Neuroscience 19b – Memory
Anil Chopra
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Outline the main differences between sensory, working and long-term memory
Give an account of working memory
Describe the structure of long-term memory
Explain different types of amnesia
Appreciate that patients forget much of what doctors say to them
Memory involves a number of different stages:
- Registration: Information input from senses
- Encoding: processing and combining of that information
- Storage: Holding that information in the memory system. (not everything that is
registered and encoded is stored)
- Retrieval: Recovering stored information from the memory system. (not
everything that is stored can be retrieved).
There are different types of memory store, each with its own performance
characteristic, function and neuroanatomical position. They are classified in different
ways:
Durations of Memory Retention
Sensory Memory: gives us information on what is happening around us – can
include iconic (visual) or echoic (sound) information. It only lasts for a very short
time (2 seconds) after which is either forgotten or encoded into a different type of
memory. It’s written over by subsequent perceptual information.
Short term Memory: or working memory. It is limited by its amount rather than its
time. Things are remembered more easily when they are split into chunks. Subsequent
information also causes old information to be pushed out, but rehearsal can maintain
the information. The frontal cortex, parietal cortex, anterior cingulate, and parts of
the basal ganglia are crucial for functioning.
The serial position effect shows
that recall accuracy depends on
the position of an object in a list.
Probability
of recall
1.0
Phonological
Loop
Central
Executive
Primacy
Effect
Components of Working
Memory
The central executive is the
attentional control and
manipulation of information
within short term memory which
suppressed the irrelevant
information and co-ordinates
VisuoSpatial
Sketchpad
Recency
Effect
0.5
Episodic Buffer
0
Early
Middle
Order of items
Late
cognitive processes when more than one task needs to be done at the same time. This
relays information to and from the visiospatial sketchpad and the phonological loop.
- Visiospatial sketchpad: stores visual and spatial information. Used in
constructing images and mental maps.
- Phonological loop: storage of sounds and prevents decay by articulating its
contents.
- Episodic buffer: this has links with long-term memory and is associated with
linking visual, spatial, and phonological information.
Long term memory: storage for information not currently in use but possibly used in
the future. It can hold an unlimited amount of information and allow information
about the past to be used in the present. Retrieval from long term memory may be:
 Implicit/Non-declarative (unconscious) - knowing how. Also known as
procedural. Familiarity and knowledge of how to interact with an object or a
situation without having to think about it. e.g. walking, eating.
 Explicit/Declarative (conscious) i.e. knowing that. Our store of knowledge.
There are 2 types:
 Episodic: relating to an experience. “memories”
 Semantic: relating to facts. “general knowledge”
Normally people can recognize more than they can recall and when brain tissue is
damaged recall is affected more than recognition is.
Distinguishing different Types of Memory
 Experimental Psychology - e.g. Serial Position Effect
 Neuropsychology - e.g. brain lesions
 Functional Imaging - e.g. PET scans, fMRI
Why do we forget?
 Trace decay – i.e. storage failure
 Substitution – i.e. storage limit
 Interference – i.e. retrieval failure Can be proactive or retroactive interference
Different memory stores forget things for different reasons:
» Sensory memory – trace delay
» Working memory – trace delay and substitution
» Long-term memory – interference
 Generally people can recognise more information than they can recall
 Brain injury or disease affects recall more than recognition
o Recognition involves matching to a memory trace
o Recall always involves memory search and matching
Rehearsal
Information
in
Sensory
Registers
Attention
Working
Memory
Storage
Retrieval
Information Lost
Information Lost
Long
Term
Memory
Clinical Conditions
Anterograde Amnesia
A condition characterised by ongoing difficulty in remembering and taking in new
information as a result of brain injury or disease. It generally affects long-term
memory rather than working or sensory memory.
Retrograde Amnesia
A condition characterised by difficulty in remembering events that occurred before
the onset of amnesia – recent events are most severely affected. It normally occurs
following brain injury and its effects are reversed with time with more distal
memories returning first.
Post-Traumatic Amnesia
A condition caused by brain injury resulting in unconsciousness. It is defined by the
time in between the brain injury and return to full consciousness in which patients
experience great lucidity and periods of confusion. The length of time patients are in
post-traumatic amnesia can give an indication as to the severity of brain injury and the
degree of disability. Post traumatic amnesia is very difficult to measure accurately.
Transient global Amnesia
A condition characterised by repetitive questioning and confusion but no difference
personal identity. It can last several hours (4-12hrs) and occurs most commonly in
middle-aged of elderly men, sometimes preceded by headache or nausea, a stressful
life event, a medical procedure, intense emotion or vigorous exercise.
Psychogenic Amnesia
Also known as psychogenic fugue/dissociative amnesia, psychogenic amnesia is the
repression or forgetting of a traumatic event. There are 2 types:
- Global: patient forgets events and personal identity as a result of severe stress.
Usually accompanied by depressed mood and frontal lobe dysfunction.
- Situation specific: patient forgets stressful lifetime events e.g. sexual abuse,
criminal offence. This is possibly due to the implication of amygdaloid circuits
which are different from those in normal learning.
Confabulation
A condition characterised by unprovoked pouring of untrue or exaggerated memories
which are often bizarre. Can occur as a result of damage to the basal forebrain and
frontal lobes, aneurysm, damage to the anterior communicating artery or a thiamine
deficiency caused by alcoholism (Kosakoff’s syndrome).
It has also been shown to occur in normal patients using a choice blindness
experiment. This is when patients are asked to make a choice and then when their
incorrect choice is presented to them, they are able to confabulate as to why they
made that choice.
False Memory Syndrome
Similar to confabulation in that patients experience a falsely perceived memory,
usually of a traumatic experience. In treatment, a therapist may ask the patient to form
a detailed mental image of the event. As this imagery is repeated over multiple
treatment sessions, it grows successively more vivid, until the entire memory is
"recalled". At this point, some patients strongly maintain its validity even when they
are presented with evidence to the contrary.
Doctor-Patient Consultation
In a consultation, memory for medical information is a prerequisite for good
adherence to recommended treatment. A large proportion of information told to
patients is forgotten immediately and often, the more that is presented the less is
retained. The amount remembered is affected by:
- factors relating to the medical professional e.g. terminology used
- factors relating to the information e.g. written information is better than oral.
- factors relating to the patient e.g. age, clinical condition, education level.
o Distress and anxiety is shown to decrease the amount remembered by
patients.
o Perceived importance of the information has an effect on how much is
remembered. E.g. diagnosis is deemed more important than treatment.