Dynamically changing neuronal activity supporting working memory for predictable and unpredictable durations

Jong Chan Park,Min Whan Jung,Jung Won Bae,Jieun Kim

doi:10.1038/s41598-019-52017-8

Jong Chan Park, Min Whan Jung + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-52017-8

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Abstract

Diverse neural processes have been proposed as the neural basis of working memory. To investigate whether the medial prefrontal cortex (mPFC) relies on different neural processes to mediate working memory depending on the predictability of delay duration, we examined mPFC neural activity in mice performing a delayed response task with fixed (4 s) or random (between 1–7 s) delay durations. mPFC neural activity was strongly influenced by the predictability of delay duration. Nevertheless, mPFC neurons seldom showed persistent activity spanning the entire delay period and instead showed dynamically-changing delay-period activity under both the fixed-delay and random-delay conditions. mPFC neurons conveyed higher working memory information under the random-delay than fixed-delay conditions, possibly due to a higher demand for stable working memory maintenance. Our results suggest that the rodent mPFC may rely on dynamically-changing neuronal activity to maintain working memory regardless of the predictability of delay duration.

Highlights

Diverse neural processes have been proposed as the neural basis of working memory
We found that the predictability of delay duration strongly influences medial prefrontal cortex (mPFC) delay-period activity in the current task
Previous studies in rodents have shown that persistent neuronal activity spanning the entire delay period is seldom found in rodent mPFC, parietal cortex and hippocampus during spatial working memory tasks[4,15,16,18,19,20]

Summary

Introduction

Diverse neural processes have been proposed as the neural basis of working memory. To investigate whether the medial prefrontal cortex (mPFC) relies on different neural processes to mediate working memory depending on the predictability of delay duration, we examined mPFC neural activity in mice performing a delayed response task with fixed (4 s) or random (between 1–7 s) delay durations. mPFC neural activity was strongly influenced by the predictability of delay duration. In the rodent PFC, persistent activity is seldom found and, instead, sequential firing is observed during the delay period[4,15,16], suggesting that the PFC neural network may support working memory based on dynamically-changing neuronal population activity. Dynamically-changing activity would be useful to get ready for a proper behavioral response before delay offset These considerations raise the possibility that a given neural system may rely more on persistent or dynamically-changing activity to support working memory according to task requirement[17]. To test this possibility, we examined whether and how the predictability of delay duration affects delay-period neural activity in the rodent medial PFC (mPFC). Our results suggest that working memory may be supported primarily by dynamically-changing neuronal population activity in the rodent prefrontal cortex

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