The Cortical “Upper Motoneuron” in Health and Disease

Upper motoneurons (UMNs) in motor areas of the cerebral cortex influence spinal and cranial motor mechanisms through the corticospinal tract (CST) and through projections to brainstem motor pathways. The primate corticospinal system has a diverse cortical origin and a wide spectrum of fibre diameters, including large diameter fibres which are unique to humans and other large primates. Direct cortico-motoneuronal (CM) projections from the motor cortex to arm and hand motoneurons are a late evolutionary feature only present in dexterous primates and best developed in humans. CM projections are derived from a more restricted cortical territory (‘new’ M1, area 3a) and arise not only from corticospinal neurons with large, fast axons but also from those with relatively slow-conducting axons. During movement, corticospinal neurons are organised and recruited quite differently from ‘lower’ motoneurons. Accumulating evidence strongly implicates the corticospinal system in the early stages of ALS, with particular involvement of CM projections to distal limb muscles, but also to other muscle groups influenced by the CM system. There are important species differences in the organisation and function of the corticospinal system, and appropriate animal models are needed to understand disorders involving the human corticospinal system.

Agonist-antagonist myoneural interface amputation preserves proprioceptive sensorimotor neurophysiology in lower limbs

The brain undergoes marked changes in function and functional connectivity after limb amputation. The agonist-antagonist myoneural interface (AMI) amputation is a procedure that restores physiological agonist-antagonist muscle relationships responsible for proprioceptive sensory feedback to enable greater motor control. We compared results from the functional neuroimaging of individuals (n = 29) with AMI amputation, traditional amputation, and no amputation. Individuals with traditional amputation demonstrated a significant decrease in proprioceptive activity, measured by activation of Brodmann area 3a, whereas functional activation in individuals with AMIs was not significantly different from controls with no amputation (P < 0.05). The degree of proprioceptive activity in the brain strongly correlated with fascicle activity in the peripheral muscles and performance on motor tasks (P < 0.05), supporting the mechanistic basis of the AMI procedure. These results suggest that surgical techniques designed to restore proprioceptive peripheral neuromuscular constructs result in desirable central sensorimotor plasticity.

Postcentral Topectomy for Pain Relief: A Historical Review and Possible Improvements

Postcentral topectomy is a neurosurgical procedure, practiced in the mid-20th century, in which surgical ablations of the primary somatosensory cortex were used as a therapeutic means of treating patients suffering from intractable chronic pain. While successful in curing some—but not all—patients, the procedure was poorly understood and eventually became displaced by methods that more consistently stopped patient complaints of pain, such as opiates and frontal lobotomies. However, a more recent discovery of a nociresponsive region in the transitional zone between the primary somatosensory cortex and the primary motor cortex (lying in Brodmann Area 3a anterior to its better known proprioceptive region) raises the possibility that the outcome of postcentral topectomy depended in each patient on whether the ablation extended deep enough into the central sulcus to remove this cortical region. Here we review every postcentral topectomy case we could find in the neurosurgical literature in order to evaluate its past effectiveness and to reassess its potential in light of modern knowledge of the cerebral cortex. We found 17 full-text reports from 16 different surgical teams describing outcomes of the procedure in 27 patients. Among those, in only 5 patients the procedure either failed to abolish the targeted chronic pain or the pain returned to its preoperational levels several weeks or months after the surgery. In the other 22 patients, their pain stayed abolished or at least significantly reduced as of the last evaluation by the treating physician (which was one year or more for 9 patients). We propose that the probability of a successful outcome might be brought to near 100% by selective targeting—guided by functional imaging—of the nociresponsive region in Area 3a.

FAULT PATTERN AND ACTIVE DEFORMATION OF OUTER ARC RIDGE OF NORTHWEST OF SIMEULUE ISLAND, ACEH, INDONESIA

New bathymetric map of northwest Simeuleu Island area (3° 01’N-4°57’N and 93°16’E-94°08’E) has evidently illustrated fine morphological image of Outer Arc ridge and Aceh Fore Arc. The structural lineament pattern, inferred from the bathymetric map, could define in general elongated major NW-SE thrust fault complex, thrust fold, or bedding trace and N-S, NNE-SSW, WNW-ESE or ENE-WSW and E-W structural lineament trend. High intensity deformation processes related to high degree obliquity subducted plate was represented by rough and sigmoidal morphological shape, landward and steep to very steep dip angle of bedding plan. Rough morphology, V to U shape valley, dissected ridge and circular shape of landslide trace are common morphology features of active deformation zone. In the near future, high resolution marine seismic will be planned across this area to capture and confirm the subsurface structure configuration and fault movement. Keyword: bathymetric map, Outer Arc ridge, thrust fault, thrust fold, bedding trace, sigmoidal morphological, V to U shape valley,and landslide. Peta batimetri baru di sebelah barat laut Pulau Simelue (3° 01’LU - 4°57’LU and 93°16’BT-94°08’BT), memperlihatkan citra morfologi yang halus pada punggungan busur luar dan busur depan Aceh. Pola kelurusan struktur mengacu pada peta batimetri, dibagi dalam komplek sesar naik yang berarah umum baratlaut - tenggara, lipatan, atau jejak perlapisan dengan kecendrungan arah struktur utara-selatan, utara timur laut – selatan barat daya, barat - barat daya, timur tenggara atau timur laut - barat daya dan timur - barat. Proses deformasi intensitas tinggi berkaitan dengan derajat kemiringan penunjaman yang tinggi, diwakili oleh bentuk morfologi sigmoid dan kasar, ke arah darat dicirikan oleh kemiringan bidang lapisan terjal hingga sangat terjal. Bentuk morfologi kasar seperti bentuk lembah V hingga U, punggungan yang terpotong dan bentuk melingkar dari jejak longsoran merupakan gambaran morfologi umum dari zona deformasi aktif. Dalam waktu dekat, seismik laut resolusi tinggi akan direncanakan memotong daerah ini untuk menggambarkan dan mengkonfirmasi konfigurasi struktur bawah permukaan dan pergerakan sesar. Kata kunci : peta batimetri, punggungan busur luar, sesar naik, lipatan, jejak bidang perlapisan, morfologi sigmoid, bentuk lembah V hingga U,dan longsoran.