Monthly summary of general news, case histories,
and introductory articles about neurofeedback
for the interested layperson
Vol. 11 No. 6 - June 2008
Past issues are available at start.eegspectrum.com/News/
Copyright (C) 2008 by EEG Spectrum International or David Kaiser, Ph.D.. All rights reserved.
|
|
|---|
Of the 19 electrodes in the 10-20 electrode placement system (Jasper, 1958), 8 are on the left hemisphere, 8 on the right hemisphere, and 3 are down the midline, but in terms of function, is my C4 your C4?
By this I mean, is activity of my right motor strip (the cortex under site C4, the brain area which controls my left hand and other body parts) equivalent to the activity of your right motor strip? If you're left handed, you surely control your left hand better than I and the activity below C4 will be different than mine, more organized, perhaps less intense, less busy, not all over the place like mine, especially when I try to dribble with my left hand or make a lay-in from this side of the basketball court.
Electrode site F7 lies over or near Broca's area, the cortical tissue involved in speech motor programs for most people. Its homologue, site F8, over the right-brain analog to Broca's area, does very little in terms of speech execution and mostly gets activated in perspective taking and deception detection. In laterality research we talk about "hemisphere dominance" which is shorthand for which cerebral hemisphere houses the speech centers, which side is Broca's area on. Wherever speech lies, so do most language functions, especially those hard-core linguistic elements such as grapheme-phoneme conversion (i.e., converting letter strings into sounds), syntax, function words, as well as abstract and infrequent words. Knowing the location of a person's speech center tells us whether we should analyze activity at site F7 during language processing or whether we ought to relocate the electrode to the other side (F8) to overhear the electric chatter given out by Broca. In the latter cases we call the brain's organization atypical, and we must recognize it as such, especially when we compare individuals to a normative neuroimaging database.
Verbal functions are typically housed in the left hemisphere (LH) and non-verbal functions such as spatial and emotional processes in the right hemisphere (RH). One of the most telling signs of atypical brain organization is one's handedness, especially its degree.
Rasmussen & Milner (1977), a famous study of hemisphere dominance using the Wada (sodium amytal) test, determined that speech occurred in the LH for 96% of right handers and in the RH in 1 out of every 25 right-handers. In left handers, the pattern was different: 7 out of 10 had speech centers in the LH, instead of 96%, and 15 % had speech localized to the RH (as opposed to 4%) and confusing the picture more, the remaining 15% had speech divided across the hemispheres, with spontaneous speech in one brain and naming in the other. Of course the problem with assuming these percentages map to the general population is that they were not derived from the general population, but came from epileptic patients who had one hemisphere, then the other, pharmacologically knocked out via carotid injection in the process of undergoing brain surgery for seizure management. Many of these patients would be expected to have atypical brain organization due to their history.
A better population to compare to healthy adults are those who acquired speech problems randomly from the environment. We can thank WWII for this next set of data. More than 220 WWII British dysphasics (poor speakers) after unilateral damage were studied by Annett, who determined that of those right handed soldiers, 94% had a left-sided lesion and of the left-handers, 67% had a left-sided lesion, nearly the same results of the Wada research. Zangwill (1967) looked at brain injury in general and determined that of those who were right handed and suffered a left-sided lesion were aphasia 57% of the time but only 3% of the time when the lesion was right-sided. For lefties, a left-sided lesion produced aphasia in 54% of patients but a right-sided lesion produced aphasia in 31% of patients. These numbers are harder to pull together because the direction of investigation is reverse of the previous studies (Zangwill looked at who had lesions first, then who had speech problems), but if you do the math, righties were 20 times more likely to have speech centered in the LH and lefties were more like 2:1 odds, which is what the other researchers determined as well.
Recent research by Knecht et al. (2000) used an fMRI machine to assess healthy adults and they determined a simple function between handedness and direction of language dominance, see http://brain.oxfordjournals.org/cgi/content/full/123/12/2512 In this work, handedness was assessed by the Edinburgh Inventory (Oldfield, 1971), which ranges from –100 for strong left-handedness to +100 for strong right-handedness (see below). As it turns out, the likelihood of right language dominance is the following function: 15 percent minus one's handedness percent divided by 10.
Here is a handedness questionnarie you can use, based on Oldfield (1971) and Annett (1970), to compute the likelihood that a client's F7 is actually F8, and vice versa.
With which hand do you...
Score as follows: Always Left (-10), Mostly Left (-5), Either (0), Mostly Right (+5) and Always Right (+10). Add up the score to the ten questions and that is his or her handedness index. Take this value, which is my case is +100, and compute the probability of atypical (right brain) language dominance. In my case it is 15 percent minus 100 score divided by 10 which equals 5 percent. So if 20 Davids existed, only one would likely have his brain on backwards.
