Final answer:
LTP in the hippocampus is a strengthening of synaptic connections through AMPA receptor insertion after calcium influx through NMDA receptors, while LTD is a weakening of synapses via removal of AMPA receptors after a different calcium-dependent signalling response.
Step-by-step explanation:
The mechanisms behind long-term potentiation (LTP) and long-term depression (LTD) in the hippocampus involve changes in synaptic strength that are crucial for memory formation and learning. LTP is characterized by a persistent strengthening of synaptic connections, which is driven by the insertion of AMPA receptors into the postsynaptic membrane following calcium influx through NMDA receptors. On the other hand, LTD involves a long-term weakening of synapses, where a different signalling cascade triggered by calcium entry through NMDA receptors leads to the removal of AMPA receptors from the postsynaptic membrane. This dichotomy allows the nervous system to effectively encode and store memories by reinforcing frequently used synapses while pruning less significant ones.