Department of Neurobiology, School of Medicine, Stanford University, Stanford, California 94305, USA.
J Neurosci. 2011 Apr 20;31(16):6088-97. doi: 10.1523/JNEUROSCI.0023-11.2011.
In a natural scene, multiple stimuli compete for the control of gaze direction and attention. The nucleus isthmi pars parvocellularis (Ipc) is a cholinergic, midbrain nucleus that is reciprocally interconnected to the optic tectum, a structure known to be involved in the control of gaze and attention. Previous research has shown that the responses of many Ipc units to a visual stimulus presented inside the classical receptive field (RF) can be powerfully inhibited when the strength of a distant, competing stimulus becomes the stronger stimulus. This study investigated further the nature of competitive interactions in the Ipc of owls by using two complementary protocols: in the first protocol, we measured the effects of a distant stimulus on responses to an RF stimulus located at different positions inside the RF; in the second protocol, we measured the effects of a distant stimulus on responses to RF stimuli of different strengths. The first protocol demonstrated that the effect of a competing stimulus is purely divisive: the competitor caused a proportional reduction in responses to the RF stimulus that did not alter either the location or sharpness of spatial tuning. The second protocol demonstrated that, for most units, the strength of this divisive inhibition is regulated powerfully by the relative strengths of the competing stimuli: inhibition was strong when the competitor was the stronger stimulus and weak when the competitor was the weaker stimulus. The data indicate that competitive interactions in the Ipc depend on feedback and a globally divisive inhibitory network.
在自然场景中，多个刺激因素会争夺眼球方向和注意力的控制权。小脑顶核（Ipc）是一种胆碱能的中脑核团，与视顶盖（optic tectum）相互连接，视顶盖是一个已知参与眼球运动和注意力控制的结构。先前的研究表明，当一个遥远的竞争刺激物变得更强时，许多 Ipc 单位对经典感受野（RF）内呈现的视觉刺激的反应可以被强烈抑制。本研究通过使用两种互补的方案进一步研究了猫头鹰 Ipc 中的竞争相互作用的性质：在第一个方案中，我们测量了远距离刺激对位于 RF 内不同位置的 RF 刺激的反应的影响；在第二个方案中，我们测量了远距离刺激对不同强度的 RF 刺激的反应的影响。第一个方案表明，竞争刺激的作用是纯粹的除法：竞争者导致对 RF 刺激的反应成比例减少，而不会改变空间调谐的位置或锐度。第二个方案表明，对于大多数单位来说，这种除法抑制的强度是由竞争刺激的相对强度强有力地调节的：当竞争者是较强的刺激时，抑制作用较强，而当竞争者是较弱的刺激时，抑制作用较弱。这些数据表明，Ipc 中的竞争相互作用取决于反馈和全局除法抑制网络。
