The idea that a person’s personality, skills, or creativity can be neatly assigned to either the “left brain” (logic) or the “right brain” (creativity) is a persistent cultural concept. This notion often leads to the assumption that left-handed individuals are inherently “right-brained” and therefore more artistic or intuitive.
The Overly Simplified Dual-Brain Myth
The popular split between being “left-brained” or “right-brained” is largely a misconception that modern neuroscience has debunked. This pervasive theory suggests that an individual is dominated by one cerebral hemisphere, which dictates their fundamental nature, such as being analytical or artistic. However, brain imaging studies have consistently shown that complex mental processes require constant communication and integration across both hemispheres.
Research, including a two-year study examining the resting brain scans of over a thousand individuals, found no evidence that people use one brain network more strongly than the other. Functional magnetic resonance imaging (fMRI) reveals that even for tasks traditionally associated with one side, both hemispheres are actively engaged.
It is true that the brain exhibits lateralization, meaning specific functions are specialized in one hemisphere, but this does not equate to hemispheric dominance over personality. For instance, language processing is typically lateralized to the left side, while attention and spatial awareness often involve the right side.
Handedness and True Brain Lateralization
The relationship between hand preference and brain organization is primarily focused on the lateralization of motor control and language, not on personality traits. Handedness itself is controlled by the motor cortex, where the left hemisphere governs movement on the body’s right side, and the right hemisphere controls the left side. The vast majority of the population, about 90%, is right-handed, which correlates strongly with left-hemisphere dominance for fine motor skills.
The most significant functional lateralization is seen in language processing. For nearly all right-handed people, approximately 90 to 95%, the left hemisphere contains the main language centers.
Left-handed individuals show much greater variability in their brain organization for language. While a majority of left-handers, around 70 to 78%, also process language primarily in their left hemisphere, a notable minority exhibits different patterns. About 15% of left-handers show bilateral language representation, meaning both hemispheres are involved. The remaining left-handers, around 7%, show a reversed pattern where language is dominantly processed in the right hemisphere. This means that while a left-hander is statistically more likely to have an atypical brain organization than a right-hander, most still rely on the left side for language.
The Factors Determining Hand Preference
Hand preference is rooted in a complex interplay of genetic and developmental factors. Hand preference begins to establish itself very early, with fetuses showing a tendency to suck the thumb of one hand more than the other starting around the eighth to tenth week of gestation.
Genetics contribute to the trait, but not through a single, simple inheritance pattern. Studies suggest that multiple genes, possibly up to 40, each contribute a small effect to the establishment of hand preference. Overall, genetic factors are estimated to account for only about 25% of the variance in handedness, indicating a strong role for non-genetic influences.
Environmental and developmental factors that occur prenatally account for the remaining determination. These include processes that establish the overall right-left asymmetry of the body during development. The specific neurological development within the womb contributes to which hand becomes dominant.