The association was independent of factors known to impact dream content and cognitive impairment in these patients, its researchers noted.
The study, “Do dreams tell the future? Dream content as a predictor of cognitive deterioration in Parkinson’s disease,” was published in the Journal of Sleep Research.
The dreams of Parkinson’s patients include more aggressive content, being overall more vivid and nightmarish, than those of elderly people without the condition. Researchers at Hospital de Egas Moniz, in Portugal, have reported that this kind of vivid dreaming is significantly associated with greater cognitive impairment in patients.
However, this association has only been assessed in patients at a single point in time, and it is currently unknown whether the content of dreams can predict cognitive decline in the long run.
To find out, the same team of researchers studied a group of 98 Parkinson’s patients without dementia who visited their outpatient clinic between March 2014 and March 2015. Participants were asked to keep a dream diary for two weeks and were assessed for motor and non-motor symptoms, such as anxiety, depression, psychosis, and sleep problems.
Cognitive impairment was assessed at baseline and four years later, through the Montreal Cognitive Assessment (MoCA) test. Higher scores indicate better cognitive function.
Only 58 patients could be assessed after four years, either due to death, loss to follow-up, or because they were later given a different diagnosis other than Parkinson’s.
Participants in this study were 68 years old on average, a near equal mix of men and women, and had had the disease for a mean of 7.5 years at the time of the analysis. For most patients, symptoms were mild on both sides, and did not yet affect balance. Over the four-year period, MoCA scores significantly decreased from 22.4 to 19.3.
Regarding dreams, 23 of the final 58 patients reported at least one dream over the two weeks, but there were no differences in symptom scores between those who reported having dreams during the two-week period and those who did not. Seven dreams was the reported average during that period, ranging from one to 27 dreams.
Dreams were classified according to their content, with categories including animals, friends, deaths, aggressions, friendliness, physical activity, misfortunes, failures, and negative emotions, among others. The most commonly reported by these patients were physical activities, followed by negative emotions and failure.
A statistical analysis identified negative emotions in dreams, dreams with animals, gender, psychosis, and cognitive function at baseline as potential factors that predicted changes in MoCA scores.
However, after taking into account other factors known to influence dreams and cognitive status, only negative emotions in dreams and initial MoCA scores were significantly associated with MoCA scores after four years. The presence of negative emotions showed the strongest association, the investigators noted.
Overall, the findings show “a significant, positive and independent association between negative emotions in dreams and a reduction in MoCA scores after 4 years, meaning that patients showing more negative emotions per dream at baseline experienced a more significant decline in MoCA at follow‐up,” they wrote.
The results show that the content of dreams not only associates with cognitive impairment at a given point in time, it may function as a predictor of cognitive decline over time, independent of other factors.
“However, given the small number of patients included, our present results should be considered preliminary, and would need confirmation from further reports, involving larger cohorts and a wider set of neuropsychological instruments,” the researchers concluded.
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