DOI: 10.5061/dryad.qz612jmpv
title: NMDA receptors involvement in memory and prediction

description: Memory and prediction are fundamental cognitive functions shaping our
 daily activities, with prediction enhancing the likelihood of successful
 action and relying heavily on memory. Studies indicate that spike
 timing-dependent plasticity (STDP), a mechanism altering synaptic weights
 based on temporal coordination, is crucial for memory, with NMDA
 activation playing a pivotal role. Our investigation aimed to assess the
 impact of inhibiting NMDA activation on long-term memory and prediction in
 random in-vitro networks of dissociated rat cortical neurons using MEAs.
 During long-term memory formation, experiences are initially encoded in
 the hippocampus and later reactivated, triggering neocortical areas in
 systems consolidation. To study memory and prediction, we subjected
 cultures to focal, low-frequency electrical stimulation. For memory, a 10
 min stimulation with 1 h intervals of spontaneous activity was employed.
 For prediction, 20 h focal stimulation with random interstimulus intervals
 was applied. NMDA receptors were blocked with amino-5-phosphonovaleric
 acid (APV). Long-term memory formation was assessed  estimating
 functional connectivity with Conditional Firing Probabilities and possible
 connectivity changes using Euclidean distances. In control cultures, focal
 stimulation induced persistent connectivity changes, indicating memory
 trace formation. APV treated cultures showed no connectivity changes.
 Prediction and its relationship with memory were studied using mutual
 information between activity and future (prediction) or past (short-term
 memory) stimuli. Prediction occurred in both groups, but its dependence on
 short-term memory decreased over time only in the control group when
 long-term memory traces are formed. In conclusion, our findings suggest
 that formation of long-term memory traces in random cortical networks
 critically depends on NMDA activation. Additionally, if long-term memory
 is impaired, prediction still requires short-term memory. Our in-vitro
 model using MEAs provides a simulation of the long-term memory process and
 prediction.
description: # NMDA receptors involvement in memory and prediction Our goal was to
 answer the following questions: given the important role of spike timing
 dependent plasticity in memory, and the role played by NMDA receptors in
 STDP, which effects would have blocking NMDA receptors activation on
 memory consolidation, and consequently on long-term memory? And also,
 given the recently proven ability of cultured neural networks to predict
 upcoming stimuli, would, blockage of these receptors, have an effect also
 on prediction? To answer these questions we applied focal electrical
 stimulation through one electrode to networks plated on micro electrodes
 array (MEAs), undergoing control conditions or transfected with APV (an
 NMDA antagonist). 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).
 In case of APV transfection we acquired 1h baseline, transfected the
 cultures, and acquire 1h of spontaneous activity after transfection
 (Baseline APV), and only then started with the stimulation protocol.
 Stimulation protocol for prediction in transfected cultures: acquisition
 of 1h spontaneous activity (Baseline),transfection with APV and following
 1h of spontaneous activity (Baseline APV) and then stimulation for 20h
 with inter stimulus intervals taken from a distribution with known
 predictability (Prediction stim protocol). Control prediction experiments
 data can be found at : doi:10.5061/dryad.18931zd2t There are four main
 folders: “Memory control” , “Memory APV”, “Prediction APV”, “Test APV
 concentration”. They contain recorded experimental data after artifact
 removal. Each folder contains all data of one specific analysis. ● Memory
 control: data used to study memory consolidation under control conditions.
 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 APV: data used to
 study the effects on memory consolidation of blocking NMDA receptors,
 using APV. We used same cultures used for control experiments
 (experimental numbers indicates matches with controls). Inside there are
 three subfolders: ○ Baseline – containing 1h baseline recordings. ○
 Baseline APV – containing 1h baseline recording after addition of APV in
 cultures. ○ Memory stim protocol – containing recordings of the entire
 memory stimulation protocol (total 17h 30min). ● Prediction APV: data used
 to quantify prediction in cultures transfected with APV (blocking NMDA
 receptors). Inside there are three subfolders: ○ Baseline – containing 1h
 baseline recordings. ○ Baseline APV – containing 1h baseline recording
 after addition of APV in cultures. ○ Prediction stim protocol – containing
 recordings of the entire prediction stimulation protocol (20h). ● Test APV
 concentration : data used to test three different APV concentrations.
 Inside there are three subfolders, one per each tested concentration (15,
 20 and 25uM) each one containing data for baseline recordings (“baseline”
 folder), baseline after APV addition (“baseline after apv” folder) and
 activity after 10 min stimulation (“activity post” 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 For the files regarding the stimulation
 period in Prediction APV : ● StimTime= time of each stimulus (in sec)