Eifuku S, Wurtz R H
Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Neurophysiol. 1998 Jul;80(1):282-96. doi: 10.1152/jn.1998.80.1.282.
The medial superior temporal area of the macaque monkey extrastriate visual cortex can be divided into a dorsal medial (MSTd) and a lateral ventral (MSTl) region. The functions of the two regions may not be identical: MSTd may process optic flow information that results from the movement of the observer, whereas MSTl may be related more closely to processing visual motion related specifically to the motion of objects. If MSTl were related to such object motion, one would expect to see mechanisms for the segregation of objects from their surround. We investigated one of these mechanisms in MSTl neurons: the effect of stimuli falling in the region surrounding the receptive field center on the response to stimuli falling in the field center. We found the effects of the surround stimulation to be modulatory with little response to the surround stimulus itself but a clear effect on the response to the stimulus falling on the receptive field center. The response to motion in the center in the direction preferred for the neuron usually increased when the surround motion was in the opposite direction to that in the center and decreased when surround motion was in the same direction as that in the center. Fifty-seven percent of the neurons showed a ratio of response for center motion with a surround moving in the opposite direction to that in the center for center motion alone that was >1. The response to motion in the center also increased when the surround stimulus was stationary, and this increase was sometimes larger than that with a moving surround. Nearly 70% of the neurons showed a ratio of response to center motion with a stationary surround to center motion alone that was >1. This is in contrast to the minimal effect of stationary surrounds in middle temporal area neurons. When the stimulus presentation was reversed so that the stimulus in the center was stationary and the surround moved, some MSTl neurons responded when the direction of motion in the surround was in the direction opposite to the preferred direction of motion in the center of the receptive field. Stimulation of the surround thus had a profound effect on the response of MSTl neurons, and this pronounced effect of the surround is consistent with a role in the segmentation of objects using motion.
猕猴纹外视觉皮层的颞上内侧区可分为背内侧区（MSTd）和腹外侧区（MSTl）。这两个区域的功能可能并不相同：MSTd可能处理由观察者运动产生的光流信息，而MSTl可能与专门处理与物体运动相关的视觉运动关系更为密切。如果MSTl与这种物体运动有关，人们会期望看到将物体与其周围环境分离的机制。我们在MSTl神经元中研究了其中一种机制：落在感受野中心周围区域的刺激对落在感受野中心的刺激反应的影响。我们发现周围刺激的影响具有调制性，对周围刺激本身几乎没有反应，但对落在感受野中心的刺激反应有明显影响。当周围运动方向与中心运动方向相反时，神经元偏好方向上的中心运动反应通常会增加；当周围运动方向与中心运动方向相同时，反应会减少。57%的神经元在中心运动且周围向相反方向运动时的反应与仅中心运动时的反应之比大于1。当周围刺激静止时，中心运动反应也会增加，这种增加有时比周围运动时更大。近70%的神经元在周围静止时对中心运动的反应与仅中心运动时的反应之比大于1。这与颞中区神经元中静止周围刺激的最小影响形成对比。当刺激呈现顺序颠倒，即中心刺激静止而周围运动时，一些MSTl神经元在周围运动方向与感受野中心运动偏好方向相反时会产生反应。因此，对周围的刺激对MSTl神经元的反应有深远影响，这种明显的周围效应与利用运动进行物体分割的作用一致。
