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

Keary N, Bischof H-J. Activation Changes in Zebra Finch (Taeniopygia guttata) Brain Areas Evoked by Alterations of the Earth Magnetic Field. PLoS ONE. 2012;7(6): e38697.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

Oscillating magnetic field disrupts magnetic orientation in Zebra finches, Taeniopygia guttata

Background Zebra finches can be trained to use the geomagnetic field as a directional cue for short distance orientation. The physical mechanisms underlying the primary processes of magnetoreception are, however, largely unknown. Two hypotheses of how birds perceive magnetic information are mainly discussed, one dealing with modulation of radical pair processes in retinal structures, the other assuming that iron deposits in the upper beak of the birds are involved. Oscillating magnetic fields in the MHz range disturb radical pair mechanisms but do not affect magnetic particles. Thus, application of such oscillating fields in behavioral experiments can be used as a diagnostic tool to decide between the two alternatives. Methods In a setup that eliminates all directional cues except the geomagnetic field zebra finches were trained to search for food in the magnetic north/south axis. The birds were then tested for orientation performance in two magnetic conditions. In condition 1 the horizontal component of the geomagnetic field was shifted by 90 degrees using a helmholtz coil. In condition 2 a high frequently oscillating field (1.156 MHz) was applied in addition to the shifted field. Another group of birds was trained to solve the orientation task, but with visual landmarks as directional cue. The birds were then tested for their orientation performance in the same magnetic conditions as applied for the first experiment. Results The zebra finches could be trained successfully to orient in the geomagnetic field for food search in the north/south axis. They were also well oriented in test condition 1, with the magnetic field shifted horizontally by 90 degrees. In contrast, when the oscillating field was added the directional choices during food search were randomly distributed. Birds that were trained to visually guided orientation showed no difference of orientation performance in the two magnetic conditions

Multiple Visual Field Representations in the Visual Wulst of a Laterally Eyed Bird, the Zebra Finch (Taeniopygia guttata)

Bischof H-J, Eckmeier D, Keary N, Löwel S, Mayer U, Michael N. Multiple Visual Field Representations in the Visual Wulst of a Laterally Eyed Bird, the Zebra Finch (Taeniopygia guttata). PLOS ONE. 2016;11(5): e0154927.The visual wulst is the telencephalic target of the avian thalamofugal visual system. It contains several retinotopically organised representations of the contralateral visual field. We used optical imaging of intrinsic signals, electrophysiological recordings, and retrograde tracing with two fluorescent tracers to evaluate properties of these representations in the zebra finch, a songbird with laterally placed eyes. Our experiments revealed that there is some variability of the neuronal maps between individuals and also concerning the number of detectable maps. It was nonetheless possible to identify three different maps, a posterolateral, a posteromedial, and an anterior one, which were quite constant in their relation to each other. The posterolateral map was in contrast to the two others constantly visible in each successful experiment. The topography of the two other maps was mirrored against that map. Electrophysiological recordings in the anterior and the posterolateral map revealed that all units responded to flashes and to moving bars. Mean directional preferences as well as latencies were different between neurons of the two maps. Tracing experiments confirmed previous reports on the thalamo-wulst connections and showed that the anterior and the posterolateral map receive projections from separate clusters within the thalamic nuclei. Maps are connected to each other by wulst intrinsic projections. Our experiments confirm that the avian visual wulst contains several separate retinotopic maps with both different physiological properties and different thalamo-wulst afferents. This confirms that the functional organization of the visual wulst is very similar to its mammalian equivalent, the visual cortex

Magnetic field perception in the zebra finch

Keary N. Magnetic field perception in the zebra finch. Bielefeld; 2012

The use of the geomagnetic field for short distance orientation in zebra finches

Voß J, Keary N, Bischof H-J. The use of the geomagnetic field for short distance orientation in zebra finches. NEUROREPORT. 2007;18(10):1053-1057.Although the ability to use the Earth's magnetic field for long distance orientation and navigation has been demonstrated in many animals, the search for the appropriate receptor has not yet finished. It is also not entirely clear whether the use of magnetic field information is restricted to specialists like migrating birds, or whether it is a sense that is also suited to short distance orientation by avian species. We successfully trained nonmigratory zebra finches in a four-choice food-search task to use the natural magnetic field as well as an experimentally shifted field for short distance orientation, supporting the view that magnetic field perception may be a sense existing in all bird species. By using a conditioning technique in a standard laboratory animal, our experiments will provide an ideal basis for the search for the physiological mechanisms of magnetic field perception

Quantification of c-Fos IR-neurons in two groups of zebra finches.

<p>Differences in the density of c-fos-activated neurons within 14 brain regions between two groups of birds, exposed to a stationary normal earth magnetic field (NEMF) or a variable earth magnetic field (VEMF) are shown. The density of c-Fos IR-neurons is given as a mean/mm² ± SEM. A. C-Fos activated neurons in the rostral and caudal parts of Hyperpallium apicale and Hyperpallium densocellulare. All four regions show an increased density in birds of the VEMF group with an almost significant difference within the rostral HD. B. C-Fos activated neurons in the ventral, dorsomedial and dorsolateral part of the rostral Hippocampal formation and the ventral and dorsomedial part of the caudal Hippocampal formation. Of the five regions four show an increased density in birds of the VEMF group with a significant difference within the dorsomedial part of rostral hippocampus. A slight decrease can be seen within the dorsolateral rostral hippocampus. C. C-Fos activated neurons in layers two to four of the dorsal, lateral and ventral Optic tectum, the nucleus of the basal optic root and the principal nucleus of the trigeminal brainstem complex. The dorsal TO shows an increased number in c-Fos positive cells in the VEMF group birds. Equal numbers of activated neurons are found in the lateral TO and the nBOR, whereas a decreased density can be seen in the ventral TO and PrV.</p

Hyperpallial and Hippocampal subdivisions.

