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| Aleea Devitt |
In our
first blog post we discussed how a consequence of the constructive nature
of memory is that we are susceptible to memory distortions. In this post I hope
to bring together theories of how changes in the brain can increase
susceptibility to false beliefs and memories as we age.
Healthy
aging is associated with reduced memory accuracy, as well as increased
susceptibility to memory distortions, which can have serious consequences on
the quality of life for older adults. For example, an individual might be
confused about whether they had taken their medication or just imagined taking
it. Older adults also tend to be more
confident in their memory errors, which can have implications for everyday
social interactions as well as more formal situations such as eye witness
testimony.
A number of
cognitive mechanisms have been proposed to underlie this effect, including
reduced recollection, overreliance on familiarity, and dysfunction in feature
binding. Together these theories provide a comprehensive outline of how the cognitive
and neural changes accompanying healthy aging can result in imperfect
cognitions.
Reduced recollection:
The Source Monitoring Framework
postulates that different mental experiences (memories, imaginations, dreams,
etc.) tend to have different phenomenal characteristics, allowing source to be
distinguished. For example, memories for perceived events typically have more
sensory, temporal and affective information than imagined events. However,
sometimes the characteristics of an imagined event can overlap with those of an
authentic experience; in such cases, a source monitoring error may be made. We
have all had dreams so vivid that later we cannot distinguish whether the
‘events’ we are remembering were really experienced (in the external world) or
just imagined (in the internal world); in essence, we cannot attribute the
source of the memory.
Brain areas involved in memory storage, binding and
retrieval (particularly medial temporal regions) typically decline both functionally and structurally
with age, with a resultant reduction in recollective ability. These deficits in
recollection mean that the enhanced recollective quality we normally use to tag
a memory as veridical is no longer available or reliable; authentic memories
and imagined events are more
similar in quality, resulting in greater opportunity for an imagined event
to be misattributed as a veridical memory.
Overreliance on familiarity:
While
recollection tends to decrease with age, one’s sense of familiarity
with a stimulus is relatively preserved. This can result in a tendency to
falsely identify new events as previously experienced, as source judgements are
based on the overall feeling of familiarity with the event, rather than recollection
of a prior encounter. A strong sense of familiarity can be garnered if the gist
of the event is consistent with previous information, or one has been exposed
to the event multiple times (perhaps through imagination). Functional and neural
decline in prefrontal areas involved in source monitoring, in addition to
reductions in recollection, mean that fabricated events can surpass the usual
reality monitoring checks, so that familiarity with the event may be
incorrectly attributed as an indicator
of memory authenticity.
Dysfunction in feature binding:
Finally, age-related
dysfunction in neural areas vital for memory feature binding (specifically the hippocampus)
may result in either under- or over-binding of memory details. Under-binding occurs
when fewer features of an event are bound together at encoding, so activation
of one detail at retrieval does not activate all the other features of the
event. The result is impaired recollection and subsequent overreliance on
familiarity. Furthermore, the context in which an event was encoded might not
be bound with the event itself, making subsequent source monitoring difficult. Over-binding
can occur due to disinhibition of binding processes, with the effect that
features of one event may be miscombined with features from another, resulting
in a type of false memory known as a memory conjunction error.
It is not
all bad news however! Increased susceptibility to false memories may not be a
universal and inevitable feature of aging. Older adults who perform well on
tests tapping frontal
and medial temporal lobe functioning are no more vulnerable to false
memories than younger adults. When
the studied stimuli are distinctive, older
adults can effectively use source monitoring strategies based on recollection. Minimal
false memories have been observed when older adults were tested at an optimal
time of day (usually the morning). Lastly, reliance on prior knowledge
rather than recently learned (mis)information may actually protect
older adults from distortions in some circumstances. We could all benefit
from further research on the circumstances under which we may become more or
less vulnerable to imperfect cognitions as we age.