Despite being widely studied, the underlying mechanisms of transcranial magnetic brain stimulation (TMS) induced motor evoked potential (MEP), early cortical silent period (CSP) and rebound activity are not fully understood. Our aim is to better characterize these phenomena by combining various analysis tools on firing motor units. Responses of 29 tibialis anterior (TA) and 8 abductor pollicis brevis (APB) motor units to TMS pulses were studied using discharge rate and probability-based tools to illustrate the profile of the synaptic potentials as they develop on motoneurons in 24 healthy volunteers. According to probability-based methods, TMS pulse produces a short-latency MEP which is immediately followed by CSP that terminates at rebound activity. Discharge rate analysis, however, revealed not three, but just two events with distinct time courses; a long-lasting excitatory period (71.2 ± 9.0 ms for TA and 42.1 ± 11.2 ms for APB) and a long-latency inhibitory period with duration of 57.9 ± 9.5 ms for TA and 67.3 ± 13.8 ms for APB. We propose that part of the CSP may relate to the falling phase of net excitatory postsynaptic potential induced by TMS. Rebound activity, on the other hand, may represent tendon organ inhibition induced by MEP activated soleus contraction and/or long-latency intracortical inhibition. Due to generation of field potentials when high intensity TMS is used, this study is limited to investigate the events evoked by low intensity TMS only and does not provide information about later parts of much longer CSPs induced by high intensity TMS. Adding discharge rate analysis contributes to obtain a more accurate picture about the characteristics of TMS-induced events. These results have implications for interpreting motor responses following TMS for diagnosis and overseeing recovery from various neurological conditions.
After tissue or limb loss, the development of sensation and perception of the lost or deafferent tissue is defined as a phantom phenomenon. We investigated the presence of phantom phenomena in individuals who underwent a full face transplant as well as those who had a hand transplant. Specifically, we investigated sensory perception of the face on the fingers and sensory perception of the fingers on the face in three full face and four hand transplant patients. In all seven individuals, we used a brush to separately stimulate the right and left sides of the face or the palmar and dorsal faces of the hand. We then asked the individuals if they felt a sensation of touch on any other part of their body and, if so, to describe their perceptions. Changes in the regions of the primary sensory cortex representing the hand and face were defined using fMRI obtained via tactile sensory stimulation of the clinical examination areas. Two of the full face transplant patients reported sensory perceptions such as a prominent sensation of touch on their faces during sensory stimulation of their fingers. Three of the hand transplant patients reported sensory perceptions, which we referred to as finger patches, during sensory stimulation of the face area. In fMRI, overlaps were observed in the cortical hand and face representation areas. We consider the phantom hand and phantom face phenomena we observed to be complementary due to the neighborhood of the representations of the hand and face in the somatosensory cortex.
Although there have been numerous reports of major replantation of upper extremity amputations, limited numbers of above-elbow amputation replantation have been reported. We present the technical details of two successful replantations of forequarter amputations in a nine-year-old girl and a three-year-old boy. In both cases, the forequarter was amputated due to avulsion traction injuries resulting in amputation including the entire upper limb, while the integrity of the scapula and parascapular muscles was maintained, with no injury to the glenohumeral joint. Replantation was performed, involving a shorter ischemia time with proper fixation, and vascular and neural repairs.Postoperative recovery was uneventful, and motor and sensorial acquisition were quite satisfactory during follow-up periods of 9 and 6 years, respectively. Proper fixation of the amputated part mimicking the original anatomy, radical debridement of avulsed vessels, and reconstruction of the defect using long vein grafts and neural repair while
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