Hand preference and skilled hand performance among individuals with successful rightward conversions of the writing hand

Handedness in Alzheimer Disease: A Systematic Review

Handedness has been a topic of scientific interest for many years. However, false and misleading ideas have dominated this field with a still limited amount of research into the association with clinical disorders like Alzheimer disease (AD). In accordance with PRISMA guidelines, PubMed, Embase, and Cochrane Library were searched for studies regarding the association of handedness and AD. Twelve articles were included. Case-control studies show that left-handedness is not a risk factor for late-onset AD (LOAD). However, nonright handedness was found to be more prevalent in patients with early-onset AD (EOAD). Moreover, handedness does not seem to affect neuropsychological performance. We also show that collapsing versus separating mixed and left-handedness may yield different results. Future research on the relation between handedness and AD may provide new insight into disease pathogenesis, improve rehabilitation, and help identify patients who will progress, aiding the design of prevention trials.

Handwriting kinematics during learning to write with the dominant left hand in converted left-handers

Converting left-handers to their non-dominant right hand was previously widespread, particularly for handwriting. The present study aimed to explore the extent to which adult, converted left-handers can learn writing with their dominant left hand during a 2-year training program. Eleven converted left-handers participated in the training. Handwriting kinematics were assessed at regular intervals (seven sessions) and compared to those of 11 innate left-handed controls matched for age, gender, and overall handedness score for basic (Finger, Wrist, Circle) and complex (Sentence, Copy) handwriting tasks. Regarding basic tasks in the training group, we found rapid increases in left and right-hand frequency and no significant differences between both hands at any time point, indicating successful hand transfer. After 24 months, training participants significantly surpassed controls for writing frequency in basic tasks with their left hand. For complex tasks, we identified significant increases in the training groups' left-hand writing frequency and duration between the first and last session. While training participants' left-hand writing remained significantly slower than their right-hand writing, statistics confirmed final differences between hands only for the duration of the Sentence task. Importantly, left-hand writing in the training group was characterized by lower frequency, lower automaticity, and prolonged duration after 24 months compared to innate left-handers. With training participants' left-hand writing skills significantly increasing for complex tasks and no final statistically significant differences between hands for frequency and automaticity, the program was considered effective. Nevertheless, within 2 years, training participants did not reach innate left-handers handwriting proficiency for complex tasks. Underlying reasons may be various, such as a non-optimal training program, a sensitive period for learning to write, irreversible neural changes during conversion in childhood, age-related decline of motor learning capacity, or retrograde interference between right- and left-hand writing.

Cultural and environmental aspects influence lateral preferences

Transcultural approaches comparing the distribution of lateral preference between countries focused primarily on handedness. However, other laterality dimensions may also be susceptible to cultural variations. The present study compared lateral preference in five dimensions (hand, foot, trunk, hearing, and visual) of young adults from Brazil and Mozambique. Two hundred and two undergraduate students participated in the study, of which 101 were Brazilian (21.7 ± 1.66 years old) and 101 Mozambican (25.6 ± 6.2 years old). The participants' lateral preference direction and degree were assessed using the global lateral preference inventory. Most Brazilians were classified in the moderate preference category, while Mozambicans had a higher frequency of individuals with strong preferences. Hence, Mozambicans presented a higher lateralization degree for all dimensions. A subsequent analysis considering only preference direction (right, left or indifferent), and not degree, did not show the same outcomes, revealing similarities in preference distribution between the two groups. This finding highlights the necessity to incorporate preference degrees in future analysis to not overlook potential differences. We also conclude lateral preference investigations with transcultural approaches should analyse beyond handedness, as other dimensions can also be modulated by cultural characteristics.

Changing handedness: What can we learn from preference shift studies?

Handedness is a dynamic and complex aspect of human behavior. Changing it through practice, either willingly or obliged by some reason, requires a considerable amount of effort. Analyzing studies that presented handedness shifts may expand our comprehension of this phenomenon, since knowing how to change it might provide insights into how it develops. Therefore, we reviewed the outcomes of handedness shifts. The results suggest that neural asymmetries related to handedness are likely a consequence of lateralized practice since they correlate with modifications in the behavioral patterns. Clearly, practice is not the only factor influencing handedness development, but it seems to play a significant role in the formation and consolidation of neural and behavioral asymmetries. Another key finding of our review is the suggestion of a ceiling effect for the capacity to change handedness direction and degree, considering none of the reviewed studies reported complete shifts in behavioral measures and brain activation patterns.

Is it possible to change handedness after only a short period of practice? Effects of 15 days of intensive practice on left-hand writing in strong right-handers

Previous studies have argued that a person's ability to write legibly with the non-dominant hand after a limited amount of practice suggests that manual skill can be easily transferred. The present study investigated the degree to which handedness can be altered by short-term practice on the highly complex manual activity of handwriting. Nine strongly right-handed individuals practiced writing with their left hand daily for 15 consecutive days. On three occasions, at baseline, at the end of the practice period and after a one-month retention interval, the similarity of left- and right-hand writing was inspected and handedness was tested by means of the Purdue Pegboard as well as handedness questionnaires. All participants demonstrated more legible writing with their left hand after practice, and the writing was more similar to that of their preferred, right-hand writing, although to different degrees. Pegboard performance improved with the left hand, but equally as much with the right, and there were no other changes in participants' manual preference patterns. The findings of the present study do not indicate any degree of change in handedness, outside the impressive progress in left-hand writing. The large inter-individual variability, suggests that further research should focus on more individual analyses.

Patterns of hand preference and unintentional injuries among Indian attempted hand switchers and hand non-switchers

This study examines the patterns of hand preference and unintentional injuries of attempted hand switchers and hand non-switchers. Data were collected from 3698 participants in Kharagpur, India, on measures of hand preference, hand switching, and unintentional injuries. The direction of left- or right-handedness was on the basis of hand used for the item "writing on paper" and the degree of handedness was based on the average score of remaining items in the handedness inventory. Results reveal that, among attempted hand-switchers, learned right-handers were not right-sided in hand continuum as the natural right-handers, but left-handers were left-sided as natural left-handers. With increasing age the learned right-handers become less right-sided and natural right-handers become more right-sided. Females (males) are found to be more right-handed than males (females) among learned right-handers (natural right-handers). On the direction of handedness, the learned right-handers have more than twice the risk of unintentional injuries than the natural right- and left-handers. On degree of handedness, the use of inconsistent left and both hands among natural left-handers, the use of inconsistent right and both hands among natural right-handers, and the use of weak right hand among learned right-handers increase their vulnerability to unintentional injuries. Any deviation from the genetic make-up in hand use elevates the risk of unintentional injuries, suggesting that one should not change the biological hand.