Department of Psychology, University of California, San Diego, La Jolla, CA 92093;
Department of Psychology, Arizona State University, Tempe, AZ 85287.
Proc Natl Acad Sci U S A. 2018 Jan 30;115(5):1093-1098. doi: 10.1073/pnas.1716443115. Epub 2018 Jan 16.
Neurocomputational models have long posited that episodic memories in the human hippocampus are represented by sparse, stimulus-specific neural codes. A concomitant proposal is that when sparse-distributed neural assemblies become active, they suppress the activity of competing neurons (neural sharpening). We investigated episodic memory coding in the hippocampus and amygdala by measuring single-neuron responses from 20 epilepsy patients (12 female) undergoing intracranial monitoring while they completed a continuous recognition memory task. In the left hippocampus, the distribution of single-neuron activity indicated that only a small fraction of neurons exhibited strong responding to a given repeated word and that each repeated word elicited strong responding in a different small fraction of neurons. This finding reflects sparse distributed coding. The remaining large fraction of neurons exhibited a concurrent reduction in firing rates relative to novel words. The observed pattern accords with longstanding predictions that have previously received scant support from single-cell recordings from human hippocampus.
神经计算模型长期以来一直假设，人类海马体中的情景记忆由稀疏的、特定于刺激的神经编码表示。一个相应的提议是，当稀疏分布的神经组合变得活跃时，它们会抑制竞争神经元的活动（神经锐化）。我们通过测量 20 名接受颅内监测的癫痫患者（12 名女性）在完成连续识别记忆任务时的单个神经元反应，研究了海马体和杏仁核中的情景记忆编码。在左海马体中，单个神经元活动的分布表明，只有一小部分神经元对给定的重复单词表现出强烈的反应，并且每个重复单词都会在一小部分不同的神经元中引起强烈的反应。这一发现反映了稀疏的分布式编码。其余大部分神经元的放电率相对于新单词同时降低。所观察到的模式与长期以来的预测一致，这些预测以前很少得到来自人类海马体单细胞记录的支持。
