is destiny freud anatomy is merely a suggestion anatomy
Anatomy is destiny – FreudAnatomy is merely a suggestion – Anatomy

Functional connectivity and neuroplasticity

neural recruitment into larger functional groups
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)

slide4
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

generation of spindles 7 14 hz
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)
the more neurons recruited into a rhythm the higher the spectral magnitude
The more neurons recruited into a rhythm, the higher the spectral magnitude

Spectral magnitude = proportion of neurons in the functional group (rhythm)

time delay between brain areas recruited into the same function rhythm is indicated by phase
Time delay between brain areas recruited into the same function (rhythm) is indicated by phase
detecting networks through timing and number
Detecting networks through timing and number

Network organizes around event

phase and magnitude consistency
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

shared information between eeg signals
Shared information between EEG signals
  • Phase:
    • Mean consistency (coherence)
    • Mean difference (phase lag)
  • Magnitude
    • Mean consistency (comodulation)
    • Mean difference (asymmetry, unity)
similarity of coh and comod
Similarity of Coh and Comod

Kaiser, 2008 (n=43 children, 58 adults)

kaiser 2008 n 101
(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)

effect of age on connectivity
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)

role of myelin in cerebral connectivity
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

functional connectivity in adulthood 20 35 years of age24
Functional connectivity in adulthood (20-35 years of age)
  • Red areas are last to myelinate
  • Functional changes
slide27

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
spectral parameters c 1994
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
slide30

Periodicity Table

(Kaiser, in press)