Friday, 7 February 2014

Imperfect Cognitions and Aging

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.

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