Duijnhouwer Jacob, Noest André J, Lankheet Martin J M, van den Berg Albert V, van Wezel Richard J A
Center for Molecular and Behavioral Neuroscience, Rutgers University Newark, NJ, USA.
Front Behav Neurosci. 2013 Apr 4;7:22. doi: 10.3389/fnbeh.2013.00022. eCollection 2013.
Several models of heading detection during smooth pursuit rely on the assumption of local constraint line tuning to exist in large scale motion detection templates. A motion detector that exhibits pure constraint line tuning responds maximally to any 2D-velocity in the set of vectors that can be decomposed into the central, or classic, preferred velocity (the shortest vector that still yields the maximum response) and any vector orthogonal to that. To test this assumption, we measured the firing rates of isolated middle temporal (MT) and medial superior temporal (MST) neurons to random dot stimuli moving in a range of directions and speeds. We found that as a function of 2D velocity, the pooled responses were best fit with a 2D Gaussian profile with a factor of elongation, orthogonal to the central preferred velocity, of roughly 1.5 for MST and 1.7 for MT. This means that MT and MST cells are more sharply tuned for speed than they are for direction; and that they indeed show some level of constraint line tuning. However, we argue that the observed elongation is insufficient to achieve behavioral heading discrimination accuracy on the order of 1-2 degrees as reported before.
在平稳跟踪过程中，几种航向检测模型依赖于这样一种假设：在大规模运动检测模板中存在局部约束线调谐。一个表现出纯约束线调谐的运动检测器，对于一组向量中的任何二维速度都会产生最大响应，这些向量可以分解为中心或经典的首选速度（仍能产生最大响应的最短向量）以及与之正交的任何向量。为了验证这一假设，我们测量了孤立的颞中（MT）和颞上内侧（MST）神经元对在一系列方向和速度上移动的随机点刺激的放电率。我们发现，作为二维速度的函数，汇总响应与二维高斯分布最拟合，对于MST，与中心首选速度正交的伸长因子约为1.5，对于MT约为1.7。这意味着MT和MST细胞对速度的调谐比对方向的调谐更敏锐；并且它们确实表现出一定程度的约束线调谐。然而，我们认为，观察到的伸长不足以实现如之前报道的1-2度量级的行为航向辨别精度。
