title: Tremor-related motor unit firing in Parkinson's disease: implications for tremor genesis.
abstract: Muscle tremors reflect rhythmical motor unit (MU) activities. Therefore, the MU firing patterns and synchrony determine the properties of the parkinsonian force tremor (FT) and the neurogenic components of associated limb tremors. They may also be indicative of the neural mechanisms of tremor genesis which to date remain uncertain. We examined these MU behaviours during isometric contractions of a finger muscle in 19 parkinsonian subjects. Our results reveal that the parkinsonian FT is abnormally large. Like the physiological FT, it is accompanied by in-phase rhythms in all MU activities. However, there exist two important differences. Firstly, the synchrony during the parkinsonian FT is stronger than the normal one and therefore contributes to the FT enhancement. Secondly, the synchronous MU components partly represent rhythmical sequences of spike doublets and triplets whose incidences directly reflect the differences of the MU firing rates to the FT frequency. According to our analyses, the latter frequency coincides with the MU recruitment rate. Consequently, the numerous medium- and small-sized active MUs contribute rhythmical twitch doublets and triplets, i.e. large force pulses, to the parkinsonian FT. The impact of this effect on the FT amplitude is found to predominate over the impact of the augmented synchrony. Importantly, apart from the rule governing the occurrence of doublets/triplets, the mean interspike intervals within such spike events are fairly fixed around 50 ms. Such regularities in MU activities may reflect properties of the neural input underlying the FT, and thus represent a basis for more focused studies of the generator(s) of parkinsonian tremors.
authors.affiliation: Laboratory of Systems Physiology, Division of Basic Sciences, Medical School, University of Crete, 71003 Heraklion, Greece. ccnncc@med.uoc.gr
authors.forename: C N
authors.initials: CN
authors.lastname: Christakos
authors.forename: S
authors.initials: S
authors.lastname: Erimaki
authors.forename: E
authors.initials: E
authors.lastname: Anagnostou
authors.forename: D
authors.initials: D
authors.lastname: Anastasopoulos
mesh_terms: D000200:Action Potentials; D000368:Aged; D000369:Aged, 80 and over; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010300:Parkinson Disease / Q000503:physiopathology*; D010507:Periodicity; D011999:Recruitment, Neurophysiological; D014202:Tremor / Q000209:etiology* / Q000503:physiopathology
references.citation: Clin Neurophysiol. 2005 Nov;116(11):2510-9
references.pmid: 16029963
references.citation: Mov Disord. 1995 Sep;10(5):658-63
references.pmid: 8552120
references.citation: J Neurophysiol. 2006 Jan;95(1):53-66
references.pmid: 16162838
references.citation: J Neurophysiol. 1978 May;41(3):557-71
references.pmid: 660226
references.citation: IEEE Trans Biomed Eng. 1980 Mar;27(3):120-31
references.pmid: 6244222
references.citation: Brain Res Bull. 2007 Jul 12;73(4-6):155-202
references.pmid: 17562384
references.citation: Biol Cybern. 1982;45(1):5-12
references.pmid: 7126693
references.citation: J Physiol. 1973 Jan;228(2):285-306
references.pmid: 4687100
references.citation: Neurology. 1986 Aug;36(8):1061-6
references.pmid: 2942795
references.citation: Neuroscience. 1998 Mar;83(1):107-21
references.pmid: 9466402
references.citation: J Neurol Neurosurg Psychiatry. 1987 May;50(5):568-79
references.pmid: 3585382
references.citation: Brain Res. 1979 Oct 19;175(2):372-6
references.pmid: 226227
references.citation: Exp Brain Res. 1997 Mar;113(3):557-63
references.pmid: 9108220
references.citation: Clin Neurophysiol. 2002 Nov;113(11):1667-72
references.pmid: 12417218
references.citation: Brain. 1996 Aug;119 ( Pt 4):1115-21
references.pmid: 8813276
references.citation: Eur J Neurosci. 2003 Jun;17(11):2388-400
references.pmid: 12814370
references.citation: Exp Neurol. 1987 Aug;97(2):327-39
references.pmid: 3609216
references.citation: J Appl Physiol. 1976 Jun;40(6):990-8
references.pmid: 931943
references.citation: Clin Neurophysiol. 2000 Nov;111(11):2046-56
references.pmid: 11068241
references.citation: Neurosci Lett. 1994 Mar 28;170(1):94-8
references.pmid: 8041521
references.citation: J Neurophysiol. 2008 Feb;99(2):473-83
