title: Neural pathways mediating cross education of motor function.
abstract: Cross education is the process whereby training of one limb gives rise to enhancements in the performance of the opposite, untrained limb. Despite interest in this phenomenon having been sustained for more than a century, a comprehensive explanation of the mediating neural mechanisms remains elusive. With new evidence emerging that cross education may have therapeutic utility, the need to provide a principled evidential basis upon which to design interventions becomes ever more pressing. Generally, mechanistic accounts of cross education align with one of two explanatory frameworks. Models of the "cross activation" variety encapsulate the observation that unilateral execution of a movement task gives rise to bilateral increases in corticospinal excitability. The related conjecture is that such distributed activity, when present during unilateral practice, leads to simultaneous adaptations in neural circuits that project to the muscles of the untrained limb, thus facilitating subsequent performance of the task. Alternatively, "bilateral access" models entail that motor engrams formed during unilateral practice, may subsequently be utilized bilaterally-that is, by the neural circuitry that constitutes the control centers for movements of both limbs. At present there is a paucity of direct evidence that allows the corresponding neural processes to be delineated, or their relative contributions in different task contexts to be ascertained. In the current review we seek to synthesize and assimilate the fragmentary information that is available, including consideration of knowledge that has emerged as a result of technological advances in structural and functional brain imaging. An emphasis upon task dependency is maintained throughout, the conviction being that the neural mechanisms that mediate cross education may only be understood in this context.
authors.affiliation: School of Psychology, Queen's University Belfast Belfast, UK ; Trinity College Institute of Neuroscience and School of Psychology, Trinity College Dublin Dublin, Ireland.
authors.forename: Kathy L
authors.initials: KL
authors.lastname: Ruddy
authors.forename: Richard G
authors.initials: RG
authors.lastname: Carson
keywords: bilateral; interhemispheric; interlimb; motor learning; transfer
references.citation: Brain Stimul. 2013 Mar;6(2):101-7
references.pmid: 22659022
references.citation: Brain. 1999 Jun;122 ( Pt 6):1049-62
references.pmid: 10356058
references.citation: Acta Physiol (Oxf). 2009 Oct;197(2):161-73
references.pmid: 19392872
references.citation: J Neurophysiol. 2005 Mar;93(3):1209-22
references.pmid: 15525809
references.citation: Clin Neurophysiol. 2012 Nov;123(11):2227-31
references.pmid: 22608486
references.citation: J Appl Physiol (1985). 2008 Jun;104(6):1656-64
references.pmid: 18403447
references.citation: Brain Res Brain Res Rev. 2005 Nov;49(3):641-62
references.pmid: 15904971
references.citation: Exp Brain Res. 1998 Feb;118(3):421-6
references.pmid: 9497149
references.citation: Exp Brain Res. 1994;98(3):523-34
references.pmid: 8056072
references.citation: Cereb Cortex. 2012 Nov;22(11):2643-52
references.pmid: 22166764
references.citation: J Neurophysiol. 1999 Jan;81(1):383-7
references.pmid: 9914297
references.citation: Neurosci Lett. 2008 Nov 21;445(3):209-13
references.pmid: 18793696
