The Reconstitution of Hemisphericity

Awareness of laterality of brain function appears to be at least as old as written history. For example, Diocles of Carystus in the fourth century BC wrote: “There are two brains in the head, one which gives understanding, and another which provides sense-perception. That is to say, the one which is lying on the right side is the one that perceives: with the left one, however we understand.”

However, Marc Dax, was the first in the modern era to observe a difference in function between the hemispheres. In 1836 he noticed that victims of injury to the left hemisphere (LH) but not the right hemisphere (RH) could not speak. Paul Broca in 1865 extended this work, also noting that often hand dominance was contralateral to the language hemisphere as well. For the following century, the term “hemispheric dominance” was used to refer to this language laterality of the brain.

Then, a large study by Weisenberg and McBride in 1935 demonstrated a RH preeminence in visuospatial skills. This called for the invention of a second term, “cerebral asymmetry”, which has been used to distinguish these and later non-language dominance differences discovered in brain laterality.

With the advent of split-brain research in the mid nineteen fifties, a third laterality term, “hemisphericity”, came to be used, especially in pop-psychology, as a convenient word to divide people intuitively into two different personality types beyond male and female. Very broadly defined, hemisphericity was thought to specify which side of the brain was involuntarily and chronically ascendant in terms of the production of an individual’s habitual mood, personality, cognitive approach, and behavioral style. Thus, one was either a right brain-oriented or a left brain-oriented person, based upon personality stereotypes thought to be related to intrinsic brain asymmetry, such as in linguistic or spatial skills.

Unfortunately, especially for psychological research, someone’s behavioral laterality could also be thought to be somewhere on a continuum between these two extremes. Thus, until recently, attempts to determine a person’s hemisphericity have been plagued by the lack of agreement upon the meaning of the term, lack of a primary standard for comparison, lack of reliable measurement methods, and lack of certainty that the phenomenon even existed.

Thus, by the 1980s, the topic of hemisphericity had fallen into disrespect among Psychologists and Psychiatrists.  Because there were no practical, much less quantitative methods to determine the hemisphericity individuals or groups, these professionals were prevented from proper evaluation of the many sometimes inflammatory speculations being made in the popular literature regarding the hemisphericity of individuals or groups. This has created an atmosphere of political incorrectness about behavioral brain laterality that has severely limited both basic and applied research on the entire topic. Yet, because it is intuitively correct, the concept of right brain, left brain differences in individual personality remains popular among the general populace. 

 The research reported here describes the reconstitution of hemisphericity made possible by the discovery of several biophysical methods to assess hemisphericity quantitatively.  Use of these made it obvious that an individual's hemisphericity was not somewhere on a gradient between right and left extremes.  Rather, hemisphericity was the inevitable result of the brain’s ancient Executive System inherently being imbedded either within the right or left hemisphere Unpublished Manuscript.  This new context of brain behavioral laterality has resulted in the discovery of two brain structural differences between left and right brain oriented individuals thus far.  One of these neuroanatomical differences was found at the purported site of the brain's executive, the anterior cingulate cortex.  These discoveries are described in Brain and Cognition, 62, 1-8 (2006) and in another Unpublished Manuscript and are summarized in an Unpublished Review.

Definitions of Hemisphericity and the Hemisphericity Subtypes:

    With this absolute anatomical standard for hemisphericity in place, the biophysical standards were quickly validated, and preference questionnaires were designed to give highly accurate estimates of individual and group hemisphericity.  Using these new instruments, it was found that in the US, hemisphericity sorting had not yet occurred at the high school level.  That is, there were equal numbers of right and left brain oriented high school students.  However, upon entry into college sorting became increasingly pronounced moving through college into graduate school and was at its extreme in the professions.  There for example, 75% of astronomers were found to be right brain oriented individuals, while only 25% of particle physicists were.  This was in keeping with the "big picture" orientation of right-brainers and the "important details" orientation of left-brainers.  This work was published in Brain and Cognition 52 (2003) 319-325.

One of the outcomes of the investigation of the behavioral traits associated with right or left brain oriented individuals was the discovery that of 28 significant “either or pairs”, about half are currently mistakenly associated with gender traits, such as those in the book “Men are from Mars, Women are from Venus” by John Grey, not with hemisphericity. These comparisons are described in Book Chapter in “Contemporary Research on Aggression”.

    Measurement of the hemisity of spouses and their offspring led to the startling discovery of FAMILIAL POLARITY, the important topic of another part of this website.