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Every person’s circadian system involves biochemical processes in the body that recur periodically, approximately once every 24 hours. Our organism synchronises our internal processes with external stimuli. Our internal clock is located in the so-called suprachiasmatic nuclei (SCN) in the part of the hypothalamic brain, which responds to external lighting conditions. Depending on whether it is day or night, SCNs further modulate the excitation or inhibition of our body activities. At the same time, peripheral centres are located in almost all tissues, such as muscles or nerves. Peripheral clocks are controlled by the main internal clock but also provide feedback from the body, supporting the overall synchronisation of biological processes  .
Disruptions of daily activity and sleep, which also reflect general abnormalities in the functioning of the circadian system, are typical in various somatic and mental illnesses .
In mood disorders, especially in bipolar disorder, disruptions in the functioning of the circadian system are observed and are also reflected in sleep disturbance, its quality and continuity .
In addition to studies in patients with bipolar disorder examining abnormalities in hormonal production or body temperature   , sleep disturbances were found through actigraphic measurements (see more in the following article). Sleep disorders are observed in patients with bipolar disorder in both relapse and remission phases . Abnormalities in the circadian system are more pronounced in patients with bipolar disorder than in patients with depressive disorder  .
Research conducted in collaboration with Mindpax also confirms these findings. In patients with bipolar disorder, there are significant irregularities in the activity and sleep routine. Delayed onset and sleep phase is manifested in patients with bipolar disorder, and there are significant differences in sleep duration and daily rhythm fragmentation (intradaily variability) between days, compared to healthy controls .
Thanks to these findings, we can see a direct connection between mood abnormalities and individual episodes of bipolar disorder and abnormalities in daily activity and sleep routines .
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