Passage of time: why people with dementia switch back to the past

People diagnosed with dementia often have a distorted sense of time passing. My friends who are clinicians often comment on their patients with dementia preparing and arriving for their appointments many hours before they’re scheduled.

Dementias such as Alzheimer’s disease progressively impair cognition, causing problems with memory and planning, and day-to-day functioning, making it difficult to do things like shopping and cleaning.

Accurate time perception is critical in our modern society (and for much more important reasons than waiting room congestion) so this disorientation significantly affects those with dementia and their families and carers.

The Australian population is ageing, and with this comes an increased prevalence of dementia, Alzheimer’s disease being the most common. One in ten over-65s and one in three over-85s have dementia.

There are neurological reasons why those affected by dementia judge the passage of time differently, and can access remote memories from many decades ago while unable to remember events of the past few hours.

Time perception in dementia

Those with dementia judge the passage of time quicker than older adults without dementia, as well as younger adults. This is for prospective time perception, where people are instructed to estimate an upcoming time interval; and retrospective time estimation, where people judge time after the event has occurred, requiring them to mentally travel back in time.

As a practical example, a person with dementia is likely to underestimate how long they waited at a bus stop (if asked when the bus arrived; retrospective time perception) and how long they will be on the bus for their specified journey (if asked as the bus started; prospective time perception).

Those diagnosed with dementia may underestimate time due to difficulties in recollecting all events in the short-term past, creating a feeling of a relative empty time travel. Someone without dementia may remember the boy cycling his bike, the yellow car parked next to the shop, the noisy lawn mower, and the couple playing tennis, on their walk to the bus stop; while someone with dementia is likely to remember fewer of these events, creating the sense that less has occurred and therefore less time has past.

Living in the past

There is a link between the perception of time and memory function in those with dementia. Family members often report their loved ones with dementia sometimes live in the past, even reverting back to first languages.

This is because memory is not just one process in the brain, but a collection of different systems. Those with Alzheimer’s disease may have impairments in short-term memory, however remote memory can be left relatively intact. So they’re able to remember public and personal events many decades ago, but unable to recall what happened earlier that day.

A fascinating case study illustrates this dissociation in remote and short-term memory in Alzheimer’s disease. A retired taxi driver diagnosed with Alzheimer’s disease showed remarkable spatial memory of downtown Toronto, Canada, where he had driven taxis and worked as a courier for 45 years. This was despite showing impairments in short-term memory and general cognitive functioning.

But while those with Alzheimer’s disease can typically remember events in the distant past better than those in the immediate past, they still perform worse than older adults without Alzheimer’s disease in memory retrieval.

Interestingly, it appears that events and facts most frequently retrieved and used over a lifetime are those better recalled by those with Alzheimer’s disease in late life, rather than those encountered at any particular age.

This frequency of use memory pattern is mirrored in bilingual people with dementia. A friend commented that her Yia-Yia (Grandmother), who immigrated to Australia from Greece over 50 years ago, is increasingly conversing in Greek despite predominantly speaking English for decades (causing problems for my monolingual English-speaking friend).

Those with dementia often revert to their first language. This commonly begins with utterances from the first language appearing in conversation from the second language. This occurs more often in those less proficient in their second language, rather than being related to the age of acquisition of their second language.

So, how does this happen? Probably because familiar memories rely more on the brain’s cortex, its outer layer, while short-term memories rely more on a structure called the hippocampus. The hippocampus is typically affected at the start of late-life dementias such as Alzheimer’s disease, with regions of the cortex affected subsequently.

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How to best respond?

Families and friends of those affected by dementia often do not know how to respond when their loved ones rely on these remote memories, at heart, living in the past. It’s certainly not the case that these remote memories should be ignored or suppressed.

Rather than trying to bring the person with dementia back to reality, families and carers may try to enter their reality; building trust and empathy, and reducing anxiety. This is known as validation therapy but many families and carers will practise this technique without knowing its name.

Reminiscence therapy has also been shown to increase mood, well-being and behaviour in those with dementia. This involves the discussion of past activities, events and experiences (usually with help of artefacts such as photographs, music and familiar items).

Alzheimer’s Australia has some fantastic help sheets and phone line to help carers and family members communicate with loved ones with dementia.

Building resilience

There is nothing that can completely protect us from a future diagnosis of dementia. But a cognitively stimulating lifestyle can at least delay the onset of dementia. This means using your memory and other cognitive skills as much as possible, for example, working in a mentally challenging job, doing crosswords, and engaging in social activities.

The more frequently we recall and use memories over our lifetimes, the more likely we will have access to them in our old age.

Hannah Keage receives funding from the National Health and Medical Research Council (NHMRC). She is affiliated with the Australian Association of Gerontology and Australian Cognitive Neuroscience Society.

Tobias Loetscher does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.