Biological Understanding of Learning

Memory formation occurs in two discrete stages: short-term memory and long-term memory. Short-term memory involves an increase in the efficiency with which nerve impulses are conducted across a particular synapse. As its name suggests, it is very short in duration, and it is also very small in capacity. Short-term memory only lasts for a few seconds, and it has a capacity of 7(+- 2) bits of information, a capacity that scientists refer to as "Miller's Magic Number" (Learning and Memory). Scientists are aware of short-term memory because patients undergoing electrical shock therapy are unable to recall events that occurred moments before treatment, but they are able to recall earlier events. The therapy affects short-term memory, but not long-term memory. The only way for short-term memory to be permanently stored in the brain is if it is passed on to long-term memory. Long-term memory is infinite in capacity and can last forever. It involves the translation of new proteins to form new synaptic junctions. Its molecular foundation is understood through two physiological processes: sensitization and the aforementioned Long Term Potentiation. Long Term Potentiation is the process by which animals learn new tasks, and it is the most popular scientific explanation for the broader process of learning.

Scientists studying slices of brain kept alive in culture repeatedly stimulated a synapse and observed the action potential response to the stimulus. If the neuron was continuously stimulated by simultaneous action potentials, scientists noticed that the neuron began responding differently. The magnitude of the post-synaptic potential became much greater, and this lasted for up to several weeks. This effect was later discovered to be the result of the activation of post-synaptic NMDA receptors, which contain channels for calcium ions to enter the cell. These ions produce long term changes in the structure of the post-synaptic neuron.

To prove the effect of the activation of these NMDA receptors, Professor Joe Tsien of Princeton University genetically engineered mice with enhanced NMDA receptors that remained activated for longer than normal spans of time. This resulted in a quicker process of learning a maze, and longer retention of this memory in the mice. (Sadava et. al.).

Its contribution to the learning process is further exemplified in an experiment described by Professor John Kimball (Learning, Memory, and Long Term Potentiation) in which a mouse placed in a pool of murky water is allowed to swim around in search of a platform to climb onto. After repeated exposure to this environment, the mice are able to locate the platform more quickly. Mice with damage to the hippocampus, however, are unable to do so more quickly upon repetition. This is because the hippocampus is constantly producing new neurons that are particularly sensitive to Long Term Potentiation. As new neurons are formed, repeated exposure to a particular scenario allows the individual neurons to learn. This has led scientists to believe that such a process allows for the larger, abstract process of learning.