From the Guidelines
The dominant hemisphere for ambidextrous individuals is typically less lateralized, with a more balanced distribution of brain functions between both hemispheres, though they often still have some degree of left hemisphere dominance for language processing. According to the study by Bryden (1982) 1, approximately 70% of left-handed people lateralize language functions to the left hemisphere, as do all right-handed people, and it can be inferred that ambidextrous individuals may have a similar or even more balanced distribution. Some key points to consider when determining cerebral dominance include:
- The site of application of a unilateral electrode may be decided according to methods such as the Duke University Medical Center ECT Cerebral Dominance Test (Harris, 1988) 1
- Identification of the preferred hand for writing may be insufficient to determine cerebral dominance for language and verbal memory
- Standard tests are available for determining cerebral dominance, and these may be used in situations in which there is doubt about cerebral dominance. It is essential to note that individual variation exists, and some ambidextrous people may still show stronger lateralization toward one hemisphere for specific cognitive functions despite their manual dexterity with both hands.
From the Research
Dominant Hemisphere for Ambidextrous Individuals
- The dominant hemisphere for language in ambidextrous individuals is not as clear-cut as in right-handed or left-handed individuals 2, 3.
- Studies have shown that the incidence of right-hemisphere language dominance increases with the degree of left-handedness, and ambidextrous individuals have a higher incidence of atypical language lateralization compared to right-handed individuals 2.
- One study found that 15% of ambidextrous individuals had right-hemisphere language dominance, while another study found that 22% of left-handed and ambidextrous individuals had atypical language lateralization 2, 3.
- Functional transcranial Doppler sonography and fMRI studies have revealed subtle differences in language lateralization between left-handed and right-handed individuals, particularly in semantic processing tasks 4.
- The relationship between handedness and language dominance is complex, and more research is needed to fully understand the underlying mechanisms 2, 3, 4.
Language Lateralization in Ambidextrous Individuals
- Language lateralization in ambidextrous individuals can be more variable and less lateralized compared to right-handed or left-handed individuals 3, 4.
- One study found that ambidextrous individuals exhibited more balanced activity between the two hemispheres, while another study found that they had a higher incidence of symmetric language lateralization 3, 4.
- The use of advanced imaging techniques, such as fMRI, has allowed for a more detailed understanding of language lateralization in ambidextrous individuals and has revealed subtle differences in language processing between left-handed and right-handed individuals 4.
Cognitive Impairments and Language Lateralization
- Cognitive impairments, such as those resulting from stroke or traumatic brain injury, can affect language lateralization and cognitive function 5, 6.
- Occupational therapy has been shown to improve cognitive function and language abilities in individuals with cognitive impairments, although the evidence is not yet conclusive 5, 6.
- More research is needed to fully understand the relationship between cognitive impairments, language lateralization, and occupational therapy 5, 6.