Cortical plasticity after hand prostheses use: Is the hypothesis of deafferented cortex "invasion" always true?

OBJECTIVE

To study motor cortex plasticity after a period of training with a new prototype of bidirectional hand prosthesis in three left trans-radial amputees, correlating these changes with the modification of Phantom Limb Pain (PLP) in the same period.

METHODS

Each subject underwent a brain motor mapping with Transcranial Magnetic Stimulation (TMS) and PLP evaluation with questionnaires during a six-month training with a prototype of bidirectional hand prosthesis.

RESULTS

The baseline motor maps showed in all three amputees a smaller area of muscles representation of the amputated side compared to the intact limb. After training, there was a partial reversal of the baseline asymmetry. The two subjects affected by PLP experienced a statistically significant reduction of pain.

CONCLUSIONS

Two apparently opposite findings, the invasion of the "deafferented" cortex by neighbouring areas and the "persistence" of neural structures after amputation, could vary according to different target used for measurement. Our results do not support a correlation between PLP and motor cortical changes.

SIGNIFICANCE

The selection of the target and of the task is essential for studies investigating motor brain plasticity. This study boosts against a direct and unique role of motor cortical changes on PLP genesis.

Somatosensory Evoked Potentials of Inferior Alveolar Nerve: confirmation of a possible non-invasive neurophysiological approach

INTRODUCTION

The use of inferior alveolar nerve (IAN) somatosensory evoked potentials (SEPs) may represent a non-invasive method to evaluate the sensory nerve function in the maxillofacial region. The aim of this work is to confirm the feasibility of a technique, previously reported in the literature, and the data previously obtained.

MATERIALS AND METHODS

SEPs were obtained following electrical stimulation (square wave pulses 0.2 millisecond [ms] in duration, 4 to 6.5 mA, 0.7/second repetition rate, 200 averages) of the gum at the mental foramen level, in the IAN region, via a new designed type of intraoral surface electrodes and recorded from the contralateral central scalp sites.

RESULTS

We recognized waveforms of sufficient quality and consistently recorded a "W"-shaped response. Peak latencies of waves were at 14, 20, 27, 34 and 43 ms respectively. One side of the lower lip can be compared with the contralateral side.

CONCLUSIONS

IAN SEPs, obtained with the present technique, may represent an objective, non-invasive, and reliable way of testing sensory nerve function in the maxillofacial region.