An Atlas of Depression
by David S. Baldwin, Jon Birtwistle
A Monthly Summary of News and Events
Vol. 5 No. 11 - November 2002
This newsletter is sponsored by EEG Spectrum International Intl, Inc.,
a leader in providing clinical service and training professionals.
Past issues are available at www.eegspectrum.com/newsletter/
Information on how to subscribe or cancel a subscription appear at the end.
The opinions related in this newsletter reflect those of the author only.
Copyright (C) 2002 by EEG Spectrum International Intl, Inc. All rights reserved.
|
|
|---|
In 1875, English physician Richard Caton published a report on "the electrical currents of the brain" in animals in the British Medical Journal. Using a reflecting galvanometer invented by Lord Kelvin in 1858, he was able to measure electrical brain signals from the surface of exposed brains of monkeys and rabbits. A mirror was attached to galvanometer coils so that electrical potentials would almost imperceptibly jiggle the mirror, causing a spot of light against a distant background to move, thus providing the necessary amplification to observe the minute electrical changes. In 1887, Caton reported to an international medical conference how light striking the animal's eye produced changes in the electrical activity on the opposite side of the brain.
Unaware of Caton's work, Adolph Beck of Poland repeated it, and also discovered "alpha blocking" of sorts -- how slow even pattens of brain waves could be interrupted by a sudden sensory stimulus such as a light flash or loud noise.
At this time in history, the continuity model between humans and animals was not firmly established so the existence of brain potentials in humans remained unknown and unexplored, and even unexpected by many, until Hans Berger (1929) published his first report on electrical activity of the human brain, which he designated the electroencephalogram, or EEG. Five years passed before his findings were confirmed in the English-speaking world (Adrian & Matthews, 1934). Berger's initial paper focused on recordings acquired from his son Klaus in 1924, starting on July 6th of that year, the date of discovery of the human EEG. Between 1924 and 1929, working in total secrecy, Berger cautiously explored whether the electrical activity recorded from the scalp had a cerebral origin. He made numerous physiological recordings in himself and others to ensure that blood circulation in the body or brain, or potentials from the skin, or head and body positions, or respiration, were not responsible for the weak signals recorded at the scalp. All this time he lectured on topics such as telepathy while hiding his research program. By 1930, Berger had accumulated more than 1,000 EEG recordings from 76 subjects.
In his first report, Berger (1929) characterized the "waves of the first order" in human EEG, which for the sake of brevity he designated the alpha rhythm. (Adrian and Matthews called it the Berger rhythm, but Berger refused the honor and his original name remained.) Alpha activity consisted of large (up to 200 uV) sinusoidal waveforms 90 ms to 120 ms in duration which appeared against smaller background waves, "waves of the second order" or beta rhythm. Alpha waves were pronounced in posterior regions but could also be recorded from central and frontal areas. Most importantly, alpha activity diminished in response to stimulation and mental effort.
Between 1929 and 1937 Berger published his investigation of the relationship between mental processing and alpha activity. He described the phenomenon of alpha blocking, an abrupt suspension of alpha waveforms in ongoing EEG, which can readily be observed when an individual with eyes closed in a relaxed state opens his or her eyes. Berger (1929) claimed that alpha blocking was independent of respiratory, vascular, or motoric responses (confirmed many times over) and resulted when individuals attended to objects in their field of view. When individuals open their eyes in a darkened room, there is little or no change in alpha activity and, conversely, alpha suppression can occur to stimulation or task demands when one's eyes are closed. In 1931 he noted how alpha waves diminished during sleep, during general anaesthesia, and during cocaine stimulation. He noted how epileptic patients produced large amplitude waves and commented on the unusual EEGs in Alzheimer and multiple sclerosis patients, thus laying the foundation for neurological application of EEG technologies. However he failed to uncovered any obvious EEG abnormalities in schizophrenia, manic depression, or melancholia, thus starting the ambivalent relationship between EEG and psychiatry which continues to this day. By 1937, Berger was world famous, although he did not know this until he visited an international congress in Paris. He was twice considered for the Nobel Prize, but he was living during the rise of Hitler and Nazism -- they blocked any acceptance and forced Berger to retire in 1938. He hanged himself three years later.
Perhaps as much as half of what we know about human EEG, Berger knew in his day. He concluded that directing attention toward a stimulus was responsible for fluctuations in alpha activity and the amount of alpha activity reflected the extent of mental processing. He speculated that interhemispheric EEG synchrony was mediated by the thalamus and rejected the claim that the alpha rhythm was generated in occipital cortex exclusively. Beyond these conjectures, he remain curiously silent on the physiological mechanisms responsible for the production of alpha activity.
