Low‐intensity magnetic fields alter operant behavior in rats

Abstract

The present study demonstrates that operant behavior is affected by a combination of a 60-Hz magnetic field and a magnetostatic field 2.6 X 10(-5) T (about half the geomagnetic field). Rats exposed to this combination for 30 min consistently exhibited changes in the rate and pattern of responding during the differential reinforcement of low rate (DRL) component of a multiple fixed ratio (FR) DRL reinforcement schedule. By contrast, there were no measurable changes following exposure to the static field alone or to the oscillating field alone, even with a 10-fold increase in intensity (5 X 10(-5) to 5 X 10(-4) Trms). A cyclotron resonance mechanism has been suggested as a possible explanation for the observation that weak static magnetic fields modify the response of in vitro brain tissue to low-frequency magnetic fields. The choice of static field intensity Bo and frequency nu in the present study follows from the cyclotron resonance condition nu = (1/2 pi)(q/m)Bo, for singly charged lithium, an element in extensive use in the clinical treatment of affective disorders in humans. The present research is consistent with a cellular cyclotron resonance mechanism and tends to imply a functional dependence of behavior on the geomagnetic field.

Exposure to combined static and 60 Hz magnetic fields: Failure to replicate a reported behavioral effect

“…Different observers did not detect any sensory effects when a hand was placed at the locus of the rat restraint device and the field was switched on and off, nor was vibration of the coils themselves detected. More rigorous measurements would have been made had the behavioral results confirmed the observations of Thomas et al [1986a].…”

“…Table 1 summarizes the exposure conditions for both experiments and compares them to the Thomas et al [1986a] background found in the Bethesda laboratory and to their combined field condition, which altered the operant behavior. Measured magnetic field flux densities are expressed in Telsa (T) or for ease in reading and for relating effects to the nominal geomagnetic field of 0.5 Gauss ( G ) , we frequently specify flux density in units of Gauss, where 1 G = 1 x T. The static field of our laboratory differed from that of Thomas et al The total local field was 4.46 x 1 0-5 T, with the measured vertical and horizontal components being 4.42 x T and 1.49 x T, respectively.…”

“…Such a programmatic approach would assist in formulating testable hypotheses about mechanisms and would ultimately lead to the information urgently sought by those concerned about potential risks from exposure to electric and magnetic fields. This research was designed explicitly to test the hypothesis that the conditions reported to be effective by Thomas et al [1986a] altered the behavior as described. Because an effect had not been expected and a mechanism was not known, we also evaluated the more general hypothesis that such lowlevel fields could produce any effect on the behaviors being studied.…”

“…Changes in responding were not observed when the rats were exposed to either the static field or the 60 Hz field independently nor during sham exposures to the fields. In the present experiments, only the combined fields, i.e., those reported to be effective, were studied in rats using the same general behavioral and exposure protocol used by Thomas et al [1986a]. In experiment 1, the 2.61 x Telsa was achieved by reducing the vertical component of the static field.…”

Seasonal Patterns of Melatonin, Cortisol, and Progesterone Secretion in Female Lambs Raised Beneath a 500-kV Transmission Line

“…"A 17-G 60-Hz magnetic field significantly increased locomotion activity in mice (Smith and Justesen, 1976). Laboratory rats exposed simultaneously to a 0.5-G 60-Hz magnetic field and to a 0.26-G d-c magnetic field responded differently in a behavioral test compared to a sham group (Thomas et al, 1986).…”