Abstract
Concept neurons in the medial temporal lobe respond to semantic features of presented stimuli. Analyzing 61 concept neurons recorded from twelve patients who underwent surgery to treat epilepsy, we show that firing patterns of concept neurons encode relations between concepts during a picture comparison task. Thirty-three of these responded to non-preferred stimuli with a delayed but well-defined onset whenever the task required a comparison to a response-eliciting concept, but not otherwise. Supporting recent theories of working memory, concept neurons increased firing whenever attention was directed towards this concept and could be reactivated after complete activity silence. Population cross-correlations of pairs of concept neurons exhibited order-dependent asymmetric peaks specifically when their response-eliciting concepts were to be compared. Our data are consistent with synaptic mechanisms that support reinstatement of concepts and their relations after activity silence, flexibly induced through task-specific sequential activation. This way arbitrary contents of experience could become interconnected in both working and long-term memory.
Highlights
Concept neurons in the medial temporal lobe respond to semantic features of presented stimuli
During 38 experimental sessions, we recorded from 2512 neurons in the amygdala, parahippocampal cortex, entorhinal cortex, and hippocampus of twelve neurosurgical epilepsy patients implanted with depth electrodes for pre-surgical evaluation
Patients were asked to compare either the semantic content (“Bigger?”, “Last seen in real life?”, “More expensive?” or”Older?” depending on the stimulus set, “Like better?”) or non-semantic stimulus features (“Brighter?”) of two pictures presented on a laptop screen (Fig. 1a). For this task we showed pairs from four pictures selected based on a previous screening procedure to maximize the number of responsive concept neurons
Summary
Concept neurons in the medial temporal lobe respond to semantic features of presented stimuli. Our data are consistent with synaptic mechanisms that support reinstatement of concepts and their relations after activity silence, flexibly induced through task-specific sequential activation. This way arbitrary contents of experience could become interconnected in both working and long-term memory. Concept neurons in the human medial temporal lobe (MTL) respond to semantic features of presented stimuli and are thought to represent elements of experience[1]. Trial-wise sequential firing patterns suggested a synaptic[18,19,20] and/or cellintrinsic[21,22] storage mechanisms to account for the activity-silent retrieval of concepts and their relations
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