Hemispheric Dominance

If you are right-handed, as is roughly 92% of the population, your left hemisphere is dominant for language; right for music and emotional response. If you are left-handed, there is about an 85% chance that you’ll be the same as the righties. Roughly 1.2% of the population has brains that have organized to use the right hemisphere for language (for which it’s not as well suited) and the left for music and mood (also for which it’s not as well suited).

There are tests of dominance of sight, dominance of hearing, various tests crossing arms and folding hands, etc. that purport to tell you which of what is dominant for whatever, but people usually end up pretty split on those.   There was a very good test of asking a person to (as I recall) remember something, or count backward by sevens or something where you would watch to see if the person looked up and to the left or the right that I used to use.

Looking at the EEG, if you have a lefty to train, you might look at the Theta/Beta Ratio section on the Analyze page of the TQ8. You can see if the theta/beta ratio is lower (or more in the white range) at C3 or C4, and which one best activates at task.   That can be helpful in determining at least which side is working harder on a language task when one is assigned.   If it really becomes a training issue, which it has only twice in my career as a trainer, try reversing the training for cognitive performance and see it the response improves.  If you have been training up beta at C3 and SMR at C4, reversing those may give you an idea if you should train that way. You can look at the same things in the frontal and parietal lobes.  If you find the right side activating more strongly in all of them, that would be a stronger indication of right-dominance for cognitive tasks.

One of the interesting unanswered questions in neurofeedback for me is whether reversal for language has any effect on alpha and beta reversals and their relation to mood.  As far as I have seen, it does not, but then, as I wrote above, I haven’t had much experience with left-handers reversed for language.

Head Injury and Dominance

If someone has a head injury of whatever sort, then the issue of hemispheric dominance would drop way down in importance as I developed a training plan for that brain. Obviously if you chop off a right-hander’s right hand, he probably won’t be a right-hander any more. The issues of hemispheric dominance are important absent more foundational issues.

Mixed/Incomplete Dominance

Remember also that there are several different conditions related to dominance.  There is clear left dominance related to language tasks, which is by far the most common condition.  There is clear right dominance related to language tasks, which is fairly rare and seems to be limited to clear left-handed people.  There is also mixed or cross or incomplete dominance. This is a lack of complete organization in the brain, and it shows up in a high percentage of people with Filtering problems.  The client will tend to do some things left-handed and others right-handed.  It may or may not be clear in the EEG in various areas.  Some people test for multiple indicators of dominance (eye, hand, finger, arm, foot, etc.).

Eye-Movement Test for Dominance

One of my favorites of these tests is the “conjugate lateral eye-movement” test, which is also neurologically based.

Sit facing the client and give him/her a moderately challenging mental math problem to perform (don’t make eye contact).  Watch for movement of the eyes, which should go either left or right, when the client is performing the task.  Repeat several times (I like to do this during the parietal assessment challenge task).  If the eyes consistently move to the right, the client is using left hemisphere for math calculation.  If the eyes move consistently to the left, the client is using the right hemisphere. There is a very high correlation between dominant hemisphere for calculation and for language.  Some clients shift back and forth, which indicates mixed or incomplete dominance. My favorite client of all time in this test went left..then went right..then up…then rolled her eyes in a complete circle.  I have no idea what that meant.

It is important not to make the task “impossibly” difficult in the client’s mind, or you’ll get no movement at all.