These researchers had an fMRI machine available and although access to bulky machinery is always fun, most of us need quick inexpensive means for assessment brain typicality. Here are two simple and easy techniques:
Assessment #1: Competitive motor task. Have a person tap their finger on the keyboard while they perform a mental operation that is known to be housed in one hemisphere, such as speech or computation. First run a baseline: have the person tap his or her pointer finger of each hand for a minute each. Once the baselines are collected, have the individual perform the designated unihemispheric task while tapping each hand's pointer finger. Compare baseline rate of each hand to task rate and whichever hand suffered the most proportionally from baseline, we assume the contralateral hemisphere was performing the primary task (math, language, etc), to explain the motor performance decline.
For example, I start with my right pointer finger, tap tap tap for a minute as fast as I can any key on the keyboard: rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr, then I do the same with the left hand pointer finger.... lllllllllllllll... Using a PC makes counting easy, but this task can be done without any equipment except a timepiece. After I complete my baseline, now I am asked to do an ongoing math task, such as count backwards by 7s from 300 while tapping with my right pointer finger .....rrrrrrrrr .... and then count backwards from 400 by 7s while tapping with my left pointer ... llllllllllll...
Let's assume my right hand baseline tapping rate was 100 taps per minute, and my right-hand task-rate dropped to 60 taps per minute during the counting. This is a 40% decline. Compare this decline with my left hand, which might have a slow baseline of 50 taps per minute but which was nearly matched by the task-rate of 45 during counting, for only a 10% decline. So now I know that the hemisphere that controls my right hand also performs my mathematical computations, and as my right hand is controlled by my LH, so is my math processing (computation).
We can run the same technique again while I visualize objects in my kitchen to test spatial skills, or while I name emotions on the faces of people on TV, etc.
Assessment #2: Lateralized eye movements (LEM). Brain function typicality can be observed in the eye movement we make while thinking. When you ask a person to give three words that are similar to "moving" or "intelligence" or ask them to define "impish," you should task the verbal brain and see it momentarily squash the incoming right visual field so as not to be distracted by perceptual information while it is working. A leftward eye movement means the LH is working hard (its right visual field is squashed), and a rightward movement from your perspective (not theirs) means the RH is working hard. The same range of functions can be tested with LEMs as with competitive motor tasks, spatial to emotional to verbal to math processes. Be warned that LEMs are often quick and subtle, but in many they are obvious. But above all do not inform the person being assessed that you are observing their eye movements -- use a video camera if you must -- else you may get them self-conscious of these movements and they'll stop or go in all directions.
-DK
Selected references:
News & Reviews NEW BOOKS
Chemical Dependence Treatment Documentation Sourcebook
by James R. Finley, Brenda S. Lenz
Sourcebook to free addiction treatment professionals to spend more of their
time and energy helping clients instead of "re-inventing the wheel" on
admininstrative and documentation tasks.
Perceptual Neuroscience: The Cerebral Cortex
by Vernon B. Mountcastle
The cerebral cortex, occupying over 70 percent of our brain mass, is key to
any understanding of the workings and disorders of the human brain.
The Prozac Alternative: Natural Relief from Depression ...
by Ran Knishinsky
Knishinsky explores a range of subjects from depression, herbs and the
health food industry, prescription drugs, St. John's wort, homeopathy, kava, and more.
Rehabilitation of the Adult & Child with Traumatic Brain Injury
by M Rosenthal, JS. Kreutzer, ER Griffith, MR Bond (Eds)
Resource for clinicians and students in health care and related professions; includes substantial pediatric section.
The A.D.D. Book: New Understandings, New Approaches to Parenting...
by William Sears, Lynda Thompson
Sears and Thompson offer parents dealing with an ADD child an effective
choice for treatment in neurofeedback and a refreshingly positive,
supportive way for such parents to contemplate their challenging children.
They emphasize qualities such as creativity, spontaneity, focus, and high energy in ADD children.
Psychiatric disorders in children with autism spectrum disorders: prevalence, comorbidity, and associated factors
:
Autism spectrum disorders are a major public health concern because of early onset, lifelong persistence, and high impairment. 70% of children with ASD have comorbidites, the most common being social anxiety disorder, ADHD, & ODD.
Perceived sleep quality of psychiatric patients.
:
More than one-third of psychiatric patients perceived a sleep problem, and two-thirds are assessed as being 'bad sleepers'.
Right anterior cingulate cortical volume covaries with respiratory sinus arrhythmia magnitude in combat veterans.
:
Respiratory sinus arrhythmia magnitude was correlated with right but not left hemisphere ACC volume, regardless of PTSD diagnosis.
Neurobiology of attention deficit/hyperactivity disorder.
:
ADHD involves catecholaminergic hypofunction.
Neural mechanisms underlying the vulnerability to develop compulsive drug-seeking habits and addiction.
:
The transition from controlled to compulsive drug seeking may reflect a shift from prefrontal to striatal control over drug-seeking.