How is a memory formed?

There is really no such thing as ‘a memory’. Memory is a process, or set of inter-related processes, in which the brain changes in response to events. These changes then result in us being able to repeat a name or phone number (short-term memory), recall a specific event (episodic memory), recite a poem we learned at school (long-term verbal memory) or exercise a learned skill such as riding a bike or skateboarding (procedural memory).

Among the important mechanisms that underlie memory are changes to the strength of synapses (the gaps between nerve cells that signals have to cross), the growth of the tiny dendritic spines that grow out of the cells’ branching dendrites, and many chemical changes that strengthen some of the networks of neurons at the expense of others. These changes occur all over the brain but some areas, such as the tiny hippocampus in the temporal lobe of the brain, are especially important. Damage here can mean a permanent loss of any ability to lay down new memories.