Human Cognition - Memory

Every morning before dawn Alph could hear them rustling around outside Mum’s tent as the clan’s men prepared for the day’s hunt. The clan needed fresh food daily. So without fail, rain or shine, the men would leave to forge and hunt. They traveled many miles returning home, sometimes late in the evening, with the day’s bounty. No matter how strong, no matter how adept at hunting and killing these men might have been; the clan’s ability to survive depended on their ability to identify landmarks and spatial relations. Alph’s life depended on the clan’s men having a sense of direction and spatial awareness of their surroundings, and the capability to recall this information. Without good memory storage and recall, all of humanity would have never survived.

Memory is the sum total of what is remembered. It is the brain’s ability to encode, store, retain and subsequently recall information and past experiences. It is the process of recalling previously learned facts, experiences, impressions, skills and habits. Memory is, at its simplest, a set of encoded neural connections in the brain. It is the re-creation or reconstruction of past experiences by the synchronous firing of neurons that were involved in the original experience. It can be thought of as the use of past experience to affect or influence future behavior. Without individual memory, there would be no way to transmit knowledge from generation to generation. There would be no collective memory to bind us together, to adapt and survive. Without it, we would be hopelessly lost in the forest of experiences without a clue as to the way home.

Encoding is the crucial first step to creating a new memory. Perceived sensations are decoded in the various sensory areas of the cortex, and then combined in the brain’s hippocampus into one single experience where new sensations are compared and associated with previously recorded ones. The more personally meaningful the associations, the more effective the encoding and consolidation, the more elaborate the processing which tends to improve recall. 

Consolidation is the process of stabilizing a memory trace after the initial acquisition. It consists of two specific processes, synaptic consolidation (which occurs within the first few hours after learning or encoding) and system consolidation (where hippocampus-dependent memories become independent of the hippocampus over a period of weeks to years). 

Storage is a passive process of retaining information in the brain. Memories are not stored in our brains like books on shelves, but must be actively reconstructed from elements scattered throughout various areas of the brain by the encoding process. Memories may be encoded redundantly, several times, in various parts of the cortex, so if one engram (memory trace) is wiped out, there are duplicates or alternative pathways elsewhere through which the memory may still be retrieved. Memory storage is therefore an ongoing process of reclassification resulting from continuous changes in our neural pathways, and parallel processing of information in our brains. 

Recall or retrieval of memory (remembering) refers to the subsequent re-accessing of events or information from the past, which have been previously encoded and stored in the brain. During recall, the brain "replays" a pattern of neural activity that was originally generated in response to a particular event, echoing the brain's perception of the real event. Initial perception of the real event can be viewed as the first rendering and the replaying of the memory of initial perception is, therefore, a rendering of the rendering. There is no real solid distinction between the act of remembering and the act of thinking. Replays are not identical to the original, but are mixed with an awareness of the current situation which sets up the reflective rendering process all over again. Memories are not frozen in time. New information and suggestions become incorporated into old memories. Thus, remembering can be thought of as an act of creative re-imagination; something that we talk about in detail when we discuss self awareness, collective memory and spirituality.

Sensory memory is the shortest-term element of memory. It is the ability to retain an impression of sensory information after an original stimulus has ended. It acts as a buffer for stimuli received through the senses which are retained accurately, but very briefly. The ability to look at something and remember what it looked like after just a second of observation is an example of sensory memory. Sensory memory is ultra-short-term and decays or degrades very quickly, typically 200 - 500 milliseconds (1/5 - 1/2 second) after perception, although echoic memory is now thought to last a little longer, up to three or four seconds. It lasts for such a short time that it is often considered part of the process of perception. It represents an essential step for storing information in short-term memory.

