My other major project, in collaboration with Dr. Jim Smith, analyzes the behavioral and neural effects of high strength magnetic fields. This project takes advantage of the unique resources of the National High Magnetic Field Laboratory at FSU.
This project is exciting because we have shown that rodents are possessed of a completely novel sensory ability to detect magnetic fields. Furthermore, our research is of great potential significance to public health and medical practice. Although the magnetic fields of typical clinical MRI machines are only 1-4 Tesla in strength, experimental MRI machines are reaching fields of 9 Tesla and higher. These high strength MRI machines have the advantage of being able to resolve anatomical structures nearly to the level of individual cells. While numerous studies have demonstrated that there is no long-term effect of MRI scans on most of the body, we think it is important to know that some patients may experience nausea and dizziness, and potentially long-term inner ear damage after high field exposure.
Although mammals are not thought to be receptive to static magnetic fields, we have found that magnetic fields of the strength used in experimental high resolution MRI machines (7 Tesla and above) have several dramatic effects on rats and mice:
When rats were exposed to the magnetic field, ingestion was affected in two ways. If thirsty rats were placed in the magnetic field prior to getting access to a sweet solution, their drinking behavior was suppressed (Houpt et al. in preparation). If the rats were given access to a sweet solution before being placed in the magnetic field, the rats learned a conditioned taste aversion: this suggests that experiencing the magnetic field was aversive and may have induced sickness in the rats (which they attributed to the sweet solution, as if the solution was poisonous.) (Houpt et al. submitted).
When rats were removed from the magnetic field and placed in a large open test chamber, they consistently walked in tight circles (as if chasing their tails). There was a specific effect of their orientation in the field on the direction they circled: if the rats were placed in the field facing the north pole of the magnet, they walked in clockwise circles; after facing the south pole of the magnet, they walked in counter-clockwise circles (Snyder et al. 2000, Houpt et al. submitted). This effect is not species specific: mice also circle in the same fashion after being in the magnets (Lockwood et al, submitted). This phenomenon is unexplained: because the rats act as if they have a vestibular problem (e.g., an inner ear infection), we hypothesize that the rats are feeling dizzy after magnetic field exposure.
The behavioral effects above suggest that the magnetic field is activating the vestibular system, affecting the rats’ sense of balance, and perhaps inducing motion sickness. By staining tissue sections of the brain for a protein synthesized whenever electrical activity is increased in a neuron, we have been able to visualize activity in the neurons of the brain. Using this technique, we have found physiological evidence for stimulation of vestibular regions of the rat brainstem (Snyder et al. 2000). Stress centers of the brain, and areas of the brain responsible for taste aversion learning, are also activated by the magnetic field. The strength of the brain activation is proportional to the strength of the magnetic field. This result is significant, because MRI machines are often used to monitor activity of the brain in neurological and psychological tests: if the magnetic field itself can cause brain activation, then a significant confound may be present in these studies.
This project has been funded by an R01 grant from the National Institute of Deafness and Other Communication Disorders, specifically because of the hypothesized effects of magnetic fields on the vestibular apparatus of the inner ear.
© 2014 T.A. Houpt. Last updated 2014-10-17.