The Aging Mind

An Owner's Manual

Patrick Rabbitt

• Publisher: Routledge
• Year: 2019
• ISBN:
  9781351035200
• Edition: 2
• Topic: Psychologie
• Subtopic: Geschichte & Theorie in der Psychologie

The Aging Mind offers an accessible introduction to what research has revealed about how our bodies and brains age, and how these changes affect our everyday experiences and lives. This second edition is fully updated with contemporary studies and neuroscientific findings, to offer an engaging exploration of 25 facets of the physical and mental aging processes.

Written by eminent gerontologist Patrick Rabbitt, who interprets research through his own personal daily experiences, it explores what aging really is and how to accept and manage it. It explores why our sensory and cognitive experiences change as we get older, and what these developments mean for our overall physical and emotional well-being. Key topics explored include memory, intelligence, attention, sleep, vision and hearing, taste and smell, touch and balance, anxiety, depression and perception of the passage of time. It also discusses how far we can keep and develop the skills we have mastered over our lifetimes.

The Aging Mind debunks unhelpful myths about the aging process and offers guidance on how we can age better, allowing us to continue to manage and enjoy our lives. This second edition is invaluable for students and researchers of cognitive gerontology, for professionals working with clients experiencing issues around aging, and for all those interested in understanding their own, or their relatives' aging.

PART I

What is aging?

2

WHY AND HOW DO WE AGE?

To live long means to grow old, and with our present medical knowledge this means enduring painful and embarrassing difficulties. Things may get much better. Studying fruit flies seems a humble approach to this problem but, since the work by Rose and others in the 1990s, hints at greater comfort for future generations. Fruit flies are convenient creatures to study biological aging because they can be bred in laboratories and have short lives so that we can rapidly learn how successive generations can be selected for longer and more robust lives. One advantage contributing to successful fruit-fly aging seems to be selection for a gene that helps to inhibit production of free radicals, the accumulation of which is damaging to cell-life in humans. Laboratory experiments with other humble creatures suggest further steps we can take to prolong healthy lives, even if many of us would find some of these uncomfortable. For example, we know that rats kept on a low-calorie diet live longer and remain more active and competent than their peers. At present we can only complain that it is a pity that factors contributing to our built-in obsolescence remain as design flaws that unnecessarily add to human misery. If we must die, surely our bodies and brains could continue functioning, perfectly fit and merry, until everything falls apart so fast that we hardly have time to notice this? What has gone so badly wrong?

When biologists find a feature that is almost universal to all living things, their first assumption is that it must be selected by evolution because it brings survival advantages. For progress to inevitable death through an uncomfortable old age, this seems a tough case to argue. How can degeneration of every member of a species increase chances of survival? As individuals, we are dying continuously and piecemeal. Each cell in our bodies has a limited lifespan. Some, such as the neurones in our nervous systems, have quite long lives. Most of our brain cells are dwindling survivors of those we were born with. Most of our other cells reproduce and replace themselves but can do this only from 40 to 120 times before reliably accurate replication becomes impossible. This maximum is named “The Hayflick Limit” after Leonard Hayflick, who discovered that cell cultures were not, as had been thought, potentially immortal [1]. Copying errors of instructions to make new cells increase until fatal errors occur. The viability of chromosomes in cells that are the active blueprints and assembly instructions to accurately copy themselves is marked by the length and integrity of their telomeres: structures that can be thought of as “caps” that prevent them unravelling [2]. There is now a “decline industry” in measuring the telomere length of cells harvested from individuals’ bodies to estimate the progress of their cell aging and thus how much time they may have left. I find it easier to think of unfortunate uses for this information than of its practical value for most of us.

A benign effect of the Hayflick limit is that it restricts the development of genetic abberations in individual cells that might result in their becoming cancerous, but, in the longer run, it limits their lives and so our own. Exceptional human bodies like that of the witty¹ and gallant French Centenarian, Marie Calman have survived for over 11 decades. Her, and other, exceptional bodies manage survival by replacing themselves almost in their entirety until their cellular self-reproductive limit is reached. Throughout all our lifetimes, we are patterns in a time-stream of changing matter, like eddies and ripples in brooks that seem solid but are always braids of new water.

An exception to this continual churn of death and replacement is that even in our old age most cells that make up our brains and nervous systems are the ones that we were born with. Their numbers slowly diminish, but because we start with many billions of cells, with luck, enough will survive to keep us active, competent and amused to the end. This is a sensible design feature. To lose and renew all our brain cells every 10 years might seem a good way to maintain a competent young brain, but our nerve cells, and the connections between them, store everything that we have ever learned. Continuous substitutions would gradually erode our memories of all that we know about the world, ourselves and each other.

It matters less if the other cells in our bodies replace themselves and die because they do not have to hold all that we have ever learned. Apart from the continually diminishing viability of their components, our bodies are always liable to damage, whether from accidents or from the accumulating burdens of the illnesses and mishaps that we experience. We try our best to survive in an ocean of frantically and indefatigably reproducing viruses, bacteria and microorganisms with which we continually compete. Over millions of years, we have made alliances with hundreds of families of these creatures and now could not live without these treaties. As things are, most of our body-mass is made up of cells that were, originally, of quite different species to our own indigenous “human” cells. They were once humble economic migrants to our succulent swamps of flesh and fluids from less affluent lifestyles. They are now fully paid-up assimilated citizens making an essential contribution to our body-economy.² Throughout our lives, viruses and bacteria continually challenge our defences, and the declining efficiency of cell-replacement reduces the effectiveness with which we can resist them and repair damage. During our first years, we improve rather than wear out, and for many decades all goes pretty well, but in the long run the energy and resources to defend and repair ourselves become increasingly hard to find.

