Sleep and Apathy

Does sleep fuel willpower?

Posted Aug 18, 2018

When you don’t get enough sleep you often feel lack of energy, or a lack of “get up and go” that is different from just feeling tired. I can feel tired and yet still feel motivated, focused, goal-driven and ambitious. But sometimes lack of sleep is associated with loss of these sorts of drives, these forward-oriented, energized and focused states. When I lose these motivational states there is also a conspicuous lack of self-initiated goal driven behaviors. I do not initiate things; I just let things happen. I am passive.

The sleep-deprived person in this kind of zombie state simply passively muddles through the day until sleep intervenes and restores passion and drive. The lack of feeling, passion and drive, accompanied by the loss of self-initiated behaviors, is the very definition of apathy. In the neurology clinic, apathy is often associated with brain dysfunction in specific, high-level cortical circuits concerned with self-regulation and “will.” These circuits include the mesolimbic dopaminergic system that innervates the frontal lobes and adjacent limbic cortex. Sleep deprivation is associated with impairment on neuropsychological tests that tap these circuits. It may be that these circuits are crucial in generating what we call willpower.

Apathy occurs when willpower is lost. Without willpower we are at the mercy of environmental cues. If there is a delicious-looking piece of pie available, I cannot summon the willpower to resist the urge to indulge. When the apathy is severe it can lead to more than just loss of willpower. It can also dramatically increase passivity. The severely apathetic individual appears to have lost a sense of agency or self; he appears indifferent to events around him. This severe form of apathy is common in neuropsychiatric disorders, with over 50 percent of patients with schizophrenia, Alzheimer's dementia, or depression being severely apathetic. Yet you can be without psychiatric or neurologic disease and still be apathetic—at least transiently. Even healthy people can get apathetic at times. Some studies suggest that up to one in five otherwise healthy people experience transient but severe apathy at least once in their lives.

But what does sleep have to do with apathy? As mentioned, loss of sleep can put you into a transiently apathetic state. I know of no studies that have looked at clinically significant apathy as a function of sleep deprivation. But a recent study of apathy in patients with REM Behavior Disorder (RBD) suggests some deep relationships between sleep and willpower that go beyond mere fatigue. In RBD, patients act out their dreams as the normal REM-related motor inhibition fails. Barber and colleagues at Oxford University studied severe apathy in patients with RBD and in patients with Parkinson’s Disease (PD). They found that 46 percent of RBD and 31 percent of PD patients were apathetic.  

That is a striking finding, given that RBD patients do not appear to have anywhere near as severe a disease as patients with PD. RBD patients can appear to be relatively normal. Their only major symptom is that they act out their dreams during the night. PD patients, on the other hand, are coping with a severe and debilitating motor illness that makes it difficult for them to move or perform actions. So why are RBD patients apparently more likely to be apathetic than PD patients? Depression alone could not explain the apathy in RBD patients in the study, as two-thirds of them had no depressive symptoms. Almost half of the RBD patients were on clonazepam, but clonazepam does not seem to cause apathy in other patients who take it (for example people with recurrent nightmares). In addition, Barber and colleagues factored in effects of the drug on apathy scores and yet almost half of the RBD patients still scored in the clinical range for severe apathy. Most of the PD patients were on dopaminergic medicine and that could have made them appear less apathetic. But again the authors controlled for effects of medicine, and the results remained unchanged. And in any case, the point here is that a very large percentage of RBD patients experienced clinically severe apathy, despite appearing otherwise healthy. So something about the sleep disorder itself seems to be generating the apathy.

We are left with an intriguing link between apathy, willpower and sleep—a link that at present has no explanation.

References

Barber T, Kinan M, Drew D, et al. Apathy in rapid eye movement sleep  behaviour  disorder  is  common  and under-recognized. Eur J Neurol 2018; 25: 469–476.