Teaching old dogs new tricks

What's the first thing that comes to mind when you think about getting old? Worsening health; a failing memory; not being quite as 'quick' as you once were? We have every reason to fear old age: along with its associated impact on our physical health, in the UK, one in twenty-five people between the ages of 70 and 79 currentlylive with some form of dementia, and of those people in their more senior years (80+ years old), one in six currently live with some form of dementia¹.

While these statistics are shocking, it is at least somewhat comforting to know that, even in old age, the majority of us will not suffer this horrific syndrome. Even so, unless you're Benjamin Button, unfortunately there's no getting away from the fact that as you enter older age, you will have already started to suffer some degree of age-related cognitive decline. However, the severity of this decline is highly variable between individuals. What this means, of course, is that drawing any firm conclusions about the effects of ageing on our cognition is very difficult. Despite this, researchers continue in their efforts to better understand the consequences of the normal ageing process for cognition, focusing in particular on learning and memory.

So, what do we know about the consequences of the normal ageing process for learning? At a biological level, when it comes to age-related cognitive decline, the brain appears not to be equal². It has been suggested, for example, that certain areas of the brain - such as the hippocampus and the dorsolateral prefrontal cortex (dlPFC) - are particularly vulnerable to the consequences of ageing, due to the fact that the cognitive functions they support (e.g. working memory) are often the first to show age-related decline. Moreover, certain types of synapse - structures within the nervous system that allow signals to pass from one neuron to another and, therefore, afford communication in the brain - have been shown to be more vulnerable than others. Finally, spine-like structures that protrude from the dendrites (arms) of a neuron also appear to be more or less susceptible to ageing depending on their type. These spine-like structures come in three main types - thin, mushroom and stubby (yes, they're really called this!) - and recent findings from neuroscience have shown that the majority of age-related spine loss is of the thin type³.

Why this is interesting is that the learning of new information has been hypothesised to be closely linked to the formation of these thin spines^4,5, tending to support the common belief that learning becomes increasingly impaired with age. Crucially, however, the loss of these thin spines with increasing age does not seem to be absolute: for instance, indications suggest that, as you age, you will lose approximately 46% of the thin spines from a specific prefrontal area of your brain³, suggesting that effective new learning is not, at least, impossible in old age.

At a behavioural level, the picture - perhaps not surprisingly - is also not a straightforward one. Nevertheless, over the last decade or so, research has been presented supporting some commonly held beliefs. For example, a body of research from a number of different animal species^6,7(including humans⁸) has shown that while many simple forms of learning - such as having to learn to choose a yellow circle over a blue circle to get a reward - often remain unimpaired in aged individuals (e.g., around 70 years old), relative to their younger counterparts (e.g., around 20 years old), more cognitively flexible (and therefore more complex) forms of learning - such as having to engage in the reversal of one's previous learning, so that now the blue circle must be chosen over the yellow circle to get the reward - are often significantly impaired in aged individuals, relative to their younger counterparts.

This reduction in the flexibility of aged individuals' cognition indicates that, sadly, as we enter old age we become less able to (quickly) adapt to a changing environment - which might be one reason why we become stuck in our ways in our later years of life. What this also means, of course, is that any wrongly learned behaviour will likely become increasingly difficult to change in old age. So, the next time you try to teach your grandfather how to use a new piece of technology, be sure to teach it to them correctly the first time round!

More recently, evidence has also surfaced indicating that older seniors (around 77 years of age) experience a greater bias towards learning better from the things they get wrong (negative feedback) - as opposed to the things they get right (positive feedback) - than do younger seniors (around 67 years of age)⁹. However, things appear not to be as straightforward as they were indicated to be, as large individual differences have been found to exist. This means that while some people show a bias for better learning from positive feedback, others show a bias for better learning from negative feedback¹⁰.

What is notable, though, is that if an individual is biased towards better learning from negative feedback - and this persists into old age - then this bias will likely become increasingly pronounced in later life, rendering them particularly poor at learning from positive feedback10 (which is a rather depressing thought). Interestingly, better learning from negative feedback has been associated with depleted levels of the neurotransmitter dopamine in the brain¹¹. This is noteworthy as dopamine has been shown to be critical for successful trial and error (reinforcement) learning¹².

Of course, one of the most common popular beliefs about the consequences of normal ageing is that our memory worsens, and sadly, behavioural research supports this belief. Consider the following simple memory task: you are initially presented with a picture of a house that is made up of 25 rooms. In one of these rooms, the light is on. After a short period in which you are able to study the house, the house disappears and then reappears after some period of delay. When the house reappears, all of the rooms are dark, and your task is to identify the room that had the light on. While this task sounds incredibly easy, it has been shown that even at relatively short delays of 15 - 30 seconds between the first and second presentation of the house, older individuals (aged 57 to 85 years old) perform significantly worse than younger individuals (aged 18 to 42 years old) at identifying the room that had the light on¹³.

Indeed, the ability to remember spatial relationships between different objects in an environment has been widely shown to be impaired in old age. What is more, impairments in aged individuals' ability to successfully navigate newly learned routes from memory have also been shown. In a particularly noteworthy study for hospital practitioners, compared to younger individuals (around 20 years old), older individuals (around 70 years old) were found to be both slower at committing to memory a marked route on a map around one floor of a hospital, and then poorer at navigating that route from memory using a blank map¹⁴; thank God for GPS.

So what should we make of the above? Should we be tempted to simply give up on the hope of learning new things in later life and accept that certain aspects of our memory will fail us? The answer, of course, is no: one of the magnificent things about being old is that you have at your disposal a vast reserve of learned knowledge which can, if you are willing, be put to good use in establishing cognitive strategies that can help promote successful learning¹⁵. For example, if you have discovered over the course of a great deal of life experience that you tend to learn best from negative feedback, then, whenever possible, you can use this knowledge to adapt a new learning situation to suit your learning needs. Moreover, as you age and gain experience, it is more likely that you will have encountered a situation before that is similar to any new learning situation that faces you now, meaning that you can apply your pre-existing knowledge to help you in this new situation. Perhaps most importantly, however, is the fact that you are the holder of one of the most amazing things to ever develop in the natural world: an adaptive brain.

这意味着,虽然大家的日子都不会好过age-related cognitive decline, compensatory mechanisms within the brain - such as those areas of the brain (and the neural circuitry they support) that are less vulnerable to ageing being recruited to undertake some of the functions originally undertaken by areas of the brain that are more vulnerable to ageing - help to minimise (as much as possible) the most severe effects of this decline¹⁶.

许多认知正常的后果geing process are not set in stone: while it is true that some people will experience a substantial reduction in their ability to acquire new learning and remember new information as they enter old age, others will experience rather little reduction in these abilities - until they reach a very old age, at least. Whatever the case, the negative consequences of ageing are typically not absolute as the old adage "You can't teach old dogs new tricks!" would have us believe. You can teach old dogs new tricks, but the old dog is just going to have to work a lot harder.

REFERENCES

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