NMDA receptors involvement in memory and prediction
Data files
Apr 29, 2024 version files 14.07 GB
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Memory_APV.zip
1.81 GB
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Memory_Control.zip
8.30 GB
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Prediction_APV.zip
3.35 GB
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README.md
4.17 KB
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Test_APV_concentration.zip
617.40 MB
Abstract
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.
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)