Dunn James S, Mahns David A, Nagi Saad S
School of Medicine, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia.
Department of Clinical and Experimental Medicine, Center for Social and Affective Neuroscience, Linköping University, 58183, Linköping, Sweden.
BMC Neurosci. 2017 Jan 3;18(1):4. doi: 10.1186/s12868-016-0322-3.
It has long been known that a concomitantly cooled stimulus is perceived as heavier than the same object at a neutral temperature-termed Weber's Phenomenon (WP). In the current study, we re-examined this phenomenon using well-controlled force and temperature stimuli to explore the complex interplay between thermal and tactile systems, and the peripheral substrates contributing to these interactions. A feedback-controlled apparatus was constructed using a mechanical stimulator attached to a 5- × 5-mm thermode. Force combinations of 0.5 and 1 N (superimposed on 1-N step) were applied to the ulnar territory of dorsal hand. One of the forces had a thermal component, being cooled from 32 to 28 °C at a rate of 2 °C/s with a 3-s static phase. The other stimulus was thermally neutral (32 °C). Participants were asked to report whether the first or the second stimulus was perceived heavier. These observations were obtained in the all-fibre-intact condition and following the preferential block of myelinated fibres by compression of ulnar nerve.
In normal condition, when the same forces were applied, all subjects displayed a clear preference for the cooled tactile stimulus as being heavier than the tactile-only stimulus. The frequency of this effect was augmented by an additional ~17% when cooling was applied concurrently with the second stimulus. Following compression block, the mean incidence of WP was significantly reduced regardless of whether cooling was applied concurrently with the first or the second stimulus. However, while the effect was abolished in case of former (elicited in <50% of trials), the compression block had little effect in four out of nine participants in case of latter who reported WP in at least 80% of trials (despite abolition of vibration and cold sensations).
WP was found to be a robust tactile-thermal interaction in the all-fibre-intact condition. The emergence of inter-individual differences during myelinated block suggests that subjects may adopt strategies, unbeknownst to them, that focus on the dominant input (myelinated fibres, hence WP abolished by block) or the sum of convergent inputs (myelinated and C fibres, hence WP preserved during block) in order to determine differences in perceived heaviness.
长期以来，人们一直知道，与处于中性温度的同一物体相比，同时冷却的刺激会让人感觉更重——这一现象被称为韦伯现象（WP）。在本研究中，我们使用精心控制的力和温度刺激重新审视了这一现象，以探索热觉和触觉系统之间的复杂相互作用，以及促成这些相互作用的外周基质。我们构建了一种反馈控制装置，该装置使用连接到一个5×5毫米热刺激器的机械刺激器。将0.5牛和1牛的力组合（叠加在1牛的阶跃力上）施加于手背部的尺侧区域。其中一种力具有热成分，以2℃/秒的速率从32℃冷却至28℃，并保持3秒的静态阶段。另一种刺激在热方面是中性的（32℃）。要求参与者报告第一种还是第二种刺激感觉更重。这些观察结果是在所有纤维完整的条件下以及在通过压迫尺神经优先阻断有髓纤维之后获得的。
在正常情况下，当施加相同的力时，所有受试者都明显倾向于认为冷却的触觉刺激比仅触觉刺激更重。当冷却与第二种刺激同时施加时，这种效应的频率增加了约17%。在压迫阻断后，无论冷却与第一种还是第二种刺激同时施加，WP的平均发生率都显著降低。然而，虽然在前者的情况下这种效应消失了（在不到50%的试验中出现），但在后者的9名参与者中有4名，压迫阻断几乎没有影响，这些参与者在至少80%的试验中报告了WP（尽管振动和冷觉消失）。
在所有纤维完整的条件下，WP被发现是一种强大的触觉 - 热觉相互作用。在有髓纤维阻断期间个体差异的出现表明，受试者可能会采用他们自己不知道的策略，这些策略侧重于主导输入（有髓纤维，因此阻断会消除WP）或汇聚输入的总和（有髓纤维和C纤维，因此阻断期间WP得以保留），以便确定感觉重量的差异。
