Bussières L, Casanova C
École d'optométrie, Université de Montréal.
Département de Physiologie, Faculté de Médecine, Université de Montréal, Montréal, QC, Canada H3C 3J7.
Cereb Cortex. 2017 Feb 1;27(2):1347-1357. doi: 10.1093/cercor/bhv320.
Neuronal responses to second-order motion, that is, to spatiotemporal variations of texture or contrast, have been reported in several cortical areas of mammals, including the middle-temporal (MT) area in primates. In this study, we investigated whether second-order responses are present in the cat posteromedial lateral suprasylvian (PMLS) cortex, a possible homolog of the primate area MT. The stimuli used were luminance-based sine-wave gratings (first-order) and contrast-modulated carrier stimuli (second-order), which consisted of a high-spatial-frequency static grating (carrier) whose contrast was modulated by a low-spatial-frequency drifting grating (envelope). Results indicate that most PMLS neurons responded to second-order motion and for the vast majority of cells, first- and second-order preferred directions were conserved. However, responses to second-order stimuli were significantly reduced when compared to those evoked by first-order gratings. Circular variance was increased for second-order stimuli, indicating that PMLS direction selectivity was weaker for this type of stimulus. Finally, carrier orientation selectivity was either absent or very broad and had no influence on the envelope's orientation selectivity. In conclusion, our data show that PMLS neurons exhibit similar first- and second-order response profiles and that, akin primate area MT cells, they perform a form-cue invariant analysis of motion signals.
在包括灵长类动物的颞中区（MT区）在内的哺乳动物的几个皮质区域中，已报道了神经元对二阶运动（即对纹理或对比度的时空变化）的反应。在本研究中，我们调查了猫的后内侧外侧上薛氏回（PMLS）皮质中是否存在二阶反应，该区域可能是灵长类动物MT区的同源区域。所使用的刺激是基于亮度的正弦波光栅（一阶）和对比度调制载波刺激（二阶），后者由一个高空间频率的静态光栅（载波）组成，其对比度由一个低空间频率的漂移光栅（包络）调制。结果表明，大多数PMLS神经元对二阶运动有反应，并且对于绝大多数细胞而言，一阶和二阶偏好方向是一致的。然而，与一阶光栅诱发的反应相比，对二阶刺激的反应显著降低。二阶刺激的循环方差增加，表明PMLS对这种类型刺激的方向选择性较弱。最后，载波方向选择性要么不存在，要么非常宽泛，并且对包络的方向选择性没有影响。总之，我们的数据表明，PMLS神经元表现出相似的一阶和二阶反应特征，并且与灵长类动物MT区细胞类似，它们对运动信号进行形式线索不变分析。
