On 27 Jun 2003, J L Edwards wrote: > Hi all: > > Why isn't there a similar effect when people undergo MRIs? I read > somewhere the units generate a magnetic field 30,000 times stronger > than the earth's magnetic field. What am I missing?
I have to reach back into brain cells zapped by more than TMS to try to answer this one, but I think the answer is "alternating current". A coil of wire is placed on the scalp and an alternating current passed through it. This induces a magnetic field which also alternates. The magnetic field crosses the skull, no problem, and somehow induces (note the poverty of explanation at this point) an electric current in neural tissue. In summary, alternating electric current induces alternating magnetic field which induces alternating electric current. In MRI, the field is instead unvarying although admittedly enormous. Perhaps if they tried turning it on and off you'd get a real charge out of it. Stephen ______________________________________________________________ Stephen L. Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's University e-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Dept web page at http://www.ubishops.ca/ccc/div/soc/psy TIPS discussion list for psychology teachers at http://www.frostburg.edu/dept/psyc/southerly/tips _________________________________________________________ --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