references.citation: Front Integr Neurosci. 2013 Mar 11;7:9
references.pmid: 23483798
references.citation: Neurosci Lett. 2008 Aug 22;441(2):153-7
references.pmid: 18582535
references.citation: J Physiol. 2009 Nov 15;587(Pt 22):5393-410
references.pmid: 19770195
references.citation: Clin Neurophysiol. 2013 Jul;124(7):1353-63
references.pmid: 23478202
references.citation: Eur J Neurosci. 1996 Apr;8(4):637-48
references.pmid: 9081615
references.citation: Ann Neurol. 1998 Mar;43(3):360-9
references.pmid: 9506553
references.citation: J Mot Behav. 1970 Dec;2(4):261-71
references.pmid: 23941320
references.citation: Ann Neurol. 1994 Jan;35(1):45-52
references.pmid: 8285591
references.citation: J Physiol. 1992;453:525-46
references.pmid: 1464843
references.citation: J Neurophysiol. 2000 Oct;84(4):2148-60
references.pmid: 11024102
references.citation: J Neurosci. 1993 Mar;13(3):952-80
references.pmid: 7680069
references.citation: Brain Res Cogn Brain Res. 2002 Aug;14(2):277-93
references.pmid: 12067701
references.citation: Neuropsychologia. 2012 Aug;50(10):2515-23
references.pmid: 22781812
references.citation: J Appl Physiol (1985). 1997 Nov;83(5):1448-53
references.pmid: 9375304
references.citation: Cereb Cortex. 2003 May;13(5):475-85
references.pmid: 12679294
references.citation: J Physiol. 2002 Oct 15;544(Pt 2):641-52
references.pmid: 12381833
references.citation: J Neurol. 2012 Sep;259(9):1860-7
references.pmid: 22289969
references.citation: Eur J Neurosci. 2012 Dec;36(12):3749-57
references.pmid: 23033874
references.citation: Exp Brain Res. 2003 Nov;153(2):140-5
references.pmid: 12955383
references.citation: Hum Brain Mapp. 2011 Feb;32(2):218-28
references.pmid: 20336657
references.citation: Behav Brain Res. 2013 Mar 1;240:33-45
references.pmid: 23174210
references.citation: IEEE Eng Med Biol Mag. 2005 Jan-Feb;24(1):22-8
references.pmid: 15709532
references.citation: Nature. 2000 Aug 31;406(6799):995-8
references.pmid: 10984053
references.citation: Cereb Cortex. 2011 Aug;21(8):1761-70
references.pmid: 21139077
references.citation: Neurosci Behav Physiol. 1980 Jan-Feb;10(1):76-82
references.pmid: 7383329
references.citation: Exp Brain Res. 2000 Jul;133(1):55-65
references.pmid: 10933210
references.citation: Neuroimage. 2013 Feb 15;67:283-97
references.pmid: 23194819
references.citation: Arch Neurol. 1961 Feb;4:165-72
references.pmid: 13691977
references.citation: Clin Neurophysiol. 2009 Jun;120(6):1195-203
references.pmid: 19410505
references.citation: J Exp Psychol Hum Percept Perform. 1995 Aug;21(4):719-33
references.pmid: 7643045
references.citation: Cereb Cortex. 2011 Jul;21(7):1475-84
references.pmid: 21131448
references.citation: Trends Neurosci. 2008 Jul;31(7):361-70
references.pmid: 18538868
references.citation: Exp Brain Res. 2002 Oct;146(3):369-78
references.pmid: 12232693
references.citation: J Comp Neurol. 1979 Nov 1;188(1):137-45
references.pmid: 115906
references.citation: Trends Neurosci. 1999 Oct;22(10):464-71
references.pmid: 10481194
references.citation: J Neurosci. 1991 Mar;11(3):667-89
references.pmid: 1705965
references.citation: Neuroreport. 1994 Dec 20;5(18):2541-4
references.pmid: 7696599
references.citation: J Mot Behav. 1999 Jun;31(2):107-111
references.pmid: 11177624
references.citation: Behav Brain Res. 1991 Dec 13;46(1):1-8
references.pmid: 1786110
references.citation: J Neurosci. 2008 Sep 24;28(39):9664-9
references.pmid: 18815252
