The Cellular Mechanism of Learning

Long Term Potentiation

The brain is made up of cells called neurons and the brain sends messages to the rest of the body by sending electrical impulses along a series of neurons. For an electrical impulse to cross from one neuron to another it has to cross a gap between cells called a synapse.

When the impulse reaches the end of the axon, neurotransmitters are released into the synaptic cleft. The neurotransmitter crosses the gap and attaches to receptor cells on the dendrite. When the dendrite detects these chemicals on its receptors, the electrical impulse is stimulated and the message continues along its pathway.

A specific thought or action follows the same neuron pathway in the brain and these pathways can be strengthened or weakened by certain actions. The strenthening of the pathways can lead to learning as the impulses can travel faster so it is easier for us to complete a certain task, as the electrical impulses have an easier journey and we therefore find it easier.

To strengthen these pathways the synapses between the cells have to be strengthened by making them release more neurotransmitter more often and to make more and more sensitive receptors. LTP, or long term potentiation has been shown to be able to do this by stimulating specific synapses with high  frequency stimulation at certian intervals. The synaptic activity was then measured and showed that once an initial 'barrier' was overcome, the levels of activity increased significantly each time. This effect produced long lasting improvements and could be topped up by more stimulation.

These effects are thought to have been produced because receptors become 'tethered' to the neurotransmitters so it takes less new neurotransmitter to be realeased to stimulate the receptors enough to produce an impulse. It also produces better effects than learning by repetition becasue it stimulates the NMDA receptors which are harder to stimulate because they are normally blocked by magnesium. The high frequency stimulation gives the neurotransmitter enough energy to replace the magnesium and stimulate the receptors which are essential for LTP.