Modulation of synaptic transmission refers to the ability of the nervous system to alter the strength and efficacy of communication between neurons at synapses. Synaptic transmission is the process by which information is passed from one neuron to another, and it can be modified by a variety of factors, including neurotransmitter release, receptor activation, and presynaptic and postsynaptic processes.

There are several ways in which synaptic transmission can be modulated, including:

1. Neuromodulation: This involves the release of neurotransmitters or other signaling molecules that can alter the strength of synaptic connections over longer timescales than traditional neurotransmitters. Neuromodulators can include substances such as dopamine, serotonin, and acetylcholine.
2. Synaptic plasticity: As discussed earlier, synaptic plasticity can alter the strength and number of synaptic connections, allowing for modulation of synaptic transmission over longer timescales.
3. Presynaptic modulation: This involves the modulation of neurotransmitter release from the presynaptic neuron, which can alter the strength of communication between neurons. Presynaptic modulation can involve the release of other neurotransmitters or neuromodulators, as well as changes in the amount or efficacy of calcium signaling.
4. Postsynaptic modulation: This involves the modulation of the responsiveness of the postsynaptic neuron to neurotransmitter release. Postsynaptic modulation can involve changes in receptor density, receptor sensitivity, or intracellular signaling pathways.

Overall, the modulation of synaptic transmission is a critical mechanism that allows the nervous system to adjust to changing inputs and optimize its function. Dysregulation of synaptic transmission can contribute to a range of neurological and psychiatric disorders, highlighting the importance of understanding and targeting these mechanisms in research and treatment.