{"title":"Hand preference and the corpus callosum: Is there really no association?","authors":"Nora Raaf, René Westerhausen","doi":"10.1016/j.ynirp.2023.100160","DOIUrl":null,"url":null,"abstract":"<div><p>Originating from a series of morphometric studies conducted in the 1980s, it appears a widely held belief in cognitive neuroscience that the corpus callosum is larger in left or mixed handers than in right handers (RH). However, a recent meta-analysis challenges this belief by not finding significant differences in corpus callosum size between handedness groups. Yet, relying on the available published data, the meta-analysis was not able to account for a series of factors potential influencing its outcome, such as confounding effects of brain size differences and a restricted spatial resolution of previous callosal segmentation strategies. To address these remaining questions, we here analysed N = 1057 participants' midsagittal corpus callosum of from the Human Connectome Project (HCP 1200 Young Adults) to compare handedness groups based on consistency (e.g., consistent RH vs. mixed handers, MH) and direction of hand preference (e.g., dominant RH vs. dominant left handers). A possible relevance of brain-size differences was addressed by analysing callosal variability by both using forebrain volume (FBV) as covariate and utilising relative area (callosal area/thickness divided by FBV) as a dependent variable. Callosal thickness was analysed at 100 measuring points along the structure to achieve high spatial resolution to detect subregional effects. However, neither of the conducted analyses was able to find significant handedness-related differences in the corpus callosum and the respective effect-sizes estimates were small. For example, comparing MH and consistent RH, the effect sizes for difference in callosal area were below a Cohen's <em>d</em> = 0.1 (irrespective of how FBV was included), and narrow confidence intervals allowed to exclude effects above |<em>d</em>| = 0.2. Analysing thickness, effect sizes were below <em>d</em> = 0.2 with confidence intervals not extending above |<em>d</em>| = 0.3. In this, the possible range of population effect sizes of hand preference on callosal morphology appears well below the effects commonly reported for factors like age, sex, or brain size. Effects on cognition or behaviour accordingly can be considered small, questioning the common practise to attribute performance differences between handedness groups to differences in callosal architecture.</p></div>","PeriodicalId":74277,"journal":{"name":"Neuroimage. Reports","volume":"3 1","pages":"Article 100160"},"PeriodicalIF":0.0000,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Neuroimage. Reports","FirstCategoryId":"1085","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S2666956023000053","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"Neuroscience","Score":null,"Total":0}
引用次数: 0
Abstract
Originating from a series of morphometric studies conducted in the 1980s, it appears a widely held belief in cognitive neuroscience that the corpus callosum is larger in left or mixed handers than in right handers (RH). However, a recent meta-analysis challenges this belief by not finding significant differences in corpus callosum size between handedness groups. Yet, relying on the available published data, the meta-analysis was not able to account for a series of factors potential influencing its outcome, such as confounding effects of brain size differences and a restricted spatial resolution of previous callosal segmentation strategies. To address these remaining questions, we here analysed N = 1057 participants' midsagittal corpus callosum of from the Human Connectome Project (HCP 1200 Young Adults) to compare handedness groups based on consistency (e.g., consistent RH vs. mixed handers, MH) and direction of hand preference (e.g., dominant RH vs. dominant left handers). A possible relevance of brain-size differences was addressed by analysing callosal variability by both using forebrain volume (FBV) as covariate and utilising relative area (callosal area/thickness divided by FBV) as a dependent variable. Callosal thickness was analysed at 100 measuring points along the structure to achieve high spatial resolution to detect subregional effects. However, neither of the conducted analyses was able to find significant handedness-related differences in the corpus callosum and the respective effect-sizes estimates were small. For example, comparing MH and consistent RH, the effect sizes for difference in callosal area were below a Cohen's d = 0.1 (irrespective of how FBV was included), and narrow confidence intervals allowed to exclude effects above |d| = 0.2. Analysing thickness, effect sizes were below d = 0.2 with confidence intervals not extending above |d| = 0.3. In this, the possible range of population effect sizes of hand preference on callosal morphology appears well below the effects commonly reported for factors like age, sex, or brain size. Effects on cognition or behaviour accordingly can be considered small, questioning the common practise to attribute performance differences between handedness groups to differences in callosal architecture.
源于20世纪80年代进行的一系列形态计量学研究,认知神经科学中似乎普遍认为,左撇子或混合手的胼胝体比右撇子(RH)大。然而,最近的一项荟萃分析挑战了这一观点,因为没有发现利手组之间胼胝体大小的显著差异。然而,根据现有的已发表数据,荟萃分析无法解释一系列可能影响其结果的因素,如大脑大小差异的混杂效应和先前胼胝体分割策略的空间分辨率受限。为了解决这些剩余的问题,我们分析了来自人类连接体项目(HCP 1200 Young Adults)的N=1057名参与者的中矢状胼胝体,以根据一致性(例如,一致性右手与混合手,MH)和手偏好方向(例如,显性右手与显性左手)对利手性组进行比较。通过使用前脑体积(FBV)作为协变量和使用相对面积(胼胝体面积/厚度除以FBV)为因变量分析胼胝体变异性,解决了大脑大小差异的可能相关性。在结构沿线的100个测量点分析了Callosal厚度,以实现高空间分辨率,从而检测次区域效应。然而,两项分析都未能在胼胝体中发现与利手相关的显著差异,并且各自的效应大小估计值较小。例如,比较MH和一致RH,胼胝体面积差异的影响大小低于Cohen’s d=0.1(无论如何包括FBV),并且窄的置信区间允许排除|d|=0.2以上的影响。分析厚度时,效应大小低于d=0.2,置信区间不超过|d|=0.3。在这方面,手偏好对胼胝体形态的群体效应大小的可能范围似乎远低于年龄、性别或大脑大小等因素的常见影响。因此,对认知或行为的影响可以被认为是很小的,质疑将利手组之间的表现差异归因于胼胝体结构差异的常见做法。