Thomas Hansson

Tactile stimulation of the hand causes bilateral cortical activation: a functional magnetic resonance study in humans

The purpose of the present study was to assess the somatotopy of the cortical sensory representation of the fingers using a natural tactile stimulation of the glabrous skin. Multislice echoplanar imaging techniques were utilized to investigate blood oxygen level dependent (BOLD) signal changes as a measure of cortical activation. Repetitive sensory stimulation of the glabrous skin of digit II-III and digit IV-V resulted in a multifocal signal increase in a restricted area near the central sulcus in the contralateral hemisphere with a considerable overlap between the activated areas of digit II-III and digit IV-V. In addition, in all subjects tactile stimulation resulted in ipsilateral signal increase near the central sulcus, which was 15-22% of the contralateral effect. Stimulation of digit II-III caused significantly (P < 0.05) more activated voxels than digit IV-V in the contralateral hemisphere for both hands and for the left hand in the ipsilateral hemisphere. These findings suggest an ipsilateral activation of the primary somatosensory cortex during a natural tactile stimulation of the digits in humans.

Artificial sensibility of the hand based on cortical audiotactile interaction: A study using functional magnetic resonance imaging.

The capacity of the central nervous system for plastic alterations is the base for our ability to adapt to environmental needs. The crossmodal capacity of the brain makes interaction between senses possible, and deprivation of one sense leads to compensatory changes in other senses. We have recently shown how hearing can substitute for sensation in a transplanted insensitive hand by using a sensor glove equipped with small microphones that pick up the sound of friction, which is elicited by active touch. Here we have used functional magnetic resonance imaging (fMRI) in healthy people to illustrate their capacity for cortical audiotactile interaction with activation of the somatosensory cortex induced by auditory stimuli. The phenomenon occurred only in subjects trained to substitute sensibility by hearing, and no audiotactile interaction was found in untrained subjects.

Cortical activity and hand function restoration in a patient after spinal cord surgery

Background. Following a motorcycle accident, a 9-year-old boy experienced a complete right-sided (dominant) arm and hand paralysis with total sensory loss, Horner syndrome and severe constant pain. This study assessed the long-term outcome of spinal cord surgery undertaken on the patient, focusing on the restored hand function and related cortical activity. The study follows on from previous reports on the same patient.Investigations. Clinical functional and electrophysiological examinations. Functional MRI of cortical activity.Diagnosis. Complete brachial plexus (C5–T1) avulsion from the spinal cord.Management. Spinal cord surgery to restore motor trajectories.

Sights of touching activates the somatosensory cortex in humans

We report our observations of cross-modal interactions between sight and touch using functional magnetic resonance imaging (fMRI). Experiments were devised to show that sight and touch are linked in a cross-modal arrangement, and two separate experiments were done in an MRI scanner. In the first, the subjects right hand was stimulated with a brush; in the second, a video sequence was presented to the subject inside the scanner through video goggles in visual three-dimensional stereo, showing one brushstroke every second on a hand in the same manner as the subject had just previously experienced. The result was that both the primary and the secondary somatosensory cortexes were activated in the participants when the hands were touched, and when the subjects saw only a hand being touched in the same manner. The results indicated cross-modal links between sight and touch of the hand in humans.

Osteogenically-induced human dermal fibroblasts as a tool to regenerate bone

Abstract Engineering of bone tissue could help to overcome the need for extensive reconstruction and associated donor site morbidity, and it has been proposed that osteogenic biomaterials, which are scaffolds that contain osteocompetent cells, could be used to fill large bone defects. This study investigated the potential of osteogenically-induced human dermal fibroblasts cultured on gelatin microcarriers combined with platelet-rich plasma in a model of a femoral defect in athymic rats. Defects were transplanted with one of the following six combinations: 1 = sodium chloride, 2 = platelet-rich plasma, 3 = microcarriers + platelet-rich plasma, 4 = human dermal fibroblasts on microcarriers + platelet-rich plasma, 5 = human osteoblasts on microcarriers + platelet-rich plasma, and 6 = osteogenically induced human dermal fibroblasts on microcarriers + platelet-rich plasma. The femoral defects were assessed 4 weeks postoperatively with computed tomography (CT), routine histological staining, fluorescence in situ hybridisation, and polyclonal antibodies directed towards osteocalcin and osteonectin. Radiographs of all groups taken 4 weeks postoperatively showed unhealed defects. Femoral defects transplanted with osteogenically-induced human dermal fibroblasts on microcarriers (group 6) contained dense clusters of cells with large quantities of extracellular matrix. These clusters were exclusive to this group and stained strongly for osteocalcin and osteonectin. Fluorescence in situ hybridisation showed viable human cells in femoral defects that had been transplanted with microcarriers seeded with cells, which confirmed the survival of implanted cells. In conclusion, osteogenically-induced human dermal fibroblasts survived in this new niche, and bone-like structures were apparent in the defects.

Inter-hemispheric plasticity in patients with median nerve injury.