Moruzzi and Magoun (1949) shed light on the origins of rhythmicity in EEG. Stimulation of the reticular formation of the brainstem produces fast low-amplitude waves in cortical recordings, usually with concomitant behavioral arousal. They concluded that the reticular formation regulated gross changes in alpha activity (i.e., nonspecific arousal). Other experiments in animals, particularly the dog, revealed that specific reactivity observed in the alpha rhythm in response to task and stimulation depended on thalamocortical networks. Alpha rhythms recorded simultaneously from visual cortex and associated thalamic nuclei (lateral geniculate, pulvinar) exhibit identical peak frequency and bandwidth, high degrees of coherence, and similar responses to stimulation. The biocircuitry of the reticular thalamic nuclei (RTN) acts as a pacemaker, recruiting thalamic nuclei into 8-13 Hz (alpha) rhythms by means of powerful inhibitory postsynaptic potentials (Andersen & Andersson, 1968; Steriade, Gloor, Llinas, Lopes da Silva, & Mesulam, 1990). During information processing activation of specific thalamic nuclei by sensory afferences, along with localized basal forebrain excitation of RTN, which itself inhibits thalamic nuclei, results in preferential activation of certain thalamic cells. Visual perception, for example, activates neurons in pulvinar nuclei, yielding diverse (desynchronized) rates of oscillations for these cells while other thalamic nuclei remain relatively synchronized. Nonspecific afferents from the brainstem, namely the pedunculopontine tegmental and laterodorsal tegmental nuclei, also act on thalamocortical networks, affecting general tonic activity of these networks. Electrical potentials measured from the scalp are presumed to be a function of postsynaptic potentials of millions of pyramidal cells in cortical layers IV and V.
The physiology of rhythmic activity has been summarized into a general model. According to this model, metabolic characteristics of (isolated) neurons generate instrinic oscillations usually between 1 to 20 Hz. In an intact brain, activity of single neurons are regulated by pacemaking biocircuitry (RTN) which incorporates actions of single cells into larger ensembles, uniting random discharges of individual cells into simultaneous uniform volleys. Synchronization of cellular firing results in a summation of electrical potentials that can be recorded at the scalp as high-amplitude oscillations of slow frequencies (i.e., alpha rhythm). Desynchronization arises when individual neurons or neural groups are recruited out of these uniform volleys and become dedicated to specific information processing. As neuronal ensembles are uncoupled from synchronized firing into their own (diverse) oscillatory frequencies, large, slower waveforms are replaced by faster frequencies of lower amplitude.
In neuropsychological terms, intrinsic (alpha) rhythms become partially or wholly desynchronized when sensory information is anticipated, attended to, or otherwise processed. Uncommitted cortical areas can remain in an "idling" state while other areas are desynchronized. Desynchronization can be localized to a single electrode or involve several electrodes and cortical areas. Regional patterns of simultaneous desynchronization and synchronization may characterize specific cognitive or behavioral states such as sensorimotor performance. EEG may prove useful in identifying processing strategies employed by different subjects.
Alpha activity is sensitive to stimulus properties and demonstrates topographic specificity associated with modality. Visual stimulation activates occipital and parietal cortex and acoustic stimulation activates temporal cortex. Similarly, sensory and motor event-related potentials (ERPs) are largest over corresponding primary and association areas. Stimulus intensity, complexity, familiarity, and meaningfulness can influence alpha activity, presumably due to attentional factors in response to each of these properties. The degree of alpha attenuation also shows habituation, diminishing after repeated presentations of the same stimulus.
The most reliable and well-known finding in EEG research occurs when an individual resting with eyes closed opens his or her eyes. When eyes are opened in a lit room, alpha blocking occurs: the dominant alpha rhythm is displaced by faster, lower amplitude waveforms. This attenuation in alpha activity is widespread, incorporating most or all cortical areas -- a good example of nonspecific arousal.
Statistical results of topographic EEG lend themselves to two general physiological characterizations. A significant main effect occurs when one condition elicits a global change in attention or resource allocation that is not localized to any brain region (i.e., nonspecific arousal). Task by site interactions indicate when specific cortical functions are activated by one task but not others -- in other words, selective attention.
