Shizgal P
Centre for Studies in Behavioural Neurobiology, Department of Psychology, Concordia University.
Neurosci Biobehav Rev. 1989 Summer-Fall;13(2-3):81-90. doi: 10.1016/s0149-7634(89)80015-6.
Since the discovery of brain stimulation reward by Olds and Milner, researchers have struggled to identify the underlying neural circuitry. This goal has proved surprisingly elusive. For example, the identity of the directly-activated neurons ("first stage" neurons) responsible for the rewarding effect of stimulating the numerous brain sites that support self-stimulation remains largely or entirely unknown. It was to address this problem that the collision test was adapted for use in experiments on intracranial self-stimulation. By estimating the trajectory, conduction velocity and axonal diameter of the first stage neurons, it was hoped that their identification would be facilitated. Indeed, the choice of candidate pathways has been tightly constrained by collision data. For example, such data suggest that the circuitry underlying brain stimulation reward includes myelinated fibers directly linking self-stimulation sites in the lateral hypothalamus and ventral tegmental area; the conduction velocity of these fibers has been estimated at 1-8 meters/sec. Additional collision data suggest direct axonal links between self-stimulation sites in the preoptic area and lateral hypothalamus, as well as between sites in the ventral tegmental area and periaqueductal gray matter. Although collision data constrain the choice of candidate pathways, they cannot prove that a given population of neurons is part of the first stage. No matter how closely the anatomical and physiological characteristics of a given population match the properties inferred from collision data, the possibility remains that the population in question plays no role in reward but happens to resemble neurons that do. This ambiguity can be reduced by assessing how collision effects are altered by lesions of the candidate pathway. Coupled with data from single-unit recording experiments, inferences drawn from such lesion-induced changes provide a powerful means of linking an identified population of neurons to the rewarding effect of electrical brain stimulation.
自从奥兹和米尔纳发现脑刺激奖赏以来，研究人员一直在努力确定其潜在的神经回路。事实证明，这一目标出奇地难以实现。例如，对于刺激众多支持自我刺激的脑区所产生的奖赏效应，负责的直接激活神经元（“第一阶段”神经元）的身份在很大程度上或完全未知。正是为了解决这个问题，碰撞测试被改编用于颅内自我刺激实验。通过估计第一阶段神经元的轨迹、传导速度和轴突直径，希望能够促进对它们的识别。实际上，候选通路的选择一直受到碰撞数据的严格限制。例如，此类数据表明，脑刺激奖赏背后的神经回路包括直接连接下丘脑外侧和腹侧被盖区自我刺激位点的有髓纤维；这些纤维的传导速度估计为1-8米/秒。额外的碰撞数据表明，视前区和下丘脑外侧的自我刺激位点之间，以及腹侧被盖区和导水管周围灰质的位点之间存在直接的轴突连接。尽管碰撞数据限制了候选通路的选择，但它们无法证明某一特定群体的神经元是第一阶段的一部分。无论某一特定群体的解剖和生理特征与从碰撞数据推断出的特性有多匹配，仍有可能该群体在奖赏中不起作用，只是碰巧与起作用的神经元相似。通过评估候选通路损伤如何改变碰撞效应，可以减少这种模糊性。结合单单元记录实验的数据，从这种损伤诱导的变化中得出的推论提供了一种强大的方法，将已识别的神经元群体与脑电刺激的奖赏效应联系起来。
