Effect of stimulation of an upper limb on motor evoked potentials in lower limb muscles to transcranial magnetic stimulation in normal subjects and patients with thalamic infarction

Exploring the Role of Cortical Reorganization in Postamputation Phantom Phenomena, Including Phantom Limb Pain in Lower Limb Amputees: A Cross-Sectional Study of the Patterns of Referral of Sensations into the Phantom

BACKGROUND

Cortical reorganization and pain memory are theories to explain phantom limb pain and other postamputation phantom phenomena. This study was undertaken to identify evidence of cortical reorganization in lower limb amputees and to find evidence for the pain memory theory.

METHODS

This was a qualitative interview study using structured questionnaires with lower limb amputees. Participants were asked to identify body areas and activities that stimulate postamputation phantom phenomena to confirm the cortical reorganization theory. We tested the pain memory theory by comparing traumatic amputees with surgical amputees.

RESULTS

A total of 122 participants (response rate 42%) were recruited. Prevalence of postamputation phantom phenomena was similar to previous studies with phantom pain reported as 84%. Twenty (16.3%) identified body regions that could stimulate postamputation phantom phenomena and 32 (26%) identified activities that could stimulate postamputation phantom phenomena. Not all body areas or activities were related to somatotopic regions adjacent to the leg on the sensory homunculus. Overall, 47 (38.2%) exhibited attributes suggestive of cortical reorganization into areas adjacent to the leg. No associations were found between presence of pain or length of time in pain before amputation and the presence of phantom pain (p = .1-1.0). No statistical difference was found between surgical and traumatic amputees for any postamputation phantom phenomena (p = .3-1.0).

CONCLUSIONS

The cortical reorganization and pain memory theories for the development and maintenance of postamputation phantom phenomena have only limited support from our data. Taking this into account, it may be worth reopening the debate on the mechanism for postamputation phantom phenomena, including phantom limb pain. The cortical reorganization theory and memory theory for the mechanism of phantom limb pain are questioned by these results. Both may play a role, but neither can explain the presence of postamputation phantom phenomena on their own.

Impact of different stimulation types on orthostatic tremor

OBJECTIVE

Primary orthostatic tremor (OT) is thought to be generated by a unique supraspinal tremor generator. Here we studied the effect of ipsi- and contralateral stimulation of the central and peripheral nervous system on OT.

METHODS

In 7 patients with primary OT, surface EMG was recorded from both tibialis anterior muscles. We performed transcranial magnetic stimulation (TMS) over the vertex, and lumbar magnetic stimulation (LMS) over the lumbar spine. Supramaximal electrical nerve stimuli were applied to the tibial or peroneal nerve at the knee. Proprioceptive input was evoked by rhythmical submaximal stimulation of the tibial, peroneal or sural nerve at the ankle.

RESULTS

TMS reset OT significantly in the contralateral as well as the ipsilateral tibialis anterior muscle. The resetting in both muscles was identical. In contrast, peripheral input by means of LMS, supra- or submaximal nerve stimulation had no impact on OT.

CONCLUSIONS

Transcranial magnetic stimulation of one cortical leg area resets OT in both legs whereas OT is not modified by any peripheral stimuli applied in this study.

SIGNIFICANCE

Our results support the hypothesis of n unique supraspinal OT generator. This generator receives a modulating input from the motor cortex.