references.pmid: 18057114
references.citation: Brain. 2008 Dec;131(Pt 12):3395-409
references.pmid: 18986993
references.citation: J Neurosci. 2008 Jan 16;28(3):633-49
references.pmid: 18199764
references.citation: Phys Ther. 1994 Jan;74(1):61-70
references.pmid: 8265729
references.citation: J Neurophysiol. 1995 Oct;74(4):1800-5
references.pmid: 8989416
references.citation: Electroencephalogr Clin Neurophysiol. 1986 Mar;63(3):209-22
references.pmid: 2419077
references.citation: J Neurosci. 1988 Mar;8(3):754-64
references.pmid: 3346719
references.citation: Brain. 2002 Jun;125(Pt 6):1196-209
references.pmid: 12023310
references.citation: Pflugers Arch. 1984 Jan;400(1):100-5
references.pmid: 6709485
references.citation: Muscle Nerve. 2004 Sep;30(3):347-55
references.pmid: 15318346
references.citation: Mov Disord. 2000 Mar;15(2):244-54
references.pmid: 10752573
references.citation: Brain. 1963 Mar;86:95-110
references.pmid: 13928399
references.citation: Exp Brain Res. 1986;63(3):639-49
references.pmid: 2944760
references.citation: Brain. 1986 Feb;109 ( Pt 1):115-41
references.pmid: 3942853
references.citation: J Neurol Neurosurg Psychiatry. 1963 Jun;26:265-8
references.pmid: 14025167
references.citation: J Neurophysiol. 1999 Nov;82(5):2839-46
references.pmid: 10561452
references.citation: Brain. 1992 Feb;115 Pt 1:137-54
references.pmid: 1559149
references.citation: Proc Natl Acad Sci U S A. 1999 Feb 16;96(4):1674-9
references.pmid: 9990083
references.citation: Brain. 2003 Jan;126(Pt 1):199-212
references.pmid: 12477707
references.citation: Electroencephalogr Clin Neurophysiol. 1974 May;36(5):457-64
references.pmid: 4135343
references.citation: Mov Disord. 1998;13 Suppl 3:2-23
references.pmid: 9827589
references.citation: Mov Disord. 2003 Apr;18(4):357-63
references.pmid: 12671940
references.citation: J Physiol. 1999 Apr 15;516 ( Pt 2):559-70
references.pmid: 10087353
references.citation: Neurosci Lett. 2008 Sep 19;442(3):195-9
references.pmid: 18634849
references.citation: J Neurophysiol. 2006 May;95(5):2787-95
references.pmid: 16452261
references.citation: J Neurophysiol. 2007 May;97(5):3206-18
references.pmid: 17360826
references.citation: Ann Neurol. 1991 Jul;30(1):83-9
references.pmid: 1929231
references.citation: Biol Cybern. 1982;44(2):91-106
references.pmid: 7115792
references.citation: J Neurophysiol. 1997 Dec;78(6):3453-9
references.pmid: 9405560
references.citation: Exp Brain Res. 2006 Jul;172(4):507-18
references.pmid: 16489433
references.citation: Electromyogr Clin Neurophysiol. 1989 Mar;29(2):113-7
references.pmid: 2707140
references.citation: J Clin Neurophysiol. 2002 Jan;19(1):84-9
references.pmid: 11896358
references.citation: J Neurophysiol. 1999 Dec;82(6):3188-95
references.pmid: 10601452
references.citation: Brain Res. 1976 Jun 18;109(3):515-29
references.pmid: 1276932
references.citation: Electroencephalogr Clin Neurophysiol. 1991 Aug;81(4):279-83
references.pmid: 1714822
references.citation: Trends Neurosci. 1994 Jul;17(7):299-305
references.pmid: 7524216
references.citation: Brain Res. 1988 Nov 1;463(2):362-7
references.pmid: 3196923
references.citation: Int J Neurosci. 1986 Mar;29(1-2):103-7
references.pmid: 3699995
references.citation: J Physiol. 1969 Feb;200(3):723-43
references.pmid: 4237132
references.citation: J Neurosci Methods. 2004 Jul 30;136(2):197-205
references.pmid: 15183272
references.citation: Neurology. 2004 Oct 12;63(7):1234-9
references.pmid: 15477544
references.citation: J Neurol Neurosurg Psychiatry. 1974 Aug;37(8):927-37
references.pmid: 4419618
references.citation: J Neurophysiol. 2003 Aug;90(2):1346-9
references.pmid: 12904514
references.citation: Neuroscience. 1994 Jan;58(1):43-57
references.pmid: 8159296
references.citation: J Neurol Neurosurg Psychiatry. 2002 Mar;72 Suppl 1:I3-I9
references.pmid: 11870197
references.citation: J Neurol Neurosurg Psychiatry. 1981 Jun;44(6):534-46
references.pmid: 7276968
references.citation: Biophys J. 1967 Jul;7(4):391-418
references.pmid: 4292791
references.citation: Prog Biophys Mol Biol. 1989;53(1):1-31
references.pmid: 2682781
references.citation: J Physiol. 1962 Jul;162:259-69
references.pmid: 13919908
references.citation: Brain. 2004 Sep;127(Pt 9):2131-43
references.pmid: 15240437
references.citation: Mov Disord. 2002;17 Suppl 3:S28-40
references.pmid: 11948753