An assumption underlying much of QEEG analysis is the conception of psychological or physiological "macrostates". According to this model, the various perceptual and cognitive operations associated with a mental or behavioral condition is thought to constitute a single distinguishable neurophysiological state with a distinct and reliable spectral pattern. Eyes closed and eyes open resting conditions are very good tests of this model. Both conditions are uncontrolled, self-paced, and may include dissimilar processes between subjects. Assuming that EEG is sensitive enough to measure functional differences between conditions, the fact that replications of these conditions usually do not differ topographically (e.g., Kaiser, 1994) is evidence which supports the macrostate assumption.
-DK
News & Reviews
NEW BOOKS
An Atlas of Depression
by David S. Baldwin, Jon Birtwistle
Autism: Explaining the Enigma
Neuropsychiatry of Epilepsy
Stimulant Drugs and ADHD: Basic and Clinical Neuroscience
Cerebral Reorganization of Function After Brain Damage
Clinical Guide to Depression in Children and Adolescents
Regional cerebral perfusion abnormalities in ADHD
:
Functional defects in the prefrontal cortex and problem areas in the limbic area, somatosensory areas and in the cerebellum were found during the resting state of brains of ADHD children.
Children's brain injury: a postal follow-up of 525 children from one health region in the UK.
:
About 1/5th of children with mild TBI suffer from poor concentration, personality change and educational problems post-injury.
Sources of EEG activity in learning disabled children.
:
Learning disabled children showed more theta activity in the frontal lobes and control children more alpha in occipital areas, supporting the maturational lag hypothesis.
Lateral asymmetries in the frontal brain: depression and alcoholism
:
Different neurophysiological substrates of depression and familial risk can be distinguished through the use of QEEG analysis.
Specificity of quantitative EEG analysis in adults with ADHD
:
ADHD adults show elevated theta activity during eyes open baselines compared to controls.
Effects of stimulant medications on EEG of children with ADHD
:
Use of stimulant medications resulted in normalization of the EEG, primarily changing theta and beta bands.
Increased amygdala activation to angry faces in generalized social phobia.
:
The amygdala may be particularly active in the processing of disorder-salient stimuli in generalized social phobia.
Synaptic plasticity in drug reward circuitry.
:
Alterations in glutamatergic synaptic efficacy brought on by synaptic plasticity may play key roles in the addiction process.
Quantitative EEG methods and measures in human psychopharmacological research.
:
Recommends methodological standards that ensure valid pharmaco-EEG profiling -- i.e., central impact of medications.
Upcoming Courses
Prerequisites:
All Adv. classes require successful completion of the 4 Day Comprehensive Beta/SMR.
|
Conferences for Neurofeedback Clinicians & Researchers | ||
|---|---|---|
| CONFERENCE | LOCATION | DATES |
| AAPB - http://www.aapb.org | Jacksonville, FL | Mar 27-30 |
In my March 1999 issue of What's New in Neurofeedback, I predicted that, given the current trends in ADD/ADHD diagnoses, 100% of school-aged children would be diagnosed with this condition (which doesn't mean they have the condition) by 2010. I called this upcoming crisis "Y2KD" (see http://www.eegspect.com/newsletter/mar1999.htm ]
But my tongue-in-cheek prediction was apparently a gross underestimation. According to Massachusetts psychiatrist Edward Hallowell, half of the entire population suffers from this disorder (see The Philadelphia Inquirer, Nov 22, 1999 issue). When a trait prominance exceeds 50% of the population, those without the condition become "abnormal" and those with it normal. Benjamin Franklin, the ultimate American, he claims, might have had the disorder. Others speculate that Thomas Edison, Winston Churchill, Albert Einstein and even Wolfgang Amadeus Mozart suffered from the condition. Oh well.
Is genius a diagnosable condition? One with pharmaceutical remedies? For the good of the child, should we wipe out creativity when they're still young. I'd like to think ADD is an evolutionary spur, as it occurs so widely in our population. It could be a continuation of our neoteny. Humans are the dominant species on the planet (excluding bacteria) due to our neoteny -- that is, retention of juvenile characteristics into adulthood, like curiosity and tolerance of same-sex members. We much more closely resemble chimp or gorilla infants than adults of either species. We retain a plasticity of behavior that is typically found among animals only in the young. Is ADD a continuation of this trend? Adolescence now spilling well into the late 20s and early 30s. Perhaps Generation-Y, the victim of the ADHD epidemic, will push childhood unto the grave. One day we may venture to distant star systems, colonize the galaxy, with the minds of infants.