RT Journal Article
SR Electronic
T1 Mnemonic encoding and cortical organization in parietal and prefrontal cortices
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 3903-16
DO 10.1523/JNEUROSCI.3903-16.2017
A1 Nicolas Y. Masse
A1 Jonathan M. Hodnefield
A1 David J. Freedman
YR 2017
UL http://www.jneurosci.org/content/early/2017/05/25/JNEUROSCI.3903-16.2017.abstract
AB Persistent activity within the frontoparietal network is consistently observed during tasks which require working memory. However, the neural circuit mechanisms underlying persistent neuronal encoding within this network remain unresolved. Here, we ask how neural circuits support persistent activity by examining population recordings from posterior parietal (PPC) and prefrontal (PFC) cortices in two male monkeys that performed spatial and motion direction based tasks that required working memory. While spatially selective persistent activity was observed in both areas, robust selective persistent activity for motion direction was only observed in PFC. Crucially, we find that this difference between mnemonic encoding in PPC and PFC is associated with the presence of functional clustering: PPC and PFC neurons up to ∼700 microns apart preferred similar spatial locations, and PFC neurons up to ∼700 microns apart preferred similar motion directions. In contrast, motion-direction tuning similarity between nearby PPC neurons was much weaker, and decayed rapidly beyond ∼200 microns. We also observed a similar association between persistent activity and functional clustering in trained recurrent neural network models embedded with a columnar topology. These results suggest that functional clustering facilitates mnemonic encoding of sensory information.SIGNIFICANCE STATEMENTWorking memory refers to our ability to temporarily store and manipulate information. Numerous studies have observed that during working memory, neurons in higher cortical areas such as the parietal and prefrontal cortices mnemonically encode the remembered stimulus. However, several recent studies have failed to observe mnemonic encoding during working memory, raising the question as to why mnemonic encoding is observed during some, but not all conditions. In this study, we show that mnemonic encoding occurs when a cortical area is organized such that nearby neurons preferentially respond to the same stimulus. This result provides plausible neuronal conditions that allow for mnemonic encoding, and gives us further understanding of the brain's mechanisms that support working memory.