Burgess P R, Mei J, Tuckett R P, Horch K W, Ballinger C M, Poulos D A
J Neurosci. 1983 Aug;3(8):1572-85. doi: 10.1523/JNEUROSCI.03-08-01572.1983.
Psychophysical tests on human subjects showed that judgments of skin indentation depth made when the fingertip was indented at rates from 0.2 to 16 mm/sec were quite insensitive to changes in indentation velocity. Similar results were obtained on the forearm at indentation velocities of 0.4 to 16 mm/sec. Recordings were made from mechanoreceptors in the monkey's hand that were able to respond over the same range of velocities and at comparable depths to determine how skin indentation depth might be signaled (coded) at the receptor level and to examine the rate sensitivity of the possible depth codes. It was found that most of the receptors with foci under the stimulator were recruited relatively early during an indentation, especially at velocities of 1.6 mm/sec and higher, making it improbable that the full range of indentation depths is signaled by the "subsurface" recruitment of different receptors at different indentation depths. A subsurface recruitment code involving subcutaneous receptors is not likely since subjects could feel virtually none of the stimuli after skin anesthesia. Progressive recruitment with depth of receptors whose foci lie further and further away from the stimulator ("lateral" recruitment) was considered an unlikely depth code because changing the area of the stimulator had little effect on its perceived depth. Also, it was shown that subjects could sense the curvature of the indentation (the profile of the depth at right angles to the skin surface), which requires information about the depth of individual patches of skin beneath the stimulator. There is no obvious way that a lateral recruitment code can provide this information. Thus it is probable that the discharge rate of some or all of the receptors excited by the indentation is involved in indicating its depth. Both impulse frequency and receptor recruitment at any given depth increased as the velocity of the indentation increased. The demonstrated reliability of information about skin indentation depth in humans indicates that the central neural circuitry responsible for judgments of skin indentation depth is able to compensate for the rate-sensitive receptor signals.
对人类受试者进行的心理物理学测试表明，当指尖以0.2至16毫米/秒的速度被压痕时，对皮肤压痕深度的判断对压痕速度的变化相当不敏感。在前臂以0.4至16毫米/秒的压痕速度也得到了类似的结果。从猴子手部的机械感受器进行记录，这些感受器能够在相同的速度范围内并在相当的深度做出反应，以确定皮肤压痕深度在感受器水平可能如何被信号化（编码），并检查可能的深度编码的速率敏感性。研究发现，大多数刺激器下方有焦点的感受器在压痕过程中相对较早被激活，特别是在速度为1.6毫米/秒及更高时，这使得不同压痕深度下不同感受器的“皮下”激活来信号化整个压痕深度范围的可能性不大。由于皮肤麻醉后受试者几乎感觉不到任何刺激，涉及皮下感受器的皮下激活编码不太可能。随着感受器焦点离刺激器越来越远，其随深度逐渐激活（“横向”激活）被认为是一种不太可能的深度编码，因为改变刺激器的面积对其感知深度影响很小。此外，研究表明受试者能够感知压痕的曲率（与皮肤表面成直角的深度轮廓），这需要关于刺激器下方各个皮肤区域深度的信息。横向激活编码没有明显的方式可以提供此信息。因此，很可能压痕激发的一些或所有感受器的放电率参与指示其深度。在任何给定深度，脉冲频率和感受器激活都随着压痕速度的增加而增加。在人类中关于皮肤压痕深度信息的已证明的可靠性表明，负责判断皮肤压痕深度的中枢神经回路能够补偿速率敏感的感受器信号。
