Types of Memory

Discuss about the Awareness of Recent Autobiographical Episodes.

Memory is a mental faculty that allows the storage, encoding and retrieval of information (gathered from learning, experiences, and sensory stimuli) [1].  Based on the type of information stored, memory can be of different types: sensory, short term, long term, episodic, topographic, declarative, procedural, prospective and retrospective memory. The brain centers mainly considered to be responsible for the formation of memories include the hippocampus, amygdale, striatum and mammilary bodies [2; 3]. Forgetting is the failure or the inability to retrieve or remember one’s memories.  Various theories and explanations exist that explains the phenomenon of forgetfulness.

According to this theory, our memory slowly decays with time, slowly fading, for not having being accessed over time [4]. This phenomenon can be compared to messages written in the sand, where every wave of the ocean slowly erodes the message away, until noting of the message ultimately remains.

This theory posits that memories can be made less accessible due to interference from similar memories or information, which was acquired before or after the formation of the said memory. This suggests one memory can be influenced by another similar, but possibly stronger memory [5]. In the context of the previous analogy, this phenomenon can be understood as the message written in the sand becoming undecipherable, after someone else writes another message on top of it. Thus the original message gets overwritten and inaccessible, in other words, forgotten [6].

Interference of memories can also be differentiated into two types: proactive interference and retroactive interference. Proactive interference occurs when the formation or retrieval of new memories are impeded or prevented by an older memory. Retroactive memory occurs when previously learned memories cannot be retrieved due to a new memory [5].

This theory suggests that the decay theory and interference theories are not mutually exclusive, and both are vital to understand forgetfulness. The theory is based upon how memories are represented in our minds, pointing out that the main reason for forgetfulness depends on the nature of the memory formed initially. Studies suggested that memory can be related to two types of representations in our mind: recollection and familiarity. Familiarity is a type of representation of memories where the specific details or the contexts are not remembered, often seen in cases of familiar faces where the person would seem very familiar, but hard to recollect the name. In comparison, recollection is another representation of memories that have contexts and specific details, such as names [2].

Brain Centers Involved in Memory Formation

Studies show that the two types of memory representations (discussed above) behave differently and also look different in the brain. Each of this representation has differential dependencies on the hippocampus (a brain center vital in the process of memory formation). Memories represented by recollections, inside the hippocampus are comparatively resistant to interference from each other. Their forgetting is mainly due to decay. In comparison, memories represented by familiarity are mainly supported by the extrahippocampal structures and are prone to interference. So in the previously used analogy, a person who looks familiar is a message prone to be overwritten by another message over time, while recollections of a particular event would just fade away with time [3].

Due to failures to encode information, it might not enter the long term memory, which would make it susceptible to be forgotten [1]. Encoding failure can also cause incorrect encoding of information which can cause the memory to be misrepresented and thus also make it prone for decay or interference [7]. The analogy would be the message tried to be written on a concrete surface instead of the sea beach, but with the same equipments, making it impossible for the message to be etched in the first place or an incorrect message is being written.

At times forgetting certain memories might be actively sought after, like that of disturbing or traumatic memories. The motivated forgetfulness can be of two types: conscious forgetting and unconscious forgetting. The former involves a conscious effort in the attempt to forget or cause interference to a certain memory, while unconscious forgetfulness refers to the involuntary and unconscious process that leads to the decay or interference of the memory [8].

This refers to an abnormal forgetting in a span of hours or weeks, despite the memory being normally acquired. The memories are encoded and retained normally for up to 30 minutes, but are then forgotten abnormally at a quick pace. This phenomenon was first reported among people with epilepsy, especially, temporal lobe epilepsy. Further studies termed the phenomenon as long term amnesia [9; 10; 11].

Age is a significant factor related to memory. Some studies have proposed that with advancing age, the forgetfulness increases, and information are converted to long term memory more slowly. Also the rate of forgetfulness among older adults was linked to the type of information they needed to remember. It was found that complex visual scenes were more prone to be forgotten after a delay of 4 weeks among older adults, compared to their younger counterparts. In studies, it was found that the source memories were the primary problem for older adults, which increased the probability of the information to be forgotten. This shows that with progressing age, the performance of the memory can slowly decrease, and facilitate forgetfulness [12; 13].

Theories of Forgetting

A positive correlation has been found between the intellectual performance of people and memory. This implies that the intellectual function plays an important role in the formation of memories, and that people with higher IQ tend to remember things better and lower IQ increases the propensity to forget things. Tests show that people with higher IQ were able to make more associations and better organization of information, thereby allowing the information to be remembered. Similarly, it was also found that people with higher level education can remember more information [14; 15]. Thus cognitive dysfunctions, and a lack of education can increase the chances of forgetting information.

Studies have also indicated that forgetfulness can have practical benefits for individuals and might even by a product of the natural selection. Understanding how forgetfulness can be advantageous, can help us comprehend why we forget information, and how it is evolutionarily significant [16; 17; 18].

Memories of traumatic and painful experiences can cause stress, which in turn can affect the physical and psychological wellbeing of people. With time these memories however decays and diminishes in its details, making it inaccessible progressively, thereby leading towards the memory being forgotten [19].

Specific neurotransmitters in our brain called the cannabinoid neurotransmitters play a key role in the dampening the effects of the memories and focusing more on the present. The system of cannabinoid transmitted increases the sensory experience and prevents the intrusions or interferences from memories. The presence of this neurotransmitter further proves that phenomenon of forgetfulness have been structurally woven into our neuroanatomy through the system of the cannabinoid neurotransmitters, and thus is an evolutionary trait [20].

For practical purposes, our memory is selective to decide which memories to save and which ones to forget. In our day to day life, not everything that we see is remembered, and fine details of events are generally missed, until a person consciously focuses on that detail. Due to this we are unable to recall small details that skip our observation. Overall, we remember the jest or an abstract form of the information, which is generally enough to give us an understanding of it. Selective memory allows us an easy way to remember a wider array of events, without overwhelming us with too much information. Studies have shown that remembering too much details or specifics of an event can slow down the processing of information to the point of incapacitating the natural thinking process [21]. This have been seen in cases of people who have the ability to remember every bit of information they encounter (also known as Mnemonist), as studied in the book, The Mind of a Mnemonist. Even though the Mnemonist are able to recall exact refries of words, numbers or images presented to them to test their memory, in exact order, they also find it difficult to get rid of trivial information, preventing them to focus on important or relevant information [22].

Decay Theory

Forgetting some old and outdated information can also allow the recollection of new and relevant information. For example old passwords, pin codes, which are replaced are no longer needed to be remembered, and are replaced with the newer information, which takes its place. Even when learning a new language, it is useful to suppress the memories of the native language, which can interfere with the learning of the new one. This is especially so in case of two completely different languages with different grammar and structure [17; 18].

Conclusion:

Memory is a mental faculty that is associated with the storage and retrieval of information of past experiences and events, and can be of different types based on the information being stored.  The process involves specific brain centers such as the hippocampus and amygdale, which takes a central role in how we remember and forget things. Different theories explain how memories might be lost or forgotten, and include decay theory, interference theory and representation theory. Other factors that are associated with forgetfulness are the functions of the hippocampus, inability to store information properly, motivated forgetfulness, accelerated long term forgetting, as well as age, cognitive performance and education levels of a person. Forgetting can also be seen as an evolutionary trait that helps the survivors of traumatic or painful experiences forget the incident and moving forward, it helps in the relevant memories to be better accessible, allows memories to be more selective and also enhances relevant memories.

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