Thomas Weiss

Decrease in phantom limb pain associated with prosthesis-induced increased use of an amputation stump in humans

The experience of phantom limb pain, non-painful phantom limb sensation and telescoping was ascertained by questionnaire in a group of upper extremity amputees wearing a functionally effective Sauerbruch prosthesis which permits extensive use of the affected limb and in a group of patients wearing a cosmetic prosthesis that did little to increase the utilization of the amputation stump. The Sauerbruch prosthesis group exhibited a significant and large decrease in amount of phantom limb pain while the cosmetic prosthesis group showed no change. Neither group experienced a decrease in non-painful phantom limb sensation or telescoping. The amount of phantom limb pain has been found to be highly correlated with the amount of injury-related, afferent-decrease cortical reorganization. It is possible that the increased use of the amputation stump induced by wearing a Sauerbruch prosthesis produced a countervailing use-dependent, afferent-increase type of cortical reorganization that reversed the phantom limb pain. These preliminary results require replication. Their therapeutic implications are discussed.

Rapid functional plasticity of the somatosensory cortex after finger amputation

Abstract. Recent research indicates that areas of the primary somatosensory (SI) and primary motor cortex show massive cortical reorganization after amputation of the upper arm, forearm or fingers. Most of these studies were carried out months or several years after amputation. In the present study, we describe cortical reorganization of areas in the SI of a patient who underwent amputation of the traumatized middle and ring fingers of his right hand 10 days before cortical magnetic source imaging data were obtained. Somatosensory-evoked magnetic fields (SEF) to mechanical stimuli to the finger tips were recorded and single moving dipoles were calculated using a realistic volume conductor model. Results reveal that the dipoles representing the second and fifth fingers of the affected hand were closer together than the comparable dipoles of the unaffected hand. Our findings demonstrate that neural cell assemblies in SI which formerly represented the right middle and ring fingers of this amputee became reorganized and invaded by neighbouring cell assemblies of the index and little finger of the same hand. These results indicate that functional plasticity occurs within a period of 10 days after amputation.

Dipole analysis of ultralate (C-fibres) evoked potentials after laser stimulation of tiny cutaneous surface areas in humans

Ultralate (C-fibres) laser evoked potentials (LEP) can be obtained by stimulation of a tiny skin surface area (0.23 mm(2)). Since their generators are unknown up to now, we performed brain source analyses of ultralate LEPs using high resolution electroencephalography (64 channels) and a realistic head model that was based on individual magnetic resonance images. Ultralate LEPs were characterized by a negative-positive complex with a large positive component maximal at the vertex. Source analysis revealed that ultralate LEPs could be explained by two dipole sources in the upper bank of the contralateral and ipsilateral Sylvian fissure (SII) and one dipole in the median region corresponding to the anterior cingulate gyrus.

Increased excitability in the primary motor cortex and supplementary motor area in patients with phantom limb pain after upper limb amputation

Using functional magnetic resonance imaging and single slice FLASH technique, we investigated reorganization of the hand representation of the primary sensorimotor cortex (SMC) in 16 patients with upper extremity amputation. Patients were asked to perform finger tapping with the intact hand, repetitive eye closing and anteflexion of the amputation stump or intact shoulder. Six normal volunteers served as control. In the normal volunteers activations during shoulder anteflexion, finger tapping and eye closure were located within the central sulcus in a medio-lateral fashion. Patients demonstrated invasion of the face or shoulder representation into the hand representation of the amputated limb. Eight phantom limb pain patients showed significantly greater activation in SMC and supplementary motor area (SMA) in contrast to eight patients without phantom limb pain. We conclude, that different parts of the motor system are affected in patients with phantom limb pain--possibly in the sense of an up-regulation of excitability.

Sensory feedback prosthesis reduces phantom limb pain: Proof of a principle

BACKGROUNDnConstrained functionality and phantom limb pain (PLP) are major concerns for forearm amputees. Neuroscientific investigations of PLP suggest that behaviorally relevant stimulation of the stump can decrease PLP. Furthermore the prosthesis user could use feedback information of the prosthesis hand for optimizing prosthesis motor control when handling soft and fragile objects. Somatosensory feedback information from a prosthetic hand may therefore help to improve prosthesis functionality and reduce phantom limb pain.nnnOBJECTIVESnWe wanted to find out whether a two weeks training on a hand prosthesis that provides somatosensory feedback may help to improve prosthesis functionality and reduce phantom limb pain.nnnMETHODSnEight forearm amputees with phantom limb pain were trained for two weeks to use a hand prosthesis with somatosensory feedback on grip strength.nnnRESULTSnThe current study demonstrates a significant increase of functionality of the prosthesis in everyday tasks. Furthermore, the study shows that usage of a prosthesis that provides somatosensory feedback on the grip strength is effective to reduce phantom limb pain.nnnCONCLUSIONSnA prosthesis with a feedback function appears to be a promising therapeutic tool to reduce phantom limb pain and to increase functionality in everyday tasks. Future studies should further investigate the scope of application of that principle.

Power of theta waves in the EEG of human subjects increases during recall of haptic information

Several studies have reported a functional relationship between spectral power within the theta-band of the EEG (theta-power) and memory load while processing visual or semantic information. We investigated theta power during the processing of different complex haptic stimuli using a delayed recall design. The haptic explorations consisted of palpating the structure of twelve sunken reliefs with closed eyes. Subjects had to reproduce each relief by drawing it 10 s after the end of the exploration. The relationship between mean theta power and mean exploration time was analysed using a regression model. A linear relationship was found between the exploration time and theta power over fronto-central regions (Fp1, Fp2, F3, F7, F8, Fz, C3) directly before the recall of the relief. This result is interpreted in favour of the hypothesis that fronto-central theta power of the EEG correlates with the load of working memory independent of stimulus modality.

