title: Synaptic and functional linkages between spinal premotor interneurons and hand-muscle activity during precision grip.
abstract: Grasping is a highly complex movement that requires the coordination of a number of hand joints and muscles. Previous studies showed that spinal premotor interneurons (PreM-INs) in the primate cervical spinal cord have divergent synaptic effects on hand motoneurons and that they might contribute to hand-muscle synergies. However, the extent to which these PreM-IN synaptic connections functionally contribute to modulating hand-muscle activity is not clear. In this paper, we explored the contribution of spinal PreM-INs to hand-muscle activation by quantifying the synaptic linkage (SL) and functional linkage (FL) of the PreM-INs with hand-muscle activities. The activity of 23 PreM-INs was recorded from the cervical spinal cord (C6-T1), with EMG signals measured simultaneously from hand and arm muscles in two macaque monkeys performing a precision grip task. Spike-triggered averages (STAs) of rectified EMGs were compiled for 456 neuron-muscle pairs; 63 pairs showed significant post-spike effects (PSEs; i.e., SL). Conversely, 231 of 456 pairs showed significant cross-correlations between the IN firing rate and rectified EMG (i.e., FL). Importantly, a greater proportion of the neuron-muscle pairs with SL showed FL (43/63 pairs, 68%) compared with the pairs without SL (203/393, 52%), and the presence of SL was significantly associated with that of FL. However, a significant number of pairs had SL without FL (SL∩!FL, n = 20) or FL without SL (!SL∩FL, n = 203), and the proportions of these incongruities exceeded the number expected by chance. These results suggested that spinal PreM-INs function to significantly modulate hand-muscle activity during precision grip, but the contribution of other neural structures is also needed to recruit an adequate combination of hand-muscle motoneurons.
authors: Department of Neurophysiology, National Institute of Neuroscience Tokyo, Japan ; Department of Developmental Physiology, National Institute for Physiological Sciences Okazaki, Japan.
authors: Tomohiko
authors: T
authors: Takei
authors: Kazuhiko
authors: K
authors: Seki
keywords: cross-correlation; grasping; muscle synergy; spike-triggered average; spinal cord
references: Exp Brain Res. 2002 Sep;146(2):233-43
references: 12195525
references: J Neurophysiol. 2000 Jan;83(1):99-115
references: 10634857
references: Science. 2007 Jan 19;315(5810):390-3
references: 17234950
references: J Comp Neurol. 2002 May 20;447(1):57-71
references: 11967895
references: J Neurophysiol. 2001 Apr;85(4):1461-78
references: 11287470
references: J Comp Neurol. 1979 Jul 15;186(2):189-211
references: 87406
references: Neuron. 2002 Aug 15;35(4):773-82
references: 12194875
references: J Neurosci. 2012 Sep 5;32(36):12349-60
references: 22956825
references: Primates. 2012 Oct;53(4):391-6
references: 22526462
references: J Neurophysiol. 1992 Apr;67(4):875-89
references: 1588388
references: J Neurophysiol. 2005 Nov;94(5):3325-41
references: 16014801
references: Exp Brain Res. 1995;102(3):546-50
references: 7737401
references: J Neurophysiol. 2001 Feb;85(2):605-19
references: 11160497
references: Brain Res. 1983 Feb 21;261(2):312-6
references: 6831213
references: Exp Brain Res. 1999 Dec;129(3):401-16
references: 10591912
references: J Neurophysiol. 2002 Mar;87(3):1473-87
references: 11877520
references: Curr Opin Neurobiol. 2009 Dec;19(6):601-7
references: 19828310
references: J Neurophysiol. 1996 May;75(5):1826-42
references: 8734583
references: Science. 2007 Jan 19;315(5810):339-40
references: 17234936
references: J Neurophysiol. 2008 Apr;99(4):2012-20
references: 18234981
references: J Neurosci. 2003 Oct 22;23(29):9611-9
references: 14573541
references: Neurosci Lett. 1981 Apr 9;23(1):7-12
references: 6164967
references: J Neurosci Methods. 2007 Jul 30;163(2):283-94
references: 17477974
references: J Neurosci Methods. 1998 Feb 20;79(2):143-50
references: 9543480
references: J Physiol. 2002 Feb 1;538(Pt 3):919-30
references: 11826175
references: Nat Neurosci. 2003 Mar;6(3):300-8
references: 12563264
references: J Neurosci. 1993 Feb;13(2):467-91
references: 8426224
references: J Neurosci. 2008 Jan 23;28(4):880-92
references: 18216196
references: J Neurophysiol. 1998 Nov;80(5):2475-94
references: 9819257
references: J Neurophysiol. 1980 Oct;44(4):751-72
references: 6253604
references: J Neurophysiol. 1998 Sep;80(3):1391-406
references: 9744948
references: J Neurosci. 2010 Jan 27;30(4):1322-36
references: 20107059
references: J Physiol. 1993 Sep;469:213-43
references: 8271199
references: J Neurophysiol. 1991 Dec;66(6):1965-77
references: 1812229
references: Proc Natl Acad Sci U S A. 1994 Aug 2;91(16):7534-8
references: 8052615
references: Neuroscientist. 2002 Oct;8(5):437-42
references: 12374428
references: J Physiol. 1986 Dec;381:529-49
references: 3625544
references: J Neurosci. 2010 Dec 15;30(50):17041-50
references: 21159974
references: J Neurophysiol. 2004 Sep;92(3):1770-82
references: 15163676
references: Nat Neurosci. 1999 Feb;2(2):162-7
references: 10195201
references: J Neurophysiol. 1984 Apr;51(4):777-92
references: 6201596