Until his death, former U.S. president Ronald Reagan was the world’s most famous Alzheimer’s sufferer. “I now begin the journey that will lead me into the sunset of my life,” he wrote in his poignant farewell message to Americans when he was first diagnosed at 83.

The acknowledgment marked the formal onset of his long, sad decline, but it may be that Mr. Reagan’s entire life history and long-established emotional patterns had prepared the ground for the illness that eventually robbed him of thought, speech and movement.

For all his charm, Mr. Reagan lacked the capacity for genuine emotional expression. His stereotypical response when emotions were called for was, “Really, there are no words.” He described himself once as “the calm vacant centre of the hurricane.” His only reply to the physician who informed him of his wife Nancy’s breast cancer was a brusque, “Well, you’re the doctors, and I’m confident you’ll be able to take care of it.”

According to his official biographer, Mr. Reagan was characterized by an “immense insularity, a paralysis of sensibility.” From childhood onward, he was “sheathed in a strange calm.” Could these traits have been harbingers of the dreadful insularity that would ultimately envelop him?

Evidence strongly suggests that a lack of full emotional capacity is a risk factor for the later development of Alzheimer’s disease. In the famous “nun study” published in 2000 by the Sanders-Brown Center on Aging at the University of Kentucky, researchers gained access to autobiographies that had been written by young novitiates as they entered religious orders many decades earlier. By the time of the study, the subjects were elderly nuns, and beginning in 1986, the researchers observed them closely, watching for signs of normal aging but also for signs of dementia. After the nuns died, the researchers performed autopsies on their brain tissue. Three findings from this study have startling implications for our understanding of Alzheimer’s.

Nuns who had greater linguistic facility in youth, who were able to express more ideas in grammatically more complex language, were less likely to succumb to Alzheimer’s as they grew older. Nuns in this group were more able to retain their intellectual and interactive capacities into advanced old age, even if it turned out on autopsy that their brains were rife with the pathological markers typical of Alzheimer’s. And nuns whose autobiographical recollections as young people were happier and more filled with positive emotions such as joy and gratitude were likely to live longer and were, again, at a lower risk for dementia.

From other studies, it is well known that a person’s ability to give an articulate and coherent autobiographical narrative reflects healthy attachments with family. A paucity of emotional expression in adulthood tells of emotional deprivation early in life. Mr. Reagan’s emotional poverty and his need to cocoon himself against reality can be understood as the responses of a sensitive child to the trauma of living with an alcoholic, unreliable father and an emotionally absent mother. At an early age, he distanced himself from the vulnerability of genuine emotion by hiding behind sentiment and learned to maintain a surface tranquillity by failing to recognize his own emotional pain or that of others. His apparently nonchalant response to news of his wife’s potentially fatal malignancy did not denote a lack of caring — on the contrary, it betrayed more caring and more anxiety than he could ever allow himself to experience.

In an atmosphere of severe psychological stress, a young child’s brain may perform an evasive manoeuvre: It shuts down awareness of painful feelings. The brain can never defend us against being wounded, but it can suppress our sense of hurt, forcing it into the unconscious. In the absence of authentic feeling, we then act the role of a feeling person; in place of genuine intimacy, we learn how to “communicate.” For warmth, we substitute charm. Instead of being authentic at the core, we develop sincerity. We mean what we say without being in touch with our truest meanings.

Neurologist Oliver Sacks was intrigued once to witness a group of his patients respond with helpless mirth to a televised speech by Mr. Reagan, then the president. These people suffered from aphasia, an inability to process spoken language, usually because of a stroke. “There he was,” Dr. Sacks wrote, “the old charmer, the actor, with his practised rhetoric, his histrionisms, his emotional appeal — and all the patients were convulsed with laughter. Well, not all: Some looked bewildered, some looked outraged, one or two looked apprehensive, but most looked amused.”

To this group at least, the Great Communicator was communicating something he had not intended. “What could they be thinking?” Dr. Sacks wondered. “Were they failing to understand him? Or did they, perhaps, understand him all too well?”

Aphasiacs, it turns out, have a finely honed capacity to distinguish emotional truth from fiction. Just as the blind learn to pay close and nuanced attention to sound, so aphasiacs compensate for their impairment by reading astutely a speaker’s body language, facial expression and tone of voice. Dr. Sacks’s aphasiac clients could not decipher Mr. Reagan’s words, but they perceived a fundamental inauthenticity in his manner, one that escaped most of the president’s television audience.

“Either he is brain-damaged, or he has something to conceal,” one patient told the neurologist. Yet Mr. Reagan was, quite probably, not lying. He didn’t have to — all his life he had a renowned aptitude for confounding story with fact, movie reality with history. It was self-delusion and lack of emotional truth that, underneath the president’s charm and sincerity, these patients could discern. Long before his death, Alzheimer’s disease deprived the ex-president of his ability to play his greatest part: the role of Ronald Reagan himself.

Alzheimer’s is a complex disorder to which many factors contribute, including genetics, diet and cardiovascular health. Inflammatory processes and the immune system, both heavily affected by chronic emotional stress, are also implicated. Many scientists now consider Alzheimer’s to be an autoimmune disease, one in which the body’s own immune apparatus attacks the very host it is meant to protect. The regulation of stress hormones such as cortisol, closely linked with emotions, have been shown to be abnormal in patients with the disorder.

As the nun study showed, and as Mr. Reagan’s case illustrates, people’s earliest experiences and the emotional patterns they develop in response can be a significant influence. We need to pay just as much diligent attention to emotional clarity and emotional health as we devote to our physical bodies.

The good news is that emotional transformation and brain development can occur even in adults, and even in relatively old age. Emotional aliveness and intellectual stimulation are both worthwhile goals in themselves and, at the same time, valuable tools in the prevention of Alzheimer’s disease.