Coherence and Comodulation: Coherence and Comodulation: Phase Synchrony and Magnitude SynchronyPhase Synchrony and Magnitude Synchrony

David A. Kaiser, Ph.D.David A. Kaiser, Ph.D.Sterman-Kaiser Imaging Laboratory, Inc.Sterman-Kaiser Imaging Laboratory, Inc.

ISNR 16th Annual Conference - San Antonio, Texas ISNR 16th Annual Conference - San Antonio, Texas August 28-September 1, 2008August 28-September 1, 2008 Saturday Aug 30 9:10-9:30amSaturday Aug 30 9:10-9:30am

Anatomy is destiny – FreudAnatomy is destiny – Freud

Anatomy is merely a suggestion – AnatomyAnatomy 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 Neurons fire around 80+ times a second intrinsically (and up to 800 second intrinsically (and up to 800 times a second during seizure).times a second during seizure).

To process information of relevance to To process information of relevance to the organism, autorhythmicity is the organism, autorhythmicity is greatly suppressed and firing greatly suppressed and firing synchronized across neurons by synchronized across neurons by means of inhibitory and excitatory means of inhibitory and excitatory influences.influences.

(Hopfield, 1999; Goldensohn & Purpura, 1963; Mountcastle, 1957; Casanova & Tillquist, 2008)

When autorhythmicity is suppressed in ~2,000,000 cortical When autorhythmicity is suppressed in ~2,000,000 cortical minicolumns (6 cmminicolumns (6 cm22), it can be detected by scalp electrodes.), it can be detected by scalp electrodes.

Mountcastle, 1957; 1978; Cooper et al., 1965

Voltage rhythmsVoltage rhythms correspond well correspond well with mental and physical behaviorswith mental and physical behaviors

High information STATE Low informationHigh information STATE Low information

Certain rhythms are generated by inhibitory networks

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 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 receptors) . The potential determines the time until another burst of spikes is generated by the TC neuron (Franks, 2008)by the TC neuron (Franks, 2008)

The more neurons recruited into a rhythm,The more neurons recruited into a rhythm, the higher the spectral magnitude the higher the spectral magnitude

Spectral magnitude = proportion of Spectral magnitude = proportion of neurons in the functional group neurons in the functional group

(rhythm)(rhythm)

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

Detecting networks through Detecting networks through timing and number timing and number

Network organizes around eventNetwork organizes around event

Synchrony between sites as indicated by Synchrony between sites as indicated by phase and magnitude relationshipsphase and magnitude relationships

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 amplitudeComod = average normalized cross-product amplitude

Coh ranges from 0.0 to 1.0Comod ranges from -1.0 to 1.0

Comodulation

Shared information between EEG signalsShared information between EEG signals

Phase:Phase:• Mean consistency Mean consistency

((coherencecoherence))• Mean difference Mean difference

((phase lagphase lag) )

MagnitudeMagnitude• Mean consistency Mean consistency

((comodulationcomodulation))• Mean difference Mean difference

((asymmetry, unityasymmetry, unity))

Functional Connectivity from 5 to 35 years of ageFunctional Connectivity from 5 to 35 years of age

Four possible connectivity parametersFour possible connectivity parameters

Normalizing with Fisher z-transform (1921)Normalizing with Fisher z-transform (1921)

Similarity of Coh and ComodSimilarity of Coh and Comod

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

(Kaiser, 2008)(Kaiser, 2008)n =101n =101

Left posterior temporal lobe has longest maturation (Sowell et al., 2003)

Sowell ER, Peterson BS, Thompson PM, Welcome SE, Henkenius Sowell ER, Peterson BS, Thompson PM, Welcome SE, Henkenius AL, & Toga AW (2003). Mapping cortical change across the AL, & Toga AW (2003). Mapping cortical change across the human life span. Nature Neuroscience, 6, 309-15.human life span. Nature Neuroscience, 6, 309-15.