Activation processes during mental practice in stroke patients.

In healthy subjects, mental practice is known to improve motor performance. It is also known to be accompanied by a higher central nervous activity. Since such effects seem to be desirable for rehabilitation, we investigated the possibility of detecting changes in central nervous activity by means of EEG in stroke patients, and whether these changes were similar to those observed in healthy subjects. 12 left-sided hemiplegic patients who underwent a specific post-stroke rehabilitation treatment were requested to perform a simple arm movement sequence. In the following mental practice period the patients were requested to image the same sequence without any real movement. EEG background activity was recorded during rest and imagination periods. After the calculation of z-transformed power values within the theta, alpha, and beta-1 band, differences between rest and imagination periods were evaluated for their significance. Stroke patients show significant decreases of theta, alpha, as well as beta-1 power during mental practice in comparison to the rest period. These changes are similar to those obtained in healthy subjects. Theta power decreases in central and parietal leads. Central alpha power diminishes only during imagination of the contralateral arm. This phenomenon as well as the decrease of beta-1 power in central derivation were also obtained during real motor performance and might indicate an activation of the sensorimotor cortex. In accordance with the hypothesis of internal feedback mechanisms, this activation is a necessary prerequisite for motor learning during mental practice.

Mental Practice of Motor Skills Used in Poststroke Rehabilitation has Own Effects on Central Nervous Activation

In the last years it has been shown that the use of the EMG triggered electrical myostimulation (ETEM) brings good results in poststroke rehabilitation. It has been hypothesized that the relearning effects obtained by means of ETEM are due to the reinstatement of proprioceptive feedback. However, the technique is most powerful if imagination of motor acts (the so called mental practice) is used as an initial part of ETEM. Since mental practice in healthy people leads to central nervous activation processes as well as to an improvement of motor skills, we investigated the effects of mental practice alone on central nervous activity by means of EEG in stroke patients. Twelve left-sided hemiplegic patients who underwent a specific poststroke rehabilitation treatment were requested to perform a simple arm movement sequence. In the following mental practice period the patients were requested to imagine the same sequence without any real movement. EEG background activity was recorded during baseline and imagination periods. After the calculation of z-transformed power values within the alpha and beta-1 band, differences between rest and imagination periods were evaluated for significance. Stroke patients showed significant decreases of alpha as well as beta-1 power during mental practice in comparison to the rest period. These changes are similar to those obtained in healthy subjects. Central alpha power diminished only during imagination of the contralateral arm. This phenomenon as well as the decrease of beta-1 power in central derivation were also obtained during real motor performance and might indicate an activation of the sensorimotor cortex. In accordance with the hypothesis of internal feedback mechanisms, this activation is a necessary prerequisite for motor learning during mental practice. We conclude that mental practice of motor skills might have own effects in poststroke rehabilitation.

Scalp topography of ultralate (C-fibres) evoked potentials following thulium YAG laser stimuli to tiny skin surface areas in humans.

AIMnTo investigate (1) the scalp topography of ultralate laser evoked potentials (LEPs) related to C-fibre activation, which can directly be obtained by thulium YAG (Tm YAG) laser stimulation of tiny skin surface areas (about 0.23 mm(2)) and (2) the influence of the performance of a motor task on ultralate LEPs.nnnMETHODSnLaser stimuli were applied to the dorsum of the left hand. LEPs were recorded with 58 scalp electrodes from 9 healthy subjects in two different conditions, with and without a reaction time (RT) task (press a button upon detection).nnnRESULTSnOn high resolution electroenchephalogram recordings, ultralate LEPs were characterized by a broad positive component (peak latency: 1133+/-91 ms) with maximum amplitude about the vertex. Moreover, the performance of a RT task had no influence on latency, amplitude and topographical patterns of two maps chosen at the positive peak latency in ultralate LEPs. Nevertheless, a negative inflexion (latency 1300 ms) appeared after the positive component in the task condition possibly reflecting movement-related potentials.nnnCONCLUSIONnTm YAG laser stimulation of tiny skin surface areas allows recording the dynamic scalp topography of ultralate (C-fibres) LEPs, with or without the performance of a RT task.

Gray Matter Changes Following Limb Amputation with High and Low Intensities of Phantom Limb Pain

Limb amputation and chronic phantom limb pain (PLP) are both associated with neural alterations at all levels of the neuraxis. We investigated gray matter volume of 21 upper limb amputees and 14 healthy control subjects. Results demonstrate that amputation is associated with reduced gray matter in areas in the motor cortex representing the amputated limb. Additionally, patients show an increase in gray matter in brain regions that belong to the dorsal and ventral visual stream. We subdivided the patient group into patients with medium to high PLP (HPLP; N = 11) and those with slight PLP (SPLP; N = 10). HPLP patients showed reduced gray matter in brain areas involved in pain processing. SPLP patients showed a significant gray matter increase in regions of the visual stream. Results indicate that all patients may have an enhanced need for visual control to compensate the lack of sensory feedback of the missing limb. As we found these alterations primarily in the SPLP patient group, successful compensation may have an impact on PLP development. Therefore, we hypothesize that visual adaptation mechanisms may compensate for the lack of sensorimotor feedback and may therefore function as a protection mechanism against high PLP development.