When we talk about memories, we immediately associate it with some sort of neural activity. Learning a language includes being exposed to a massive quantity of new information, where our brains try to save as much as it can. But have you ever wondered how does this process happen?
A natural comparison would be to think of our brains as computers that save all the information that they receive. But that doesn’t happen quite often, sometimes we forget what we have learned unless we are actively exposed to it. Then, you might wonder, how do brain cells actually form memories?
Connections between brain cells happen through junctions called synapses. The word synapse comes from the Greek synapsis, meaning “conjunction”. Neurons are always communicating to each other through synapses, and the strengthening of these connections is associated with memory formation through a process called Long Term Potentiation (LTP).
Synapses are classified in pre- and post- synapses, which correspond to the cell sending the message (pre-synapse) and the cell receiving the message (post-synapse). When a neuron tries to send a message, a change in the membrane voltage occurs. This change induces the release of the amino acid glutamate (the message), which activates a series of proteins located at the recipient cell called glutamate receptors. Once glutamate receptors are turned on, ions such as sodium are able to enter into the post synapse producing a change in postsynaptic membrane voltage. However, sodium itself doesn't trigger any machinery to strength memory formation. In order to induce memory formation, calcium needs to enter the recipient cell to activate the machinery for LTP. Think about it as glutamate being the message from the pre-synapse and calcium representing the translated message at the post-synapse. There is one kind of glutamate receptors, which are unique among other receptors because they are the only doors for calcium to get into the post-synapse. These unique receptors are called NMDA receptors and they are the main molecular character involved in memory formation.