The sixth sense; in primitive species, the only function of the limbic system is the regulation of the sense of smell. As the brain becomes more complex, the limbic system diversifies to regulate aspects of behavior, such as emotional expression, while retaining its tie to the olfactory system. It is interesting to note that ANUBIS- the jackalheaded god of Egypt, the guardian of the threshold, and symbol for the limbic system –had a particular acute sense of smell.
The limbic system’s ability to determine “this is it –this is truth,” is vital to creation of our mental realities. As “guardian at the inner threshold” it opens the heart to new understanding and facilitates the process of recollection and learning.
In the human mind, perceptions presented by the FIVE SENSES are compared to memory perceptions. Through its instrument, the limbic system, the faculty of imagination harmonizes inner and outer perceptions. The images created by imagination then become material for the intellect. Thus, imagination is the intermediary between perception, memory, and thought. Indeed, thought and learning are made possible by the image making part of the soul.
Scientists have long sought the physical instrument wherein resides the capacity for imagination, memory, and learning. Many believe that these faculties are located in the outer brain, or the two cerebral lobes. In one famous experiment the American psychologist, Karl Lashley, searched for the elusive site of memory storage. He found that rats did not suffer significant deterioration of their ability to thread their way through a learned maze even though they were missing up to 90 percent of their cerebral lobes. From this and other experiments one may theorize that each specific memory is distributed over the brain as a whole. Perhaps the images of imagination and memory are developed in the brain in a manner analogous to a hologram. What is apparent from the study of much neural structure is that the brain relies on patterns of increasing refinement, simplicity, elegance, and wholeness.
If the images of memory are experienced over the entire surface of the outer brain and perhaps even throughout the brainstem as well, how are we able to evoke those memories which are important to us? What physical structures participate in our ability to recall images by processes of order and association? To investigate this question we must search more deeply into the inner mysteries of the brain. Deep within the temporal lobes of the outer brain we must seek out those structures comprising the limbic system.
The portion of the limbic system which appears to be especially concerned with facilitating memory and learning is called the HIPPOCAMPUS, or sea horse. The hippocampus is a rather large structure reaching a peak size in man. The internal architecture of the hippocampus is curious, resembling a series of leaves like the pages of a book. Viewed a great number of circuit-boards arranged in stacks. The input lines from the sense organs run through the stack of leaves and make contact with the neurons [brain cells] in each leaf. The output lines connect with forebrain, other portions of the limbic system, mammillary bodies, thalamic and hypothalamic nuclei –all structures participating in the facilitation of memory and learning.