Left Handedness

Left handedness, once considered as a social stigma is now gaining social acceptance (and of course why not? nothing is wrong with them).

Majority of the human beings are right handed and the remained are either ambidextrous or left-handed. Approximately about 10 to 15% of people are considered as left-handed.

A complete left-handed person will favor left hand for almost all hand related daily activities including writing. A partial left-handed person generally writes with left hand but does favor right hand for some activities. When a person uses both hands comfortably and equally or nearly equally then word ambidextrous is preferred.

There are lots of issues left-handed people will have to encounter including; social stigmas, the difficulties they face in the world while using various tools, instruments and gadgets (manufactured mostly for right handed people), the question they frequently face whether left-handed people are more clumsy or whether they are more intelligent than the right handed people etc etc.

But this article is not focusing on those aspects of being a southpaw rather it is about the neurological relevance of handedness.

In neurology when we start taking the patient’s history one of the first questions we ask is about the handedness. So why is that so important for a neurologist (or for any doctor) to know the handedness of their patients?

The answer is this piece of information helps in localization of the pathology (when brain pathology is suspected); whether the pathology lies in the right or left side of the brain.

In general the left brain controls the right side and vice versa. Consistent with this, almost all right handed people have their speech & language centers located in the left brain. So if a right handed patient presents with speech & language problems (called as aphasia) then on most of occasions the pathology should lie in the left brain and it is very much true.

Now the opposite is not totally true - the deduction that if a left handed patient present with aphasia then the pathology must be on the right side. This is because the majority of left handed people still have their speech & language centers housed in the left brain only, so the brain pathology still more likely to be on the left side.

The remaining left handed individuals have their speech & language centers either on both sides (pathology will be on either side of the brain) or mostly on the right side (so pathology on the right side of the brain).

To cut a long story short neurologists use the knowledge of handedness to localize the pathology in the brain; whether the pathology is located on the left or right side of the brain.

While the neurology doctors continue to ask about the handedness of their patients during the process of taking the clinical history even in these days, however the significance of this has comedown since the advent of CT or MRI scan of brain because the CT or MRI scan of the brain can easily show the pathology and also tell us easily where this pathology is located (on which side of the brain - right side or left side). In the pre CT or MRI era neurology specialists would significantly depend upon the handedness information to know the side of the lesion (whether the lesion lies in the right brain or in the left brain). When there are other neurological findings present, for example paralysis of the limbs, facial droop etc then the handedness information was not that much needed, but some times patients present with predominant aphasic manifestations (speech problems) without much or without any paralysis of the limbs or facial droop etc and in these circumstances the handedness was helping them a lot to localize the brain lesion (whether located in the right or the left brain). In the recent technologically advanced era a CT or MRI of the brain will easily identify any structural pathology that is causing aphasia, and also these tests will tell with ease whether the pathology is present on the right or the left brain.

Anyway the practice of asking the handedness will and must continue during history taking because a doctor is supposed to arrive at the diagnosis or differential diagnosis first by history taking followed by the examination of the patient, the investigations like CT or MRI scan are only an extension to this approach or a complement but not a substitute. And before finishing let me once again reiterate that left handedness is not an abnormality of any kind rather it is just a normal variation without any pathological consequences attributed to it.