Weak 50-Hz electromagnetic fields activate rat open field behavior.

Rats were tested in an open field after previous exposure to a weak, 50-Hz electromagnetic field of the same order of magnitude as the earth's magnetic field. Animals exposed to the artificial field at the beginning of the light phase showed 40% more rearing activity than controls, together with a slight increase in ambulation and a tendency towards less defecation and a shortened rearing latency. A replication experiment yielded the same results. Animals exposed at the beginning of the dark phase manifested no significant changes in open field activity. The results show that weak electromagnetic stimuli can modify some behavioral responses, and that these responses are sensitive to circadian phase.