<p>Four sections taken from the zebra finch brain atlas, with their coordinates anterior to the Y-Point indicated in mm on the right, depict the middle of the areas defined as rostral and caudal Hyperpallium (A 5.13 and A 4.41) and rostral and caudal Hippocampus (A 3.15 and A 1.71). The extent of HA and HD are shown by the light green background, whereas the confines of the Hippocampal region can be distinguished by the light pink background. The borders of hippocampal subdivisions are indicated by red lines. In the lower left corner the sectional planes of the above displayed sections can be distinguished on the lateral view of a whole zebra finch brain. The vertical black line indicates the Y-Point at 0 mm. The vertical green and red lines indicate the sectional planes of the rostral and caudal Hyperpallium, and the rostral and caudal Hippocampus, respectively. HA  =  Hyperpallium apicale, HD  =  Hyperpallium densocellulare, dm  =  dorsomedial, dl  =  dorsolateral, v  =  ventral. Scale bar  = 1 mm.</p

Oscillating magnetic field disrupts magnetic orientation in Zebra finches, 'Taeniopygia guttata'

Background: Zebra finches can be trained to use the geomagnetic field as a directional cue for short distance orientation. The physical mechanisms underlying the primary processes of magnetoreception are, however, largely unknown. Two hypotheses of how birds perceive magnetic information are mainly discussed, one dealing with modulation of radical pair processes in retinal structures, the other assuming that iron deposits in the upper beak of the birds are involved. Oscillating magnetic fields in the MHz range disturb radical pair mechanisms but do not affect magnetic particles. Thus, application of such oscillating fields in behavioral experiments can be used as a diagnostic tool to decide between the two alternatives. Methods: In a setup that eliminates all directional cues except the geomagnetic field zebra finches were trained to search for food in the magnetic north/south axis. The birds were then tested for orientation performance in two magnetic conditions. In condition 1 the horizontal component of the geomagnetic field was shifted by 90 degrees using a helmholtz coil. In condition 2 a high frequently oscillating field (1.156 MHz) was applied in addition to the shifted field. Another group of birds was trained to solve the orientation task, but with visual landmarks as directional cue. The birds were then tested for their orientation performance in the same magnetic conditions as applied for the first experiment. Results: The zebra finches could be trained successfully to orient in the geomagnetic field for food search in the north/south axis. They were also well oriented in test condition 1, with the magnetic field shifted horizontally by 90 degrees. In contrast, when the oscillating field was added, the directional choices during food search were randomly distributed. Birds that were trained to visually guided orientation showed no difference of orientation performance in the two magnetic conditions. Conclusion: The results indicate that zebra finches use a receptor that bases on radical pair processes for sensing the direction of the earth magnetic field in this short distance orientation behavior

Activity elicited by stimulation at different elevations.

<p>In (A–C), three different elevation stimuli are illustrated, confined to either the upper (A) or lower part of the stimulus monitor (B) or extending over the entire monitor (C). In (D–F), the corresponding azimuth stimuli are illustrated: confined to the upper (D) or lower part of the monitor (E) or extending over the entire monitor (F). The colour coding used to visualise the wulst response is shown below the monitors. Colour-coded phase (Ai-Fi) and polar maps of retinotopy (Aii-Fii) and grey-scale-coded response magnitude maps (Aiii-Fiii) are illustrated. The magnitude of the optical responses is illustrated as fractional change in reflection×10⁴: the darker the activity patch the more active was the corresponding brain region. The absolute magnitude of the darkest spot within the activity patch is given as a number in the upper right corner in the graphs. Activity patches are marked by circles. An artefact is marked by a small circle in images (Diii) to (Fiii) and was excluded from the calculation of the absolute magnitude of these images. As can be seen from the magnitude maps with additional absolute magnitude values (Aiii) and (Biii) stimulation of the upper and also the lower monitor half with a vertically moving stimulus generated a strong neuronal response with corresponding colours displayed in the phase maps (Ai) and (Bi). Stimulation of the entire monitor, however, induced a weaker neuronal response (Ciii). The corresponding green and blue coloured activity patch in phase map (Ci) was lacking activation from the upper monitor half, represented by red colours. Stimulation of the upper monitor half with a horizontally moving stimulus induced a weaker neuronal response (Diii) than stimulation of the lower monitor half (Eiii), whereas stimulation of the entire monitor induced an even stronger neuronal response (Fiii). For further explanations see text. In (G) the surface vascular pattern corresponding to the representation in (Ai) to (Fiii) is shown. l, lateral; r, rostral. Scale bar in (Ai to Fiii) and (G)  = 500 µm. Monitor distance d = 30 cm, α = 68° (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0011912#pone-0011912-g001" target="_blank">Figure 1</a>).</p