Short-term memory acts as a kind of “scratch-pad” for temporary recall of the information which is being processed at any point in time, "the brain's Post-it note". It can be thought of as the ability to remember and process information at the same time. Small amounts of information (typically around 7 items or less) can be held in consciousness in an active, readily-available state for a short period of time (typically from 10 to 15 seconds, or sometimes up to a minute). For example, in order to understand this sentence, the beginning of the sentence needs to be held in mind while the rest is read, a task which is carried out by the short-term memory. What are actually held in short-term memory, though, are not complete concepts, but rather links or pointers which the brain derives from long term memory. These associations quickly disappear, however, unless a conscious effort is made to retain them. Such a conscious effort might be considered an act of "free will”. The retention of these associations creates and/or modifies long term memory. 

Long-term memory is intended for storage of information over a long period of time. The establishment of long-term memory involves a process of physical changes in the structure of neurons in the brain. This process known as long-term potentiation is an area of neuroscience which is still open for debate. It has been assumed that long term memory is attributed to strengthened synaptic connections among neurons (brain cells). However, neuronal synaptic components are transient, whereas memories endure. In recent years, Penrose and Hameroff have hypothecated that long term memory is encoded into microtubules, the major structural components of the neuron cytoskeleton which are composed of tubulin proteins. The creation of new microtubule chains within the neuron (which encodes the memory) and the electrochemical transfer of neurotransmitters across synapse gaps to receptors (which creates the association with other memories) builds long term memory which is based on both meaning and association. 

Long-term memory can be divided into two main types: explicit (or declarative) memory and implicit (or procedural) memory. Declarative memory (“knowing what”) is memory of facts and events, and refers to those memories that can be consciously recalled (or "declared"). Procedural memory (“knowing how”) is the unconscious memory of skills and how to do things, particularly the use of objects or movements of the body, such as tying a shoelace, playing a guitar or riding a bike. These memories are typically acquired through repetition and practice, and are composed of automatic sensor motor behaviors that are so deeply embedded, we are no longer aware of them.

Declarative memory can be sub-divided into episodic memory and semantic memory. Episodic memory represents our memory of experiences and specific events in time in a serial form, from which we can reconstruct the actual events that took place at any given point in our lives. It is the memory of autobiographical events (times, places, associated emotions and other contextual knowledge) that can be explicitly stated. Semantic memory, on the other hand, is a more structured record of meanings, concepts and knowledge about the external world that we have learned from others. It refers to general knowledge, shared with and by others, and is independent of personal experience. Much of semantic memory is abstract, relational and symbolic. Declarative semantic memory is called collective memory.

When Alph turned six, Mum made good on her promise and took her son to the place in the earth where the clan came to gather and rituals were performed, where Ra held services and the young were taught the ways of the clan and Mother Goddess. Mum took him to Chauvet cave.

They walked and then climbed for a good bit in silence that morning. The cave entrance was high above the river on the side of the plateau. Once there, Alph turned and looked down to see the camp below and felt the breeze you feel when it blows across a rock cliff. The tree leaves swirled reflecting the sun's rays. His excitement was overwhelming. He stepped into the darkness reaching out for Mum. He smelled the cave; he felt the moist clay floor and heard the rush of the breeze from outside. His eyes dilated as he moved forward. Mum lit fires and the cave exploded in light. Alph screamed! 

There on the cave walls in front and above him were all the animals of his world; horses, deer, bear, lions, mammoth, rhinoceros and some that didn't have names. He screamed again and grabbed at Mum. Mum calmly told Alph to be quiet and to listen to her. She sat down on the floor and laid out her drawing tools. 

Time seemed to past quickly as Mum talked and drew a picture of a bison on the cave ceiling. Alph held a torch for her. She told him of the history of the clan. There had been many more people when she was young but that there had been a split, with some people leaving. She was very proud that her mother was the clan Shaman and that the Mother Goddess was proud of him. She talked about the bison. She told him to always remember that each animal and plant had a spirit and that his spirit was strong.

Then it was time to go. As they walked back to camp, his mind raced with what he had felt and heard. Although Mum had told him there would be many more climbs up the cliff wall, Alph knew that he would never forget his first day in the cave.