Between-hand difference in ipsilateral deactivation is associated with hand lateralization: fMRI mapping of 284 volunteers balanced for handedness
Front. Hum. Neurosci.. 2015-02-06; 9:
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1. Front Hum Neurosci. 2015 Feb 6;9:5. doi: 10.3389/fnhum.2015.00005. eCollection
Between-hand difference in ipsilateral deactivation is associated with hand
lateralization: fMRI mapping of 284 volunteers balanced for handedness.
Tzourio-Mazoyer N(1), Petit L(1), Zago L(1), Crivello F(1), Vinuesa N(1), Joliot
M(1), Jobard G(1), Mellet E(1), Mazoyer B(1).
(1)GIN UMR5296, CNRS CEA Université de Bordeaux Bordeaux, France.
In right-handers (RH), an increase in the pace of dominant hand movement results
in increased ipsilateral deactivation of the primary motor cortex (M1). By
contrast, an increase in non-dominant hand movement frequency is associated with
reduced ipsilateral deactivation. This pattern suggests that inhibitory processes
support right hand dominance in right-handers and raises the issues of whether
this phenomenon also supports left hand preference in left-handers (LH), and/or
whether it relates to asymmetry of manual ability in either group. Thanks to the
BIL&GIN, a database dedicated to the investigation of hemispheric specialization
(HS), we studied the variation in M1 activity during right and left finger
tapping tasks (FTT) in a sample of 284 healthy participants balanced for
handedness. An M1 fMRI localizer was defined for each participant as an 8 mm
diameter sphere centered on the motor activation peak. RH exhibited significantly
larger deactivation of the ipsilateral M1 when moving their dominant hand than
their non-dominant hand. In contrast, LH exhibited comparable ipsilateral M1
deactivation during either hand movement, reflecting a bilateral cortical
specialization. This pattern is likely related to left-handers’ good performances
with their right hand and consequent lower asymmetry in manual ability compared
with RH. Finally, inter-individual analyses over the whole sample demonstrated
that the larger the difference in manual skill across hands, the larger the
difference in ipsilateral deactivation. Overall, we propose that difference in
ipsilateral deactivation is a marker of difference in manual ability asymmetry
reflecting differences in the strength of transcallosal inhibition when a given
hand is moving.