What's New in Neurofeedback

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Most EEG rhythms are the product of bidirectional traffic between thalami and cortex. Hypersynchrony between cortex and thalamus produces a loss of consciousness, with a complete lack of responsiveness to sensory input altogether, as in sleep, coma, or seizure. The amount of synchrony varies across brain sites and frequencies during different stages of maturation, and one of our jobs as neurotherapists is to identify whether each brain area is functioning properly in our clients. Is it showing the proper amount of synchrony or dependence for the individual's age group? Which sites show too little autonomy or independence, or too much?

Neurotherapy training has started to expand beyond the handful of spectral parameters it has relied on for most of its history -- magnitude (or power), relative magnitude, coherence, phase, band ratio. We can summarize the family of spectral parameters by the following: consistency or difference of magnitude or phase for multiple sites or frequencies. If we limit electrode sites and frequency to no more than two, we generate a set of 2x2 tables that contain familiar as well as unfamiliar terms. The unfamiliar terms can be applied to help complete our picture of brain function at this level of measurement, EEG.

These tables, along with transformational properties, comprise a periodicity table, the start of an organizing scheme for understanding EEG dynamics. Tables contain measures of activity or connectivity, depending upon whether a spectral parameter is capturing negotiation across cortex or between cortex and thalamus or similar local activity (see http://www.skiltopo.com/period.htm to see pictures of the tables).

Activity Table # 1 - 1 site, 1 frequency.
Autocoherence (phase consistency),
Autophase (phase difference),
Variability (magnitude consistency), and
Magnitude (magnitude difference, from zero)

Connectivity Table #1 - shared activity between two sites, one frequency.
Coherence (phase consistency),
Phase Lag (phase difference),
Comodulation (magnitude consistency), and
Asymmetry (magnitude difference). I added another approach here called Unity, which is the epoch-level absolute value of Asymmetry.

Activity Table 2 - one site, two frequencies. Selection between systems, one site.
Bicoherence (phase consistency),
Biphase (phase difference),
Bimodulation (magnitude consistency), and
Band Ratio (magnitude difference between frequencies, same site, e.g., theta/beta ratios). If more frequencies were including, spectral entropy would also squeeze in here along with relative magnitude, a noisy version of SE.

Connectivity Table 2. Shared activity between sites, between frequency. Selection by equals. Division of labor connectivity.
Cross-bicoherence (phase consistency),
Cross-biphase (phase difference),
Cross-bimodulation (magnitude consistency), and
Cross-band Ratio (magnitude difference between frequencies, different sites, e.g., frontal theta/central beta ratio).

EEG transitions, when network activity impacts local events, or vice versa, may be measured as well. I call them transformational properties, and they refer to the connection or disconnection between local and network responses. In four Asperger syndrome individuals we observe spectral magnitude values inconsistent with network changes, as measured by global comodulation. Energy was poorly correlated with network traffic in this small group compared to healthy adults, which may suggest too much focality in information processing. Energy changes were too localized, without attendant changes in network traffic. In normal individuals we see a greater coupling of energy and network action. Network synchrony may fuel local cortical events, or vice versa. This is just one way in which intelligence shows lower coupling to normative standards.

When most people think of synchrony measures in EEG they think of coherence. Coherence is a measure of phase consistency between signals developed apparently by Norbert Weiner and colleagues to understand quantum mechanics and other avenues of research. Early pioneers in the application of coherence analysis in EEG are Walter (1968), Orr and Naitoh, 1976; and Thatcher (1992). How to compute coherence is clearly described by Thatcher et al. (2007; online). Comodulation, on the other hand, is a complementary measure, one based on magnitude and not phase, orthogonal to coherence. Comodulation is magnitude consistency between EEG signals (Kaiser, 1994) and is very easy to calculate compared to coherence. Compute magnitude of a frequency at each moment in time for two sites and Pearson product moment correlate the magnitudes across time. The orthogonal nature of these two measures is obvious in definition -- phase consistency, magnitude consistency -- and in their computation. Coherence is spectral analysis of correlation coefficients and comodulation is correlation of spectral coefficients.

Short moving segments provide a fluidic and point-like representation of energy or timing changes, so the above tables can be extended into the time dimension as well.

Coherence measures stability of phase between signals. Shared timing indicates a common origin (degrees of freedom, none). Comodulation measures stability of amplitude between signals Shared energy indicates functional unity. Energy is independence, higher degrees of freedom. Both are across time. Coherence averages across time (sameness) whereas Comod evaluates changes across time (differences). Coherence quantifies the degree of similar influences and comodulation quantifies the degree of similar autonomy

In comodulation we are looking at shared energies, coherence shared timings. If these definitions don’t grab you, metaphorically or mathematically, try stability of phase difference and stability of magnitude difference.