Why we could not live for ever

Staying permanently and perfectly self-replicating would not solve the death problem because accidents would inevitably occur. Witty mathematical models, devised for practical reasons such as budgeting for replacement of crockery and wineglasses in restaurants, accurately predict the diminishing survival chances of brittle objects in a risky world. Inevitable accidents and chance erosions mean that all objects have limited life expectancies and, even without the Hayflick limit, so would we. Though exceptionally lucky individuals might survive the disaster lottery for millennia, damage must accumulate, and time and chance will get us all in the end.

Not all for each but each for all

Unlike wineglasses, we can avoid total annihilation because we can reproduce ourselves so that our individual deaths do not end our species. Some animals have settled for a simple scheme in which they combine the tasks of keeping their bodies alive by replacing failing cells and fabricating entire new organisms. Bacteria simply split and carry on as pairs of new entities and so are at least potentially immortal although they change from generation to generation. Some simple many-celled creatures do a little better. A tiny animal, called a “hydra” because it resembles a bush of serpents sprouting from a single trunk, occasionally indulges in its dull form of sex and buds off entire new entities. A single severed hydra limb can also re-grow an entire new body. This seems a real but unexciting form of immortality. If my severed arm grows a new body and brain, in what sense could this new entity still be part of the continuous trajectory of the “me” that I experience? What could it retain of the information and skills I have acquired during my earlier, separate life? We do not believe that hydras have minds to worry about such things, but more complicated creatures like dogs, monkeys and ourselves remember their lives and so have a sense of experiential continuity that each feels is uniquely its own. We might not agree that this is a more attractive form of personal immortality than we already achieve by the alternative method of deputing some of our (sex) cells to detach themselves from the rest of us so that they can get together with other people’s (sex) cells to construct different independent beings. Whatever we may feel about this, the evolutionary dice were cast millions of years ago, and we have to accept the only deal in the known universe: as individuals we each die, but our species can live on though, also, in gradually changing forms. Like individuals, species are patterns in time, deceptively constant at brief inspection but in longer perspectives constantly changing to stay alive in the world.

Besides dutifully carrying on our species, could we not also survive as individuals so long as chance allows? Surely the indefinite survival of individuals could also be a good plan for a species because it would perpetuate valuable knowledge of how to survive in the world.

An early idea was that the indefinite survival of individuals would be counter-productive because they compete for the same food and other resources. This seems convincing as we watch a pullulating human population gobble the resources of our entire vast planet. The lesson that aging members of a species, rather than new infants, exhaust resources is implicit in the realisation that our current population explosion is driven as much by longer survival of individuals as by increasing numbers of successful births. The technologies that have enabled this calamity are unique to us but, in the wild, many factors combine to cull species. As the number of individuals in a species increases, so do the numbers of its increasingly well-fed and efficient predators and the odds of epidemics of infectious diseases. Many studies of animal populations find that diminished resources and overcrowding not only increase the risk of mortality for individuals but also reduce fertility and slow down reproduction. Slowing down reproduction is not an optimal solution because it limits the speed with which a species can adapt to a changing environment. New generations progressively modified to cope with the new problems of a continuously changing world are key to species survival.

Sexual reproduction combines genes from different individuals and so makes each birth a new experiment in survival. Darwin’s big idea was that if altered genetic legacies (mutations) are unhelpful, they lower the odds that the individual animals that carry them will live long enough to pass them forward along the species timeline. Carriers of helpful mutations are more likely to survive to breed and so make their individual novel inheritances a common legacy. Without mutations a species would remain fixed over time. Stasis would be an option for a species perfectly adapted to an everlastingly unchanging world – but no paradise is future-proof. The world changes continually, and drastically, and species that cannot meet new threats or seize new advantages are locked in ruts that they may cosily inhabit for millennia but within which they will perish when dire changes inevitably occur.

This is the core of the story, but there are a few twists in the plot, mainly involving sex and violence, the staple plots of the natural history films that we all enjoy so much. Tom Kirkwood, a clever observer of this scenario claims to have had, in his bath, an Archimedean moment in which he realised that mutations are most useful if they are passed on early in life because losses to predators, illnesses and accidents will ensure that, as time passes, fewer and fewer individuals survive [2]. The essence of his idea is that individual members of a species are disposable tools for long-term species survival – as he terms it, “a disposable soma theory”. Even in a species in which all animals could indefinitely keep youthful resilience and the capacity to find mates and reproduce, the inevitability of terminal accidents would ensure that longer-lived individuals will become increasingly rare so that the young will always monopolise breeding opportunities. Mutations that increase chances of youthful survival and successful early breeding will be passed on more often than those t...

Table of contents

• Cover Page
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Introduction
• PART I What is aging?
• PART II Memory
• PART III Senses
• PART IV Intelligence, skills and wisdom
• PART V Living with aging
• PART VI Aging well
• Index