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Memory and the brain

Forgetting and Amnesia

At the cellular level, when no illness or injury is involved, forgetting short-term memories and forgetting long-term memories represent two different processes.

In short-term memory, when something is forgotten, it means that a nerve impulse has ceased being transmitted in a particular neural network. In general, unless an impulse is reactivated, it stops flowing through a network after a few seconds.

In long-term memory, forgetting occurs when the formerly strengthened connections among the neurons in a network weaken, or when the activation of a new network is superimposed on an older one, thus causing interference.


In our everyday lives, it does not take an accident or an illness to cause significant disturbances in our memory.

Strong emotions and prolonged stress can affect synaptic plasticity and hence memory. When we are subjected to stress, the sympathetic nervous system activates the adrenal glands, causing them to secrete certain hormones.

The presence of these hormones in the blood stream significantly affects the plasticity of the brain’s neurons, especially those in the hippocampus. Thus, when people experience intense stress, the plasticity of the circuits in their hippocampi is reduced.


Paradoxically, when people are bored or understimulated, the plasticity of their neurons will be reduced as well.


Thus, moderate concentrations of stress hormones seem to have the optimal effect on the neurons of the hippocampus. This corresponds to the intuitive notion of the “happy medium” that the body seeks naturally.


But even a balanced lifestyle cannot keep us immune from injuries that can affect the neurons that are the foundation of memory.

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