LaMotte R H, Friedman R M, Lu C, Khalsa P S, Srinivasan M A
Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
J Neurophysiol. 1998 Nov;80(5):2446-66. doi: 10.1152/jn.1998.80.5.2446.
The representations of orientation and shape were studied in the responses of cutaneous mechanoreceptors to an isolated, raised object on a planar surface stroked across the fingerpad. The objects were the top portions of a sphere with a 5-mm radius, and two toroids each with a radius of 5 mm along one axis and differing radii of 1 or 3 mm along the orthogonal axis. The velocity and direction of stroking were fixed while the orientation of the object in the horizontal plane was varied. Each object was stroked along a series of laterally shifted, parallel, linear trajectories over the receptive fields of slowly adapting, type I (SA), and rapidly adapting, type I (RA) mechanoreceptive afferents innervating the fingerpad of the monkey. "Spatial event plots" (SEPs) of the occurrence of action potentials, as a function of the location of each object on the receptive field, were interpreted as the responses of a spatially distributed population of fibers. That portion of the plot evoked by the curved object (the SEPc) provided a representation of the shape and orientation of the two-dimensional outline of the object in the horizontal plane in contact with the skin. For both SAs and RAs, the major vector of the SEPc, obtained by a principal components analysis, was linearly related to the physical orientation of the major axis of each toroid. The spatial distribution of discharge rates [spatial rate surface profiles (SRSs), after plotting mean instantaneous frequency versus spatial locus within the SEPc] represented object shape in a third dimension, normal to the skin surface. The shape of the SA SRSs, well fitted by Gaussian equations, better represented object shape than that of the RA SRSs. A cross-sectional profile along the minor axis [spatial rate profile (SRP)] was approximately triangular for SAs. After normalization for differences in peak height, the falling slopes of the SA SRPs increased, and the base widths decreased with curvature of the object's minor axis. These curvature-related differences in slopes and widths were invariant with changes in object orientation. It is hypothesized that circularity in object shape is coded by the constancy of slopes of SA SRPs between peak and base and that the constancy of differences in the widths and falling slopes evoked by different raised objects encodes, respectively, the differences in their sizes and shapes regardless of differences in their orientation on the skin.
研究了皮肤机械感受器对在平面上划过指腹的孤立凸起物体的反应中方向和形状的表征。这些物体是半径为5毫米的球体顶部，以及两个环面，每个环面在一个轴上的半径为5毫米，在正交轴上的半径分别为1毫米或3毫米。抚摸的速度和方向固定，而物体在水平面上的方向变化。每个物体沿着一系列横向移动、平行的线性轨迹在支配猴子指腹的慢适应I型（SA）和快适应I型（RA）机械感受传入纤维的感受野上抚摸。动作电位发生的“空间事件图”（SEP），作为每个物体在感受野上位置的函数，被解释为空间分布纤维群体的反应。由弯曲物体诱发的图的那部分（SEPc）提供了与皮肤接触的水平面上物体二维轮廓的形状和方向的表征。对于SA和RA，通过主成分分析获得的SEPc的主向量与每个环面主轴的物理方向呈线性相关。放电率的空间分布[在绘制平均瞬时频率与SEPc内的空间轨迹后得到的空间速率表面轮廓（SRS）]在垂直于皮肤表面的第三维中表示物体形状。SA SRS的形状由高斯方程很好地拟合，比RA SRS更能代表物体形状。对于SA，沿短轴的横截面轮廓[空间速率轮廓（SRP）]近似为三角形。在对峰值高度差异进行归一化后，SA SRP的下降斜率增加，基部宽度随着物体短轴曲率的增加而减小。这些与曲率相关的斜率和宽度差异在物体方向变化时不变。据推测，物体形状的圆形度由SA SRP在峰值和基部之间斜率的恒定性编码，并且不同凸起物体诱发的宽度和下降斜率差异的恒定性分别编码了它们在大小和形状上的差异，而不管它们在皮肤上的方向差异如何。
