Homosynaptic interactions are events that occur at the junctions (synapses) where neurons meet. Homosynaptic events occur at a single synapse or group of synapses but do not involve interactions between synapses or groups of synapses. This term is often used in relation to long-term depression

Long-term depression

Long-term depression , in neurophysiology, is an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer. LTD occurs in many areas of the CNS with varying mechanisms depending upon brain region and developmental progress...

 and long-term potentiation

Long-term potentiation

In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...

of neuronal firing. For example, homosynaptic long-term potentiation has been observed to occur at the synapses that connect two neurons as a result of their firing being correlated in time.

There can be four changes at synapse:

1. Synaptic depression
2. Synaptic facilitation
3. Long-term potentiation
4. Post-tetanic potentiation