Final answer:
The suprachiasmatic nucleus (SCN) of the hypothalamus is the brain's 'time clock' that regulates circadian rhythms by receiving light information from the eyes and influencing sleep-wake cycles.
Step-by-step explanation:
The specific collection of neurons in the brain functioning as the 'time clock' for circadian rhythms is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. This structure receives input from photosensitive retinal ganglion cells (RGCs) which relay light information and allow the internal clock to adjust to the external environment. The SCN regulates the release of melatonin from the pineal gland, influencing sleep-wake cycles and other physiological processes that follow a daily pattern. Moreover, circadian rhythms are found in nearly all eukaryotic organisms and involve the internal perception of the daily cycle of light and dark, which is crucial for establishing consistent physiological events each day.