references.citation: Neurosci Behav Physiol. 1981 Jul-Aug;11(4):328-35
references.pmid: 6283417
references.citation: Cortex. 2009 Oct;45(9):1035-42
references.pmid: 19371866
references.citation: AJNR Am J Neuroradiol. 1998 Feb;19(2):275-80
references.pmid: 9504477
references.citation: Neuroimage. 2002 Oct;17(2):851-8
references.pmid: 12377159
references.citation: Exp Brain Res. 2006 Sep;174(2):199-209
references.pmid: 16604315
references.citation: J Physiol. 2006 May 1;572(Pt 3):857-68
references.pmid: 16497712
references.citation: J Appl Physiol (1985). 2010 Dec;109(6):1887-94
references.pmid: 20966196
references.citation: J Cogn Neurosci. 2005 Jan;17(1):124-36
references.pmid: 15701244
references.citation: Exp Brain Res. 2010 Sep;205(3):423-33
references.pmid: 20686888
references.citation: J Neurosci. 2006 Nov 29;26(48):12466-70
references.pmid: 17135408
references.citation: Exp Brain Res. 2005 Mar;161(3):325-34
references.pmid: 15517219
references.citation: Exp Brain Res. 2005 Aug;165(1):114-24
references.pmid: 15965762
references.citation: J Neurosci. 2005 Feb 9;25(6):1375-86
references.pmid: 15703391
references.citation: J Physiol (Paris). 1978;74(3):297-312
references.pmid: 102777
references.citation: Exerc Sport Sci Rev. 2000 Oct;28(4):177-84
references.pmid: 11064852
references.citation: J Neurosci. 1998 Mar 1;18(5):1827-40
references.pmid: 9465007
references.citation: Exp Brain Res. 2001 Oct;140(3):290-300
references.pmid: 11681304
references.citation: J Neurophysiol. 2003 Mar;89(3):1256-64
references.pmid: 12611955
references.citation: Cortex. 2010 Feb;46(2):264-7
references.pmid: 19321164
references.citation: J Neurophysiol. 2003 Oct;90(4):2451-9
references.pmid: 14534271
references.citation: Electroencephalogr Clin Neurophysiol. 1998 Apr;106(4):283-96
references.pmid: 9741757
references.citation: Eur J Neurosci. 1992;4(2):154-165
references.pmid: 12106378
references.citation: Invest Radiol. 2009 May;44(5):279-84
references.pmid: 19346962
references.citation: J Neurophysiol. 2003 Feb;89(2):1039-56
references.pmid: 12574479
references.citation: Cerebellum. 2008;7(4):572-6
references.pmid: 18855092
references.citation: J Physiol. 1999 Jun 1;517 ( Pt 2):591-7
references.pmid: 10332104
references.citation: J Neurophysiol. 1997 Mar;77(3):1313-24
references.pmid: 9084599
references.citation: Neuroimage. 2007 Jan 1;34(1):156-68
references.pmid: 17081770
references.citation: Physiol Behav. 2002 Dec;77(4-5):677-82
references.pmid: 12527018
references.citation: J Appl Physiol (1985). 2005 Oct;99(4):1558-68
references.pmid: 15890749
references.citation: J Physiol Paris. 1999 Sep-Oct;93(4):271-84
references.pmid: 10574117
references.citation: Cerebellum. 2004;3(4):204-11
references.pmid: 15686098
references.citation: Neuroreport. 1996 Sep 2;7(13):2103-10
references.pmid: 8930968
references.citation: J Physiol Paris. 2006 Jun;99(4-6):414-24
references.pmid: 16730432
references.citation: Neurosci Lett. 1993 Oct 1;160(2):153-5
references.pmid: 8247346
references.citation: PLoS Biol. 2007 Nov;5(11):e316
references.pmid: 18044990
references.citation: J Neurol Sci. 1997 Oct 22;151(2):195-205
references.pmid: 9349676
references.citation: Clin Neurophysiol. 2001 Nov;112(11):2138-45
references.pmid: 11682353
references.citation: J Neurosci. 2007 Oct 31;27(44):12058-66
references.pmid: 17978047
references.citation: J Physiol. 2000 Apr 1;524 Pt 1:293-304
references.pmid: 10747199
