Transcription-Translation Feedback Loop (TTFL)

Transcription-translation feedback loop (TTFL) is the fundamental molecular mechanism that generates circadian rhythms within an organism’s cells. It consists of a “positive limb” (activator proteins like CLOCK and BMAL1) that triggers the production of “negative limb” proteins (PER and CRY). Once these negative proteins accumulate to a threshold, they inhibit their own production by returning to the cell nucleus, creating a self-sustaining cycle of approximately 24 hours. In the bipolar brain, the TTFL is often unstable. The “Off” phase might be delayed, or the proteins might degrade too quickly, causing the “clock” to run at the wrong speed. This makes the brain hypersensitive to external disruptions (like blue light or irregular mealtimes), which can lead to the “desynchrony” that triggers manic or depressive episodes.