Abstract
Many animals are able to perceive the earth magnetic field and to use it for orientation and navigation within the environment. The mechanisms underlying the perception and processing of magnetic field information within the brain have been thoroughly studied, especially in birds, but are still obscure. Three hypotheses are currently discussed, dealing with ferromagnetic particles in the beak of birds, with the same sort of particles within the lagena organs, or describing magnetically influenced radical-pair processes within retinal photopigments. Each hypothesis is related to a well-known sensory organ and claims parallel processing of magnetic field information with somatosensory, vestibular and visual input, respectively. Changes in activation within nuclei of the respective sensory systems have been shown previously. Most of these previous experiments employed intensity enhanced magnetic stimuli or lesions. We here exposed unrestrained zebra finches to either a stationary or a rotating magnetic field of the local intensity and inclination. C-Fos was used as an activity marker to examine whether the two treatments led to differences in fourteen brain areas including nuclei of the somatosensory, vestibular and visual system. An ANOVA revealed an overall effect of treatment, indicating that the magnetic field change was perceived by the birds. While the differences were too small to be significant in most areas, a significant enhancement of activation by the rotating stimulus was found in a hippocampal subdivision. Part of the hyperpallium showed a strong, nearly significant, increase. Our results are compatible with previous studies demonstrating an involvement of at least three different sensory systems in earth magnetic field perception and suggest that these systems, probably less elaborated, may also be found in nonmigrating birds.
Highlights
Wiltschko and Merkel [1] were the first to publish experiments demonstrating the use of the earth magnetic field for spatial orientation
It was found that earth magnetic field information is used either for compass orientation or for the construction of a navigational map
While there is no doubt that earth magnetic field information can be detected by animals and is used for orientation in space, the question of how this information is perceived and processed by the central nervous system is not answered as yet
Summary
Wiltschko and Merkel [1] were the first to publish experiments demonstrating the use of the earth magnetic field for spatial orientation. Heyers et al [38] provide information about brain areas involved in the processing of the magnetic field information received by the beak SPM particle system According to their results, the activation within and near the principal (PrV) and spinal tract (SpV) nuclei of the trigeminal brainstem complex, which are known to receive primary input from the trigeminal nerve, was enhanced after magnetic stimulation. We decided to conduct an experiment using natural magnetic stimuli and the zebra finch as experimental subject This nonmigrating songbird has previously been shown to be able to use magnetic field information for orientation in space [40], and has provided evidence for the participation of the photoreceptor based radical pair process as transducer [24]. We found out that the applied magnetic conditions were sufficient to induce activity changes in several brain regions of the zebra finch
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