Failla Michelle D, Peters Brittany R, Karbasforoushan Haleh, Foss-Feig Jennifer H, Schauder Kimberly B, Heflin Brynna H, Cascio Carissa J
Department of Psychiatry, Vanderbilt University Medical Center, Nashville, TN 37212 USA.
South Carolina Department of Mental Health, Columbia, SC 29202 USA.
Mol Autism. 2017 Jun 13;8:25. doi: 10.1186/s13229-017-0143-y. eCollection 2017.
The human somatosensory system comprises dissociable paths for discriminative and affective touch, reflected in separate peripheral afferent populations and distinct cortical targets. Differences in behavioral and neural responses to affective touch may have an important developmental role in early social experiences, which are relevant for autism spectrum disorder (ASD).
Using probabilistic tractography, we compared the structural integrity of white matter pathways for discriminative and affective touch in young children with ASD and their typically developing (TD) peers. We examined two tracts: (1) a tract linking the thalamus with the primary somatosensory cortex, which carries discriminative tactile information, and (2) a tract linking the posterior insula-the cortical projection target of unmyelinated tactile afferents mediating affective touch-with the anterior insula, which integrates sensory and visceral inputs to interpret emotional salience of sensory stimuli. We investigated associations between tract integrity and performance on a standardized observational assessment measuring tactile discrimination and affective responses to touch.
Both the thalamocortical and intrainsular tracts showed reduced integrity (higher mean diffusivity) in the ASD group compared to those in the TD group. Consistent with the previous findings, the ASD group exhibited impaired tactile discriminative ability, more tactile defensiveness, and more sensory seeking (e.g., enthusiastic play or repetitive engagement with a specific tactile stimulus). There was a significant relation between intrainsular tract integrity and tactile seeking. The direction of this relation differed between groups: higher intrainsular mean diffusivity (MD) (reflecting decreased tract integrity) was associated with increased tactile seeking in the TD group but with decreased tactile seeking in the ASD group. In the TD group, decreased tactile defensiveness was also associated with higher intrainsular MD, but there was no relation in the ASD group. Discriminative touch was not significantly associated with integrity of either tract in either group.
These results support previous findings suggesting a central role for the insula in affective response to touch. While both discriminative and affective touch and both somatosensory tracts are affected in ASD, the restriction of brain-behavior associations to the intrainsular tract and tactile seeking suggests more complex and perhaps higher-order influence on differences in tactile defensiveness and discrimination.
人类体感系统包含用于辨别性触觉和情感性触觉的可分离路径，这反映在不同的外周传入神经群体和不同的皮质靶点上。对情感性触觉的行为和神经反应差异可能在早期社交体验中具有重要的发育作用，而这些体验与自闭症谱系障碍（ASD）相关。
我们使用概率纤维束成像技术，比较了患有ASD的幼儿及其发育正常（TD）的同龄人中用于辨别性触觉和情感性触觉的白质通路的结构完整性。我们检查了两条纤维束：（1）连接丘脑与初级体感皮层的纤维束，它传递辨别性触觉信息；（2）连接后岛叶（介导情感性触觉的无髓触觉传入神经的皮质投射靶点）与前岛叶的纤维束，前岛叶整合感觉和内脏输入以解释感觉刺激的情感显著性。我们在一项标准化观察评估中调查了纤维束完整性与触觉辨别和对触摸的情感反应表现之间的关联。
与TD组相比，ASD组的丘脑皮质纤维束和岛叶内纤维束均显示完整性降低（平均扩散率更高）。与先前的研究结果一致，ASD组表现出触觉辨别能力受损、更多的触觉防御性以及更多的感觉寻求行为（例如，热情玩耍或反复接触特定的触觉刺激）。岛叶内纤维束完整性与触觉寻求之间存在显著关系。两组之间这种关系的方向不同：较高的岛叶内平均扩散率（MD）（反映纤维束完整性降低）与TD组中触觉寻求增加相关，但与ASD组中触觉寻求减少相关。在TD组中，触觉防御性降低也与较高的岛叶内MD相关，但在ASD组中没有这种关系。辨别性触觉与两组中任一纤维束的完整性均无显著关联。
这些结果支持了先前的研究结果，表明岛叶在对触摸的情感反应中起核心作用。虽然在ASD中辨别性触觉和情感性触觉以及两条体感纤维束均受到影响，但脑 - 行为关联仅限于岛叶内纤维束和触觉寻求，这表明对触觉防御性和辨别差异存在更复杂且可能是更高层次的影响。
