that it is not the secretion of pheromones which act to suppress reproductive function but rather the queen's extremely high levels of circulating testosterone, which cause her to exert intense dominance and aggressiveness on the colony and thus "scare" the other mole-rats into submission. Research has shown that removal of the queen from the colony allows the reestablishment of reproductive function in sub-dominant individuals. To see if a priming pheromone secreted by the queen was indeed causing reproductive suppression, researchers removed the queen from the colony but did not remove her bedding. They reasoned that if a primer pheromones were on the bedding then the sub-dominant's reproductive function should continue to be suppressed. Instead however, they found that the sub-dominants quickly regained reproductive function even in the presence of the queen's bedding and thus it was concluded that primer pheromones do not seem to play a role in suppressing reproductive function. Glucocorticoids, signaling molecules which stimulate the fight or flight response, may be implicated in dominance hierarchies. Higher ranking individuals tend to have much higher levels of circulating glucocorticoids than subdominant individuals, the opposite of what had been expected. Two core hypotheses attempt to explain this. The first suggests that higher ranking individuals exert more energy and thus need higher levels of glucocorticoids to mobilize glycogen for energy use. This is supported by the fact that when food availability is low, cortisol levels increase within the dominant male. The second suggests that elevated stress hormones are a result of social factors, particularly when the hierarchy is in transition, perhaps resulting in increased aggression and confrontation. As a result, the dominant individual fights more and has elevated glucocorticoids during this period. Field studies of olive baboons in Kenya seem to support this, as dominant individuals had lower cortisol levels in a stable hierarchy than did subdominant individuals, but the reverse was true at unstable times. Brain pathways and hierarchy Several areas of the brain contribute to hierarchical behavior in animals. One of the areas that has been linked with this behavior is the prefrontal cortex, a region involved with decision making and social behavior. High social rank in a hierarchical group of mice has been associated with increased excitability in the medial prefrontal cortex of pyramidal neurons, the primary excitatory cell type of the brain. High ranking macaques have a larger rostral prefrontal cortex in large social groups. Neuroimaging studies with