Kobayashi T, Nishijo H, Fukuda M, Bures J, Ono T
Department of Physiology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Japan.
J Neurophysiol. 1997 Aug;78(2):597-613. doi: 10.1152/jn.1997.78.2.597.
It is suggested that the hippocampal formation is essential to spatial representations by flexible encoding of diverse information during navigation, which includes not only externally generated sensory information such as visual and auditory sensation but also ideothetic information concerning locomotion (i.e., internally generated information such as proprioceptive and vestibular sensation) as well as information concerning reward. In the present study, we investigated how various types of information are represented in the hippocampal formation, by recording hippocampal complex-spike cells from rats that performed three types of place learning tasks in a circular open field with the use of intracranial self-stimulation as reward. The intracranial self-stimulation reward was delivered in the following three contexts: if the rat 1) entered an experimenter-determined reward place within the open field, and this place was randomly varied in sequential trials; 2) entered two specific places, one within and one outside the place field (an area identified by change in activity of a place neuron); or 3) entered an experimenter-specified place outside the place field. Because the behavioral trails during navigation were more constant in the second task than in the first task, ideothetic information concerning locomotion was more relevant to acquiring reward in the second task than in the first task. Of 43 complex-spike cells recorded, 37 displayed place fields under the first task. Of these 37 place neurons, 34 also had significant reward correlates only inside the place field. Although reward and place correlates of the place neuron activity did not change between the first and second tasks, neuronal correlates to behavioral variables for locomotion such as movement speed, direction, and turning angle significantly increased in the second task. Furthermore, 6 of 31 place neurons tested with the third task, in which the reward place was located outside the original place field, shifted place fields. The results indicated that neuronal correlates of most place neurons flexibly increased their sensitivity to relevant information in a given context and environment, and some place neurons changed the place field per se with place reward association. These results suggest two strategies for how hippocampal neurons incorporate an incredible variety of perceptions into a unified representation of the environment: through flexible use of information and the creation of new representations.
有人认为，海马结构对于空间表征至关重要，它在导航过程中通过灵活编码各种信息来实现，这些信息不仅包括外部产生的感觉信息，如视觉和听觉感受，还包括与运动有关的本体感受信息（即内部产生的信息，如本体感觉和前庭感觉）以及与奖励有关的信息。在本研究中，我们通过记录大鼠海马复合锋电位细胞来研究各种类型的信息在海马结构中是如何表征的，这些大鼠在圆形开放场中执行三种类型的位置学习任务，并使用颅内自我刺激作为奖励。颅内自我刺激奖励在以下三种情况下给予：如果大鼠1）进入开放场内实验者确定的奖励位置，且该位置在连续试验中随机变化；2）进入两个特定位置，一个在位置场（由位置神经元活动变化确定的区域）内，一个在位置场外；或3）进入位置场外实验者指定的位置。因为在第二项任务中导航期间的行为轨迹比第一项任务中更稳定，所以与运动有关的本体感受信息在第二项任务中比在第一项任务中与获得奖励更相关。在记录的43个复合锋电位细胞中，37个在第一项任务下显示出位置场。在这37个位置神经元中，34个也仅在位置场内具有显著的奖励相关性。尽管位置神经元活动的奖励和位置相关性在第一项任务和第二项任务之间没有变化，但在第二项任务中，与运动的行为变量（如运动速度、方向和转弯角度）相关的神经元相关性显著增加。此外，在第三项任务（奖励位置位于原始位置场外）中测试的31个位置神经元中有6个移动了位置场。结果表明，大多数位置神经元的神经元相关性在给定的背景和环境中灵活地增加了它们对相关信息的敏感性，并且一些位置神经元随着位置奖励关联改变了位置场本身。这些结果提出了两种关于海马神经元如何将各种各样的感知整合到环境的统一表征中的策略：通过灵活使用信息和创建新的表征。
