What Actually Is Memory?
He was conscious of a thousand odors floating in the air, each one connected with a thousand thoughts and hopes and joys, and cares long, long forgotten. — Dickens writing of Scrooge in A Christmas Carol Can you really say that you understand memory? We all forget how essential to our daily lives memory can be. In fact, without it we forget everything! So what exactly is memory? Is it a process, a thing, a chemical, an idea? Memory is actually where sensations that we receive through our senses are retined over time and used to both consolidate into a system of knowledge about a particular thing or situation, and then is used to assess and react to future situations. So in a way, it is our protective mechanism, and it is also our predictor of how we will relate and react to the world around us.
Our senses are the pathways through which these sensations are taken in, beginning as an infant. These sensations can be both unconscious and conscious. Information is pooled at many different levels, and is then communicated to other areas of the brain. This can all be integrated to form complete impressions. At any point, this information can be increased, decreased or eliminated, simply by input from other sections of the brain and neuroreceptors. In addition each time the sensation or information must cross a synapse (division between nerves), it can be strengthened or weakened by collateral impulses [such as from one of our other senses such as hearing or sight].
This is the essence of memory, the storage, consolidation and use of experiences throughout our lifetime. For an experience to become part of memory, it must produce persistent functional changes in the brain that represent that experience. Memory occurs in three stages over a period of time. Sensory Memory is essentially the gathering of the original sensory impressions, which is constant and generally subconscious. These are intended to be short-term unless the experience is longer in duration or strong in emotion as well (allowing for more volume of collateral information). Short-Term or Working Memory is electrical in nature and is designed for brief processing or the temporary holding of small pieces of information such as words, objects or ideas common in our daily activities. These memories will fade if not repeated or practiced.
Long-Term Memory is created from chemical neurotransmitter activity that creates deep impressions and strong experiences. It receives elements from short-term memory due to importance, emotional impact and repetition [a process known as memory consolidation]. If often repeated, they become what are known as sensory engrams. In other words, the first step of a particular familiar sensory experience or part of an experience will elicit a response based on the "assumed" experience to come. Such as Pavlov’s experiment with the salivation of dogs at the ringing of a bell or the instant relaxation of the body when you lie down on your bed.
Memory therefore seems to rely on both electrical and chemical changes rather than on structural changes, such as the formation of new nerve connections. The hippocampus is important in memory because it is the main consolidating center for long-term memory, the neurons within it being stimulated by a neurotransmitter known as glutamate. Acetylcholine also seems to affect memory, as in Alzheimer’s patients where a key enzyme to synthesize Acetylcholine has been depleted, and thus memory is "locked". The hippocampus contains one of the highest groups of estrogen receptors and so is highly affected by estrogen levels. In women, as estrogen falls with menopause, the efficiency of communication can diminish and memory can become fuzzy. Other issues that can affect the hippocampus’s ability to consolidate long-term memory can be chronic inflammation, bacterial activity (chronic strep or staph), accumulation of heavy metals or lack of proper oxygen, water and nutrition.
Memory and learning are inextricably linked from birth and throughout our lives. It is no coincidence that the nervous system is the center for learning and memory. It is the most pervasive system of the body, which organizes and determines all other tissues and systems. It also is the most radically "plastic" of all systems using both physics and chemistry to manipulate and motivate the body into action. Science terms the nervous system’s capability for change with learning, "plasticity". How interesting that the body’s defenses do not reject "plastic" components to replace damaged or missing functional parts?
In order for memory to be strong and easily utilized, the brain must maintain the ability to change. We often say that someone is "set in their ways", which literally means they may not be able to change their reaction to situations or to adapt to new environments. It may begin as a conscious attempt to screen out change from one’s environment in order to control it. Also, this reduces the impact of stress. In fact, the hormones of stress such as cortisol and adrenaline are responsible for storing information and strengthening memory. So strong emotions or stressful situations can actually bring about stronger memory. Periods of consolidation will also help long-term memory. Meditation has been shown to allow the brain time to convert short-term memory into long-term memory.
Strong aspects of memory formation are the special senses. They enable us to have subconscious or unconscious reactions to stimuli, especially in the light of emotional response and memory. Smell and taste are the only two that directly tie to the limbic system and to the hypothalamus, evoking memory non-specific information. Think of the memory that certain smells can evoke.
So even conditions that affect our senses can also affect memory by reducing or changing the flood of perceptions that we rely on for information. Only by stepping into the fray for the experience, and then stepping back for the time to process and consolidate, can we really exercise our memory to its full capacity. Without either of these two waves of process, we really are limiting our memory...