The Neurological Basis of the Magnetic Sense

ongoing

Each year millions of animals undertake remarkable migratory journeys, across oceans and through hemispheres, guided by the Earth’s magnetic field. While there is unequivocal behavioural evidence demonstrating the existence of the magnetic sense, it is the least understood of all sensory faculties. The biophysical, molecular, cellular, and neurological underpinnings of the sense remain opaque. In this application we aim to remedy this situation, exploiting an established assay, our unique infrastructure, and state-of-the-art methodology, using pigeons as a model system. The proposal will address three questions: 1) Where are the primary magnetosensors? 2) Where is magnetic information processed in the brain? 3) How is magnetic information encoded in the brain? In Aim 1 we will explore whether inner ear hair cells are the primary sensors, and if the detection of magnetic stimuli depends on the presence of magnetic crystals or electromagnetic induction. We will employ a range of physical methods to locate magnetite, and a molecular approach to identify putative electroreceptors. In Aim 2 we will use light sheet microscopy coupled with clearing methods to undertake whole brain mapping of magnetically-induced neuronal activation in the pigeon. We will complement these studies with transcriptomic methods to molecularly and anatomically define magnetosensitive circuits within the pigeon brain. We will build on this work in Aim 3 utilising in vivo 2-photon microscopy to investigate how cells within the pigeon brain encode magnetic information. We will determine whether neurons encode for specific components of the magnetic field (i.e. inclination, intensity, and polarity) and explore whether there are spatially restricted ensembles, providing a dynamic picture of magnetically induced neuronal activity. We anticipate that these experiments will reveal a secret that nature has kept hidden for millennia; How do animals detect magnetic fields?