Out of the 20 channels in the channel and collateral system, only 5 enter the brain, with unclear circulation pathway in the brain. Electrophysiologic and imaging studies indicate that the signal induced by acupuncture at acupoints can enter the brain no matter whether the channel connecting the acupoint enters the brain. Therefore, the authors put forward the hypothesis of "all the 12 channels enter the brain", i.e., the hypothesis of "channels and collaterals in brain". In the theory system of channels, less channels enter the brain with unclear circulation pathway. This possibly is related with that sensation is main way for descovery of channels. In future, we should adopt modern scientific and technical ways and strengthen the study on circulation of channels in the brain, so as to perfect the channel theory.