Left-handedness, as a relatively uncommon phenomenon, never fails . is no association between brain carcinogenesis and the dominance of. How does handedness relate to brain organization? a branch of psychology concerned with the links between biology and behavior. (Some biological psychologists call themselves behavioral . association areas. The cerebral cortex, representing the highest level of brain development, is responsible most of the cortex—its association areas—are free to process other information. . Discuss research findings on brain organization and handedness. Left-handers are more numerous among those with reading disabilities, allergies.
On the other side, children who were not lateralized in infancy and became right or left handed as toddlers had the average expected language scores for their age. There are also differences in the lateralization of visual areas of the brain between right and left-handed individuals.
In right-handers, there is much higher activation of the right fusiform face area the area responsible for face visualization and the extrastriate body area responsible for body visualization. Meanwhile, in left-handers, these areas are equally activated across both brain hemispheres.
Some researchers believe that brain volume may correlate with handedness, although the data on this subject remains controversial. One group of researchers reported that left-handed individuals had a larger brain, while another study found no difference in brain size between the right- and left-handers.
As some findings indicate, left-handers are more prone to nighttime awakenings due to sleep disorders caused by periodic limb movements. It seems that left-handed individuals are more likely to experience limb movements while asleep compared to right-handers. Since handedness has been associated with prenatal hormonal exposure, it could influence the risk of carcinogenesis later in life.
Scientists investigated the impact of handedness on brain tumorsboth malignant and benign ones. One study examined the associations between glioma, meningioma, and acoustic neuroma with self-reported handedness. Left-handers or ambidextrous with equal use of both hands individuals were at reduced risk of glioma the most common malignant brain tumor when compared with the right-handers.
This relationship was similar for both genders.
However, another very recent study found no such association. This large case-control study which included more than glioma cases and healthy controls reported no association between handedness and glioma risk after adjustment for age, gender, and race. Although the brains of left-handers and right-handers differ in their structures, the available literature shows no noteworthy differences in intelligence as measured by IQ score.
Nevertheless, these brain structure differences seem to reflect the more diverse and creative processing of language and emotions by left-handers than by right-handed individuals. This may explain why a greater proportion of left-handers are professional musicianseven in those cases when the musical instruments are designed for right-handers for example, violins.
Similarly, the gift for mathematics seems to be more common in the left-handed populace. It is obvious that right and left-handers differ not only in hand preference but also in brain structure. This further reflects the ability to perform different tasks and achieve success in different professions. Although there is a clear link between non-right handedness and developmental disorders, there is no association between brain carcinogenesis and the dominance of one hand.
It seems that handedness can be predicted in early childhood, even during fetal development, but further investigations are needed to elucidate the origins of our preference to use one hand or the other.
Mixed-handedness is associated with greater age-related decline in volumes of the hippocampus and amygdala: Left brain, right brain: Early handedness in infancy predicts language ability in toddlers. Handedness- and brain size-related efficiency differences in small-world brain networks: Hemispheric specialization for language: Many of the generalizations, simplifications and myths about handedness e. The advent of functional Magnetic Resonance Imaging fMRI scanning in the s has enabled our picture of the way the brain functions to be sharpened still further.
But, rather than clarifying the situation, recent research has if anything muddied the waters still further, and it seems that the more we find out the less clear-cut brain lateralization appears to be. For instance, Dutch research in showed that face recognition, normally a right hemisphere function, usually occurs in the left hemisphere of left-handers.
However, the research also showed that the ability to order or sequence a list of manual activities appears to be an exclusive specialty of the left hemisphere, regardless of whether a person is left- or right-handed. Other findings appear to have little or no logic to them. For example, there is some evidence that women in general tend to process language more evenly between the two hemispheres which also seems to fly in the face of the finding that more men than women are left-handed.
For instance, one eye is able to perceive both sides of a view if necessary; most but not all of one side of the body may be paralyzed after a one-sided brain injury; etc.
In fact, if a whole brain hemisphere is removed at a young age, this redundancy and the brain's innate plasticity can mean that higher mental functions can develop almost completely unimpaired.
Thus, it appears that, while there may be some general rules about hemispheric function specialization, the actual situation is much more complex than we ever thought. Rather than firm rules, they should be seen more as indicators, and the plasticity and complexity of the brain appears to allow for significant variation from these indicators.
The language functions of left-handers in particular are more diffuse and less restricted to one hemisphere than those of right-handers. Dan Geschwind, who pioneered brain comparison studies between twins, suggests that this distribution of language functions across the hemispheres in left-handers may actually put them at some risk from neurological disorders such as dyslexia, although it may also afford them some advantages.
Handedness and Brain Lateralization
Another promising model for hemispheric simplification was put forward by the British-German team of John Marshall and Gereon Fink in the s. They posited that the left hemisphere of the brain focuses on detail while the right hemisphere is more concerned with the broad background picture. Thus, the left brain and, by extension, it may be argued, a right-handed person is better adapted to mental skills requiring a series of discrete steps or to focus on a small fragment of what we perceive.
The right hemisphere and a left-handeron the other hand, is better able to represent the relative position of objects in space and to handle the emotional and metaphorical aspects of speech.
Handedness: What Does It Say About Your Brain Structure? | Brain Blogger
Initially, the model had strong experimental support: However, inexplicably, if the navon is object-based e. It appears that little about the brain is ever straight-forward.
Modern fMRI imaging has shown the extent to which both hemispheres are involved in almost all activities, often in different ways but usually working together simultaneously. One possible explanation for the more balanced hemispheres in the brains of left-handers, then, is that they are more likely to use their non-dominant hand than right-handers in order to cope with right-handed tools, appliances, etc. The Function of the Corpus Callosum Given that, as we have seen, many if not most activities require both hemispheres, at least to some extent e.
This has been dramatically illustrated in patients whose corpus callosum has been severed for medical reasons, and whose right hand can make neat well-formed drawings but with no concept of three-dimensional space or perspective, while their left hand can only make messy malformed figures that neverthless exhibit a complete understanding of three-dimensional space and form.