references.citation: Exp Brain Res. 2007 Oct;182(4):459-67
references.pmid: 17562034
references.citation: Prog Brain Res. 1993;95:317-37
references.pmid: 8493342
references.citation: J Appl Physiol. 1951 Aug;4(2):136-44
references.pmid: 14888623
references.citation: Brain Res. 2007 Dec 14;1185:136-51
references.pmid: 17996854
references.citation: J Neurophysiol. 1993 Nov;70(5):2097-116
references.pmid: 8294972
references.citation: J Cogn Neurosci. 2007 Feb;19(2):204-13
references.pmid: 17280510
references.citation: J Neurosci. 2007 Jan 31;27(5):1045-53
references.pmid: 17267558
references.citation: Neuroimage. 2008 May 1;40(4):1772-81
references.pmid: 18329904
references.citation: J Mot Behav. 1986 Jun;18(2):117-45
references.pmid: 15136276
references.citation: Neuroscience. 1994 Feb;58(3):481-91
references.pmid: 8170534
references.citation: Proc Natl Acad Sci U S A. 2002 Jan 22;99(2):1017-22
references.pmid: 11805340
references.citation: Neuroreport. 1998 Jun 1;9(8):1861-6
references.pmid: 9665616
references.citation: J Neurophysiol. 1962 Mar;25:198-208
references.pmid: 13862744
references.citation: Neuroimage. 2006 Aug 15;32(2):714-27
references.pmid: 16798015
references.citation: Exp Brain Res. 2005 May;163(1):118-22
references.pmid: 15754176
references.citation: J Neurosci. 2007 Sep 19;27(38):10073-5
references.pmid: 17881512
references.citation: Neuroimage. 2004 Jul;22(3):1336-50
references.pmid: 15219606
references.citation: Neuroscientist. 2011 Apr;17(2):185-96
references.pmid: 21403182
references.citation: J Electromyogr Kinesiol. 2007 Aug;17(4):446-52
references.pmid: 16891123
references.citation: J Neurophysiol. 2005 May;93(5):2950-8
references.pmid: 15625099
references.citation: Cortex. 1980 Dec;16(4):587-603
references.pmid: 7226856
references.citation: J Neurophysiol. 1998 Sep;80(3):1562-6
references.pmid: 9744961
references.citation: J Appl Physiol (1985). 2006 Nov;101(5):1506-13
references.pmid: 16888047
references.citation: J Neurophysiol. 2003 Feb;89(2):922-42
references.pmid: 12574469
references.citation: Curr Biol. 2007 Nov 6;17(21):1896-902
references.pmid: 17964167
references.citation: Annu Rev Neurosci. 1997;20:25-42
references.pmid: 9056706
references.citation: Brain. 1997 Sep;120 ( Pt 9):1587-602
references.pmid: 9313642
references.citation: Neurobiol Aging. 2003 Nov;24(7):1013-9
references.pmid: 12928061
references.citation: Eur J Neurosci. 1998 Feb;10(2):729-40
references.pmid: 9749734
references.citation: Neuroimage. 2003 Nov;20 Suppl 1:S120-31
references.pmid: 14597305
references.citation: Neuroimage. 2012 Aug 1;62(1):266-80
references.pmid: 22584231
references.citation: Electroencephalogr Clin Neurophysiol. 1996 Oct;101(5):395-403
references.pmid: 8913192
references.citation: J Neurophysiol. 2005 Sep;94(3):1668-75
references.pmid: 15872061
references.citation: Exp Brain Res. 1994;102(2):227-43
references.pmid: 7705502
references.citation: Hum Brain Mapp. 2013 Feb;34(2):384-95
references.pmid: 22042512
references.citation: Cereb Cortex. 2007 Jun;17(6):1350-63
references.pmid: 16920885
references.citation: Neuron. 2002 Nov 14;36(4):751-65
references.pmid: 12441062
references.citation: Ann Neurol. 1999 May;45(5):583-94
references.pmid: 10319880
references.citation: Neuroimage. 2003 Dec;20(4):2259-70
references.pmid: 14683727
references.citation: J Neurol Sci. 2008 Jun 15;269(1-2):96-104
references.pmid: 18336839
