Research Service and the Brain Rehabilitation Research Center, Malcom Randall VA Medical Center and the Department of Neurology, University of Florida College of Medicine, 1601 SW Archer Road, Gainesville, FL, 32608-1197, US.
Neuropsychol Rev. 2021 Sep;31(3):495-515. doi: 10.1007/s11065-020-09466-0. Epub 2021 Jan 29.
Cerebral representations are encoded as patterns of activity involving billions of neurons. Parallel distributed processing (PDP) across these neuronal populations provides the basis for a number of emergent properties: 1) processing occurs and knowledge (long term memories) is stored (as synaptic connection strengths) in exactly the same networks; 2) networks have the capacity for setting into stable attractor states corresponding to concepts, symbols, implicit rules, or data transformations; 3) networks provide the scaffold for the acquisition of knowledge but knowledge is acquired through experience; 4) PDP networks are adept at incorporating the statistical regularities of experience as well as frequency and age of acquisition effects; 5) networks enable content-addressable memory; 6) because knowledge is distributed throughout networks, they exhibit the property of graceful degradation; 7) networks intrinsically provide the capacity for inference. This paper details the features of the basal ganglia and thalamic systems (recurrent and distributed connectivity) that support PDP. The PDP lens and an understanding of the attractor trench dynamics of the basal ganglia provide a natural explanation for the peculiar dysfunctions of Parkinson's disease and the mechanisms by which dopamine deficiency is causal. The PDP lens, coupled with the fact that the basal ganglia of humans bears strong homology to the basal ganglia of lampreys and the central complex of arthropods, reveals that the fundamental function of the basal ganglia is computational and involves the reduction of the vast dimensionality of a complex multi-dimensional array of sensorimotor input into the optimal choice from a small repertoire of behavioral options - the essence of reactive intention (automatic responses to sensory input). There is strong evidence that the sensorimotor basal ganglia make no contributions to cognitive or motor function in humans but can cause serious dysfunction when pathological. It appears that humans, through the course of evolution, have developed cortical capacities (working memory and volitional and reactive attention) for managing sensory input, however complex, that obviate the need for the basal ganglia. The functions of the dorsal tier thalamus, however, even viewed with an understanding of the properties of population encoded representations, remain somewhat more obscure. Possibilities include the enabling of attractor state constellations that optimize function by taking advantage of simultaneous input from multiple cortical areas; selective engagement of cortical representations; and support of the gamma frequency synchrony that enables binding of the multiple network representations that comprise a full concept representation.
大脑的表示是通过涉及数十亿个神经元的活动模式进行编码的。这些神经元群体中的并行分布式处理（PDP）为许多涌现属性提供了基础：1）处理发生并且知识（长期记忆）以与概念、符号、隐式规则或数据转换完全相同的网络存储（作为突触连接强度）；2）网络具有进入对应于概念、符号、隐式规则或数据转换的稳定吸引子状态的能力；3）网络为获取知识提供了基础，但知识是通过经验获得的；4）PDP 网络擅长整合经验的统计规律以及频率和获得年龄效应；5）网络支持内容寻址内存；6）由于知识分布在网络中，因此它们表现出优雅降级的特性；7）网络内在地提供推理能力。本文详细介绍了基底神经节和丘脑系统（递归和分布式连接）的特征，这些特征支持 PDP。PDP 镜头和对基底神经节吸引子沟道动力学的理解，为帕金森病的奇特功能障碍以及多巴胺缺乏症的因果机制提供了自然的解释。PDP 镜头，加上人类基底神经节与七鳃鳗的基底神经节和节肢动物的中央复合体具有很强的同源性这一事实，揭示了基底神经节的基本功能是计算性的，涉及将复杂的多维感觉运动输入数组的巨大维度降低到从一小部分行为选项中进行最佳选择 - 反应性意图的本质（对感觉输入的自动响应）。有强有力的证据表明，感觉运动基底神经节在人类中对认知或运动功能没有贡献，但在病理状态下会导致严重的功能障碍。似乎人类在进化过程中已经发展出了皮质能力（工作记忆和意志和反应性注意力），用于管理感觉输入，无论多么复杂，都可以避免基底神经节的需要。然而，即使了解了群体编码表示的属性，背层丘脑的功能仍然有些模糊。可能性包括通过利用来自多个皮质区域的同时输入来优化功能的吸引子状态组合；皮质表示的选择性参与；以及支持使构成完整概念表示的多个网络表示绑定的伽马频率同步的支持。
