Berg Rune W, Kleinfeld David
Department of Physics, University of California at San Diego, La Jolla, California 92093, USA.
J Neurophysiol. 2003 Nov;90(5):2950-63. doi: 10.1152/jn.00511.2003. Epub 2003 Aug 6.
The rhythmic motor activity of the vibrissae that rodents use for the tactile localization of objects provides a model system for understanding patterned motor activity in mammals. Evidence suggests that neural circuitry in the brain stem provides rhythmic drive to the vibrissae. Yet multiple brain structures at higher levels of organization, including vibrissa primary motor cortex (M1), have direct projections to brain stem nuclei that are implicated in whisking. We thus asked whether output from M1 can control vibrissa movement on the approximately 10-Hz scale of the natural rhythmic movement of the vibrissae. Our assay of cortical control made use of periodic intracortical microstimulation (ICMS) to excite a region of vibrissa M1 cortex in awake, behaving animals and measurements of the stimulus-locked electromyogram (EMG) in both the intrinsic and extrinsic muscles that drive the vibrissae. We observed that ICMS evoked a prompt activation of the extrinsic muscles and a delayed and prolonged response in the intrinsic muscles. The relative timing and shape of these waveforms approximates the EMG waveforms seen during natural exploratory whisking. We further observed prompt activation of the intrinsic muscles, an occurrence not seen during exploratory whisking. Despite the latter difference in muscular activation, the motion of the vibrissae evoked by periodic ICMS strongly resembled the motion during natural, exploratory whisking. Interestingly, the extent of the movement was proportional to the level of arousal, as quantified by the amplitude of hippocampal activity in the theta frequency band. We interpret these data as demonstrating that M1 cortex can, in principle, initiate the full pattern of whisking on a cycle-by-cycle basis in aroused animals. Beyond issues of natural motor control, our result may bear on the design of algorithms for neuroprosthetic control of motor output.
啮齿动物用于物体触觉定位的触须节律性运动活动，为理解哺乳动物的模式化运动活动提供了一个模型系统。有证据表明，脑干中的神经回路为触须提供节律性驱动。然而，包括触须初级运动皮层（M1）在内的多个更高层次组织的脑结构，都直接投射到与触须运动有关的脑干核团。因此，我们询问M1的输出是否能够在触须自然节律运动的大约10赫兹尺度上控制触须运动。我们对皮层控制的检测利用周期性皮质内微刺激（ICMS）来激发清醒、行为活跃动物的触须M1皮层区域，并测量驱动触须的内在和外在肌肉中的刺激锁定肌电图（EMG）。我们观察到，ICMS引起外在肌肉的迅速激活以及内在肌肉的延迟和延长反应。这些波形的相对时间和形状接近自然探索性触须运动期间看到的EMG波形。我们还进一步观察到内在肌肉的迅速激活，这在探索性触须运动期间未见。尽管在肌肉激活方面存在后一种差异，但周期性ICMS诱发的触须运动与自然探索性触须运动期间的运动非常相似。有趣的是，运动的程度与觉醒水平成正比，觉醒水平由海马体在θ频段的活动幅度量化。我们将这些数据解释为表明M1皮层原则上可以在觉醒动物中逐周期启动完整的触须运动模式。除了自然运动控制问题之外，我们的结果可能与运动输出神经假体控制算法的设计有关。
