This is a serious request with a possible opportunity for collaboration on the
submission of a joint NIH/NSF/DoD grant proposal.

Recent experiments have demonstrated the feasibility of functional stimulation
of human motor cortex without penetration of the skull.  Some experiments used
a 500 Hz, damped, sinusoidal magnetic field (peak amplitude 4 T; decaying to
approximately 0.4 T after 20 ms) produced by a pole piece approximately 25 mm
in diameter.  Other experiments used a flat coil 9 cm in diameter generating a
magnetic field of 2 T with a peak at 150 usec.  These stimulation protocols
generally employed a single isolated stimulator with a low pulse repetition
rate (less than 1 pulse / 3 secs).  Stimulation about a single point in motor
cortex generally induced movement in the appropriate peripheral muscle system.
In other words, a single time varying 2 to 4 T magnetic field can induce some
coarse muscle movements.  However, fine grained magnetic arrays capable of
generating fine grained complex movements are not yet available.

I am curious about whether it would be possible to construct a large system of
stimulators arranged in a grid or honeycomb configuration that could generate
a fine matrix of magnetic fingers extending from the surface of the head deep
into the sulci and gyri of the cerebral cortex.  Such a matrix would be useful
for stimulating cortical regions with a complex pattern of functional inputs.
For example, fine grained stimulation of motor cortex would support complex
diagnostic studies of the cortical basis of movement disorders over a longer
time than is possible using the present intraoperative electrical stimulation
techniques.

I would appreciate any email designs, speculations, or references to available
literature on designing grid like arrays of individually controllable magnetic
fingers.  Please consider all possibilities ... cost is not presently an issue.
I am primarily interested in learning about how such a system might work.

Electronic mail replies may be sent to:

Hardcopy mail replies may be sent to:

      A. J. Annala
      Neuroscience Program
      Hedco Neuroscience Building, Room 534A
      University of Southern California
      Los Angeles, CA 90089-2520

      (213)743-3250 (office) / (213)743-3246 (lab)

Thank you for your kind assistance in this matter.

Thanks again, AJ Annala

References:

Barker, A. T. et al.  Magnetic Stimulation of the Human Brain and Peripheral
   Nervous System:  An Introduction and the Results of an Initial Clinical
   Evaluation.  Neurosurgery  20(1):100-109 (1987).
Hallett, M. & L. G. Cohen.  Magnetism: A New Method for Stimulation of Nerve
   and Brain.  JAMA 262(4):538-541 (1989).
Mills, K. R. et al.  Magnetic and Electrical Transcranial Brain Stimulation:
   Physiological Mechanisms and Clinical Applications.  Neurosurgery 20(1):
   164-168 (1987).