Neurotransmitter

One of the most exciting areas of research is the attempt to find out how learning and memory take place. One of the earliest researchers who attempted to explain learning and memory as a function of cellular change was the Canadian psychologist, Donald O. Hebb. He maintained that repeated firing of axons results in metabolic changes in the presynaptic and post synaptic neurons. In other words, learning produces lasting chemical changes in nerve cells.

Aplysia, a marine snail with only 20,000 relatively large neurons, has been used in studies to determine the biological basis of learning. A conditioned reflex in Apylsia has been shown to cause an increase in the release of a neurotransmitter that sets up a chain of reactions, one of which also increases the secretion of serotonin from a modulating neuron. In mammals, the hippocampus, part of the forebrain, stores long term memory for weeks before transferring it to the cerebral cortex. The transmitter used for long term potentiation is the amino acid, glutamate, which binds to receptors in the postsynaptic cell. This cell allows calcium to flow in and set up the activation of other molecules known as kinases. A growing body of evidence implicates the role of dopamine as one of the most important chemicals that regulate cell activity involved in working memory. Studies done with aged monkeys show that a deficiency in both dopamine and norepinephrine in the prefrontal cortex can induce a deficit in working memory. Injections of the deficient neurotransmitters restored memory function. Progress in deciphering the operation of the nervous system has helped to increase knowledge of the diverse role of the neurotransmitter.