Elucidating the mechanisms and loci of neuronal excitation by transcranial magnetic stimulation using a finite element model of a cortical sulcus.
OBJECTIVE
This work aims to elucidate by what physical mechanisms and where stimulation occurs in the brain during transcranial magnetic stimulation (TMS), taking into account cortical geometry and tissue heterogeneity.


METHODS
An idealized computer model of TMS was developed, comprising a stimulation coil, a cortical sulcus, and surrounding tissues. The distribution of the induced electric field was computed, and estimates of the relevant parameters were generated to predict the locus and type of neurons stimulated during TMS, assuming three different stimulation mechanisms.


RESULTS
Tissue heterogeneity strongly affects the spatial distribution of the induced electric field and hence which stimulation mechanism is dominant and where it acts. Stimulation of neurons may occur in the gyrus, in the lip of the gyrus, and in the walls of the sulcus. The stimulated cells can be either pyramidal cells having medium to large caliber axons, or intracortical fibers of medium caliber.


CONCLUSIONS
The results highlight the influence of cortical folding on the action of magnetic and electric fields on cortical tissue.


CONCLUSIONS
Tissue geometry and heterogeneity in electrical conductivity both must be taken into account to predict accurately stimulation loci and mechanism in TMS.
Silva
S
S
Physics Department, Institute of Biophysics and Biomedical Engineering, Faculty of Science, University of Lisbon, Campo Grande, 1749-016 Lisbon, Portugal. ssilva@fc.ul.pt
Basser
P J
PJ
Miranda
P C
PC
D002540:Cerebral Cortex / Q000166:cytology* / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation; D006801:Humans; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology* / Q000528:radiation effects; D050781:Transcranial Magnetic Stimulation
IEEE Trans Biomed Eng. 1993 Nov;40(11):1175-88
8307602
Clin Neurophysiol. 2004 Jul;115(7):1697-708
15203072
IEEE Trans Biomed Eng. 1997 Aug;44(8):727-35
9254986
Electroencephalogr Clin Neurophysiol. 1997 Oct;105(5):406-13
9363007
Neuroimage. 2007 Jul 15;36(4):1159-70
17524673
Electroencephalogr Clin Neurophysiol. 1992 Feb;85(1):17-21
1371739
IEEE Trans Biomed Eng. 1990 Jun;37(6):588-97
2354840
Proc R Soc Lond B Biol Sci. 1982 Dec 22;217(1206):29-35
6131421
Clin Neurophysiol. 2001 Feb;112(2):250-8
11165526
Electroencephalogr Clin Neurophysiol Suppl. 1991;43:227-37
1773760
Brain. 1997 Apr;120 ( Pt 4):701-22
9153131
J Physiol. 1927 Sep 9;63(4):357-77
16993895
IEEE Trans Biomed Eng. 2003 Sep;50(9):1074-85
12943275
Crit Rev Biomed Eng. 1994;22(3-4):253-305
8598130
J Neuropsychiatry Clin Neurosci. 2000 Summer;12(3):376-84
10956572
Phys Med Biol. 1996 Nov;41(11):2251-69
8938025
J Physiol. 1951 Sep;115(1):101-22
14889433
FASEB J. 1987 Nov;1(5):365-74
3315805
IEEE Trans Biomed Eng. 2003 Jun;50(6):754-67
12814242
Neuroimage. 2002 Nov;17(3):1117-30
12414254
Clin Neurophysiol. 2004 Feb;115(2):255-66
14744565
IEEE Trans Biomed Eng. 1997 Mar;44(3):220-3
9216137
Nature. 2000 Jul 13;406(6792):147-50
10910346
Brain. 1997 Jan;120 ( Pt 1):141-57
9055804
Med Biol Eng Comput. 1977 Jul;15(4):438-45
197339
J Physiol. 1989 May;412:449-73
2489409
Electroencephalogr Clin Neurophysiol. 1992 Oct;85(5):291-301
1385089
Electroencephalogr Clin Neurophysiol. 1991 Jun;81(3):224-37
1710972
Nat New Biol. 1972 Aug 16;238(85):217-9
4506206
J Clin Neurophysiol. 2002 Aug;19(4):322-43
12436088
Med Biol Eng Comput. 1991 May;29(3):261-8
1943258
Clin Neurophysiol. 2006 Jun;117(6):1388-97
16644273
J Neurophysiol. 2005 Dec;94(6):4520-7
16135552
Clin Neurophysiol. 2005 Aug;116(8):1988-93
15979404
Clin Neurophysiol. 2007 Feb;118(2):464-74
17150409
Lancet. 1985 May 11;1(8437):1106-7
2860322
Phys Med Biol. 2007 Sep 21;52(18):5603-17
17804884
Hum Brain Mapp. 2004 May;22(1):1-14
15083522