All biological organisms live through two kinds of time—internal and external. Cycles of day and night are cues of external time that flows regardless of an organism. On the other hand, cycles of waking and sleeping are manifestations of internal time. The relation of the two is not so simple.
We have free will (or underlying decision processes that create such illusion) that can delay the time to go to bed to some degree. The phases of sleep and wake are also strongly modulated by the season: we get up earlier during the summer than we do in winter by the changes of our internal, unconscious, clock known as the circadian clock. However, internal time does not run completely independently of external time, and this is where things get interesting. It is a prime question in neuroscience how an organism adapts to its surroundings. But perhaps a more interesting question is how an organism resists from adaptation. It turns out that a multi-cellular organism such as a mammal maintains diverse ‘internal time’ in many different organs and tissues (Myung et al, Nature Communications, 2018)—and in many cells, and they do not adapt uniformly to changes of external time (Myung et al, PNAS, 2015; Azzi et al, Neuron, 2017). The really exciting question is then how organization, or orchestration of these adaptations and maladaptations occur. And this is what I mostly focus on to answer.
Biological time is a bridge towards understanding of psychological time. The perception of time over a circadian cycle changes through internal regulation of mood. Mood is an ambient state of consciousness and, in my opinion, a sense of time flow. Circadian rhythms have been thought to be related to mood and time perception, but the exact connection has been indicated only in animal studies. Disruption of circadian rhythms, for example by jet lag, can lead to mood dysregulation. Forced sleep deprivation during the latter half of the sleep phase can acutely, yet temporarily, restore positive mood states in major depression disorder patients. Waking up a patient too early in the morning emulahetes the phase-advancing (eastbound flight) jet lag condition. Although systematic studies are absent, westbound intercontinental flights are episodically told to briefly cause depression-like mood states and eastbound flights cause mania-like states. These observations have not been taken seriously, while the connection between the mood and circadian rhythms has been suspected for a long time. I plan to measure signatures of brain-wide activities after an artificial jet lag is induced, by changing light-dark cycles. Initial measurements will be made from known and isolated regions but will expand to more areas to create a picture for global clock dynamics.
In this later phase, I will attempt to make connection between the circadian system and mood and motivation circuits. The experimental paradigm of using jet lag for studying mood is new and is likely to serve as a model of mood dysregulation. If it can be established that jet lag causes a transient state of mania or depression, an enormous clinical potential can be unlocked.
I have physics background (BS, Korea University and MS, POSTECH), and studied physiology and biophysics (MS, University of Washington) and life sciences (PhD, Kyoto University). After working as an assistant professor at Hiroshima University School of Medicine, I moved to RIKEN Brain Science Institute and finished up multi-clock studies. I came to join the faculty of Graduate Institute of Mind, Brain, and Consciousness (GIMBC) at Taipei Medical University as an associate professor after residence at Institute for Advanced Study in Berlin and Berliner Antike-Kolleg as a fellow. I also maintain affiliations at Okinawa Institute of Science and Technology Graduate University (OIST) and at Shuang Ho Hospital.
