J. R. Dunn

Magnetic material in the human hippocampus

Magnetic analyses of hippocampal material from deceased normal and epileptic subjects, and from the surgically removed epileptogenic zone of a living patient have been carried out. All had magnetic characteristics similar to those reported for other parts of the brain [6]. These characteristics along with low temperature analysis indicate that the magnetic material is present in a wide range of grain sizes. The low temperature analysis also revealed the presence of magnetite through manifestation of its low temperature transition. The wide range of grain sizes is similar to magnetite produced extracellularly by the GS-15 strain of bacteria and unlike that found in magnetotactic bacteria MV-1, which has a restricted grain size range. Optical microscopy of slices revealed rare 5-10 micron clusters of finer opaque particles, which were demonstrated with Magnetic Force Microscopy to be magnetic. One of these was shown with EDAX to contain AI, Ca, Fe, and K, with approximate weight percentages of 55, 19, 19, and 5, respectively.

On the confirmation of an effect of magnetic fields on the interictal firing rate of epileptic patients.

The effect of magnetic fields on interictal firing rates was investigated in three epileptic patients with depth electrode implantation in the hippocampus for pre-surgical evaluation. The protocol consisted of 10 min test periods, during which magnetic fields were cycled for 1 min on and 1 min off, and intervening 5 min rest periods. Only one patient revealed a 95% significant increase in the 10 s after the fields were switched on compared with the background estimate from the 10s before the fields were applied. This patient was also the only patient to show significant increases in firing rates during field-on compared with field-off periods, and during magnetic field test periods compared with intervening rest periods. This patient had a right hippocampal seizure onset. All patients showed increased firing rates during the 10 min periods of magnetic field testing compared to the 5 min rest periods between tests. This result was significant for the group at the 99% level. Two patients with right temporal lobe onset showed greater activity in the right hippocampus than the left. All patients exhibited a progressive increase in firing rates in rest periods between tests.