The caudate nuclei have been suggested to be a key region for sleep which may be accounted for by their role in reward/sensory processing and regulation of cortical excitability (Stoffers et al. 2014). Anatomically, caudate volume has been found to be associated with sleep duration. In older adult humans, larger caudate volume was related to both longer total sleep time and the shorter Stroop response times, i.e. enhanced executive functioning, induced by mild exercise (Won et al. 2019). In a PET study, the caudate showed significant increase in activity during REM and a notable decrease in activity from pre-sleep wakefulness to slow wave sleep (Braun, 1997). While the majority of neurons in the caudate have been found most active during REM and wakefulness, a small sector of caudate neurons demonstrated heightened activity during slow wave sleep, regulating the sleep-wakefulness cycle, along with involuntary movements (Oniani et al. 2009). These findings together suggest that sleep stages may be modulated by the caudate nucleus in some way.
Caudate disruption resulting in unsuccessful sleeping patterns has been repeatedly shown. EEG results after implementing destruction of the caudate via uni- and bilateral injections of kainic acid on rats induced a constant state of alertness and inability to sleep for two days (Vataev & Oganesyan, 2000). In humans, diminished caudate recruitment was found to be associated with sleep impairment and also with subjective report of hyper-arousal, a key element of insomnia. During an awake executive function task in fMRI, the caudate showed less activity in subjects with insomnia and control subjects assigned to experience slight sleep disruption (Stoffers et al. 2014). In addition, an association was found between increased subjective reports of hyper-arousal and the decreased caudate engagement in subjects with insomnia (Stoffers et al. 2014).
The caudate nuclei are also suggested to be involved in obstructive sleep apnea (OSA). Symptoms of depression and anxiety which can accompany OSA were found to show increased correlation to substandard resting-state functional connectivity (FC) of the caudate with other areas of the brain. The bilateral caudate showed smaller FC to the bilateral inferior frontal gyrus and right angular gyrus in OSA patients who were additionally more prone to episodes of anxiety and depression, compared to healthy controls (Song et al. 2018). These results suggest the possibility that deprived sleep due to OSA may be a result of disrupted caudate functionality. Indeed, caudate functional disconnectivity was induced by sleep deprivation in male subjects with healthy sleeping patterns who were subjected to 36 hours of total sleep deprivation, resulting in defective functional connectivity of the left caudate with the postcentral gyrus and inferior temporal gyrus of the cortex (Wang et al. 2021). On the other hand, it has been demonstrated that stimulation of the caudate can show sedative effects. Stimulation of the caudate on cats during calm wakefulness resulted in notable behavioral changes, including drowsiness, from low frequency stimulation, and even sleep, from extended moderate stimulation (Gogichadze et al. 2017).
Sleep has been found to influence executive function. Sleep continuity has been shown to be associated with better executive function across age groups (Wilckens et al. 2014). In adolescents, sleepiness but not sleep duration has been found to be associated with executive function (Anderson et al. 2009). However, while caudate recruitment was smaller in those with sleep disturbance in an executive function task, sleep disturbance did not significantly affect performance in executive function (Stoffers et al. 2014).
Previous literature strongly suggests the possible role of the caudate on sleep duration. To our best knowledge, however, the association between the caudate volume and sleep duration in other age ranges have not been studied. In this study, we aimed to examine the association between caudate volume and sleep length, as well as executive functioning across a wide age range in adult human MRI data. We employed a large data set (67 subjects, 10–85 years old) to assess the association.