The distribution of magnetic particles in human post mortem brains has been systematically mapped by scientists at Ludwig-Maximilians-Universität München.

Many living organisms, such as migratory birds, are thought to possess a magnetotactic sense, which enables them to respond to the Earth’s magnetic field. Whether or not humans are capable of sensing magnetism is the subject of debate.

However, several studies have already shown that one of the preconditions required for such a magnetic sensory system is indeed met: magnetic particles do exist in the human brain. It is unclear what function such particles serve in humans, however.

Striking Distribution Asymmetry

A team led by Stuart A. Gilder, a professor at LMU’s Department of Earth and Environmental Sciences, and Christoph Schmitz, a professor at LMU’s Department of Neuroanatomy, confirmed the presence of magnetic particles in human brains. The particles were found primarily in the cerebellum and the brainstem, and there was striking asymmetry in the distribution between the left and right hemispheres of the brain.

“The human brain exploits asymmetries in sensory responses for spatial orientation, and also for sound-source localization,"

Schmitz explained. The asymmetric distribution of the magnetic particles is therefore compatible with the idea that humans might have a magnetic sensor.

[caption id=“attachment_96746” align=“aligncenter” width=“680”]Histograms of the mass normalized saturation isothermal magnetizations (SIRM) separating the specimens by anatomy. Histograms of the mass normalized saturation isothermal magnetizations (SIRM) separating the specimens by anatomy.
Credit: Stuart A. Gilder, et al. CC-BY[/caption]

But in all probability, this sensor is much too insensitive to serve any useful biological function, he added. Furthermore, the chemical nature of the magnetic particles remains unknown.

“We assume that they are all made of magnetite (Fe3O4), but it is not yet possible to be sure,"

said Gilder.

Remanence is the magnetization left behind in a ferromagnetic material, such as iron, after an external magnetic field is removed. It is also the measure of that magnetization. In common terms, when a magnet is “magnetized” it has remanence.

Analogous Localization Studies

The data were obtained from seven human post mortem brains, which had been donated for use in medical research. In all, a total of 822 tissue samples were subjected to magnetometry.

The measurements were performed under the supervision of Stuart Gilder in a magnetically shielded laboratory located in a forest 80 km from Munich which is largely free from pervasive magnetic pollution that is characteristic of urban settings nowadays.

[caption id=“attachment_96747” align=“aligncenter” width=“680”]median, mass normalized, saturation isothermal remanent magnetization (SIRM) Contour maps using the Ferret color scale of the median, mass normalized, saturation isothermal remanent magnetization (SIRM) values using the cut-off method.
(a) Horizontal view from dorsal (above) of the cerebral cortex only.
(b) Mid-sagittal view of the entire brain including cerebral cortex, cerebellum and brain stem.
All pieces for all seven brains in a given location (plus symbols) were stacked along the projection to calculate the median at each location.
Medians at each place were retained only when N ≥ 3. The linear color scale is the same for both images, which were made with Adobe Photoshop CS6 v 13 by overlaying the contour images generated by our own python code on top of our own photo (a) and scanned image (b).
Credit: Stuart A. Gilder, et al. CC-BY[/caption]

In further experiments, the LMU team plans to characterize the properties of the magnetic particles found in human brains. In collaboration with Professor Patrick R. Hof (Fishberg Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York), they also hope to perform analogous localization studies on far larger mammals - whales. These huge marine mammals are known to migrate between feeding and breeding grounds across great distances in the world’s oceans.

“We want determine whether we can detect magnetic particles in the brains of whales, and if so whether they are also asymmetrically distributed. It goes without saying that such studies will be carried out on animals that have died of natural causes,"

said Schmitz.

There is at least one limitation to the study:

“The present study was performed on human post mortem brains and has therefore inherent limitations. For example, cutting through the skull to extract the brains could have introduced magnetic contaminants. Some peripheral cerebral cortex specimens had visible saw marks a few mm deep that had NRMs well above detection limits; however, other specimens with cut marks had NRMs below detection limits. Samples with NRMs above detection limits would be omitted when considering cut-off data. Our findings that visible blood vessels did not hold the magnetic remanence corroborated previous results that cauterization of blood vessels did not increase the magnetic fraction,"

the authors write.

Stuart A. Gilder, Michael Wack, Leon Kaub, Sophie C. Roud, Nikolai Petersen, Helmut Heinsen, Peter Hillenbrand, Stefan Milz & Christoph Schmitz Distribution of magnetic remanence carriers in the human brain Scientific Reports volume 8, Article number: 11363 (2018)

Top Image: Stuart A. Gilder, et al. CC-BY

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