Lang Eric J, Sugihara Izumi, Llinás Rodolfo
Department of Physiology and Neuroscience, New York University Medical Center, 550 First Avenue, New York, NY 10016, USA.
J Physiol. 2006 Feb 15;571(Pt 1):101-20. doi: 10.1113/jphysiol.2005.102764. Epub 2005 Dec 15.
The vibrissal movements known as whisking are generated in a pulsatile, or non-continuous, fashion and comprise sequences of brief regularly spaced movements. These rhythmic timing sequences imply the existence of periodically issued motor commands. As inferior olivary (IO) neurones generate periodic synchronous discharges that could provide the underlying timing signal, this possibility was tested by determining whether the olivocerebellar system modulates motor cortex (MCtx)-triggered whisker movements in rats. Trains of current pulses were applied to MCtx, and the resulting whisker movements were recorded using a high speed video camera. The evoked movement patterns demonstrated properties consistent with the existence of an oscillatory motor driving rhythm. In particular, movement amplitude showed a bell-shaped dependence on stimulus frequency, with a peak at 11.5+/-2.3 Hz. Moreover, movement trajectories showed harmonic and subharmonic entrainment patterns within specific stimulus frequency ranges. By contrast, movements evoked by facial nerve stimulation showed no such frequency-dependent properties. To test whether the IO was the oscillator in question, IO neuronal properties were modified in vivo by intra-IO picrotoxin injection, which enhances synchronous oscillatory IO activity and reduces its natural frequency. The ensuing changes in the evoked whisker patterns were consistent with these pharmacological effects. Furthermore, in cerebellectomized rats, oscillatory modulation of MCtx-evoked movements was greatly reduced, and intra-IO picrotoxin injections did not affect the evoked movement patterns. Additionally, multielectrode recording of Purkinje cell complex spikes showed a temporal correlation of olivocerebellar activity during MCtx stimulus trains to evoked movement patterns. In sum, the results indicate that MCtx's ability to generate movements is modulated by an oscillatory signal arising in the olivocerebellar system.
被称为“拂动”的触须运动以脉动或非连续的方式产生，由一系列短暂且间隔规律的运动组成。这些有节奏的定时序列意味着存在周期性发出的运动指令。由于下橄榄核（IO）神经元会产生周期性同步放电，这可能提供潜在的定时信号，因此通过确定橄榄小脑系统是否调节大鼠运动皮层（MCtx）触发的触须运动来检验了这种可能性。将一串电流脉冲施加到MCtx，并使用高速摄像机记录由此产生的触须运动。诱发的运动模式表现出与振荡性运动驱动节律的存在相一致的特性。特别是，运动幅度对刺激频率呈现钟形依赖性，在11.5±2.3Hz处出现峰值。此外，在特定刺激频率范围内，运动轨迹呈现谐波和次谐波夹带模式。相比之下，由面神经刺激诱发的运动没有表现出这种频率依赖性特性。为了测试IO是否是所讨论的振荡器，通过向IO内注射印防己毒素在体内改变IO神经元特性，这会增强同步振荡的IO活动并降低其固有频率。诱发的触须模式随后发生的变化与这些药理作用一致。此外，在小脑切除的大鼠中，MCtx诱发运动的振荡调制大大降低，并且向IO内注射印防己毒素不影响诱发的运动模式。另外，对浦肯野细胞复合锋电位的多电极记录显示，在MCtx刺激串期间橄榄小脑活动与诱发的运动模式存在时间相关性。总之，结果表明MCtx产生运动的能力受到橄榄小脑系统中产生的振荡信号的调制。