We used magnetic resonance imaging and cortical matching We used magnetic resonance imaging and cortical matching algorithms to map gray matter density (GMD) in 176 normal algorithms to map gray matter density (GMD) in 176 normal individuals ranging in age from 7 to 87 years. We found a individuals ranging in age from 7 to 87 years. We found a significant, nonlinear decline in GMD with age, which was most significant, nonlinear decline in GMD with age, which was most rapid between 7 and about 60 years, over dorsal frontal and rapid between 7 and about 60 years, over dorsal frontal and parietal association cortices on both the lateral and parietal association cortices on both the lateral and interhemispheric surfaces. Age effects were inverted in the left interhemispheric surfaces. Age effects were inverted in the left posterior temporal region, where GMD gain continued up to age posterior temporal region, where GMD gain continued up to age 30 and then rapidly declined. The trajectory of maturational and 30 and then rapidly declined. The trajectory of maturational and aging effects varied considerably over the cortex. Visual, aging effects varied considerably over the cortex. Visual, auditory and limbic cortices, which are known to myelinate early, auditory and limbic cortices, which are known to myelinate early, showed a more linear pattern of aging than the frontal and showed a more linear pattern of aging than the frontal and parietal neocortices, which continue myelination into adulthood. parietal neocortices, which continue myelination into adulthood. Our findings also indicate that the posterior temporal cortices, Our findings also indicate that the posterior temporal cortices, primarily in the left hemisphere, which typically support primarily in the left hemisphere, which typically support language functions, have a more protracted course of maturation language functions, have a more protracted course of maturation than any other cortical region.than any other cortical region.

Effect of age on Effect of age on connectivityconnectivity

Comodulation increases with ageComodulation increases with age

Coherence increase with age (5-35 y, n=101)Coherence increase with age (5-35 y, n=101)

Data are site-age correlations. (pink is significant)

Functional connectivity in childhoodFunctional connectivity in childhood(5-20 years of age)(5-20 years of age)

Structural changesStructural changes

Functional changesFunctional changes

Functional connectivity in adulthood Functional connectivity in adulthood (20-35 years of age)(20-35 years of age)

Structural changesStructural changes

Functional changesFunctional changes

College students show frontal plasticity compared College students show frontal plasticity compared to older adultsto older adults

Coherence Comodulation

Without myelin sheath, 2 mph With sheath, 260 mphWithout myelin sheath, 2 mph With sheath, 260 mph

Role of Role of myelinmyelin in cerebral connectivity in cerebral connectivity

Biggest 5 micron diameter “pipes” are posterior but big pipes continue frontally throughout life

Corpus callosum cross-section

Functional connectivity in adulthood Functional connectivity in adulthood (20-35 years of age)(20-35 years of age)

Red areas are last to Red areas are last to myelinatemyelinate

Functional changesFunctional changes

Global connectivity (alpha graphed)Global connectivity (alpha graphed)

Scalp coherenceScalp coherence may reflect RTN involvement in may reflect RTN involvement in cortical rhythms and cortical rhythms and comodulationcomodulation the more the more loosely organized corticocortical networksloosely organized corticocortical networks

Does phase and magnitude capture different aspects of neurophysiology?

Spectral parameters c.1994Spectral parameters c.1994

Absolute powerAbsolute power Power asymmetry (A-B)Power asymmetry (A-B) Power ratio (A/B)Power ratio (A/B) Relative power Relative power Spectral entropySpectral entropy

Spectral Correlation Spectral Correlation Coefficient (SCC)Coefficient (SCC)

CoherenceCoherence Phase lagPhase lag BicoherenceBicoherence Spectral Spectral

CorrelationCorrelation

Same spectral parameters, organizedSame spectral parameters, organized

Bicoherence

Periodicity Table

(Kaiser, in press)

““Chemistry” between periodicity typesChemistry” between periodicity types