December 03, 2004

Writing style and dementia

Bill Poser cites a study of Iris Murdoch's last novel which "raises the possibility that changes in a person's vocabulary could be used to diagnose Alzheimer's disease while it is still in its early stages". In this case, the text analyzed was written a year or two before the disease was diagnosed, and four or five years before the author died. Some studies published over the past decade suggest an even more intriguing connection between writing style and Alzheimer's. It's claimed that a simple index of stylistic complexity, measured in short texts written at about age 20, is correlated with low cognitive test scores and neuropathologically-confirmed Alzheimer's disease, 50 to 70 years later.

It's not clear how to assign cause and effect here: maybe a condition that predisposes people to Alzheimer's also affects writing; or maybe certain life-long habits of writing actually tend to ward off the disease. As we'll see, there's an intriguing connection to popular stylistic nostrums. Geoff Pullum will be happy to learn that Strunk and White's stylistic advice may actually rot the brain. Well, at least it's correlated with neurodegenerative pathology, and might even cause it.

In 1986, David Snowdon started a broad epidemiological study among 678 nuns from the School Sisters of Notre Dame. The study looked at many influencing factors and many measures of health, as well as age and cause of death. Along the way, he discovered that some of the nuns, as young women, had written short texts on a consistent topic and in a consistent context:

In September 1930, the leader of the School Sisters of Notre Dame religious congregation in North America requested that each sister write a short sketch of her life and include parentage, interesting and edifying childhood events, schools attended, and influences that led her to the convent.

These biographical sketches were preserved in the order's files, and Snowdon was given access to them. Some of the early results are described in this 1996 abstract:

OBJECTIVE--To determine if linguistic ability in early life is associated with cognitive function and Alzheimer's disease in late life. DESIGN--Two measures of linguistic ability in early life, idea density and grammatical complexity, were derived from autobiographies written at a mean age of 22 years. Approximately 58 years later, the women who wrote these autobiographies participated in an assessment of cognitive function, and those who subsequently died were evaluated neuropathologically. SETTING--Convents in the United States participating in the Nun Study; primarily convents in the Milwaukee, Wis, area. PARTICIPANTS--Cognitive function was investigated in 93 participants who were aged 75 to 95 years at the time of their assessments, and Alzheimer's disease was investigated in the 14 participants who died at 79 to 96 years of age. MAIN OUTCOME MEASURES--Seven neuropsychological tests and neuropathologically confirmed Alzheimer's disease. RESULTS--Low idea density and low grammatical complexity in autobiographies written in early life were associated with low cognitive test scores in late life. Low idea density in early life had stronger and more consistent associations with poor cognitive function than did low grammatical complexity. Among the 14 sisters who died, neuropathologically confirmed Alzheimer's disease was present in all of those with low idea density in early life and in none of those with high idea density. CONCLUSIONS--Low linguistic ability in early life was a strong predictor of poor cognitive function and Alzheimer's disease in late life.

[D. A. Snowdon, S. J. Kemper, J. A. Mortimer, L. H. Greiner, D. R. Wekstein and W. R. Markesbery. Linguistic ability in early life and cognitive function and Alzheimer's disease in late life. JAMA Vol. 275 No. 7, February 21, 1996.]

The measure of "idea density" is footnoted to a 1973 paper influenced by early transformational grammar: Kintsch, W. & J. Keenan. Reading rate and retention as a function of the number of propositions in the base structure of sentences. Cognit. Psychol. 5: 257-274 (1973). It's defined in Snowdon et al. 2000 as follows:

Idea density was defined as the average number of ideas expressed per ten words for the last ten sentences of each autobiography. Ideas corresponded to elementary propositions, typically a verb, adjective, adverb, or prepositional phrase. Complex propositions that stated or inferred causal, temporal, or other relationships between ideas also were counted. Without the linguistic coder's knowledge of the age or cognitive function of each sister during late life, each autobiography was scored for idea density. The following sentence from an autobiography illustrates the method used to compute idea density: "I was born in Eau Claire, Wis., on May 24, 1913 and was baptized in St. James Church." The ideas (propositions) expressed in this sentence were (1) I was born, (2) born in Eau Claire, Wis., (3) born on May 24, 1913, (4) I was baptized, (5) was baptized in church, (6) was baptized in St. James Church, and (7) I was born...and was baptized. There were 18 words or utterances in that sentence. The idea density for that sentence was 3.9 (i.e., 7 ideas divided by 18 words and multiplied by 10, resulting in 3.9 ideas per 10 words).

