Delirium – a serious disturbance in mental abilities that results in confused thinking and reduced awareness of the environment – is a costly and common condition. Though delirium can affect anyone, it is most prevalent in the elderly, affecting up to 50% of hospitalized seniors. However, it is not yet known why some individuals develop delirium but others do not.
Delirium is a common post-operative complication for seniors.
But researchers from Harvard Medical School and Brown University Warren Alpert Medical School have a new hypothesis: according to a special article published in Journal of the American Geriatrics Society, delirium might be a consequence of two types of brain dysfunction: weakened communication between different regions of the brain (brain connectivity) and reduced ability of the brain to reorganize itself (brain plasticity). The study suggests that when individuals with either of these forms of brain dysfunction are confronted with a major stressor, like surgery or acute illness, they will be more likely to develop delirium.
Most people return to their normal levels of cognitive functioning after delirium resolves. Unfortunately, some people experience continued cognitive problems after delirium. For instance, patients with dementia tend to deteriorate at a faster pace if they develop delirium and they continue to decline more rapidly for years after the episode. Similarly, delirium in cognitively healthy adults without dementia is associated with cognitive decline continuing at least three years after the delirium episode. The authors of this report hypothesize that individuals who have only one of the types of brain dysfunction (impaired connectivity or impaired plasticity) are able to compensate such that normal cognitive function is restored after the delirium episode ends. In contrast, people that have both types of brain dysfunction are the ones who have persistent cognitive complications – like faster cognitive decline – following delirium. This is because these people cannot compensate for the stress of the delirium, so their brain networks remain in a weakened state even after delirium symptoms go away. Consistent with this model, previous studies have shown that patients with dementia have both impaired connectivity and plasticity, which may explain why patients with dementia who develop delirium have more rapid cognitive decline.
Excerpt from an EEG reading.
A particularly promising methodology that could be used to test this model combines two neuroimaging techniques, Transcranial Magnetic Stimulation and electroencephalograpy, known as TMS-EEG. TMS-EEG enables researchers to directly measure how the brain responds to stimulation of a particular brain region. Therefore, researchers could use TMS-EEG to test the degree of dysfunction in plasticity and connectivity in people with and without delirium.
This work could have important implications for brain-based interventions to reduce risk of delirium. For instance, patients scheduled for major elective surgery who are found to have some level of brain dysfunction could receive behavioral, pharmacologic or neurostimulatory interventions to improve brain function prior to surgery. Furthermore, patients who develop delirium could receive interventions to restore normal brain function in order to facilitate recovery and reduce the risk of long-term cognitive decline following delirium.
Delirium affects approximately 12 million older adults who are hospitalized each year and associated health care costs exceed $150 billion nationally. Steps to prevent delirium and to reduce the negative impacts in the aftermath of delirium are critical to ensure the well-being of older adults and reduce the burden of this serious condition.
Author note: This post was contributed by Annie Racine, PhD, MPA, a post-doctoral fellow at the Institute for Aging Research/Hebrew SeniorLife and Harvard Medical School. Please contact us if you are interested in contributing to this blog.