Long-term coding of personal and universal associations underlying the memory web in the human brain.

Emanuela De Falco,Matias J Ison,Rodrigo Quian Quiroga,Itzhak Fried

doi:10.1038/ncomms13408

Abstract

Neurons in the medial temporal lobe (MTL), a critical area for declarative memory, have been shown to change their tuning in associative learning tasks. Yet, it is unclear how durable these neuronal representations are and if they outlast the execution of the task. To address this issue, we studied the responses of MTL neurons in neurosurgical patients to known concepts (people and places). Using association scores provided by the patients and a web-based metric, here we show that whenever MTL neurons respond to more than one concept, these concepts are typically related. Furthermore, the degree of association between concepts could be successfully predicted based on the neurons' response patterns. These results provide evidence for a long-term involvement of MTL neurons in the representation of durable associations, a hallmark of human declarative memory.

Highlights

Neurons in the medial temporal lobe (MTL), a critical area for declarative memory, have been shown to change their tuning in associative learning tasks
Evidence in favour of one or the other model has been based on lesion or imaging studies[15], but there is so far no direct evidence of neurons coding previously acquired and not task-related associations. To address this issue, following a previous observation of neurons responding to well-known and allegedly associated concepts[16,17], we designed a systematic study to determine if these co-activations were just random coincidences or if there is a consistent tendency for MTL neurons to encode meaningful associations, independent of the execution of an associative learning task
We found that MTL neurons tend to fire to associated concepts, an effect that cannot be attributed to visual similarity between the stimuli, familiarity effects, recall of associated items or broad semantic categorizations

Summary

Introduction

Neurons in the medial temporal lobe (MTL), a critical area for declarative memory, have been shown to change their tuning in associative learning tasks It is unclear how durable these neuronal representations are and if they outlast the execution of the task. Evidence in favour of one or the other model has been based on lesion or imaging studies[15], but there is so far no direct evidence of neurons coding (or not) previously acquired and not task-related associations To address this issue, following a previous observation of neurons responding to well-known and allegedly associated concepts (for example, two co-stars in a television show)[16,17], we designed a systematic study to determine if these co-activations were just random coincidences or if there is a consistent tendency for MTL neurons to encode meaningful associations, independent of the execution of an associative learning task. We show a nontopographically organized distribution of responses, which is ideal for the fast formation of new associations

Methods

Results

Conclusion