Corticospinal excitability during motor imagery of a simple tonic finger movement in patients with writer's cramp.

Motor imagery (MI) is the mental rehearsal of a motor act without overt movement. Using transcranial magnetic stimulation (TMS), we tested the effect of MI on corticospinal excitability in patients with writer's cramp. In 10 patients with writer's cramp and 10 healthy controls, we applied focal TMS over each primary motor area and recorded motor evoked potentials (MEPs) from contralateral hand and arm muscles while participants imagined a tonic abduction of the index finger contralateral to the stimulated hemisphere. In healthy controls and patients, the MEP amplitude in the relaxed first dorsal interosseus muscle (FDI) showed a muscle-specific increase during MI; however, the increase was less pronounced in patients than in healthy controls. In addition, in patients but not in controls, the MEP amplitude also increased in hand and forearm muscles not involved in the imagined movement. This abnormal spread of facilitation was observed in the affected and unaffected upper limb. MI of simple hand movements is less efficient and less focussed in patients with writer's cramp than it is in normal subjects.

Ligand-dependent structural changes in the V(1) ATPase from Manduca sexta.

The response of V(1) ATPase of the tobacco hornworm Manduca sexta to Mg(2+) and nucleotide binding in the presence of the enhancer methanol has been studied by CuCl(2)-induced disulfide formation, fluorescence spectroscopy, and small-angle X-ray scattering. When the V(1) complex was supplemented with CuCl(2) nucleotide-dependence of A-B-E and A-B-E-D cross-linking products was observed in absence of nucleotides and presence of MgADP+Pi but not when MgAMP.PNP or MgADP were added. A zero-length cross-linking product of subunits D and E was formed, supporting their close proximity in the V(1) complex. The catalytic subunit A was reacted with N-4[4-[7-(dimethylamino)-4-methyl]coumarin-3-yl]maleimide (CM) and spectral shifts and changes in fluorescence intensity were detected upon addition of MgAMP.PNP, -ATP, -ADP+Pi, or -ADP. Differences in the fluorescence emission of these nucleotide-binding states were monitored using the intrinsic tryptophan fluorescence. The structural composition of the V(1) ATPase from M. sexta and conformational alterations in this enzyme due to Mg(2+) and nucleotide binding are discussed on the basis of these and previous observations.

Long lasting effects of transcranial direct current stimulation on motor imagery.

Transcranial magnetic stimulation (TMS) was employed to probe the modulatory effects of transcranial direct current stimulation of motor cortex on motor evoked responses (MEPs) produced during motor imagery. MEP amplitudes at rest and during motor imagery were assessed before and for a period of 60 min after transcranial direct current stimulation (tDCS) applied over the primary motor cortex at 1 mA for 5 min. Cathodal stimulation induced a decrease of about 30% of MEP amplitude at rest and a 50% reduction of MEP size during imagery. Ten minutes after tDCS, MEPs at rest returned to baseline values while MEPs during motor imagery were suppressed for up to 30 min. No changes in MEP amplitude during imagery were found after anodal stimulation. tDCS could represent a powerful tool to modulate the excitability of motor areas involved in mental practice and motor imagery.