Weiss Shennan A, Preuss Thomas, Faber Donald S
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Neurosci. 2009 Mar 18;29(11):3431-41. doi: 10.1523/JNEUROSCI.3383-08.2009.
The paired teleost Mauthner (M)-cells and their associated network serve as an excellent system to study the biophysical basis of decision making. In teleosts, an abrupt sound evokes an M-spike, triggering a C-start escape that is usually directed away from a sound source. The response latency is minimized by electrical synapses between auditory afferents and the M-cell lateral dendrite. Here, we demonstrate that the electrical synapses also mediate phase encoding. Ramped sound pressure waves (150-250 Hz) evoked electrotonic postsynaptic potentials in the M-cell locked to two diametrically opposed phase angles that were frequency dependent but intensity independent. Phase encoding was also evident at the behavioral level underwater, because the stimuli evoked directional C-starts with an onset that was phase locked to the sound wave. In interneurons inhibitory to the M-cell, these same stimuli also evoked phase-locked electrotonic postsynaptic potentials and action potentials. The resulting chemical and electrical (i.e., field effect) inhibitions functioned tonically and phasically, respectively. Phase encoding could be important in underwater sound source localization, which is thought to require a neural computation involving a phase comparison between the pressure and the directional particle motion components of sound. This computation may be implemented by an interplay between phase-dependent afferent excitation and feedforward inhibition that activates the appropriate M-cell and directs the C-start away from the sound source.
硬骨鱼成对的毛特纳（M）细胞及其相关网络是研究决策生物物理基础的绝佳系统。在硬骨鱼中，突然的声音会引发M峰电位，触发C型惊吓逃逸反应，通常是朝着远离声源的方向。听觉传入神经与M细胞外侧树突之间的电突触可使反应潜伏期最短。在此，我们证明电突触还介导相位编码。斜坡式声压波（150 - 250赫兹）在M细胞中诱发电紧张性突触后电位，其锁定在两个完全相反的相位角上，这两个相位角与频率有关但与强度无关。在水下行为水平上，相位编码也很明显，因为刺激诱发的定向C型惊吓逃逸反应的起始与声波相位锁定。在对M细胞起抑制作用的中间神经元中，这些相同的刺激也诱发相位锁定的电紧张性突触后电位和动作电位。由此产生的化学抑制和电（即场效应）抑制分别以紧张性和相位性方式起作用。相位编码在水下声源定位中可能很重要，人们认为这需要一种神经计算，涉及声音压力与定向粒子运动分量之间的相位比较。这种计算可能通过相位依赖性传入兴奋与前馈抑制之间的相互作用来实现，前馈抑制激活适当的M细胞并引导C型惊吓逃逸反应远离声源。
