The after-effects of repetitive transcranial magnetic stimulation (rTMS) are highly variable between individuals. Because different populations of cortical neurons are stimulated more easily or are more excitable in different people at different times, the variability may not be due to differences between individuals in the plasticity of cortical synapses, but may instead be due to individual differences in the recruitment of cortical neurons. In this study, we examined the effects of rTMS in 56 healthy volunteers. The responses to excitatory and inhibitory theta burst stimulation (TBS) protocols were highly variable between individuals. Surprisingly, the TBS effect was highly correlated with the latency of motor-evoked potentials (MEPs) evoked by TMS pulses that induced an anterior-posterior (AP) directed current across the central sulcus. Finally, we devised a new plasticity protocol using closely timed pairs of oppositely directed TMS current pulses across the central sulcus. Again, the after-effects were related to the latency of MEPs evoked by AP current. Our results are consistent with the idea that variation in response to rTMS plasticity probing protocols is strongly influenced by which interneuron networks are recruited by the TMS pulse.
The acronym CANOMAD encompasses chronic ataxic neuropathy combined with ophthalmoplegia, M protein, cold agglutinins, and anti-disialosyl antibodies.Herein we describe 2 patients presenting with progressive ataxic neuropathy who only developed ophthalmoplegia after a significant delay post-presentation, which in 1 case had features indicative of brainstem dysfunction. Both patients were found to have an IgM paraprotein and anti-disialosyl antibodies. They responded to treatment with intravenous immunoglobulin, thus illustrating the importance of diagnosing this condition.
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