Motor cortical function and the precision grip.

Nimeshan Geevasinga,Steve Vucic,Parvathi Menon,Matthew C Kiernan

doi:10.14814/phy2.12120

Nimeshan Geevasinga, Steve Vucic + Show 2 more

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https://doi.org/10.14814/phy2.12120

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Journal: Physiological Reports	Publication Date: Dec 1, 2014
Citations: 39	License type: cc-by

Affiliation: University of Sydney

Abstract

While task‐dependent changes in motor cortical outputs have been previously reported, the issue of whether such changes are specific for complex hand tasks remains unresolved. The aim of the present study was to determine whether cortical inhibitory tone and cortical output were greater during precision grip and power grip. Motor cortex excitability was undertaken by using the transcranial magnetic stimulation threshold tracking technique in 15 healthy subjects. The motor‐evoked potential (MEP) responses were recorded over the abductor pollicis brevis (APB), with the hand in the following positions: (1) rest, (2) precision grip and (3) power grip. The MEP amplitude (MEP amplitude REST 23.6 ± 3.3%; MEP amplitude PRECISION GRIP 35.2 ± 5.6%; MEP amplitude POWER GRIP 19.6 ± 3.4%, F = 2.4, P < 0.001) and stimulus‐response gradient (SLOPEREST 0.06 ± 0.01; SLOPEPRCISION GRIP 0.15 ± 0.04; SLOPE POWER GRIP 0.07 ± 0.01, P < 0.05) were significantly increased during precision grip. Short interval intracortical inhibition (SICI) was significantly reduced during the precision grip (SICI REST 15.0 ± 2.3%; SICI PRECISION GRIP 9.7 ± 1.5%, SICI POWER GRIP 15.9 ± 2.7%, F = 2.6, P < 0.05). The present study suggests that changes in motor cortex excitability are specific for precision grip, with functional coupling of descending corticospinal pathways controlling thumb and finger movements potentially forming the basis of these cortical changes.

Highlights

Precision grip is defined as the act of grasping an object between the opposed tips of the thumb and index finger, and is vital for performance of skilled hand movements required for everyday function (Lemon and Griffiths 2005; Lemon 2010)
The mean maximal motor-evoked potential (MEP) amplitude, with stimulus intensity set to 150% Motor threshold (MT), was significantly increased during the precision grip when compared to the hand at rest and in the power grip position (MEP amplitude REST 1.9 Æ 0.2 mV; MEP amplitude PRECISION GRIP 2.8 Æ 0.4 mV; MEP amplitude POWER GRIP 1.6 Æ 0.3 mV, P < 0.001, Fig. 1B)
The mean maximal MEP amplitude, expressed as a percentage of the compound muscle action potential (CMAP) response and generated with stimulus intensity set to 150% MT, was significantly increased during the precision grip (MEP amplitude REST 23.6 Æ 3.3%; MEP amplitude PRECISION GRIP 35.2 Æ 5.6%; MEP amplitude POWER GRIP 19.6 Æ 3.4%, F = 2.4, P < 0.001, Fig. 2A)

Summary

Introduction

Precision grip is defined as the act of grasping an object between the opposed tips of the thumb and index finger, and is vital for performance of skilled hand movements required for everyday function (Lemon and Griffiths 2005; Lemon 2010). The execution of the precision grip is dependent on the ability to perform fine fractionated finger movements (Lemon et al 1996; Lemon 1997, 2010; Lemon and Griffiths 2005), largely mediated by a co-ordinated activity of the thenar group of muscles, including the abductor pollicis brevis (APB), together with first dorsal interosseous (FDI) (Napier 1956; Long et al 1970; Jeannerod 1986; Forssberg et al 1991; Maier and Hepp-Reymond 1995; Marzke 1997; Marzke et al 1998; Johanson et al 2001; Brochier et al 2004).

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