DOI: 10.5061/dryad.f1vhhmh4m
title: Impact of background input on memory consolidation in In-Vitro neural networks

description: Memory consolidation is a complex process, that can be divided into two
 stages: first, memories are temporary stored in hippocampus and in the
 second stage, repeated replay slowly transfers memories to the neo-cortex
 for long-term consolidation. This 2nd stage occurs during slow wave sleep,
 a phase characterized in the cortex by low cholinergic tone and low
 afferent input.  A recent in-vitro study showed that high
 cholinergic tone hampers memory consolidation, probably due to lowered
 network excitability (defined as the mean network response to one neuron
 spiking). Here we investigate whether low background input contributes to
 memory consolidation. We used cortical neuronal networks on multi
 electrode arrays to study memory. When input deprived, these networks
 develop an activity-connectivity balance. Focal stimuli initially disrupt
 the existing balance,  inducing connectivity changes. When
 repeated, this effect fades and the response becomes part of spontaneous
 patterns (memory formation). Application of the same stimulus hours later
 does not affect connectivity indicating that memory was consolidated. We
 applied five periods (10 min each) of focal electrical stimulation at
 different electrodes (A B A), separated by 1 hour of spontaneous activity
 . Some cultures were transfected to express channelrhopsins (ChR2)
 enabling global optogenetic background stimulation. We used 12 control, 15
 ChR2 cultures with no background input and 8 ChR2 cultures with
 superimposed random optogenetic stimulation during electrical stimulation
 periods (fmean=5 Hz) to mimic afferent input. Background stimulation
 acutely reduced network excitability during stimulation without persisting
 effects after cessation. ChR2 cultures showed significantly more dispersed
 spiking outside network bursts, and network excitability tended to be
 lower than in control cultures. Stimulation at electrodes A and B induced
 memory traces in control cultures. Return to electrode A did not further
 affect connectivity, showing that memory trace A had been consolidated.
 Background stimulation impeded the formation of memory traces following
 electrical stimulation at either electrode. ChR2 expression alone also
 obstructed memorization. These findings confirm the importance of low
 background afferent input for memory consolidation. The presence of
 background afferent inputs reduced network excitability, similar to high
 cholinergic tone. This leads to the conclusion that sufficient network
 excitability is crucial for memory consolidation, and high network
 excitability may be a critical feature of  slow wave sleep that
 makes it more suitable for memory consolidation than the awake state.
description: # Impact of Background Input on Memory Consolidation in In-Vitro Neural
 Networks
 [https://doi.org/10.5061/dryad.f1vhhmh4m](https://doi.org/10.5061/dryad.f1vhhmh4m) Our goal was to answer the following questions: given the important role of slow wave sleep in memory consolidation, and that one of the main characteristics of this sleep phase is the presence of low afferent input, which effects would have the application of background inputs on memory consolidation? To answer this question we applied focal electrical stimulation through one electrode to networks plated on micro electrodes array (MEAs), with or without contemporary background inputs. The application of background afferent inputs was done using optogenetic stimulation, which implies the use of an AAV virus in cultures in order to bring to expression channel rhodopsin 2 (ChR2). So first we checked the effects of expression of ChR2 alone on memory consolidation.  Stimulation protocol for memory: acquisition of 1h spontaneous activity (Baseline), followed by focal electrical stimulation at 2 different electrodes (A and B). Per each electrode we applied 5 stimulation periods of 10min (0.2Hz) interspersed by 1h spontaneous activity recordings (order of electrodes A, B, A) (Memory stim protocol). We had three groups of experiments control (data can be found at: [https://doi.org/10.5061/dryad.qz612jmpv](https://doi.org/10.5061/dryad.qz612jmpv)), cultures expressing ChR2 but without undergoing optogenetic stimulation (Memory ChR2) and cultures expressing ChR2 but with optogenetic stimulation superimposed on the focal electrical stimulation periods (Memory BackOpto) ## Description of the data and file structure There are three main folders: “Memory BackOpto” and “Test Opto frequencies”. They contain recorded experimental data after artifact removal. Each folder contains all data of one specific analysis. ●       Memory BackOpto: data used to study the effects of background inputs on memory consolidation. Inside there are two subfolders: ○       Baseline – containing 1h baseline recordings. ○       Memory stim protocol – containing recordings of the entire memory stimulation protocol (total 17h 30min). ●       Memory ChR2: data used to study the effects of ChR2 expression alone on memory consolidation. Inside there are two subfolders: ○       Baseline – containing 1h baseline recordings. ○       Memory stim protocol – containing recordings of the entire memory stimulation protocol (total 17h 30min). ●       Test Opto frequencies: data used to test six different optogenetic stimulation frequencies. Inside there are seven subfolders, one containing each experiment baseline recording (Baseline) and one per each tested frequency (0.1, 0.2, 0.5, 1, 2 and 5Hz). Each one of the stimulation frequencies folders contains data for 15 min spontaneous activity recording after the optogenetic stimulation at that frequency was applied (“Spontaneous activity after stim” folder) and activity recorded during the 15 min optogenetic stimulation (“Stim period” folder). All data files are Matlab formatted(*.mat), and contain the following variables necessary for the mentioned analysis: ●       Ts (nx1 array): time of recorded spikes (in sample numbers) ●       Cs (nx1 array): list of electrodes recording spikes at the corresponding Ts (Cs=60 indicates registered electrical stimuli) ●       Us (nx97 matrix): each row contains 6ms of waveshape of detected action potentials ●       numSpkes= total number of spikes ●       sampleRate= the sample frequency used for the recording ●       name= contains the number of the MEA, date and time of the acquisition