The Rat Medial Prefrontal Cortex Exhibits Flexible Neural Activity States during the Performance of an Odor Span Task

Abstract

Medial prefrontal cortex (mPFC) activity is fundamental for working memory (WM), attention, and behavioral inhibition; however, a comprehensive understanding of the neural computations underlying these processes is still forthcoming. Toward this goal, neural recordings were obtained from the mPFC of awake, behaving rats performing an odor span task of WM capacity. Neural populations were observed to encode distinct task epochs and the transitions between epochs were accompanied by abrupt shifts in neural activity patterns. Putative pyramidal neuron activity increased earlier in the delay for sessions where rats achieved higher spans. Furthermore, increased putative interneuron activity was only observed at the termination of the delay thus indicating that local processing in inhibitory networks was a unique feature to initiate foraging. During foraging, changes in neural activity patterns associated with the approach to a novel odor, but not familiar odors, were robust. Collectively, these data suggest that distinct mPFC activity states underlie the delay, foraging, and reward epochs of the odor span task. Transitions between these states likely enables adaptive behavior in dynamic environments that place strong demands on the substrates of working memory.

Roles of the medial prefrontal cortex, mediodorsal thalamus, and their combined circuit for performance of the odor span task in rats: analysis of memory capacity and foraging behavior

“…Previous work in our laboratory has shown that performance of the OST relies on the mPFC and dorsomedial striatum (Davies et al 2017a,b). We have also recently found that delay period spiking of mPFC neurons is predictive of WM performance in the OST (De Falco et al 2019), showing an involvement of delay period activity in the mPFC. However, we found in a separate experiment that performance of the OST is independent of the parietal cortex (Scott et al 2018), in contrast to ample previous research showing an important role for the PC in WM.…”

Compulsive drinking is associated with neural activity patterns reflecting diminished behavioral control and enhanced seeking representations in dorsal medial prefrontal cortex

“…7a-f). Furthermore, we analyzed neuron waveforms to differentiate excitatory and inhibitory neurons 40, 41 (Supplemental Fig. 11).…”

“…The waveform was rescaled from -1 (maximum hyperpolarization amplitude) to 1 (maximum post-action potential depolarization peak). Similar to previously used methods 40, 41 , we classified the neurons using time delays associated the waveform depolarization. We used the time to 50% depolarization and the time to 95% depolarization as the time delays to characterize the speed of the depolarization.…”

“Prefrontal cortical contributions to working memory loading, maintenance and recall are parsed by hippocampal-prefrontal oscillatory assembly dynamics”

“…Delayed non-match to sample (DNMTS) paradigms hinge on such memoryguided decisions and are subserved by interactions between executive and mnemonic hub regions including the prefrontal cortex (PFC) and hippocampus 2,3 . PFC principal neuron spike rates during delayed response tasks encode diverse features of sample identity and task rules in both non-human primates [4][5][6][7][8] and rodents [9][10][11][12][13][14][15] , with sustained PFC principal neuron firing offering an intuitive neural correlate of working memory maintenance during task delay phases 16,17,[26][27][28][29][30][31][32][18][19][20][21][22][23][24][25] . However, as analyses have extended from individual neurons to simultaneously recorded cortical populations, other informative features of PFC ensemble dynamics have emerged [33][34][35] .…”