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Synaptic Plasticity Draft

Submitted by zalam on Mon, 09/16/2019 - 11:06

Synaptic plasticity is something that always seemed very interesting to me. Even after birth, your brain is capable of changing it's connections and wiring. It best described by Santiago Cajal's words on long-term potentiation: "Neurons that wire together, fire together". The concept of long-term potentiation involves three stages: input, induction and expression. During the input period, the presynaptic neuron fires a single action potential. This causes a small post-synaptic potential. During induction, multiple action potentials are fired repeatedly along the presynaptic potential, leaving very little time for the postsynaptic neuron to fire a small action potential and then die down. As a result, the postsynaptic potentials keep bulidng up and reach a threshhold where the neuron is depolarized, leading to an action potential to be fired. This event of accumulation of potentials over a brief period of time is called temporal summation. Finally in the last stage, we see that a single action potential, like the one in the first stage, is able to cause a full action potential called the excitatory postsynaptic potential. This is essentially how we learn. If we keep introducing the same stimulus over and over again, the wiring in our brain adjusts to fire a strong action potential and so we can learn events. However, our brain does have a capacity for how much we can learn. The neurons can get too saturated with new wirings if there is no way to reverse this process. Thus certain wirings start getting weaker by time and this is called long term depression. This would be another way of saying that we are slowly forgetting what we had learned.