Note that 3.9 is a very low measure of "idea density", in the context of the study. According to the study's summary table, the mean "idea density" in early life autobiographies for nuns whose autopsied brains "met neuropathologic criteria for Alzheimer's disease" was 4.9 (95% confidence interval 4.6-5.3), while for nuns whose brains were free of Alzheimer's symptoms, the mean "idea density" was 6.1 (95% confidence interval 5.6-6.6).

No further details are given, but my guess is that under this definition, "idea density" will depend strongly on "density of adjectives and other modifiers". Here "idea" means something like "elementary predication", in a certain way of thinking about the meaning of sentences, so every time you add a modifier, you add an "idea". It's going to go something like this:

Buck Mulligan came from the stairhead.
[6 words; 2 "ideas" (B.M. came; B.M. came from the stairhead); "idea density" = 10*2/6 = 3.3]

Plump Buck Mulligan came from the stairhead.
[7 words; 3 "ideas" (as before, plus B.M. is plump); "idea density" = 10*3/7 = 4.3]

Stately, plump Buck Mulligan came from the stairhead.
[8 words; 4 "ideas" (as before, plus B.M. is stately); "idea density" = 10*4/8 = 5]

There are several other obvious ways to increase "idea density", most of them deprecated by Strunk and White. For example, connecting two simple sentences with and adds one word and one "idea", as the metric is defined, and brings the text asymptotically closer to the maximum "idea density" of 10, just as adding an adjective does.

The 2000 Snowdon et al. paper surveys stylistic predictors of neuropathology for a larger number of patients:

Findings from the Nun Study indicate that low linguistic ability in early life has a strong association with dementia and premature death in late life. In the present study, we investigated the relationship of linguistic ability in early life to the neuropathology of Alzheimer's disease and cerebrovascular disease. The analyses were done on a subset of 74 participants in the Nun Study for whom we had handwritten autobiographies completed some time between the ages of 19 and 37 (mean = 23 years). An average of 62 years after writing the autobiographies, when the participants were 78 to 97 years old, they died and their brains were removed for our neuropathologic studies. Linguistic ability in early life was measured by the idea (proposition) density of the autobiographies, i.e., a standard measure of the content of ideas in text samples. Idea density scores from early life had strong inverse correlations with the severity of Alzheimer's disease pathology in the neocortex: Correlations between idea density scores and neurofibrillary tangle counts were -0.59 for the frontal lobe, -0.48 for the temporal lobe, and -0.49 for the parietal lobe (all p values < 0.0001). Idea density scores were unrelated to the severity of atherosclerosis of the major arteries at the base of the brain and to the presence of lacunar and large brain infarcts. Low linguistic ability in early life may reflect suboptimal neurological and cognitive development, which might increase susceptibility to the development of Alzheimer's disease pathology in late life.

Snowdon DA, Greiner LH, Markesbery WR. "Linguistic ability in early life and the neuropathology of Alzheimer's disease and cerebrovascular disease." Ann N Y Acad Sci. 2000 Apr;903:34-8.

There have been some other interesting outcomes from the study of these old biographical sketches:

Handwritten autobiographies from 180 Catholic nuns, composed when participants were a mean age of 22 years, were scored for emotional content and related to survival during ages 75 to 95. A strong inverse association was found between positive emotional content in these writings and risk of mortality in late life (p < .001). As the quartile ranking of positive emotion in early life increased, there was a stepwise decrease in risk of mortality resulting in a 2.5-fold difference between the lowest and highest quartiles. Positive emotional content in early-life autobiographies was strongly associated with longevity 6 decades later. Underlying mechanisms of balanced emotional states are discussed.

Danner DD, Snowdon DA, Friesen WV "Positive emotions in early life and longevity: findings from the nun study." J Pers Soc Psychol. 2001 May;80(5):804-13.

So my advice is: "use adjectives, be happy, avoid dementia."

This may not be a joke. As I said in the beginning, the causal relations are not clear here. There are some pieces of research that point to underlying physiological differences that might contribute to cognitive deficits long before there is any overt neurodegeneration. But there is also research suggesting that "exercise" may affect neurodegenerative disorders, and some of this literature cites Snowdon et al. as evidence:

...exercise can extend somewhat the survival of transgenic mice that express SOD1 enzyme mutations that are also found in some cases of human familial ALS (Kirkinezos et al. 2003). In Parkinson's Disease, there is evidence that physical activity may be beneficial, and that lack of activity may be detrimental (Tillerson et al. 2002), and cognitive activity is thought to reduce the risk of Alzheimer's disease (Snowdon et al. 2000).

Carrasco, Rich, Wang, Cope and Pinter. Activity-Driven Synaptic and Axonal Degeneration in Canine Motor Neuron Disease. J Neurophysiol 92: 1175-1181, 2004.

Posted by Mark Liberman at December 3, 2004 08:30 AM