Task-dependent mixed handedness is controlled by specialized hemispheric lateralization in the brain.
the verdict
INSUFFICIENT LEANING
refutedsupported
the weight of evidence
3 sources for · 0 against
The retrieved evidence partially supports connections between manual preference, task demands, and hemispheric motor lateralization, but does not fully establish the specific neurological control mechanisms of task-dependent mixed handedness.
Importance: Handedness and motor asymmetry are important features of occupational performance. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence. Objective: To review the basic neural mechanisms behind handedness and their implications for central and peripheral nervous system injury. Data Sources: Relevant published literature obtained via MEDLINE. Findings: Handedness, along with performance asymmetries observed between the dominant and nondominant hands, may be due to hemispheric specializations for motor control. These specializations contribute to predictable motor control deficits that are dependent on which hemisphere or limb has been affected. Clinical practice recommendations for occupational therapists and other rehabilitation specialists are presented. Conclusions and Relevance: It is vital that occupational therapists and other rehabilitation specialists consider handedness and hemispheric lateralization during evaluation and treatment. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence. Plain-Language Summary: The goal of this narrative review is to increase clinicians’ understanding of the basic neural mechanisms related to handedness (the tendency to select one hand over the other for specific tasks) and their implications for central and peripheral nervous system injury and rehabilitation. An enhanced understanding of these mechanisms may allow clinicians to better tailor neurorehabilitation interventions to address motor deficits and promote functional independence. This rapid review examines the basic neural mechanisms behind handedness and their implications for central and peripheral nervous system injury and rehabilitation.
It is generally accepted that the contralateral cerebral hemisphere is activated during motor control of an upper limb. Most studies exploring the cerebral mechanisms of motor control have focused on right-handed individuals, who represent around 90% of the general population. However, it appears that the lateralization of cortical activation is linked to various factors such as manual preference, the use of the dominant or non-dominant hand, and the type of task performed. The aim of this study was to compare cortical activation asymmetry during two different motor tasks as a function of manual laterality. We included 25 right-handed and 25 left-handed healthy individuals. They performed a distal and a manipulation task with each hand. Cortical activity in the premotor (PMC) and sensorimotor cortices (SMC) was measured using functional near-infrared spectroscopy (fNIRS). A Laterality Index was calculated to assess the degree of left-right hemisphere activation asymmetry for each region of interest. Irrespective of the hand used, cortical activation was predominantly contralateral for right-handers and more bilateral for left-handers. These results were more marked when using the right hand (non-dominant for left-handers) and seem to be modulated by the specific motor demands of the task. Thus, brain organization was less asymmetrical in left-handers than in right-handers, probably because of enhanced interhemispheric connectivity. This organization might favor recovery mechanisms in pathologies such as stroke. These results underline the importance of considering manual laterality in both neurophysiological and clinical studies of central nervous system pathologies.
Manual laterality in nonhuman primates: a distinction between handedness and manual specialization.
This article examines individual and group manual lateralization in nonhuman primates as a function of task's demands. It is suggested to distinguish low- from high-level manual activities with respect to the novelty variable and to the spatiotemporal scale of the movements. This review shows that low-level tasks lead to (a) symmetrical distributions of hand biases for the group and (b) manual preferences that are not indicative of the specialization of the contralateral hemisphere. In contrast, behaviors expressed in high-level tasks (a) show asymmetrical distribution of hand biases for the group and (b) seem to be related to a specialization of the contralateral hemisphere. Two types of lateralization, handedness and manual specialization, correspond to the 2 levels of tasks that are distinguished.
Published in Psychological bulletin (1991)
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