Peripheral nerve injuries result in reorganization within the contralateral hemisphere. Furthermore, recent animal and human studies have suggested that the plastic changes in response to peripheral nerve injury also include several areas of the ipsilateral hemisphere. The objective of this study was to map the inter-hemispheric plasticity in response to median nerve injury, to investigate normal differences in contra- and ipsilateral activation, and to study the impact of event-related or blocked functional magnetic resonance imaging (fMRI) design on ipsilateral activation. Four patients with median nerve injury at the wrist (injured and epineurally sutured >2 years earlier) and ten healthy volunteers were included. 3T fMRI was used to map the hemodynamic response to brain activity during tactile stimulation of the fingers, and a laterality index (LI) was calculated. Stimulation of Digits II-III of the injured hand resulted in a reduction in contralateral activation in the somatosensory area SI. Patients had a lower LI (0.21±0.15) compared to healthy controls (0.60±0.26) indicating greater ipsilateral activation of the primary somatosensory cortex. The spatial dispersion of the coordinates for areas SI and SII was larger in the ipsilateral than in the contralateral hemisphere in the healthy controls, and was increased in the contralateral hemisphere of the patients compared to the healthy controls. There was no difference in LI between the event-related and blocked paradigms. In conclusion, patients with median nerve injury have increased ipsilateral SI area activation, and spatially more dispersed contralateral SI activation during tactile stimulation of their injured hand. In normal subjects ipsilateral activation has larger spatial distribution than the contralateral. Previous findings in patients performed with the blocked fMRI paradigm were confirmed. The increase in ipsilateral SI activation may be due to an interhemispheric disinhibition associated with changes in the afferent signal inflow to the contralateral primary somatosensory cortex.

Functional Regeneration of C-Fibries Inside a Silicone Tube After Sciatic Neurotomy in Rats

Peripheral nerve lesions are often complicated by difficulties in approximating the nerve stumps without tension. The aim of the present study was to evaluate C-fibre function after nerve regeneration in rats in which the nerve had been lengthened by leaving a 5 mm gap inside a silicone tube (n = 5). The outcome was compared with nerve regeneration after epineural end-to-end suture (n = 5). The innervated skin territory was defined by Evans blue extravasation after antidromic nerve stimulation. Five rats acted as controls. After three months, there was similar functional reinnervation in both experimental groups, which indicates that silicone tubes may reduce tension over a nerve repair with no adverse effects.

Functional outcome in 17 patients whose mandibles were reconstructed with free fibular flaps

Abstract Objective: The vascularised free fibular flap is considered to be a reliable choice for reconstruction of oromandibular defects, especially after resection of malignant tumours in the area. This study evaluates the functional outcome of this method. Method: From January 2001 - May 2014, 37 patients were treated at the University Hospital of Linköping using the free fibular flap. The authors present the results from 17. This study reviewed their records and used the University of Washington Quality-of-Life questionnaire (UW-QoL), the Head and Neck Performance Status Scale (PSS), and interviews to assess their outcome. Results and conclusions: Functional evaluation showed a significant decrease in chewing (16 out of 17 patients), appearance (n = 10), salivation (n = 6), sensitivity in the mouth and skin (n = 16), occlusive problems in the mouth (n = 13), and range of mouth opening (n = 12). The remaining domains showed acceptable results, although most of them probably could not compare with the preoperative function. Out of 17 patients, six had to adjust their eating in public significantly, three thought their activity to be considerably restricted and two their recreation to be notably diminished. Common postoperative complications were infections or fistula in the mandible (n = 6), partial or complete rejection of the cutaneous flap (n = 4), and rupture of some of the sutures (n = 3). Nine patients required at least one more operation to repair defects, and six required a new soft tissue flap.

Functional evaluation of regenerated and misrouted low threshold mechanoreceptors and polymodal nociceptors in the skin of rat hindfeet after crush lesions to the sciatic nerve

Tracer studies on motor axons after nerve crush injuries have indicated that misrouting may occur even when the endoneurium is intact. Misrouting of regenerated polymodal nociceptive C-fibres and low threshold mechanoreceptive axons have been studied functionally in 50 rats three months after unilateral crush lesions to the sciatic nerve. Two weeks before evaluation the tibial fascicle (or the peroneal fascicle) above the lesion was cut and tied off. In this way only functional regeneration of misrouted axons was tested. Misrouted low threshold mechanoreceptive axons and polymodal nociceptor C-fibres were found after regeneration in both glabrous and hairy skin. We conclude that functional misdirection of both myelinated and unmyelinated sensory axons innervating either glabrous or hairy skin can occur after a crush lesion to a peripheral nerve in rats.

Cortical plasticity in patients with median nerve lesions studied with MEG.

Abstract We have previously shown age- and time-dependent effects on brain activity in the primary somatosensory cortex (SI), in a functional magnetic resonance imaging (fMRI) study of patients with median nerve injury. Whereas fMRI measures the hemodynamic changes in response to increased neural activity, magnetoencephalography (MEG) offers a more concise way of examining the evoked response, with superior temporal resolution. We therefore wanted to combine these imaging techniques to gain additional knowledge of the plasticity processes in response to median nerve injury. Nine patients with median nerve trauma at the wrist were examined with MEG. The N1 and P1 responses at stimulation of the injured median nerve at the wrist were lower in amplitude compared to the healthy side (p < .04). Ulnar nerve stimulation of the injured hand resulted in larger N1 amplitude (p < .04). The amplitude and latency of the response did not correlate with the sensory discrimination ability. There was no correlation between N1 amplitude and size of cortical activation in fMRI. There was no significant difference in N1 latency between the injured and healthy median nerve. N1 latency correlated positively with age in both the median and ulnar nerve, and in both the injured and the healthy hand (p < .02 or p < .001). It is concluded that conduction failure in the injured segment of the median nerve decreases the amplitude of the MEG response. Disinhibition of neighboring cortical areas may explain the increased MEG response amplitude to ulnar nerve stimulation. This can be interpreted as a sign of brain plasticity.