Dear Gunes-Helene,

Paramecium shows a reaction to current by the interference with the membrane potential which in turn controls the beating of the cilia. I do not think they 'learn' to ignore the current, cause that would require them to totally change their physiology. I was wondering whether you might have a problem with your electrodes. When I did these kind of experiments I used silver electrodes. Your stainless steel electrodes might be changed chemically on the surface after a while. Try to use other materials for the electrodes and/or vary voltages.

Greetings, Michael 

I am amused that people - some people at least - seem to think that they can control other people by stimulating their brains with electricity. If it doesn't work with paramecia then it' s not going to work with vastly more sophisticated life forms. Seriously, the paramecia are clearly learning to ignore the current. What motivation are you providing them to take any notice of it? Maybe try guiding them to food? They stop responding because they see no selective or practical advantage in doing so. And I don't think they're going to 'unlearn' that very quickly.

Dear Gunes-Helene,

Paramecium shows a reaction to current by the interference with the membrane potential which in turn controls the beating of the cilia. I do not think they 'learn' to ignore the current, cause that would require them to totally change their physiology. I was wondering whether you might have a problem with your electrodes. When I did these kind of experiments I used silver electrodes. Your stainless steel electrodes might be changed chemically on the surface after a while. Try to use other materials for the electrodes and/or vary voltages.

Greetings, Michael 

Hi Michael,

Thank you for your clarifications and suggestion.  I knew I was interferring with they basic guiding functions, but I thought it was something they might learn to ignore (such as a specific frequency...). But with your explanation, the answer seems to be somewhere else.

When I do put new paramecia in the enclosure, without changing the electrodes, they react normally to the field. I've contacted a person who also worked with electricity and paramecium a few years back, and she did have the same problem, even with platinum electrodes. She did not try to research it more as she would just change the culture when they stopped responding. She did suggest it might have something to do with a polarisation of the water; I've tried to read on that subject but quickly got lost. If polarisation is possible, them it would mean that my water would get an overall positive charge because during electrolysis it would have lost an hydrogen atom, wich are negatively charged. It might also mean that the ph of the water would get more basic. 

This led me to think that electrolysis might also affect he salt and minerals composition of the water, maybe making it less conductive. Or by separating the elements into different compounds that could interfere either with the net charge of the water, or even with the electric potential of the paramecium's membrane.

I'm no chemist, so f someone has an input about this, it would be nice to understand what happens! I'm really trying not to hurt the paramecia and would love to know how to better care for them while they participate in my experiment. 

Thank you again!

Gunes-Helene

It appears the the electrodes are being polarised by the medium and the current stops. It is not that the paramoecium has stopped responding, but the electrodes needs to be depolarised.