Abstract
Working memory (WM) is a component of the brain's memory systems vital for interpretation of sequential sensory inputs and consequent decision making. Anatomically, WM is highly distributed over the prefrontal cortex (PFC) and the parietal cortex (PC). Here we present a biophysically detailed dynamical systems model for a WM buffer situated in the PC, making use of dynamical properties believed to be unique to this area. We show that the natural beta1 rhythm (12 to 20 Hz) of the PC provides a substrate for an episodic buffer that can synergistically combine executive commands (e.g., from PFC) and multimodal information into a flexible and updatable representation of recent sensory inputs. This representation is sensitive to distractors, it allows for a readout mechanism, and it can be readily terminated by executive input. The model provides a demonstration of how information can be usefully stored in the temporal patterns of activity in a neuronal network rather than just synaptic weights between the neurons in that network.
Highlights
We demonstrate that this pattern of network dynamics satisfies all of the relevant proposed properties: It represents a flexible memory substrate for previously active neuronal assemblies in a manner controlled by top-down, central executive inputs and requires continuous rehearsal owing to its dynamic nature
Without these well-documented substrates for memory, how can an engram be maintained? We propose that maintenance is a direct consequence of the rehearsal properties of Working memory (WM), i.e., continuous activity in the neurons involved
Fast-spiking (FS) interneurons are activated by deep layer pyramidal cells and inhibit superficial layer pyramidal cells
Summary
The above dynamic substrate for the episodic buffer is generated at the level of single parietal cortical MCs following a single episode of sensory excitation. The buffer must be able to combine multiple echoes of such prior excitation to form a useful representation of polymodal sensory input. This is proposed to occur under prefrontal, central executive (topdown) control. Prefrontal cortex, which provides top-down input to the parietal cortex, exhibits both beta and gamma rhythms [30, 31], with top-down information in general seen to use the alpha– beta frequency bands [32, 33]. We considered the effect of an input to the deep layer neurons, for rhythmic input of various frequencies, as well as tonic input
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