Hemispheric asymmetries of cortico-cortical connections in human hand motor areas.
OBJECTIVE
To evaluate possible functional asymmetries of the motor cortex on the hand-dominant versus the non-dominant hemisphere.


METHODS
We assessed the handedness of 15 consenting volunteers using the Edinburgh Inventory. They were divided in two groups: 9 right-handers and 6 left-handers. We used single- and paired-transcranial magnetic stimulation (TMS) to measure the relaxed and active motor threshold and the ipsilateral cortico-cortical inhibition and facilitation curve for both hand motor areas. We looked for hemispheric asymmetries of variables related to the side of stimulation (dominant versus non-dominant) and to handedness.


RESULTS
We found no significant intra- or intergroup hemispheric asymmetry for the relaxed and active thresholds. Among the right-handers, the cortico-cortical inhibition and facilitation curve showed an increased amount of facilitation in the dominant as compared with the non-dominant hand area. No such changes were seen among the left-handers. Both the dominant and the non-dominant hand areas of the right-handers showed more inhibition and less facilitation on the cortico-cortical inhibition and facilitation curve than the corresponding areas of left-handers.


CONCLUSIONS
In the right-handers, paired TMS studies showed a functional asymmetry of the motor cortex between the dominant and the non-dominant hand. The left-handers did not show this lateralization. Under TMS investigation their motor cortex function appeared different from that of right-handers.
Civardi
C
C
Department of Neurology, Amedeo Avogadro University School of Medicine, Ospedale Maggiore della Carità, C.so Mazzini 18, 28100, Novara, Italy.
Cavalli
A
A
Naldi
P
P
Varrasi
C
C
Cantello
R
R
D000328:Adult; D004558:Electric Stimulation; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000502:physiology*; D006801:Humans; D008280:Magnetics; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology