Research conducted by Irwin, Bjurstrom and Olmstead (2016) aimed to study the relationship between sleep and cocaine and alcohol use.⁸ In this study, the participants were individuals who has previously been dependent on these substances but were now in the early stages of abstinence.⁸ Polysomnographic sleep measures were recorded to determine sleep continuity, Stage 3 sleep and rapid eye movement (REM) sleep.⁸ In this study, sleep continuity included the total sleep time, sleep latency, which is the time required to transition from full wakefulness to sleep, sleep efficiency and wake sleep onset.⁸ Moreover, Stage 3 sleep was characterized by slow wave sleep (SWS), which consists of very slow delta waves in combination with smaller, faster waves in the brain.⁸ These measurements were then compared to the controls, which were patients that had no medical history of any mental illnesses or disorders.⁸ Although the results of the study indicated sleep continuity is not impacted by drug or alcohol use, the study did show that there was a decrease in Stage 3 sleep among both alcohol and cocaine-dependent patients.⁸ The results also indicate that loss of Stage 3 sleep occurs at an earlier age among the cocaine-dependent patients, in comparison to the alcohol-dependent patients.⁸ In addition, the amount of REM sleep increased among both groups of participants in comparison to the controls.⁸ Therefore, this study demonstrates that alcohol and cocaine have an impact on sleep disturbances.

Patients with schizophrenia often experience difficulty sleeping due to the fact that disturbances in sleep are characteristic of the first phase of a psychotic episode, known as the prodormal phase.⁹ More specifically, these patients either cannot fall asleep or cannot maintain sleep, waking up in at night or early in the morning.⁹ In addition, the severity of the illness is negatively correlated to the amount of rapid eye movement (REM) sleep patients with schizophrenia get.⁹ Therefore, depending on the severity of the disease, 30-80% of patients with schizophrenia suffer from sleep deprivation.⁹

Figure 1 - Neurons in the basal ganglia of the brain.

Figure 2 - Pre-thalamic fibres in the brain stem.

Parkinson’s Disease (PD) is the second most common neurodegenerative disease in the world.¹⁰ The pathology of PD affects all parts of the brain and recently, it has been noted that this neurodegenerative disease results in changes in sleep.¹⁰ Research conducted by Christensen et al. (2016) has demonstrated that REM sleep is less stable in patients with PD. ¹⁰ Since sleep is regulated by mechanisms that include neurons located in the basal brain regions, this research suggests that PD affects these mechanisms and, thus, leads to disturbances in sleep.¹⁰ Furthermore, the lower stability of REM sleep in patients with PD can also be attributed to the neurodegenerative nature of this disease.¹⁰ More specially, neurodegeneration affects the pre-thalamic fibres in the brain stem, which in turn may impact the neuronal mechanisms of REM sleep.¹⁰