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BackgroundPrevious studies with Transcranial Magnetic Stimulation (TMS) have focused on the cortical representation of limited group of muscles. No attempts have been carried out so far to get simultaneous recordings from hand, forearm and arm with TMS in order to disentangle a 'functional' map providing information on the rules orchestrating muscle coupling and overlap. The aim of the present study is to disentangle functional associations between 12 upper limb muscles using two measures: cortical overlapping and cortical covariation of each pair of muscles. Interhemispheric differences and the influence of posture were evaluated as well.Methodology/principal findingsTMS mapping studies of 12 muscles belonging to hand, forearm and arm were performed. Findings demonstrate significant differences between the 66 pairs of muscles in terms of cortical overlapping: extremely high for hand-forearm muscles and very low for arm vs hand/forearm muscles. When right and left hemispheres were compared, overlapping between all possible pairs of muscles in the left hemisphere (62.5%) was significantly higher than in the right one (53.5% ). The arm/hand posture influenced both measures of cortical association, the effect of Position being significant [p = .021] on overlapping, resulting in 59.5% with prone vs 53.2% with supine hand, but only for pairs of muscles belonging to hand and forearm, while no changes occurred in the overlapping of proximal muscles with those of more distal districts.Conclusions/significanceLarger overlapping in the left hemisphere could be related to its lifetime higher training of all twelve muscles studied with respect to the right hemisphere, resulting in larger intra-cortical connectivity within primary motor cortex. Altogether, findings with prone hand might be ascribed to mechanisms facilitating coupling of muscles for object grasping and lifting -with more proximal involvement for joint stabilization- compared to supine hand facilitating actions like catching. TMS multiple-muscle mapping studies permit a better understanding of motor control and 'plastic' reorganization of motor system.

Introduction: The trigeminal autonomic cephalagias (TACs) are short-lasting unilateral headaches associated with autonomic features. Even if coexistence of different ipsilateral TACs in the same patient has been previously reported in few papers, the simultaneous occurrence of contralateral TACs is not described previously. Case description: A 50 years old working man complained, at the end of his cluster period, a new TAC, fitting the criteria for probable paroxysmal hemicrania. The dramatic improvement of this last cephalalgia with indomethacin treatment confirmed the diagnosis. Discussion, evaluation and conclusion: There is a clear overlap in clinical diagnosis between cluster headache (CH) and paroxysmal hemicrania (PH) and similarities are somewhat greater than differences. The originality of this report is the coexistence of contralateral TACs in the same patients at the same moment. According neuroimaging studies, CH hypothalamic activation occurs ipsilateral to the side of the headache while in PH hypothalamic activation occurs contralateral to the side of headache. It could be suggested that a continuous hypothalamic activation give a maladaptive plasticity recruiting closed neuronal aggregates responsible for the developing of PH after a long period of CH, confirming the central origin of both CH and PH. Further studies need to confirm this hypothesis. [ABSTRACT FROM AUTHOR]