Among studies that use microanatomical methods, there is no reported evidence that human beings have active sensory neurons like those in working vomeronasal systems of other animals. Furthermore, there is no evidence to date that suggests there are nerve and axon connections between any existing sensory receptor cells that may be in the adult human VNO and the brain. Likewise, there is no evidence for any accessory olfactory bulb in adult human beings, and the key genes involved in VNO function in other mammals have pseudogeneized in human beings. Therefore, while the presence of a structure in adult human beings is debated, a review of the scientific literature by Tristram Wyatt concluded, "most in the field... are skeptical about the likelihood of a functional VNO in adult human beings on current evidence."