references.citation: Brain Topogr. 2007 Winter;20(2):77-88
references.pmid: 17932739
references.citation: J Neurosci. 1995 May;15(5 Pt 1):3284-306
references.pmid: 7538558
references.citation: Neuroreport. 1997 May 6;8(7):1729-32
references.pmid: 9189922
references.citation: Exp Brain Res. 2011 Apr;210(2):165-72
references.pmid: 21424259
references.citation: Brain. 1996 Aug;119 ( Pt 4):1199-211
references.pmid: 8813283
references.citation: Clin Neurophysiol. 2001 Jan;112(1):114-21
references.pmid: 11137668
references.citation: Int J Comput Assist Radiol Surg. 2011 May;6(3):447-55
references.pmid: 20697829
references.citation: Proc Biol Sci. 1992 Jun 22;248(1323):223-8
references.pmid: 1354360
references.citation: Hum Brain Mapp. 2008 Mar;29(3):281-99
references.pmid: 17394210
references.citation: Behav Brain Res. 1983 Feb;7(2):165-78
references.pmid: 6830650
references.citation: J Neurophysiol. 1998 Dec;80(6):3247-60
references.pmid: 9862919
references.citation: Clin Neurophysiol. 2009 Oct;120(10):1859-65
references.pmid: 19766535
references.citation: J Physiol. 2010 Jan 1;588(Pt 1):201-12
references.pmid: 19917563
references.citation: Dev Med Child Neurol. 1986 Apr;28(2):205-12
references.pmid: 3709990
references.citation: Mov Disord. 2005 May;20(5):545-51
references.pmid: 15641012
references.citation: Exp Brain Res. 2002 Aug;145(4):437-47
references.pmid: 12172655
references.citation: Exerc Sport Sci Rev. 2009 Oct;37(4):179-87
references.pmid: 19955867
references.citation: Behav Brain Res. 2009 Apr 12;199(1):61-75
references.pmid: 19061920
references.citation: J Cogn Neurosci. 2011 Sep;23(9):2468-80
references.pmid: 21268666
references.citation: Brain Cogn. 1989 Sep;11(1):98-113
references.pmid: 2789820
references.citation: J Mot Behav. 2007 Jan;39(1):29-39
references.pmid: 17251169
references.citation: J Neurophysiol. 2003 Jan;89(1):168-76
references.pmid: 12522169
references.citation: J Neuropathol Exp Neurol. 1985 Nov;44(6):578-91
references.pmid: 4056827
references.citation: J Cogn Neurosci. 2004 Jan-Feb;16(1):127-38
references.pmid: 15006042
references.citation: J Neurosci. 2007 Nov 7;27(45):12132-8
references.pmid: 17989279
references.citation: Neurosci Lett. 2002 Nov 8;332(3):205-9
references.pmid: 12399015
references.citation: J Neurophysiol. 1997 Mar;77(3):1325-37
references.pmid: 9084600
references.citation: Int J Neurosci. 1985 Jan;25(3-4):175-93
references.pmid: 3980151
references.citation: Neuroimage. 2011 Jul 15;57(2):495-501
references.pmid: 21549844
references.citation: J Neurophysiol. 1975 Jul;38(4):871-908
references.pmid: 808592
references.citation: Med Sci Sports Exerc. 2011 Jul;43(7):1188-99
references.pmid: 21200340
references.citation: Eur Neurol. 1974;12(3):142-7
references.pmid: 4426322
references.citation: J Neurophysiol. 2004 Oct;92(4):2405-12
references.pmid: 15381748
references.citation: J Physiol. 2007 Aug 15;583(Pt 1):99-114
references.pmid: 17556392
references.citation: Hum Brain Mapp. 1994;1(3):221-34
references.pmid: 24578042
references.citation: Scand J Med Sci Sports. 2013 Dec;23(6):740-8
references.pmid: 22429184
references.citation: Cereb Cortex. 2005 Jun;15(6):854-69
references.pmid: 15590909
references.citation: Brain Res. 1978 Dec 29;159(2):473-6
references.pmid: 728816
references.citation: Neurology. 1991 Nov;41(11):1795-9
references.pmid: 1944911
references.citation: J Neurophysiol. 1998 Oct;80(4):2162-76
references.pmid: 9772269
