Ear asymmetry and left-side cradling

Women and girls tend to cradle infants and dolls on the left side of the body. Left-sided cradling is found in chimpanzees and gorillas, is cross-cultural and present in historical works of art, and is transmitted down the human maternal line. One explanation for the left-cradling tendency is that it facilitates the flow of affective information from the infant via the left ear and eye to the center for emotional decoding, that is, the right hemisphere of the mother. We show that the developmental stability of the ear, as measured by ear asymmetry, is negatively correlated with the left-sided cradling tendency. Left-cradling English women holding infants and Jamaican girls holding dolls had a strong tendency to show lower ear asymmetry than right cradlers, whereas no such relationship was found in boys nor for various measures of asymmetry of the hand, with the possible exception of the wrist in Jamaican girls. Degree of handedness, as measured by the Annett peg-moving test, did not predict cradling preference in the Jamaican children, and the relationship between ear asymmetry and cradling preference was independent of hand preference. Our results suggest that developmental instability of the ear (including the pinna, external auditory meatus, and middle ear) may interfere with the flow of affective information to the right hemisphere. Ear asymmetry also showed evidence of strong maternal but not paternal transmission. It is suggested that between-individual variation of in utero stress may explain patterns of maternal transmission of lateral cradling tendencies.     

燕雀丘间复合体背内侧核对叫声的调控模式

鸣禽鸟的基本发声中枢——丘间复合体背内侧核(nucleus dorsalis medialis of the intercollicular complex,DM)对叫声的调控模式是诱发单次叫声。应用电生理与声学分析相结合的方法研究鸣禽鸟燕雀(Fringilla montifringilla)DM核团对声音调控的模式。经语图和频谱图分析,结果显示：燕雀左侧DM诱发单次叫声的声长和主能量区的带宽分别为右侧DM诱发叫声的2倍和1．7～3．1倍,提示燕雀DM对叫声声长和声强的调控能力,均呈明显的左侧优势。这与高级发声中枢(high vocal center,HVC)和古纹状体粗核(nucleus robustus archistriatalis,RA)等发声控制核团在控声模式中具有左侧优势的特征相似,从而为鸣禽发声控制通路高、低级中枢具有内源投射关系提供了声学上的证据。