How Your Memory Works (or the architecture of memory – it is not actually about retention of the past, but a future-orientation system)

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How Your Memory Works (or the architecture of memory – it is not actually about retention of the past, but a future-orientation system)

Summary:
– the brain is a time machine [Psychologist from University of Sydney]
– we do not fully understand where memories are stored
– memory changes & is influenced by present events – it serves various purposes:
– memory has an important social connection purpose
– they are crucial for our sense of self & identity – the story about ourself
– memory helps our present planning for future goals (drawing on the past to inform our future)
– our memories are precious
– memory is fallible & prone to error from time to time – interspersed with other things
– our memories are vulnerable – can be lost through brain injury trauma or Alzheimer’s (memory complaints are sometimes the earliest signs of the disease – in particular recent episodes as well as disorientation to time and place; semantic memory is lost)
– the neuroscience of memory – is still in its infancy due to its complexity
1) there are many types of memory despite the one catch all term, Memory
A) – Episodic memory or event-based memory
– The events that have occurred to us in the past
– involves encoding, storing & retrieving information from the past
– it is a very fallible form of memory
– For many years it was thought that this type of memory relied upon the brain’s hippocampus which is located deep within the temporal lobes of your brain right above your ears
– imaging studies now reveal that the hippocampus is not working on its own, but that it is communicating with the pre-frontal cortex & the posterior singular cortex at the back of the brain [it is a distributed network within the brain – therefore damage to any of these regions will result in impacts upon the ability to remember events of the past]
B) – Semantic memory
– Your repository of general conceptual world knowledge independent of a specific time or place
– we are able to recall the information without remembering the exact time or place we learned it
C) – Spatial memory
– Allows us to navigate the external environment around us
D) – Procedural memory
– A form of non-conscious memory such as riding a bike, driving a car, typing QWERTY
E) – autobiographical memory
– explains our identity/Self to us
– provides consistency over time
– all significant life events which you can evoke in rich detail
– very sensory, perceptually-rich memories
[the autobiographical interview- developed in Canada – is used to test for memory issues by fragmenting the episodic memory into the various types of other memory, include “remote memory” or older episodic memory – this gives neuropsychologists something called a “Remote Score”]

A) & B) are known as declarative memory
– For many years, A) & B) types of memory were thought to be independent, mutually exclusive, non-overlapping forms of memory, but are now seen as being independent

Semantic Dementia now involves the loss of B)
– A) & C) type memories remain while B) type memory is lost
– believed to be related to cell loss in the anterior temporal lobes (primarily in the left hemisphere initially typically, before encroaching into the right hemisphere) & the hippocampus
– grey matter shrinkage also occurs
– the vocabulary for specific events is lost
– they are also able to better remember recent memory compared with older memories – the reverse is true for people with Alzheimer’s Disease – old – not recent – memory is preserved (this is called double dissociation)

– structural MRI scans are used to determine & map which parts of the brain are damaged
– for Alzheimer’s
– the hippocampus & regions of the frontal lobes are always affected regardless of which time period (for memory) is being assessed
– the posterior singular cortex at the back of the brain – is also affected, but only for recent memory events
– for Semantic Dementia
– lateral temporal lobe cortices were correlated with remote memory loss

[note: there are two hippocampi in the brain – the left & the right]
– memories fade as we age & evocative memories become less emotionally salient for us & less visually rich
– over time episodes (memories from past events) become semanticised (or fact-like) & more lateral temporal lobe cortices become involved in memory (this occurs also the more we retrieve such memories from the past)

– the loss of the past affects our ability to plan for the future

– why has the brain evolved so?
– to assist us envisage/imagine the future
– so as to be a future-oriented species, giving us foresight
– memory – it is now believed to be – less a memory retention system – but a future orientation system [2007 studies by Maguire]
– new theories have arisen as a result:
– the Constructive Episodic Simulation Hypothesis: when we try to envisage the future, we try to dip back into the past to flexibly extract out the relevant episodic details so as to re-combine them in a new & novel way, thereby allowing us to simulate events which have not yet happened & try out different scenarios without having to engage in costly behaviour
– this explains difficulties for future thinking for Alzheimer’s Disease, Semantic Dementia, Depression & cognitive impairment more generally
– it has “prospective memory” implications:
– taking medication
– turning off the iron
– thinking ahead about the future – financial planning
– mood & motivation effects (reduce social engagement, apathy)

Alzheimer’s Disease
– cell loss in the medial temporal lobes (where the hippocampus is located)
– cell loss in the parietal and frontal cortices
– & shrinkage of the grey matter

Source: ABC RN | Big Ideas | 31 May 2017

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