This is one of those memes that refuses to die. It’s a zombie-meme, the terminator of myths, one of those ideas of popular culture that everyone knows but is simply wrong – the idea that individuals can be categorized as either left-brain or right-brain in terms of their personality and the way they process information. Related to this is the notion that any individual can either engage their left brain or their right brain in a particular task.

The most pernicious myths tend to have a kernel of truth, but are misleading or oversimplified in a significant way. In the case of brain anatomy and function, it is true that our brains are divided into two hemispheres, left and right. Each hemisphere is capable of generating wakeful consciousness by itself. And there are many higher cognitive functions that lateralize, meaning they are largely located in one hemisphere or the other.

For example, language function lateralizes to the dominant hemisphere, which is the left hemisphere for most people. Visuo-spacial reasoning lateralizes to the non-dominant hemisphere (right hemisphere for most people).

That is as far as the left-brain/right-brain popular belief goes. It ignores other important facts of brain anatomy and function. First – there is a large cable of connection going between the two hemispheres (the corpus collosum), in addition to smaller connections. The hemispheres connect together and operate as a unified whole.

In order to see each hemisphere operating on it’s own you need to specifically create a situation in which they do not communicate. Severing the corpus collosum is a treatment for certain severe forms of epilepsy. These patients have been studied in a series of studies collectively known as the split-brain research. In this situation you can see the effects of one hemisphere or the other operating on it’s own.

Another situation is a neurological test in which one hemisphere of the brain is put to sleep with a powerful anaesthetic (injected into the blood supply of that one hemisphere), so that the other hemisphere can be tested in isolation (called a Wada test, after the physician who developed it).

Further, there are many networks in the brain that include areas of both hemispheres – the two hemispheres are therefore functionally integrated. And finally, some higher cognitive functions do not lateralize to one hemisphere or the other. This is particularly true of the frontal lobes, where most functions are bilateral, including executive function – the ability to plan and control one’s behavior.

So while some specific functions do lateralize, our minds and personalities are the product of one integrated brain, not each hemisphere independently. It is misleading to the point of being wrong to describe people as either “left brain” or “right brain” in terms of their personality or how they process or learn information, and not just because it is a simplistic false dichotomy.

I recently encountered two instances of the left-brain/right-brain myth, prompting this post. One was an e-mailer asking a question about such a claim that they had heard. Fellow skeptic Chris writes:

I recently came across an interesting claim that depending to which ear your hold your phone during a conversation, the information heard is processed quite differently. For example: if a right-handed person holds their phone to their left ear, the speech heard is more likely to be inspected using reason and critical thinking by the left brain, rather than reacting emotionally via the right brain.

I mentioned the split brain experiments above. In subjects where the two hemispheres are mostly isolated you can present information visually to one hemisphere or the other (by showing it to only the left or right visual field), and that information cannot be communicated to the other side because the connection is severed. This can result in interesting results, such as the subject not being able to name with their left hemisphere what their right hemisphere just saw.

The same is not true for the auditory cortex. Both ears connect extensively to the auditory cortical regions in both hemispheres. This is why people do not lose the ability to hear on one side even after a large stroke. The primary auditory cortex responsible for discriminating pitch receives information from both ears. The auditory function that does lateralize is for language and music. Essentially language sounds are processed in the dominant hemisphere and tonal or musical sounds in the non-dominant hemisphere. But both of these regions are getting information from both ears and both primary auditory regions.

Therefore, it does not matter what ear you hold the phone up to. The sound information will get to both hemispheres and to the proper areas for processing the information.

The other left-brain/right-brain claim I heard recently was from an advertiser hoping that I would link to an article they wrote on my blog as a way of driving traffic to their online college course website (for which reason I will not provide a link to them). The article, ironically, was pushing the worst kind of left-brain/right-brain nonsense.

The point of the article was that left-brained people have different learning styles than right-brained people. I guess this means that this online college can tailor their courses to your learning style. I would stay far away from any institution of learning that bases its teaching philosophy on rank pseudoscience.

According to their article, if you are a left-brain person then your learning style is “linear” and “reality-based”, while right-brained people are “holistic” and “fantasy-oriented.” They then give specific advice. Left-brain learners like to be in control, so should volunteer to lead their study group. Right brain learners should be creative in their language choice.

All of this is evidence-free nonsense.  The entire concept of learning styles is not evidence-based. A recent review concluded:

Although the literature on learning styles is enormous, very few studies have even used an experimental methodology capable of testing the validity of learning styles applied to education. Moreover, of those that did use an appropriate method, several found results that flatly contradict the popular meshing hypothesis. We conclude therefore, that at present, there is no adequate evidence base to justify incorporating learning-styles assessments into general educational practice.

People do have different personalities and strengths and weaknesses in how they process information. This simply does not translate into specific learning styles that can be distilled down into studying tips, or even educational strategies. Further, differences in personality and information processing cannot be represented as either left-brain or right-brain.

The left-brain/right-brain dichotomy is pop-psychology pseudoscience. Be suspicious of anyone touting it as a legitimate or insightful way of looking at human personality or cognition.