references.citation: Brain. 1995 Apr;118 ( Pt 2):429-40
references.pmid: 7735884
references.citation: Cereb Cortex. 2013 Jun;23(6):1362-77
references.pmid: 22610393
references.citation: Cereb Cortex. 2008 Jun;18(6):1395-406
references.pmid: 17928331
references.citation: Neurosci Biobehav Rev. 2010 Apr;34(5):721-33
references.pmid: 19850077
references.citation: Exp Brain Res. 2002 Jul;145(1):76-82
references.pmid: 12070747
references.citation: J Neurosci. 1994 Jun;14(6):3775-90
references.pmid: 8207487
references.citation: J Neurophysiol. 1993 Jan;69(1):187-200
references.pmid: 8433130
references.citation: Annu Rev Neurosci. 2000;23:393-415
references.pmid: 10845069
references.citation: Nature. 1968 Nov 30;220(5170):914-5
references.pmid: 5722141
references.citation: Phys Ther Rev. 1955 Oct;35(10):567-9
references.pmid: 13266520
references.citation: Acta Physiol (Oxf). 2013 Feb;207(2):385-96
references.pmid: 23082845
references.citation: J Physiol. 2001 Mar 15;531(Pt 3):849-59
references.pmid: 11251064
references.citation: J Physiol. 2002 Aug 15;543(Pt 1):317-26
references.pmid: 12181302
references.citation: Arch Neurol. 2007 Jan;64(1):20-4
references.pmid: 17210805
references.citation: J Sports Sci. 1993 Apr;11(2):145-58
references.pmid: 8497017
references.citation: Neurobiol Aging. 2010 Mar;31(3):464-81
references.pmid: 18495300
references.citation: J Gen Psychol. 1982 Oct;107(2):277-281
references.pmid: 28150542
references.citation: Hum Brain Mapp. 2009 Apr;30(4):1397-412
references.pmid: 18537112
references.citation: J Comp Neurol. 2002 Jan 28;443(1):71-85
references.pmid: 11793348
references.citation: Eur J Neurosci. 2010 Oct;32(8):1397-406
references.pmid: 20846329
references.citation: J Neurosci. 2008 May 28;28(22):5631-40
references.pmid: 18509024
references.citation: Somatosens Mot Res. 2000;17(3):255-71
references.pmid: 10994596
references.citation: Nature. 1994 Sep 29;371(6496):413-6
references.pmid: 8090219
references.citation: Brain. 1998 Nov;121 ( Pt 11):2159-73
references.pmid: 9827775
references.citation: J Cereb Blood Flow Metab. 1996 Jan;16(1):23-33
references.pmid: 8530552
references.citation: J Appl Physiol (1985). 2011 Jan;110(1):166-75
references.pmid: 21088207
references.citation: J Sports Med Phys Fitness. 2001 Sep;41(3):291-9
references.pmid: 11533557
references.citation: Clin Neurophysiol. 2009 Apr;120(4):802-8
references.pmid: 19230754
references.citation: Hum Brain Mapp. 2007 Jul;28(7):636-44
references.pmid: 17080438
references.citation: Exp Brain Res. 2008 Mar;186(1):59-66
references.pmid: 18040671
references.citation: Neuroimage. 2010 May 15;51(1):300-12
references.pmid: 20156564
references.citation: Neuroimage. 2002 Aug;16(4):920-35
references.pmid: 12202080
references.citation: J Neurophysiol. 2007 Jul;98(1):54-62
references.pmid: 17507504
references.citation: Neuroimage. 2009 Jan 15;44(2):469-79
references.pmid: 18950717
references.citation: Brain Res Rev. 2007 Apr;54(1):189-204
references.pmid: 17300842
references.citation: J Neurosci. 2012 Jan 11;32(2):646-52
references.pmid: 22238100
references.citation: J Appl Physiol (1985). 2009 Mar;106(3):830-6
references.pmid: 19150859
references.citation: J Neurosci. 2002 Jan 15;22(2):554-61
references.pmid: 11784802
references.citation: J Physiol. 2004 Nov 1;560(Pt 3):929-40
references.pmid: 15331684
references.citation: Exp Brain Res. 2010 Mar;201(2):229-38
references.pmid: 19826798