For certain brain functions magnitude consistency between brain areas may be more important than coherence; for other functions, phase consistency may be. In many cases there is no clear preference. That said, we should keep in mind that comodulation, coherence, and any feasible assortment of spectral indices are but a few of the parameters that may relate brain function to mental function. Non-spectral measures, or medians and other derivatives such as slope or variability, mobility or complexity may prove useful in mapping brain to mind. Quantitative EEG needs to incorporate some of the promising new approaches to shed more light on the informational vortex that envelopes brain behavior. To date, it has barely scratched the surface.

Early phase descriptions
Adrian EDK & Yamagiwa (1935) The origin of the Berger rhythm, Brain, 58 323-351.

Motokawa K & Tuziguti K (1944). Alpha phases in EEG activity. Japanese Journal of Medical Sciences, 10, 23-38.

Computation of Coherence
Goodman, N.R. (1957, diss.). On the joint estimation of the spectra, cospectrum and quadrature spectrum of a two-dimensional stationary Gaussian process. Princeton Univ. JW Tukey advisor

Walter DO. (1961).Spectral analysis for electroencephalograms: mathematical determination of neurophysiological relationships from records of limited duration. Experimental Neurology, 8, 151-181.

Early magnitude descriptions
Berger H. (1929). Ueber das Elektroenkephalogramm des Menschen. Archiv Psy Nerv, 87, 527-570.

Dietsch, G. (1932). Fourier-analyse von Elektrenkephalog. des Menschen. Pflüger's Arch. Ges. Physiol., 230, 106-112.

Computation of Comodulation
Kaiser, DA. (1994, diss.). Interest in Films as Measured by Subjective & Behavioral Ratings and Topographic EEG. UCLA. MB Sterman, advisor

Sterman, M.B. & Kaiser, D.A. (1999). Topographic analysis of spectral density co-variation: normative database and clinical assessment. Clinical Neurophysiology, 110 (S1), S80.

-DK

News & Reviews NEW BOOKS

Eating an Artichoke: A Mother's Perspective on Asperger Syndrome
by Echo R. Fling
Parent's journey through Asperger Syndrome. www.amazon.com/exec/obidos/ASIN/1853027111/eegspectrum

Solve Your Child's Sleep Problems
by Richard Ferber
Guide to common sleeping problems for children 1 to 6 years old. www.amazon.com/exec/obidos/ASIN/0743201639/eegspectrum

An Unquiet Mind: A Memoir of Moods and Madness
by Kay Redfield Jamison
Scientific autobiography of bipolar disorder. www.amazon.com/exec/obidos/ASIN/0679763309/eegspectrum

Neuroimaging Parts A & B
by Michael F. Glabus
Two-volume set covers methods and application of various neuroimaging techniques for clinical use and research. --www.amazon.com/exec/obidos/ASIN/0123668778/eegspectrum

Neural mechanisms of aggression. : Adaptations to deal with competition, expressed out of context, may be destructive. Biological signals that mediate aggressive behavior should be targeted for therapies. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17585306

Neuroimaging on brain plasticity in recovery from stroke. : Post-stroke motor recovery is associated with activation changes in specific brain structures. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17589415

The human EEG - Physiological and clinical studies. : Temporal variability of spectral coefficients necessitates large samples of EEG. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17585964

Prevalence of alcohol abuse : Alcohol abuse/dependence was found to be 1 in 8 men and 1 in 25 women. Age, income, schooling, religion and illicit drug use mediated these prevalences. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17589746

Anterior cingulate volume in pediatric bipolar disorder and autism. : Left anterior cingulate gyrus volume was smaller in bipolar children. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17568686

Sleep-wake disturbances 6 months after traumatic brain injury: a prospective study. : Sleep-wake disturbances such as daytime sleepiness and fatigue are prevalent after TBI. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17584779

Rostral anterior cingulate cortex activity in theta predicts antidepressive response. : Resting theta activity at rostral anterior cingulate cortex correlated with med response for depression. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17515172

Ten Hz rTMS on resting EEG power spectrum in healthy subjects. : Ten Hz rTMS induced increase delta power. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17478041

Is ADHD associated with illicit substance use disorders in male teens? : Male teens with ADHD were many times above baseline likely to suffer from drug abuse. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17567400

Attention, executive functions and reading domain abilities in ADHD : Executive dysfunction should be assessed as specific comorbidity of ADHD www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17501726

Herbal medicines in the treatment of psychiatric disorders : Reviews herbal psychotherapy including safety, future areas of application, and synthetic psychotropic medicines. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17562566

Meditation on frontal alpha-asymmetry in previously suicidal individuals. : Mindfulness-based cognitive therapy is effective to counter decreased relative left-frontal activation and associated suicidality in suicide attempters. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17426604

Assessment of spirituality and its relevance to addiction treatment. : Spiritual orientation is relevant to recovery in many individuals. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=17574800

An interesting question (to neurofeedback clinicians) would be whether the strengths of qEEG exist in EEG biofeedback and cross over into mental health treatment. There are five general properties of qEEG that are advantageous compared to most subjective or behavioral measures. These are: