Added load increases the peak frequency of intermuscular coherence.

Cortical motor neuron activity appears to drive lower motor neurons through two distinct frequency bands: the ß range (15-30 Hz) during weak muscle contractions and γ range (30-50 Hz) during strong contractions. It is unknown whether the frequency of cortical drive shifts continuously or abruptly between the ß and γ frequency bands as contraction strength changes. Intermuscular coherence (IMC) between synergistic arm muscles was used to assess how the frequency of common neuronal drive shifts with increasing contraction strength. Muscle activity was recorded by surface electromyography (EMG) from the biceps and brachioradialis in nine healthy adults performing 30-second isometric holds with added loads. IMC was calculated across the two muscle groups during the isometric contraction. Significant IMC was present in the 20 to 50 Hz range with all loads. Repeated measures ANOVA show the peak frequency of IMC increased significantly when load was added, from a peak of 32.7 Hz with no added load, to 35.3 Hz, 35.7 Hz, and 36.3 Hz with three-, five-, and ten-pound loads respectively. An increase in IMC frequency occurs in response to added load, suggesting that cortical drive functions over a range of frequencies as a function of an isometric contraction against load.

Deterministic Tractography of the Descending Tract of the Spinal Trigeminal Nerve Using Diffusion Tensor Imaging.

BACKGROUND AND PURPOSE: Pain information from the face enters the pons via the trigeminal nerve before creating an anatomical "elbow" that turns caudally into the spinal trigeminal tract (SpTV). Visualization of the descending tract of the trigeminal nerve as it begins its descent from the nerve root entry zone (NREZ) in the pons would improve the accuracy of current procedures aimed at altering or lesioning the trigeminal nerve within the brainstem. The focus of this study was to develop a standardized protocol using diffusion tensor imaging (DTI) and deterministic tractography methods to image the SpTV. There are currently no standard techniques used to visualize the trigeminal nerve using DTI. METHODS: DTI and tractography were performed on 20 patients: 17 with trigeminal neuralgia (TN), 1 with hemifacial spasm, 1 with a facial nerve tumor, and 1 with an arteriovenous malformation. A standardized protocol was developed using regions of interest (ROIs) located at the SpTV, as determined by a brainstem atlas, and the NREZ. RESULTS: Using our standardized protocol, the descending tract of the trigeminal nerve was successfully visualized in all 20 patients. Trigeminal fibers entered the pons at the NREZ and descended through the SpTV. The accuracy of the visualized tract was confirmed through coregistration with a stereotactic atlas and anatomical scan. CONCLUSION: A successful, robust DTI imaging and postprocessing protocol of the SpTV contributes to our understanding of its anatomical distribution within the brainstem and is a potentially new neurosurgical planning tool.

Lateralization of simulated sources and echoes differing in frequency based on interaural temporal differences.

This study examined listeners' ability to process interaural temporal differences (ITDs) in one of two sequential sounds when the two differed in spectral content. A correlational analysis assessed weights given to ITDs of simulated source and echo pulses for echo delays of 8-128 ms for conditions in which responses were based on the source or echo, a 3000-Hz Gaussian (target) pulse. The other (distractor) pulse was spectrally centered at 1500, 2000, 3000, 4000, or 5000 Hz. Also measured were proportion correct and proportion of responses predicted from the weights. Regardless of whether the echo or source pulse served as the target, target weight, and proportion correct increased with increasing distractor frequency, consistent with low-frequency dominance [Divenyi, J. Acoust. Soc. Am. 91, 1078-1084 (1992)]. Effects of distractor frequency were observed at echo delays out to 128 ms when the source served as the target, but only out to 64 ms when the echo served as the target. At echo delays beyond 8 ms, recency effects were exhibited with higher proportions correct obtained for judgments based on the echo pulse than the source pulse.

Spinal cord cavernoma resection using a fiber-optic CO2 laser.

BACKGROUND: Spinal cord cavernomas are rare, and progressive growth can lead to neurologic deterioration. Complete microsurgical resection using the OmniGuide® fiber-optic CO2 laser is safe, precise, and can prevent further neurological deterioration. We describe the process, risks, and benefits associated with this approach. METHODS: Once the cavernoma is isolated, the CO2 laser enables the surgeon to incise and photocoagulate with the same instrument, increasing the accuracy and potentially reducing the procedure's duration. The spinal cord and surrounding tissue are protected from the laser by cerebrospinal fluid and cottonoid pledges. CONCLUSIONS: The fiber-optic CO2 laser is safe and effective when resecting spinal cord cavernomas. Personal experience, coupled with recent literature, brings us to this conclusion.

Microsurgical Pontine Descending Tractotomy in Cases of Intractable Trigeminal Neuralgia.

BACKGROUND: Current treatment strategies in patients with trigeminal neuralgia (TN) include trials of medical therapy and surgical intervention, when necessary. In some patients, pain is not adequately managed with these existing strategies. OBJECTIVE: To present a novel technique, ventral pontine trigeminal tractotomy via retrosigmoid craniectomy, as an adjunct treatment in TN when there is no significant neurovascular compression. METHODS: We present a nonrandomized retrospective comparison between 50 patients who lacked clear or impressive arterial neurovascular compression of the trigeminal nerve as judged by preoperative magnetic resonance imaging and intraoperative observations. These patients had intractable TN unresponsive to previous treatment. Trigeminal tractotomy was performed either alone or in conjunction with microvascular decompression. Stereotactic neuronavigation was used during surgery to localize the descending tract via a ventral pontine approach for descending tractotomy. RESULTS: Follow-up was a mean of 44 months. At first follow-up, 80% of patients experienced complete relief of their pain, and 18% had partial relief. At the most recent follow-up, 74% of patients were considered a successful outcome. Only 1 (2%) patient had no relief after trigeminal tractotomy. Of those with multiple sclerosis-related TN, 87.5% experienced successful relief of pain at their latest follow-up. CONCLUSION: While patient selection is a significant challenge, this procedure represents an option for patients with TN who have absent or equivocal neurovascular compression, multiple sclerosis-related TN, or recurrent TN.