Introduction:: Handedness is a multifaceted trait that is influenced by an individual’s environment, genetics, and pure chance. The majority of the human population, about 90%, is right-handed (RHD), while the other 10% is either left-handed (LHD) or ambidextrous. Because of disproportionate distributions of limb dominance, many left-handed individuals must learn to adapt to a right-handed world. Due to adaptations, many left-handed dominant individuals engage in more bilateral neural activation patterns than their right-handed counterparts. Present studies have made it known that right-handed individuals are more likely to utilize the left side of the brain to complete motor tasks and left-handed individuals were found to utilize the neural connections within both the right and left hemispheres of the brain. This fundamental difference in limb dominance and neural connectivity could greatly impact and further improve our understanding of underlying neural mechanisms of left-hand dominant individuals. The purpose of this study is to challenge the theory of lateralization of brain function by analyzing the differences in neural connectivity between right-hand dominant and left-hand dominant individuals. The data collected from this study can be used to compare the brain patterns and motor control of individuals with varying handedness. In the future, this information can be used to determine if alternate treatment methods in a clinical setting would be more beneficial for left-handed individuals and if the handedness of their caregiver is a crucial part of their learning/recovery process.
Materials and Methods:: Thirty healthy male and female volunteers (15 RHD, 15 LHD) ages 18 to 35 years have been recruited to participate. Each subject was prepared with a 64-channel EEG cap (Compumedics Neuroscan, USA), which captured brain activity. SuperLab (Cedrus, TX, USA) and Curry 7 (Compumedics Neuroscan, NC, USA) were used to present stimuli and collect data. Participants performed a random, but repetitive 13-element sequencing task with their dominant hand. A fixed 10-element movement sequence was created and inserted in a longer 13-element movement sequence at random locations. Participants were not told of the repeating sequence. Four white rectangles were displayed on a screen. When one rectangle turned black, the participant pressed the corresponding button on a keypad (see figure 1). For example, the rectangle farthest to the left on the screen represented the thumb key for a RHD individual. EEG activation patterns were compared across RHD and LHD individuals, and behavior was assessed by the rate of error reductions during the task. After completing data acquisition, data processing consisted of advanced connectivity measurements.
Results, Conclusions, and Discussions:: Results and Discussion: RHD and LHD individuals were indistinguishable in terms of behavior and voltage, but LHD and RHD individuals had very different patterns of communication across the brain (see figure 2). RHD individuals were more unilateral in their communication process and relied mainly on the left hemisphere of the brain while, LHD individuals relied heavily on both hemispheres of the brain while performing the motor sequencing task.
Conclusion: When compared, left-hand dominant and right-hand dominant individuals were similar in terms of behavior and voltage; however, the patterns in which the brain communicated during this motor sequencing task were vastly different. The RHD participants mainly relied on one hemisphere of the brain to perform the task, while LHD participants heavily relied on both hemispheres of the brain. In addition, since LHD individuals relied mainly on the left hemisphere, this conflicts with the traditional idea that more brain activation would be seen in the right hemisphere when performing such a task with LHD individuals. Overall, this study challenges the theory of lateralization of brain function by analyzing the differences in neural connectivity between RHD and LHD individuals. It is thought that this difference in brain activation patterns when performing a motor control task stems from the fact that left-limb dominant individuals have had to adapt to a right-handed world and therefore their brain has worked around these barriers to function properly. So, rather than use the same neural connectivity networks as RHD individuals, LHD individuals seem to have re-routed their brain network complete tasks in a way that is more efficient for them. With all of this in mind, studying this fundamental difference in limb dominance and neural connectivity could greatly improve our understanding of human anatomy and physiology. This information can be used to determine if alternate treatment methods exist that may be more beneficial for LHD individuals and if the handedness of their healthcare provider is a crucial part of their learning and recovery process.
