Memory capacity of the long term memory is unmeasurable,

 

Memory has been widely defined as the information that is
learned and stored inside of our brains. Attkinson and Shiffron (1968) put
forward the initial basic structure of the memory. It included three major
stores: the sensory store; short-term store and long-term store in which
information is passed through linearly. There are three different established processes
by Melton (1963) that allow the retention of a memory within the brain. The
first process is encoding, which is where information is gathered, collected
and processed in different ways; the main ways being visually, acoustically and
semantically. The semantic form refers to the application and association of a
memory to a meaning. The secondary process begins in which, the information is
stored into the short term memory, and it stays there for a duration of time –
one which vary from individual to individual. If the particular memory is
rehearsed, it is transferred into the long term memory of the brain. Finally,
the last stage is retrieval; where information that is stored within the long
term memory is then retrievable on demand. Contrastingly, Amnesia is a term
which refers to a condition in which the memories are not easily retrievable.
This inability extends beyond the everyday forgetfulness and shows a failure at
a certain point of the memory retention process mentioned beforehand. Amnesia
can occur for various different reasons, including neurological causes such as
physical injury and psychogenic causes, like mental disorders or post-traumatic
stress, even from alcohol abuse known as Korsakoff’s syndrome. This essay will
articulate our understanding of the connection between memory and amnesia and
the latter shaped the former.

 

As previously stated, the two major storage systems of
memory are the short term and long term memory. The short term memory stores
information for a more restricted period of time with a quite limited capacity.
As opposed to the long term memory, which stores information for a
significantly longer duration with a potentially unlimited capacity. The limit
of the capacity of the long term memory is unmeasurable, as the typical brain
stores a vast variety ranging from language, grammar, etiquette, social norms,
education as well as personal memories. We understand the immensity more, particularly
if we look at an extreme of the spectrum – at individuals with photographic
memories, all the information they gather is all stored into their long term
memories for their entire lives. The other end of this spectrum is represented
by those with amnesia who are often unable to retain or collect memory at all.
This understanding of memory would not exist in such detail if not for the
studies of patients with conditions such as amnesia, which has provided better
insight of the functionality of memory. These findings by psychologists have
enabled us to divide amnesia into types.

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The first type of amnesia is referred to as retrograde
amnesia, which is the inability to remember or retrieve past memories. The type
of amnesia enables us to separate the three processes that aid retention,
identify and pinpoint where the brain is failing. This appears to occur within
the final process of retention; retrieval. 
Due to the trauma, instead of the brain to allow access to these
particular memories on demand, it fails to locate them leaving those with this
condition in varying states. Some have lost only recent memory, from a few
weeks to months and some are left without memory going on years. It is
interesting to note that these memories are often not lost but rather hidden,
and how re-immersing patients into familiar settings can trigger retrieval.  Contrastingly, anterograde amnesia is
described as the inability to acquire and retain new information, after the
development of amnesia. This type of amnesia represents a breakdown of the
established processes of retention starting from the second step, as the brain
completely lacks the ability to transfer the information into the long term
memory. Patients are able to gather information, but this is retained for a
significantly shorter period of time, even as short of a few mere seconds.
Albeit, this is the worse of the two types as it has no cure, but
simultaneously it is the more interesting aspect of amnesia as we are able to
explore the other capabilities of the brain.

 

The two main distinctions of long term memory are
declarative/explicit memory and non-declarative/implicit memory. The former
stores information that require a conscious recollection. This memory can be
further divided into two sub-divisions: episodic memory and semantic memory.
Episodic refers to memories of personal experiences including their time and
the location of these events. Whilst the semantic memory retains knowledge we
have obtained through education such as worldly facts and history. Studies and
observations into the sub-divisions by Spiers et al (2001) found that the two
were distinctively different. He examined 147 cases of patients with amnesia
with damage to the hippocampus area, and discovered that there were impairments
to episodic memory in all cases, however no substantial damage to the semantic
memory. However why this occurs is still being explored. On the other hand, non-declarative
memory stores learned skills that can be retrieved unconsciously, allowing
individuals to perform actions by rote. This can also be subdivided into two
categories: procedural memory and priming. Procedural memory pertains to skills
such as riding a bicycle or tying your shoelaces, these motor actions do not
require any conscious thought or effort in most cases. Finally, priming refers
to how the prior exposure of a stimulus affects the processing of a later
stimulus, both which share a relation. For example, an individual who is
presented with an auditory stimulus of a dog allows a later auditory stimulus
of a dog to become easier to recognise, due to their connection. Thus, the
first audio would be referred to as the prime, which aids the processing of the
audio when presented the second time.

 

Henry Gustav Molaison (1926-2008), familiarly known as H.M
was a patient suffering from amnesia, from whom studies were developed that
were particularly influential in the development of the understanding of
memory. The patient suffered from extreme epilepsy, that resulted in the
surgical removal of his medial temporal lobe and parts of the hippocampus and
amygdala. Through the surgery his epilepsy improved, however the consequences
came in the form of anterograde amnesia, that
comprised his abilities to create new memories. Despite his difficulty in
forming new declarative memories, his procedural and short-term memory that
Alan Baddeley (1974) refers to as the working memory, remained intact. Brenda
Milner (1957) also learned that his digit span was completely normal she
observed this when she tested his ability to repeat the numbers that spoke,
which he was able to do perfectly – however his retention of those numbers was
only for a number of few seconds, due to damage to his brain.  Milner also examined H.M’s motor skills by
presenting him with a mirror-tracing task, where he would draw the outline of
the images in front of him by merely looking at the mirror. His task
performance gradually improved over time as he was able to unconsciously
retrieve this skill memory, however he was unable to actually remember learning
or practicing it each time. This shows that perhaps there is some leak from the
short term memory to the long term memory, particularly when it comes to
unconscious learned skills. The observation of HM resulted in the belief that the
removal of or damage to the hippocampus, can result to a deficit in the
long-term memory, . H.M was able to provide us with some of the earliest
insights into anterograde amnesia and the case study shows that long-term
memory is not necessarily indefinitely and only stored in the hippocampus since
H.M was able to recall memories prior to his surgery.

 

A double disassociation was also established through the
studies of amnesia, in this case it is where the short-term memory and
long-term memory are connected in a way where both can undergo damage but with
the other still intact. Patients with amnesia typically experience damage to
their long-term memory with either little or no impairment to their short-term
memory. This is generally caused by damage to the medial temporal lobe and
hippocampus, hence effecting episodic memory. It can also occur conversely
however it is more rare; patients can undergo damage to the short-term memory
with unimpaired long-term memory. This is usually caused by damage to the
parietal and temporal lobes. In addition, semantic dementia patients lack
semantic memory retrieval whereas their episodic memory is unaffected. In
contrast amnesic patients have deficiency in episodic memory however their
semantic memory remains rather in tact.

 

To conclude, the various studies of amnesia have provided us
with crucial information that is key to developing evidential theories about
memory. Psychologists and Neurologists alike, have been able to systemically
divide and organise the different sectors that the memory consists of, their
differences and the distinct way in which they work together to retain
information. It has also aided in the understanding of the functionality of the
brain in relation to memory. Nonetheless, as our knowledge is predominately
based on case studies and their findings, it is difficult to then generalise to
the wider population, as these studies are largely based on unique individual
cases.