Activation Changes in Zebra Finch (Taeniopygia guttata) Brain Areas Evoked by Alterations of the Earth Magnetic Field

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.

Magnetoreception and baroreception in birds

“…Ablation of the lagena, or lesion of the lagenal nerve prevents the activation of the same neurons (Wu & Dickman ). Similar results have been obtained from unrestrained zebra finch using Earth‐like strengths of magnetic field distortion (Keary & Bischof ). Although similar brain regions were activated in these zebra finch experiments, the magnitude of effect was less than that seen by Wu and Dickman ().…”

“…Although similar brain regions were activated in these zebra finch experiments, the magnitude of effect was less than that seen by Wu and Dickman (). This may reflect the overall lower levels of magnetic stimulation, or could be due to the choice of a non‐migratory experimental subject (Keary & Bischof ). Questions remain, however, over the presence of a lagena‐based magnetoreceptor; the iron content of the lagenal otoliths in pigeons has been measured using high sensitivity inductively coupled plasma mass spectrometry (ICP‐MS) and found to be no different from other vestibular otoliths (Zhao et al .…”

Sensing Magnetic Directions in Birds: Radical Pair Processes Involving Cryptochrome

“…Electrophysiological responses to changes in the direction of the magnetic field were also reported from the hippocampus of pigeons [ 92 ], a major center representing spatial information. In the brain of zebra finches, too, a directionally changing magnetic field caused some activation, which was most pronounced in the hippocampal subdivision [ 93 ]. In behavioral tests, however, birds whose hippocampus was lesioned were able to orient with their magnetic compass [ 92 ].…”

Hippocampal neurogenesis and volume in migrating and wintering semipalmated sandpipers (Calidris pusilla)

“…Indeed, their activation seems to be directly related with memory storage and to an increase in the neuronal activity in response to changes in the magnetic field [30–36]. …”