In the brain, brightness contrast exerts effects on both neuronal firing rates and neuronal synchrony. The neurobiological mechanisms of gamma synchrony induction are thus highly plastic. Researchers are divided on whether menstrual synchrony would be adaptive. This keeps migratory populations in synchrony, which increases metapopulation persistence. Strassmann argued menstrual synchrony defined as menstruation overlap should be quite common. Arden and Dye investigated women's awareness and perception of menstrual synchrony. Emotional contagion is important to personal relationships because it fosters emotional synchrony between individuals. Larvae are known to wiggle vigorously at periodic intervals in synchrony. They found no menstrual synchrony in either study. In E.I, attunement is an unconscious synchrony that guides empathy. She concluded that there was no evidence of menstrual synchrony. Bringing the replications into synchrony requires making their internal stored states the same. However, there is currently significant dispute as to whether menstrual synchrony exists. Many parallel programs require that their subtasks act in synchrony. A 2013 review concluded that menstrual synchrony likely does not exist.