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.

Intermuscular Coherence in Spinocerebellar Ataxias 3 and 6: a Preliminary Study.

Spinocerebellar ataxias (SCAs) are familial neurodegenerative diseases involving the cerebellum and spinocerebellar tracts. While there is variable involvement of corticospinal tracts (CST), dorsal root ganglia, and motor neurons in SCA3, SCA6 is characterized by a pure, late-onset ataxia. Abnormal intermuscular coherence in the beta-gamma frequency range (IMCßγ) implies a lack of integrity of CST or the afferent input from the acting muscles. We test the hypothesis that IMCßγ has the potential to be a biomarker of disease activity in SCA3 but not SCA6. Intermuscular coherence between biceps brachii and brachioradialis muscles was measured from surface EMG waveforms in SCA3 (N = 16) and SCA6 (N = 20) patients and in neurotypical subjects (N = 23). IMC peak frequencies were present in the ß range in SCA patients and in the γ range in neurotypical subjects. The difference between IMC amplitudes in the γ and ß ranges was significant when comparing neurotypical control subjects to SCA3 (p < 0.01) and SCA6 (p = 0.01) patients. IMCßγ amplitude was smaller in SCA3 patients compared to neurotypical subjects (p < 0.05), but not different between SCA3 and SCA6 patients or between SCA6 and neurotypical subjects. IMC metrics can differentiate SCA patients from normal controls.

Intermuscular coherence in spinocerebellar ataxias 3 and 6: a preliminary study.

Objective : Spinocerebellar ataxias (SCAs) are familial neurodegenerative diseases involving the cerebellum and spinocerebellar tracts. While there is variable involvement of corticospinal tracts (CST), dorsal root ganglia, and motor neurons in SCA3, SCA6 is characterized by a pure, late-onset ataxia. Abnormal intermuscular coherence in the beta-gamma frequency range (IMCbg) implies lack of integrity of CST or the afferent input from the acting muscles. We test the hypothesis that IMCbg has the potential to be a biomarker of disease activity in SCA3 but not SCA6. Methods: Intermuscular coherence between biceps and brachioradialis muscles was measured from surface EMG waveforms in SCA3 (N=16) and SCA6 (N=20) patients, and in neurotypical subjects (N=23). Results: IMC peak frequencies were present in the b range in SCA patients and in the g range in neurotypical subjects. The difference between IMC amplitudes in the g and b ranges was significant when comparing neurotypical control subjects to SCA3 (p < 0.01) and SCA6 (p = 0.01) patients. IMCbg amplitude was smaller in SCA3 patients compared to neurotypical subjects (p<0.05), but not different between SCA3 and SCA6 patients or between SCA6 and neurotypical subjects. Conclusion/significance: IMC metrics can differentiate SCA patients from normal controls.

Ophthalmic Complications Following Acoustic Neuroma Resection.

BACKGROUND: Past studies have shown high rates of ocular complications with the need for ophthalmic surgery following acoustic neuroma resection (ANR). OBJECTIVE: To determine the rates of ophthalmic complications, referrals, and surgery following ANR, and the factors associated with poor outcomes. METHODS: A retrospective study of ophthalmic outcomes in patients who underwent ANR was conducted, following institutional review board approval. Surgical approach, tumor size, tumor characteristics, completeness of resection, postoperative House-Brackmann grades, ocular complications, referrals to ophthalmology, and ophthalmic treatments were recorded. RESULTS: Between 2007 and 2012, 174 patients underwent ANR. There were 3 surgical groups: retrosigmoid (n = 97), translabyrinthine (n = 59), and combined retrosigmoid and translabyrinthine (n = 18). Median tumor size was 2.2 cm. Postoperatively, 30% of patients had facial nerve dysfunction (House-Brackmann ≥3), which recovered to 19% by 1 mo and 8.6% by 1 yr following ANR. Fifty-six (32.9%) patients experienced ocular complications postoperatively, with lagophthalmos, dry eye, and blurry vision as the most common complications. Thirty-six (67.9%) of the patients who required ophthalmic treatment were managed nonsurgically, with just 13 (7.6%) patients requiring referral to an ophthalmologist. In total, only 9 (5.3%) patients received an ophthalmic procedure. Patients with tumors >2 cm, those undergoing combined retrosigmoid and translabyrinthine resection, and those with severe facial nerve dysfunction which did not improve in the first month following surgery were more likely to have poor ophthalmic outcomes. CONCLUSION: We present lower rates of ophthalmic complications following ANR than previously reported. Improved surgical technique, better postoperative eye care, and facial nerve monitoring most likely accounted for the improved ocular outcomes.

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.

Caesarean section rates in Southwestern Ontario: changes over time after adjusting for important medical and social characteristics.

OBJECTIVE: To compare Caesarean section rates in a cohort of women in Southwestern Ontario over time, overall, and in patient subgroups defined by the Robson criteria, after adjusting for important medical and social characteristics. METHODS: We obtained data from a perinatal database on deliveries at ≥ 22 weeks' gestation at a level II centre and a level III centre in London, Ontario between 1999 and 2010. Caesarean section rates were examined overall and in subgroups defined by parity, presentation, plurality, gestational age, and history of previous Caesarean section. Multivariable modified Poisson regression was used to compare Caesarean section rates in 2003-2006 and 2007-2010 versus 1999-2002. RESULTS: In the fully adjusted models, the overall Caesarean section rate was significantly higher in 2007-2010 than in 1999-2002 for the level II centre (adjusted relative risk [aRR] 1.12; 95% CI 1.05 to 1.21). An increase was also seen in the level III centre in both 2003 to 2006 (aRR 1.19; 95% CI 1.14 to 1.24) and 2007 to 2010 (aRR 1.17; 95% CI 1.12 to 1.22). Similar increases were seen over time among patient subgroups. Notably, repeat Caesarean sections without labour increased at the level II centre (2003 to 2006 aRR 1.21; 95% CI 1.01 to 1.45, and 2007 to 2010 aRR 1.44; 95% CI 1.21 to 1.71) and the level III centre (2003 to 2006 aRR 1.72; 95% CI 1.53 to 1.94, and 2007 to 2010 aRR 1.77; 95% CI 1.57 to 2.00). CONCLUSION: There has been a significant increase over time in the Caesarean section rate overall and in important subgroups. This increase remains even after controlling for other factors which may explain the trend.

Objectif : Comparer les taux de césarienne constatés dans une cohorte de femmes du Sud-Ouest de l'Ontario au fil du temps, de façon globale et au sein de sous-groupes de patientes définis au moyen des critères de Robson, à la suite de la neutralisation de l'effet d'importantes caractéristiques médicales et sociales. Méthodes : Nous avons obtenu, auprès d'une base de données périnatale, des données sur les accouchements à ≥ 22 semaines de gestation s'étant déroulés dans un centre de niveau II et un centre de niveau III de London, en Ontario, entre 1999 et 2010. Les taux de césarienne ont été examinés de façon globale et dans le cadre de sous-groupes définis en fonction de la parité, de la présentation, de la pluralité, de l'âge gestationnel et des antécédents de césarienne. Une régression de Poisson multivariée modifiée a été utilisée pour comparer les taux de césarienne constatés au cours des périodes 2003-2006 et 2007-2010 à ceux qui ont été constatés au cours de la période 1999-2002. Résultats : Dans le cadre des modèles entièrement corrigés, le taux global de césarienne a été considérablement plus élevé pour la période 2007-2010 que pour la période 1999-2002 au sein du centre de niveau II (risque relatif corrigé [RRc], 1,12; IC à 95 %, 1,05 - 1,21). Une hausse a également été constatée au sein du centre de niveau III tant au cours de la période 2003-2006 (RRc, 1,19; IC à 95 %, 1,14 - 1,24) qu'au cours de la période 2007-2010 (RRc, 1,17; IC à 95 %, 1,12 - 1,22). Des hausses semblables ont été constatées au fil du temps au sein des sous-groupes de patientes. Notamment, le taux de césarienne itérative sans travail a connu une hausse au sein du centre de niveau II (2003-2006 : RRc, 1,21; IC à 95 %, 1,01 - 1,45 et 2007-2010 : RRc, 1,44; IC à 95 %, 1,21 - 1,71) et du centre de niveau III (2003-2006 : RRc, 1,72; IC à 95 %, 1,53 - 1,94 et 2007-2010, RRc, 1,77; IC à 95 %, 1,57 - 2,00). Conclusion : Au fil du temps, nous avons constaté une hausse significative du taux de césarienne, tant de façon globale qu'au sein d'importants sous-groupes. Cette hausse est demeurée la même à la suite de la neutralisation de l'effet d'autres facteurs qui auraient pu expliquer la tendance.

