In many previous articles we mentioned the crucial impact of light (especially bright light – blue and, sometimes green) on our circadian rhythm. Have you ever wondered how blind people adjust to 24 hour, daily rhythms without the most important stimulus, the endogenous sleep-activity rhythms. Of course this does not apply to blindness as a whole, a broad group of blind people react subliminally to bright light, but up to 50% of blind people do not react to any kind of light stimulus, thus they suffer from circadian rhythm disorder – predominantly the so-called “free-running type.”
What Does “Free-Running” Refer to?
Normally, in spite of the fact that our endogenous circadian rhythm is slightly longer than 24 hours, because of our social life, physical activities and a sufficient amount of light, we can easily adjust to “normal” conditions. People who are blind however, stick to their almost 25 hour circadian rhythm. Sometimes their endogenous rhythm is even longer. Insensitivity to bright light makes it impossible for them to adjust to a “normal” rhythm, promoting extension of their circadian rhythm. Their sleep and activity timings are different and, most of the time, not adjusted to a 24 hour day. Their circadian rhythm being longer than 25 hours, procrastinates bedtime. If you wake up at the same time as a “free-runner,” you will go to bed a little earlier in the evening than them. The next day they will wake up later and consequently go to bed even later.
Does the “Free-Running Type” Only Refer To Blind People?
Of course the great majority of people suffering from circadian rhythm disorder, “free-running type” are blind, but this sleep disorder is also present among people with no vision impairment. The pathological mechanism of this disorder in blind people seems to be clear. In contrast however, the mechanism of “free-running type” in people with no vision disturbances remains a mystery. There are several theories such as possible reduction of bright light exposure, retina insensitivity or changes in physical and social activities, all possible factors contributing to this disorder.
A longer endogenous circadian rhythm, which does not react to known therapies, is also considered a possible cause.
Sometimes “free-running type” can be iatrogenic. Patients suffering from DSPT (delayed sleep phase syndrome), when treated with chronotherapy, aggravate their disorder and evolve into “free-running type.”
What Are the Symptoms of “Free-Running Type”?
Patients suffering from “free-running type” will complain of alternating insomnia and sleepiness. However, “free-runners” do not feel sleepy all the time. There are periods when their disease is completely asymptomatic. Symptoms will depend on the timing of their bedtime. Starting from an asymptomatic phase, when a patient’s sleep time is adjusted to environmental conditions, patients will tend to have problems falling asleep (as their endogenous rhythm is longer and they will not feel sleepy at the same time as they felt sleepy the previous day). As time passes, patients will develop problems with staying awake during the day, and constant sleepiness, which will last until a patient’s rhythm is synchronized with environmental conditions once again.
Free-running type is sometimes confused with DSPT, especially when bedtime is gradually delayed for a few days. With the exception of blind people, among whom the incidence of “free-running type” is highest, this sleep disorder can also be present in patients of rest-homes or psychiatric hospitals, as they often lose their sensitivity to outside social stimuli.
How to Treat “Free-Runners”?
The question therefore arises: how to treat people with sleep disorders, who are insensitive to one of the most effective methods of treatment?
Surprisingly, the most effective method for treating “free-runners” is behavioral therapy. Education about sleep hygiene, together with structured exposure to social and physical activity, seems to work better than pharmacological methods such as taking exogenous melatonin at suitable