The National Academies report links high-power microwaves to impacts on people through the Frey effect. The human head acts as a receiving antenna for microwaves in the low gigahertz frequency range. Pulses of microwaves in these frequencies can cause people to hear sounds, which is one of the symptoms reported by the affected U.S. personnel. Other symptoms Havana syndrome sufferers have reported include headaches, nausea, hearing loss, lightheadedness and cognitive issues.