A Mechanism for Persistent Irregular Activity in Working Memory Tasks

GERMAN MATO

San Pablo

Exposición; LASCON 2016. VI Latin American School on Computational Neuroscience; 2016

NeuroMat ? Research, Innovation and Dissemination Center. for Neuromathematics

Persistent activity in cortex is the neural correlate of working memory (WM). In persistent activity, spike trains are highly irregular, evenmore than in baseline. This seemingly innocuous feature challenges our current understanding of the synaptic mechanisms underlyingWM. Here we argue that in WM the prefrontal cortex (PFC) operates in a regime of balanced excitation and inhibition and that theobserved temporal irregularity reflects this regime. We show that this requires that nonlinearities underlying the persistent activity areprimarily in the neuronal interactions between PFC neurons. We also show that short-term synaptic facilitation can be the physiologicalsubstrate of these nonlinearities and that the resulting mechanism of balanced persistent activity is robust, in particular with respect tochanges in the connectivity. As an example, we put forward a computational model of the PFC circuit involved in oculomotor delayedresponse task. The novelty of this model is that recurrent excitatory synapses are facilitating. We demonstrate that this model displaysdirection-selective persistent activity. We find that, even though the memory eventually degrades because of the heterogeneities, it can bestored for several seconds for plausible network size and connectivity. This model accounts for a large number of experimental findings,such as the findings that have shown that firing is more irregular during the persistent state than during baseline, that the neuronalresponses are very diverse, and that the preferred directions during cue and delay periods are strongly correlated but tuning widthsare not.