Short Term Memory
Short-term memory provides the holding place needed for keeping information in mind for immediate use. It is important to distinguish this memory that forms and disappears (transient) from memory that you want to have available over the long term. But before we move into the different forms of long-term memory, let’s look at what happens when a memory is formed.As a first step, the memory to be recalled—say, one of Franklin Delano Roosevelt (FDR), the president during World War II—is encoded when first learned within the hippocampus, the seahorse-shaped structure in the temporal lobe that connects via an arching circuit, the fornix (Latin for arch) to two other structures, the mammillary bodies, and the dorsal thalamus. An additional structure—the basal forebrain, located, as the name implies, at the base of the anterior portion of the brain—is also linked to the fornix. And finally, slightly behind the hippocampus is the amygdala, the almond-shaped structure that endows memory with emotion. We don’t just remember things; we also experience emotions associated with our memories. It’s emotions that anchor our memories. Whenever you exercise your memory via memory challenges, you strengthen the linkages of these structures in this circuit and the stronger your memory becomes.After the Franklin Delano Roosevelt information was stored within these memory-encoding structures, that information was next widely distributed to the rest of the brain via association fibers.Neural networks is the term used by neuroscientists when describing the linkage of association fibers. As the stimulus enters our brain, it creates an electric and then chemical event (electrochemical signal) that races along the length of a neuronal axon (an extension of the neuron) like a Formula One car. The impulse is then transferred to the next neuron by means of the release of chemicals from the first neuron (the presynaptic neuron) into a tiny cleft (the synaptic gap), where it is ferried across by various transporters to the second neuron (the post-synaptic neuron), which is then activated. The process repeats itself again and again from neuron 3 to the nth neuron depending on how many neurons were originally required to form the memory.This lattice-shaped network that forms in a particular brain differs from the networks of brains of every other person in the world. No two people experience the world in identical ways and therefore individual memories and the neuronal networks comprising them will always differ. Think of it as delicate and intricate gold sculpting—only the fundamental substance in question isn’t permanent like gold, but more evanescent like a flash of lightning. These neuronal networks that form the foundations of our memories change over our lifetime. This explains why memories change in subtle ways even from day to day. In fact, the neural network is altered electrochemically whenever a memory is brought to mind and then passes away as we move on to other matters.In general, long-term memory storage occurs in select areas of the cerebral cortex. Your recall of Franklin Delano Roosevelt’s name involves language and vocabulary stored and processed chiefly in the association areas in the left temporal lobe. Your recognition on recordings of Roosevelt’s stirring voice urging his fellow Americans to heroic efforts is stored within the right temporal lobe. Think of your experience of Franklin Delano Roosevelt as involving many distinct brain modules working together to produce the totality of all the things that you have learned and can state (i.e., declare) about Roosevelt. This type of memory, declarative memory, is based on the simple fact that the knowledge can be declared. If someone asks you a question about Roosevelt, you are able to answer (declare) it based on your long-term stored information.