Neuronal networks for control of eye movement

我们目前的研究主要集中在控制眼球运动的基底神经节神经元网络。我们已经证明，基底神经节神经元携带的感觉和认知信号会受到预期奖励的强烈影响。然后信号被传递到一个叫做上级丘（SC）的中脑结构。SC是感觉运动转换的关键结构。包含在感觉信号中的空间信息被转换成眼睛和头部的定向运动。感觉运动转换是竞争性的，因为传入的感觉信号是丰富和复杂的，而定向运动是一次一个。因此，成功的行为需要一个有效的选择机制。先前与奖励相关联的物体或位置更有可能被选择，并且因此动物更有可能定向到物体的位置。然而，目前尚不清楚SC是否以及如何参与基于奖励的选择。为了回答这个问题，我们记录了猴子SC的单细胞活动，而受试者（猕猴）进行了记忆引导的眼跳任务与不对称的奖励时间表。 在记忆引导的眼跳任务中，视觉线索刺激指示即将到来的眼跳的目标。它还指示扫视后是否会给予奖励。许多SC神经元对视觉线索作出反应。我们发现，当视觉线索表明即将到来的奖励时，视觉反应经常增加。这种增加以两种不同的方式发生：1）当刺激指示即将到来的奖励时，反应性地增加视觉反应的增益; 2）当神经元中预期奖励时，主动地增加预期活动？的响应字段。这些效应主要在深层的扫视相关SC神经元中观察到，这些神经元将接收来自皮质眼野和基底节的输入。我们的结论是，SC在定向行为的奖励选择中起着重要的作用。这些结果表明，SC神经元的奖赏选择主要来自基底节。我们研究小组以前的研究表明，基底神经节-尾状核（CD）和黑质网状部（SNr）-在同一任务中表现出前线索预期的活动变化。我们以前已经证明，眼跳是由从CD到SNr和从SNr到SC的串联抑制连接控制的。CD神经元的前线索活动将抑制SNr神经元的快速放电，因此SC神经元将从SNr的紧张性抑制中释放出来。我们在SC神经元中的偏置效应的演示提供了基底神经节中的神经元活动和眼球运动之间的关键缺失环节。这种神经元-行为关系可作为研究基底节病变病理机制的良好系统。它也为诊断和治疗基底神经节疾病，包括帕金森病提供了一个显着的潜力。

Our current research is focused on the neuronal networks in the basal ganglia which control eye movements. We have shown that sensory and cognitive signals carried by neurons in the basal ganglia are strongly modified by expected reward. The signals are then transmitted to a midbrain structure called the superior colliculus (SC). The SC is a key structure for sensorimotor transformation. Spatial information contained in sensory signals is converted into orienting movements of the eyes and the head. The sensorimotor conversion is competitive because incoming sensory signals are abundant and complex while orienting movements are made one at a time. Successful behavior, then, requires an efficient selection mechanism. An object or position that was previously associated with reward is more likely to be selected, and consequently the animal is more likely to orient to the position of the object. However, it has been unknown whether and how the SC is involved in the reward-based selection. To answer this question, we recorded from single cell activity from the monkey SC while the subjects (macaque monkeys) performed a memory-guided saccade task with an asymmetric reward schedule. In the memory-guided saccade task, a visual cue stimulus indicated the goal of an upcoming saccade. It also indicated whether or not reward would be given after the saccade. Many SC neurons responded to the visual cue. We found that the visual responses frequently increased when the visual cue indicated an upcoming reward. The increase occurred in two distinct manners: 1) reactively as an increase in the gain of the visual response when the stimulus indicated an upcoming reward; 2) proactively as an increase in anticipatory activity when reward was expected in the neuron?s response field. These effects were observed mostly in saccade-related SC neurons in the deeper layer which would receive inputs from the cortical eye fields and the basal ganglia. We concluded that the SC plays an important role in the reward-based selection of orienting behavior. These results suggest that the reward-based selection in SC neurons is derived mainly from the basal ganglia. Previous studies from our research group showed that neurons in the basal ganglia - caudate nucleus (CD) and the substantia nigra pars reticulata (SNr) - exhibit pre-cue anticipatory changes in activity in the same task. We have shown previously that saccades are controlled by the serial inhibitory connections from the CD to the SNr and from the SNr to the SC. The pre-cue activity in CD neurons would inhibit the rapid firing of SNr neurons, and therefore SC neurons would be released from the tonic inhibition by the SNr. Our demonstration of the bias effect in SC neurons supplies the crucial missing link between the neuronal activity in the basal ganglia and eye movements. This neuron-behavior relation can be used as an excellent system in which pathological mechanism of basal ganglia diseases can be studied. It also provides a significant potential for diagnosis and treatment of basal ganglia diseases, including Parkinson's disease.