a postulated biochemical change (presumably in neural tissue) that represents a memory
同义词：memory trace
engram详细解释
en.gram n.（名词）A physical alteration thought to occur in living neural tissue in response to stimuli, posited as an explanation for memory.印象：一种被认为是针对刺激而发生于活动神经中枢的身体上的变化，该概念用以解释记忆