Prediction of preterm birth in symptomatic women using decision tree modeling for biomarkers.

OBJECTIVE: The objective of the study was to use recursive partitioning (RP) to identify gestational age-specific and threshold values for infectious and endocrine biomarkers of imminent delivery. STUDY DESIGN: RP was developed using a previously collected data set and then applied to a prospectively collected cohort of women in threatened preterm labor. Predictors of preterm birth were considered, including white blood cell count (WBC), corticotrophin-releasing hormone (CRH), cortisol, and maternal age. RESULTS: At 22-27 weeks' gestation, WBC of greater than 12,000/mL was the most accurate predictor of delivery within 48 hours; at 28-31 weeks' gestation, CRH of greater than 684 pg/mL was the most accurate predictor; and at 32-26 weeks' gestation, CRH and maternal age were the most important variables. CONCLUSIONS: These results indicate that maternal WBC greater than 12,000/mL prior to 28 weeks' gestation and CRH beyond 28 weeks are the most accurate biomarkers in predicting preterm birth within 48 hours. RP assists in establishing clinically relevant and gestational age-specific threshold levels for these variables.

Edaphic Soil Levels of Mineral Nutrients, pH, Organic Matter, and Cationic Exchange Capacity in the Geocaulosphere Associated with Potato Common Scab.

ABSTRACT In order to determine possible relationships between geocaulosphere soil properties and severity of common scab of potato caused by Streptomyces scabies, soils were collected from representative commercial potato fields in Canada: in Simcoe and Dufferin Counties, Ontario and across Prince Edward Island (PEI) in August 2004. Soils immediately adjacent to tubers were sampled and analyzed for select edaphic factors and for pathogen presence using polymerase chain reaction (PCR) tests with primers that amplify a region of the TxtA gene involved in regulating the biosynthesis of the thaxtomin toxin family. Individual tubers were assessed visually for scab severity. The relationships between soil chemical factors and disease severity were investigated for each region to detect the strongest relationships. Principal component analysis revealed a distinctive clustering of samples with respect to disease severity in PEI but not in Ontario soils. Total and percent saturation of K (%K) were the only factors found associated with high disease severity in soils from both provinces. In PEI soils, pH, Mg, Ca, Cu, and %K, %Mg, %Ca, and %Na were associated with high disease severity, whereas cation exchange capacity (CEC) and Al were correlated with low disease severity soils. In Ontario, high Mn content was strongly correlated with low disease severity soils, whereas %K and organic matter content were correlated with disease severity. Partitioning samples into presence or absence of the TxtA PCR product with corresponding high or low severity showed further significant relationships in the data. There was an excellent correlation between Streptomyces spp. presence as detected by PCR and disease severity in PEI soils; however, the relationship was not as clear in Ontario soils, where many PCR-positive soils had low disease incidence. Principal component and partial least square analysis indicated that disease severity was predicted by soil factors such as organic matter, CEC, pH, Al, %Ca, %Mg, and %K for PEI but not for Ontario soils. The data reveal that the relationship between scab severity and soil chemical components is complex and potentially soil specific.