Harris Justin A
School of Psychology, University of Sydney, NSW2006, Australia.
Novartis Found Symp. 2006;270:238-45; discussion 246-50, 285-92.
Neurons in primary somatosensory cortex (S1) respond to vibrotactile stimuli by firing in phase with each cycle of the vibration. We have investigated how neural activity in S1 might contribute to people's perception of vibration frequency. The contribution of S1 was confirmed using transcranial magnetic stimulation (TMS): accuracy in comparing the frequency of two sequential vibrations was reduced by a single TMS pulse delivered to S1 in the interval between the two vibrations. More recent experiments have revealed that participants use the velocity (or energy) of the stimulus when judging its frequency. This is consistent with a contribution from S1: electrophysiological recording in S1 cortex of rats shows that neurons in S1 do not explicitly code vibration frequency, but instead code the product of frequency and amplitude (proportional to the mean velocity or energy of the vibration). Further, frequency discrimination is reduced by the addition of even very small amounts of noise to the temporal structure of the vibrations (making them irregular). However, noise has no effect if the two vibrations are presented on opposite fingertips (i.e. beyond the range of receptive field sizes of neurons in S1), or if there is no difference in their velocity. Therefore, when judging vibration frequency, humans utilize information about stimulus velocity as coded by neurons in S1, but this coding is dependent on the temporally regular input of the vibration.
初级体感皮层（S1）中的神经元通过与振动的每个周期同步放电来响应振动触觉刺激。我们研究了S1中的神经活动如何影响人们对振动频率的感知。使用经颅磁刺激（TMS）证实了S1的作用：在两次振动之间的间隔向S1施加单个TMS脉冲会降低比较两个连续振动频率的准确性。最近的实验表明，参与者在判断刺激频率时会使用刺激的速度（或能量）。这与S1的作用一致：对大鼠S1皮层的电生理记录表明，S1中的神经元并未明确编码振动频率，而是编码频率与振幅的乘积（与振动平均速度或能量成正比）。此外，向振动的时间结构中添加即使非常少量的噪声（使其变得不规则）也会降低频率辨别能力。但是，如果两次振动施加在相反的指尖上（即超出S1中神经元感受野大小的范围），或者它们的速度没有差异，则噪声没有影响。因此，在判断振动频率时，人类利用S1中神经元编码的有关刺激速度的信息，但这种编码依赖于振动在时间上的规则输入。
