Guido W, Lu S M, Vaughan J W, Godwin D W, Sherman S M
Department of Neurobiology, State University of New York, Stony Brook 11794-5230, USA.
Vis Neurosci. 1995 Jul-Aug;12(4):723-41. doi: 10.1017/s0952523800008993.
Relay cells of the lateral geniculate nucleus respond to visual stimuli in one of two modes: burst and tonic. The burst mode depends on the activation of a voltage-dependent, Ca2+ conductance underlying the low threshold spike. This conductance is inactivated at depolarized membrane potentials, but when activated from hyperpolarized levels, it leads to a large, triangular, nearly all-or-none depolarization. Typically, riding its crest is a high-frequency barrage of action potentials. Low threshold spikes thus provide a nonlinear amplification allowing hyperpolarized relay neurons to respond to depolarizing inputs, including retinal EPSPs. In contrast, the tonic mode is characterized by a steady stream of unitary action potentials that more linearly reflects the visual stimulus. In this study, we tested possible differences in detection between response modes of 103 geniculate neurons by constructing receiver operating characteristic (ROC) curves for responses to visual stimuli (drifting sine-wave gratings and flashing spots). Detectability was determined from the ROC curves by computing the area under each curve, known as the ROC area. Most cells switched between modes during recording, evidently due to small shifts in membrane potential that affected the activation state of the low threshold spike. We found that the more often a cell responded in burst mode, the larger its ROC area. This was true for responses to optimal and nonoptimal visual stimuli, the latter including nonoptimal spatial frequencies and low stimulus contrasts. The larger ROC areas associated with burst mode were due to a reduced spontaneous activity and roughly equivalent level of visually evoked response when compared to tonic mode. We performed a within-cell analysis on a subset of 22 cells that switched modes during recording. Every cell, whether tested with a low contrast or high contrast visual stimulus exhibited a larger ROC area during its burst response mode than during its tonic mode. We conclude that burst responses better support signal detection than do tonic responses. Thus, burst responses, while less linear and perhaps less useful in providing a detailed analysis of visual stimuli, improve target detection. The tonic mode, with its more linear response, seems better suited for signal analysis rather than signal detection.
爆发式和紧张式。爆发模式依赖于低阈值尖峰电位背后的电压依赖性Ca2+电导的激活。这种电导在去极化膜电位时失活，但当从超极化水平激活时，它会导致一个大的、三角形的、几乎全或无的去极化。通常，在其波峰上伴随着高频动作电位的爆发。因此，低阈值尖峰电位提供了一种非线性放大，使超极化的中继神经元能够对去极化输入做出反应，包括视网膜兴奋性突触后电位（EPSP）。相比之下，紧张式模式的特征是一连串稳定的单个动作电位，更线性地反映视觉刺激。在本研究中，我们通过构建对视觉刺激（漂移正弦波光栅和闪烁点）反应的接收者操作特征（ROC）曲线，测试了103个膝状体神经元反应模式之间在检测方面可能存在的差异。通过计算每条曲线下的面积（称为ROC面积），从ROC曲线确定可检测性。大多数细胞在记录过程中在两种模式之间切换，显然是由于膜电位的微小变化影响了低阈值尖峰电位的激活状态。我们发现，细胞以爆发模式反应的频率越高，其ROC面积越大。这对于对最佳和非最佳视觉刺激的反应都是如此，后者包括非最佳空间频率和低刺激对比度。与紧张式模式相比，与爆发模式相关的较大ROC面积是由于自发活动减少以及视觉诱发反应水平大致相当。我们对记录过程中切换模式的22个细胞的一个子集进行了细胞内分析。每个细胞，无论用低对比度还是高对比度视觉刺激进行测试，在其爆发反应模式下的ROC面积都比在紧张式模式下大。我们得出结论，爆发反应比紧张式反应更能支持信号检测。因此，爆发反应虽然线性较差，可能在提供视觉刺激的详细分析方面用处较小，但能改善目标检测。紧张式模式，因其反应更线性，似乎更适合信号分析而非信号检测。
