How permanent can a memory be?

How permanent can a memory be?

1. In almost all cases synapses are modified by modifying proteins within the synaptic membranes

   • The proteins are usually modified by phosporylation - by adding phosphate groups to them - this changes the protein’s shape (conformation) which changes the protein’s properties
   • Phosphorylation is not permanent: over time the extra phosphate groups will be removed and with it, the memory
   • Protein molecules are also not permanent – most proteins in the brain have a lifespan of ~2 weeks and are continually replaced!

2. long term memory formation

   • long-term memory storage requires protein synthesis (receptor molecules are proteins) > the number of certain neurotransmitter receptors in the synapse can be increased
   • If neuron is stimulated repeatedly over a significant time period then signalling molecules (e.g. MAPK) enter the neuron’s nucleus resulting in increased production of membrane proteins via changes in gene expression  This can lead to long-term structural changes, including increases in number of receptor molecules & even increases in the number of synapses

3. When an event is important enough (indicated by emotions) or repeated enough, neurons fire repeatedly and strongly, declaring “this is important & should be recorded!” • The relevant genes are then turned on, causing synthesis of more proteins (receptors), which are inserted into the synapse, strengthening the synapse