General features of the retinal connectome determine the computation of motion anticipation.
General features of the retinal connectome determine the computation of motion anticipation.
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DOI：
10.7554/elife.06250
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发表时间：
2015-03-18
期刊：
影响因子：
7.7
通讯作者：
Lagnado L
中科院分区：
文献类型：
--
作者：
Johnston J;Lagnado L
运动预测允许视觉系统补偿光转换的缓慢速度，从而可以准确地定位移动物体。这种校正已经存在于神经节细胞从视网膜发出的信号中，但这种计算背后的生物物理机制尚不清楚。在这里，我们表明，运动预测计算自主每个神经节细胞的树突树内，并依赖于前馈抑制。兴奋性和抑制性突触的被动和非线性相互作用使体细胞电压能够编码运动物体的实际位置，而不是其延迟表示。视网膜连接体的一般特征而不是特定特征控制着这种计算：抑制性输入超过兴奋性输入，两者都是随机分布的，允许跟踪所有方向的运动，而输入之间的平均距离决定了可以补偿的物体速度。DOI：http://dx.doi.org/10.7554/eLife.06250.001视网膜是眼睛后部的一个结构，它将光线转化为神经冲动，然后在大脑中进行处理，产生我们看到的图像。当一个物体第一次进入视野后，视网膜向大脑发送信号通常需要十分之一秒。在网球比赛中，这大约是一个网球移动几米所需的时间，但我们仍然能够看到运动中的网球在真实的时间内的位置。这是因为一种称为“运动预测”的过程能够补偿处理移动物体位置的延迟。然而，人们并不知道运动预测是如何发生的。在视网膜内部，被称为光感受器的细胞检测光，并最终将信号（通过一些中间细胞类型）发送到被称为视网膜神经节细胞的神经细胞。这些信号可以刺激视网膜神经节细胞，使其向大脑发送电信号，或者抑制它，暂时阻止电活动。每个细胞从几个光感受器接收信号，每个光感受器连接到沿着分支状结构的不同部位，这些结构称为树突，从视网膜神经节细胞中突出。约翰斯顿和拉格纳多现在已经研究了运动预测是如何发生在视网膜上的，他们使用金鱼视网膜活动的电子记录，结合计算机模拟这种活动。这揭示了抑制信号，从光感受器通过一种中间细胞（称为无长突细胞）发送到视网膜神经节细胞，在运动预测中起着关键作用。在所有方向上有效地跟踪运动的能力需要比兴奋信号更多的抑制信号被发送到视网膜神经节细胞的树突。这两种类型的输入也必须随机分布在整个单元中。此外，树突上这些输入点的密度决定了视网膜对快速移动物体的运动补偿能力。视网膜中运动预测所需的构建模块也存在于大脑中更高的视觉区域中。因此，进一步的工作可能会揭示，更高的视觉区域也使用这种机制来预测移动物体的未来位置。DOI：http://dx.doi.org/10.7554/eLife.06250.002网站
Motion anticipation allows the visual system to compensate for the slow speed of phototransduction so that a moving object can be accurately located. This correction is already present in the signal that ganglion cells send from the retina but the biophysical mechanisms underlying this computation are not known. Here we demonstrate that motion anticipation is computed autonomously within the dendritic tree of each ganglion cell and relies on feedforward inhibition. The passive and non-linear interaction of excitatory and inhibitory synapses enables the somatic voltage to encode the actual position of a moving object instead of its delayed representation. General rather than specific features of the retinal connectome govern this computation: an excess of inhibitory inputs over excitatory, with both being randomly distributed, allows tracking of all directions of motion, while the average distance between inputs determines the object velocities that can be compensated for. DOI: http://dx.doi.org/10.7554/eLife.06250.001 The retina is a structure at the back of the eye that converts light into nerve impulses, which are then processed in the brain to produce the images that we see. It normally takes about one-tenth of a second for the retina to send a signal to the brain after an object first moves into view. This is about the same time it takes a tennis ball to travel several meters during a tennis match, yet we are still able to see where the moving tennis ball is in real time. This is because a process called ‘motion anticipation’ is able to compensate for the delay in processing the position of a moving object. However, it was not known precisely how motion anticipation occurs. Inside the retina, cells called photoreceptors detect light and ultimately send signals (via some intermediate cell types) to nerve cells known as retinal ganglion cells. These signals can either excite a retinal ganglion cell to cause it to send an electrical signal to the brain, or inhibit it, which temporarily prevents electrical activity. Each cell receives signals from several photoreceptors, which each connect to a different site along branch-like structures called dendrites that project out of the retinal ganglion cells. Johnston and Lagnado have now investigated how motion anticipation occurs in the retina by using electrical recordings of the activity in the retinas of goldfish combined with computer simulations of this activity. This revealed inhibitory signals, sent from photoreceptors to retinal ganglion cells via a type of intermediate cell (called amacrine cells), play a key role in motion anticipation. The ability to track motion effectively in all directions requires more inhibitory signals to be sent to the dendrites of a retinal ganglion cell than excitatory signals. These two types of input must also be randomly distributed across the cell. Furthermore, it is the density of these input sites on a dendrite that determines how well the retina can compensate for the motion of a fast-moving object. The building blocks required for motion anticipation in the retina are also found in visual areas higher in the brain. Therefore, further work may reveal that higher visual areas also use this mechanism to predict the future location of moving objects. DOI: http://dx.doi.org/10.7554/eLife.06250.002