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There is a paper detailing how a slime mould can be guided by loading it with ferromagnetic particles and steering it with magnets, but I was wondering whether an un-modified physarum could detect a magnetic field.
I ran a set of 4 time-lapses using a strong magnet (top of picture) and starting conditions as shown in the photo so heading towards the pole would give it a guaranteed food reward. I would expect the slime to preferentially set off towards the pole if it 'learned' that food lay in that direction.
The results were negative. I could see no evidence of a directional preference developing over the course of the four runs. It was displaying the typical fan behaviour in random directions from the start condition.
My conclusion is that Polycephalum physarum can not detect and respond to a magnetic field, at least not in the way I tested it.
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Try using a dry cell and two electrodes one (+) the other (-) of course and place them at opposite sides of the petri dish. Attach the battery or dry cell and observe what happens. A single AA battery should suffice, if not try a D cell. What you are hoping to accomplish is the exhibition of galvanotropism, or a response to an electrical stimulus. Being a protist, P. polycephalum should be attracted to the positive electrode, it would be interesting to see how the organism is affected and what the end result may be. A number of other experiments could be done with varying voltages, amperage, most any thing short of capital punishment.
There's a paper that claims they can just sense it natively, I don't buy it either - I've also tried, they don't even react to hard drive magnets directly under the dish.
Some organisms do sense magnetic fields though - my water butt has Magnetotactic bacteria, you can see see the magnetic crystals under EM, physarum doesn't have those - I'd have noticed.
I wonder about getting some ultra fine iron oxide...
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