Persistently active neurons in human medial frontal and medial temporal lobe support working memory

Abstract

Persistent neural activity is a putative mechanism for the maintenance of working memories. Persistent activity relies on the activity of a distributed network of areas, but the differential contribution of each area remains unclear. We recorded single neurons in the human medial frontal cortex and the medial temporal lobe while subjects held up to three items in memory. We found persistently active neurons in both areas. Persistent activity of hippocampal and amygdala neurons was stimulus-specific, formed stable attractors, and was predictive of memory content. Medial frontal cortex persistent activity, on the other hand, was modulated by memory load and task set but was not stimulus-specific. Trial-by-trial variability in persistent activity in both areas was related to memory strength, because it predicted the speed and accuracy by which stimuli were remembered. This work reveals, in humans, direct evidence for a distributed network of persistently active neurons supporting working memory maintenance.

A Closer Look at the Hippocampus and Memory

“…These deficits occur particularly for novel visual stimuli that necessitate binding of multiple arbitrarily related stimulus features, such as novel shapes and novel associations among collections of objects and spatial locations [44–48], and therefore reflect failures of relational memory processing that occur with little or no interposed study-test delay. Hippocampal neuronal activity likewise carries evidence for memory maintenance across brief retention intervals [49, 50]. This evidence is consistent with the notion that hippocampus supports online memory representation particularly of the relations among the features of complex stimuli and/or episodes [51].…”

Using Neuroeducation as a Model to Evaluate the Effect of Imagery on Chinese Character Writing

“…al, 2005); thus, leaving better images in the immediate recall. This result conforms with the Long-Term Potentiation hypothesis, postulating that neurons are potentially active in recent activity patterns (see Kamiński et al, 2017). However, when recalling the characters from the pictures in the follow-up tests, unsuccessful or decayed neural connections occurred, due to incongruence between the picture meaning and learner's meaning, insufficient interpretation, heavy cognitive load, and distraction from character-irrelevant information in the pictures.…”

TRPC channels are not required for graded persistent activity in entorhinal cortex neurons

“…Working memory represents the ability of neuronal networks to maintain information for short periods of time after disappearance of the triggering stimulus. This transient storage may involve sustained (“persistent”) neuronal firing during the delay period, as suggested by different studies in nonhuman primates (Funahashi, Bruce, & Goldman‐Rakic, ; Miller, Erickson, & Desimone, ; Romo, Brody, Hernández, & Lemus, ), humans (Kamiński et al, ), and rodents (Harvey, Coen, & Tank, ; MacDonald, Lepage, Eden, & Eichenbaum, ; Pastalkova, Itskov, Amarasingham, & Buzsaki, ). Memory‐associated persistent firing has been observed in multiple brain areas, including cortical networks, for example, prefrontal, parietal, inferior temporal, auditory, somatosensory, and entorhinal cortex (EC) (Zylberberg & Strowbridge, ).…”