Dystonia is considered a “network” disease with an abnormal cortical plasticity induced by by paired-associated-stimulation. In this study, we applied the PAS-TMS paradigm in healthy subjects, with the aim to collect reliable data from both hemispheres in order to put the basis to future application in focal dystonia. We studied 7 healthy subjects (4 females; mean age 32.33 ± 6.79 years). We applied electrical stimulatrion of median nerve electrical and MEPs from both abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles (2), following Stefan et al. technique, with ISI set to 25 ms. MEPs before and after PAS protocol, evaluating first the dominant and then controlateral motor cortical area. Every subject performed the study in the same experimental session. Comparison between MEPs before and after PAS on homologous hemisphere disclosed a trend toward an increased of amplitude, but without reaching statistical significance for both ABP and FDI muscles, according to Quartarone et al. At the same time, no significant difference was detected by evaluating paired inter-hemisphere analysis. These bilateral findings in normal subjects could be a possible beginning for future application on focal movement disorders.

To verify the test-retest, inter and intraexaminer variability of the Compound Muscle Action Potential (CMAP) and Sensory Nerve Action Potential (SNAP) within our neurophysiology laboratory; to identify the technical variables that can affect the reproducibility of signals in the follow-up studies. Distal CMAP of Median and Ulnar nerves and SNAP of radial nerve (I ° finger), median nerve (I° and IV° fingers), ulnar nerve (IV and V fingers) of the right hand were recorded by 9 operators (5 technicians of neurophysiology and 4 physicians) in healthy volunteers. Each test was repeated 3 times randomly within 4 months. The latency, amplitude, and intensity of stimulus were collected. The montages were photographed. Our data showed a discrete stability of CMAP parameters mainly for ulnar nerve. On the contrary the amplitudes of SNAPs were fairly variables. The results suggest that it is crucial to check the neurophysiological techniques commonly applied in laboratories were several operators work. More time must be dedicated to a common training, to get consistent results useful in repeated trials.

Intraoperative neurophysiological monitoring of Facial nerve (FN) has become an integral part of CPA surgery, mainly to preserve nerves functional integrity. Deletis et al. (2009) described a technique to elicit the blink reflex (BR) during anaesthesia. Our aim was to investigate technical aspects, success rate of BR during IOM, its reliability and usefulness in predicting FN outcome. 19 pts affected by APC tumours (neurinoma, meningioma and brainstem astrocytoma) and hemifacial spasm were studied. Free run EMG, FN cMAP and BR were recorded during surgery. BR was recordable in 90%. There was a good correlation between BR stability and positive outcome. The patient who showed BR decrement or disappearance had a severe FN deficit at postIOM evaluation. BR is a method of simple execution that does not interfere with neurosurgeon activity. It can be added to other classical techniques to improve IOM reliability.