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Memory has been widely defined as the information that is
learned and stored inside of our brains. There are three different established processes
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 already
stored within both the brain’s short and long term memory. 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. This memory loss is not only limited to
personal memories, patients have presented themselves with loss of language and
inability to use their bodies. 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.

 

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.

A double disassociation in this case is where the short-term
memory and long-term memory are connected in a way where both can undergo
damage separately but with the other still intact. Patients with amnesia typically
experience damage to their long-term memory as opposed to their short-term
memory. This is generally caused by damage to the medial temporal lobe and
impairments to the short-term memory with unimpaired long-term memory are
usually caused by damage to a different section, which include the parietal and
temporal lobes (Shallice and Warrington, 1974).

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