Long-term potentiation is widely studied in the hippocampus: Long-term Potentiation of synaptic transmission is commonly referred to as LTP. It can be recorded in many parts of the nervous system, but is very widely studied in the hippocampus. Recording LTP using electrodes: Using a small slice of the brain from the hippocampus, a little less than half a millimeter thick, an electrode can be placed on the axons thus stimulating them, and another electrode can be placed on the dendrites for recording the synaptic response. It is quite simple to electrically activate the axons to produce an action potential, which then produces a postsynaptic response on the dendrites. And, it is the stimulation of this axon with different patterns and frequencies, that can lead to long-lasting changes in the efficiency of synaptic transmission. This is LTP. Measuring LTP: The response of stimulation is recorded on a computer screen. On the Y-axis here, we can see the strength of synaptic transmission, or the strength of one of these responses. Every minute or so, a single action potential is given and we can see that the strength of synaptic transmission is steady. The Y-axis is the excitatory postsynaptic potential, which is the electrical activity that occurs on the postsynaptic neuron following an action potential. This is a measure of synaptic strength. Inducing and measuring LTP: Now, at this point here, we give a high frequency stimulation for a second or so, and then return to giving a single action potential every minute. We will see that there has been a significant increase in the strength of synaptic transmission, which over the course of the next hour or so, is maintained. This is long-lasting increase in synaptic strength, called long-term potentiation. Long-term depression: At this point, a low-frequency stimulation is given, and we no go back to recording an action potential every minute. And you will see that there has been a reduction in the synaptic strength that is long-lasting. This is long-term depression. Synapses respond to many different patterns: What we have just seen is that synapses can respond to high- or low-frequency patterns, and produce different changes in synaptic strength. But synapses are capable to responding to many different types of patterns, and producing responses to them.

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