Bytautiene Juntaute, Baranauskas Gytis
Neurophysiology laboratory, Neuroscience Institute, Lithuanian University of Health Sciences, Kaunas, Lithuania.
PLoS One. 2017 Apr 5;12(4):e0174409. doi: 10.1371/journal.pone.0174409. eCollection 2017.
Spatial integration of visual stimuli is a crucial step in visual information processing yet it is often unclear where this integration takes place in the visual system. In the superficial layers of the superior colliculus that form an early stage in visual information processing, neurons are known to have relatively small visual receptive fields, suggesting limited spatial integration. Here it is shown that at least for rats this conclusion may be wrong. Extracellular recordings in urethane-anaesthetized young adult rats (1.5-2 months old) showed that large stimuli of over 10° could evoke detectable responses well outside the borders of 'classical' receptive fields determined by employing 2° - 3.5° stimuli. The presence of responses to large stimuli well outside these 'classical' receptive fields could not be explained neither by partial overlap between the visual stimulus and the receptive field, nor by reflections or light dispersion from the stimulation site. However, very low frequency (<0.1 Hz) residual responses to small stimuli presented outside the receptive field may explain the obtained results if we assume that the frequency of action potentials during a response to a stimulus outside RF is proportional to the stimulus area. Thus, responses to large stimuli outside RF may be predicted by scaling according to the stimulus area of the responses to small stimuli. These data demonstrate that neurons in the superficial layers of the superior colliculus are capable of integrating visual stimuli over much larger area than it can be deduced from the classical receptive field.
视觉刺激的空间整合是视觉信息处理中的关键步骤，但在视觉系统中这种整合发生的位置往往并不明确。在构成视觉信息处理早期阶段的上丘浅层，已知神经元具有相对较小的视觉感受野，这表明空间整合有限。在此研究表明，至少对于大鼠而言，这一结论可能是错误的。在经乌拉坦麻醉的成年幼鼠（1.5 - 2个月大）中进行的细胞外记录显示，超过10°的大刺激能够在采用2° - 3.5°刺激所确定的“经典”感受野边界之外引发可检测到的反应。对这些“经典”感受野之外的大刺激产生反应，既不能用视觉刺激与感受野之间的部分重叠来解释，也不能用来自刺激部位的反射或光散射来解释。然而，如果我们假设对感受野之外的刺激产生反应时动作电位的频率与刺激面积成正比，那么对感受野之外呈现的小刺激的极低频率（<0.1 Hz）残余反应可能解释所得到的结果。因此，对感受野之外的大刺激的反应可以通过根据对小刺激的反应的刺激面积进行缩放来预测。这些数据表明，上丘浅层的神经元能够在比从经典感受野推断出的大得多的区域上整合视觉刺激。
