Laterality in Children: Evidence for Task-Dependent Lateralization of Motor Functions

The behavioral preference for the use of one side of the body starts from pre-natal life and prompt humans to develop motor asymmetries. The type of motor task completed influences those functional asymmetries. However, there is no real consensus on the occurrence of handedness during developmental ages. Therefore, we aimed to determine which motor asymmetries emerged differently during childhood. A total sample of 381 children in grades 1 to 5 (6–11 years old) of primary school were recruited and tested for two fine coordination tasks (Floppy, led by dexterity, and Thumb, led by speed-dominated skills) and handgrip strength (HS). Data about their handedness, footedness and sports participation were also collected. Children performed better with their dominant side, especially for the Floppy and HS tests. The asymmetries were more marked in right-handed children and did not differ by age, gender or type of sport. Our findings support the thesis of a functional lateralization in complex coordinative tasks and in maximal strength during developmental ages. Furthermore, our findings extend the evidence of a stronger lateralization in right-handed individuals, demonstrating it at a functional level in primary school children performing motor tasks. Fine motor skills allow a “fine” understanding of developmental trajectories of lateralized behavior.

A large-scale estimate on the relationship between language and motor lateralization

Human language is dominantly processed in the left cerebral hemisphere in most of the population. While several studies have suggested that there are higher rates of atypical right-hemispheric language lateralization in left-/mixed-handers, an accurate estimate of this association from a large sample is still missing. In this study, we comprised data from 1,554 individuals sampled in three previous studies in which language lateralization measured via dichotic listening, handedness and footedness were assessed. Overall, we found a right ear advantage indicating typical left-hemispheric language lateralization in 82.1% of the participants. While we found significantly more left-handed individuals with atypical language lateralization on the categorical level, we only detected a very weak positive correlation between dichotic listening lateralization quotients (LQs) and handedness LQs using continuous measures. Here, only 0.4% of the variance in language lateralization were explained by handedness. We complemented these analyses with Bayesian statistics and found no evidence in favor of the hypothesis that language lateralization and handedness are related. Footedness LQs were not correlated with dichotic listening LQs, but individuals with atypical language lateralization also exhibited higher rates of atypical footedness on the categorical level. We also found differences in the extent of language lateralization between males and females with males exhibiting higher dichotic listening LQs indicating more left-hemispheric language processing. Overall, these findings indicate that the direct associations between language lateralization and motor asymmetries are much weaker than previously assumed with Bayesian correlation analyses even suggesting that they do not exist at all. Furthermore, sex differences seem to be present in language lateralization when the power of the study is adequate suggesting that endocrinological processes might influence this phenotype.

Right = Left ? The concepts of “right-left” and brain asymmetrySağ = Sol ? “Sağ-sol” kavramları ve beyin asimetrisi

<p>Although “right” and “left” are neutral words those describe directions, they have some positive and negative meanings in cultural contexts. Attributing positive meanings for right and negative meanings for left is observed in different cultures, languages and belief systems including Turkish culture. In the presented study, Turkish words, sayings and phrasses including right, left and right-left together were examined according to their meanings (positive, negative, neutral) by referencing Turkish Language Instituion. It was observed that the word “right” had 15 positive meanings and the word “left” had no positive meanings. On the other hand, it was found that the word “right” had no negative meanings and “left” had four negative meanings and there were eight negative meanings including the words “left” and “right” together. The predisposition of attributing positive/negative meanings to right and left is discussed in a neuroscientific perspective and it is assessed in the context of two hemispheric specializations in the brain: 1. Motor asymmetries and handedness 2. Emotions and Valence Hypothesis. Generally, attributing positive meanings for right and negative meanings for left seems to be related to human physiological system, structural and functional brain asymmetries and dependently human cognition and comprehension.</p><p> </p><p><strong>Özet</strong></p><p>Sağ ve sol kavramları ilk anlamları itibariyle yön belirten nötr sözcükler olmasına rağmen kültürel bağlamda bu sözcüklerin olumlu ve olumsuz anlamlara sahip olduğu görülmektedir. Sağa olumlu, sola olumsuz anlam atfetme Türk kültürü de dahil olmak üzere farklı kültürlerde, dillerde ve inanç sistemleri içerisinde gözlenmektedir. Sunulan makalede Türk Dil Kurumu referans alınarak sağ, sol ve sağ ile solun birlikte kullanıldığı sözcük, birleşik sözcük, deyim ve atasözleri içerdikleri olumlu, olumsuz ve nötr anlamlara göre gruplandırılmıştır. Buna göre Türk Dilinde “sağ” sözcüğüne ilişkin 15 olumlu anlamın olduğu, buna karşın “sol” sözcüğüne ilişkin hiçbir olumlu anlamın olmadığı gözlenmiştir. Öte yandan, “sağ” sözcüğüne ilişkin hiçbir olumsuz anlamın olmadığı, “sol”sözcüğüne ilişkin dört ve “sol” ile “sağın” birlikte kullanıldığı sekiz olumsuz anlamın olduğu bulunmuştur. Sunulan makalede insanların sağa ve sola olumlu/olumsuz anlam atfetme eğilimi nörobilim bakış açısından ele alınarak beyinde yer alan iki hemisferik özelleşme temelinde değerlendirilmiştir: 1. Motor Asimetriler ve El Kullanımı 2. Duygular ve Değerlik Hipotezi. Genel olarak sağa olumlu, sola olumsuz anlamlar atfetmek insanın fizyolojik sistemiyle, yapısal ve işlevsel beyin asimetrileriyle ve buna bağlı olarak ortaya çıkan insan bilişi ve kavrayışı ile ilgili gibi görünmektedir.</p>