Brian Corwell

Functional relevance of cross-modal plasticity in blind humans.

Functional imaging studies of people who were blind from an early age have revealed that their primary visual cortex can be activated by Braille reading and other tactile discrimination tasks. Other studies have also shown that visual cortical areas can be activated by somatosensory input in blind subjects but not those with sight. The significance of this cross-modal plasticity is unclear, however, as it is not known whether the visual cortex can process somatosensory information in a functionally relevant way. To address this issue, we used transcranial magnetic stimulation to disrupt the function of different cortical areas in people who were blind from an early age as they identified Braille or embossed Roman letters. Transient stimulation of the occipital (visual) cortex induced errors in both tasks and distorted the tactile perceptions of blind subjects. In contrast, occipital stimulation had no effect on tactile performance in normal-sighted subjects, whereas similar stimulation is known to disrupt their visual performance. We conclude that blindness from an early age can cause the visual cortex to be recruited to a role in somatosensory processing. We propose that this cross-modal plasticity may account in part for the superior tactile perceptual abilities of blind subjects.

Modulation of motor cortex excitability by median nerve and digit stimulation

Abstract We investigated the time course of changes in motor cortex excitability after median nerve and digit stimulation. Although previous studies showed periods of increased and decreased corticospinal excitability following nerve stimulation, changes in cortical excitability beyond 200 ms after peripheral nerve stimulation have not been reported. Magnetoencephalographic studies have shown an increase in the 20-Hz rolandic rhythm from 200 to 1000 ms after median nerve stimulation. We tested the hypothesis that this increase is associated with reduced motor cortex excitability. The right or left median nerve was stimulated and transcranial magnetic stimulation (TMS) was applied to left motor cortex at different conditioning-test (C-T) intervals. Motor-evoked potentials (MEPs) were recorded from the right abductor pollicis brevis (APB), first dorsal interosseous (FDI), and extensor carpi radialis (ECR) muscles. Right median nerve stimulation reduced test MEP amplitude at C-T intervals from 400 to 1000 ms for APB, at C-T intervals from 200 to 1000 ms for FDI, and at C-T intervals of 200 and 600 ms for ECR, but had no effect on FDI F-wave amplitude at a C-T interval of 200 ms. Left median nerve (ipsilateral to TMS) stimulation resulted in less inhibition than right median nerve stimulation, but test MEP amplitude was significantly reduced at a C-T interval of 200 ms for all three muscles. Digit stimulation also reduced test MEP amplitude at C-T intervals of 200–600 ms. The time course for decreased motor cortex excitability following median nerve stimulation corresponds well to rebound of the 20-Hz cortical rhythm and supports the hypothesis that this increased power represents cortical deactivation.

Inhibitory influence of the ipsilateral motor cortex on responses to stimulation of the human cortex and pyramidal tract

1 The ability of the primary motor cortex (M1) to modulate motor responses in ipsilateral hand muscles seems to be important for normal motor control and potentially also for recovery after brain lesions. It is not clear which pathways mediate this ipsilateral modulation. Transcallosal connections have been proposed, but are known to be sparse between cortical hand motor representations in primates. The present study was performed to determine whether descending ipsilateral modulation of motor responses might also be mediated below the cortical level in humans. 2 A paired‐pulse protocol was used, in which motor‐evoked potentials (MEPs) were produced by cortical transcranial magnetic stimulation (cTMS) or by electrical stimulation of the pyramidal tract at the level of the pyramidal decussation (pdTES), in both preactivated and relaxed hand muscles. Paired stimuli were applied at various interstimulus intervals (ISIs) between 2 and 100 ms. The conditioning stimulus (CS) was always magnetic, and delivered to the M1 ipsilateral to the target hand, prior to the test stimulus (TS). The magnetic TS was delivered to the M1 contralateral to the target hand; the electrical TS was applied through electrodes placed over the mastoid process bilaterally. Further experiments included cortical electrical stimulation and H‐reflexes. The MEP amplitudes were averaged separately for each ISI and the control condition (no CS), and expressed as a percentage of the unconditioned response. 3 Conditioning stimulation of the ipsilateral M1 resulted in significant inhibition of magnetically evoked MEPs, and also of MEPs produced by pdTES. Inhibition occurred at ISIs between 6 and 50 ms, and was observed in preactivated and relaxed muscles. Higher CS intensities caused greater inhibition of both cTMS‐ and pdTES‐evoked MEPs. 4 While the conditioning effects on magnetically evoked muscle responses could be explained by a transcallosal mechanism, the effects on pdTES‐evoked MEPs cannot, because they are elicited subcortically and are therefore not susceptible to inhibitory mechanisms transmitted at the cortico‐cortical level. 5 In conclusion, the present results provide novel evidence that the inhibitory influence of the human M1 on ipsilateral hand muscles is to a significant extent mediated below the cortical level, and not only through cortico‐cortical transcallosal connections. They point to a concept of inhibitory interaction between the two primary motor cortices that is relayed at multiple levels along the neuroaxis, thus perhaps providing a structurally redundant system which may become important in case of lesions.

The Emergency Department Evaluation, Management, and Treatment of Back Pain

Back pain is one of the most common symptom-related complaints for visits to primary care physicians and is the most common musculoskeletal complaint that results in visits to the emergency department (ED). With recent national health care initiatives moving toward universal coverage, an increasing number of patients with common complaints such as back pain will visit the ED. The first goal of ED assessment of patients with back pain is to evaluate for potentially dangerous causes that, if not promptly recognized, could result in significant morbidity and mortality. This article focuses on the essential elements of an efficient and effective evaluation, management and treatment of patients with back pain in the ED, with special emphasis on epidural abscess, epidural compression syndrome, malignancy, spinal stenosis, and back pain in children.

Current Diagnosis and Treatment of Hyperglycemic Emergencies

Diabetic ketoacidosis and hyperosmolar hyperglycemic state are the most feared complications of uncontrolled diabetes seen in emergency medicine. The treatment of both conditions must be tailored to individual patients and relies on aggressive fluid resuscitation, insulin replacement, and electrolyte management. Emergency medicine providers must address the underlying causes and monitor for complications of therapy. Improved understanding of the underlying pathophysiology and application of evidence-based guidelines have significantly improved prognosis and decreased mortality. The purpose of this article is to review the diagnosis, presentation, and emergency department management of diabetic ketoacidosis and hyperosmolar hyperglycemic state with an emphasis on current management and treatment guidelines.

A preliminary study of youth sport concussions: Parents' health literacy and knowledge of return-to-play protocol criteria.

ABSTRACT Primary objective: To preliminarily explore parents’ health literacy and knowledge of youth sport league rules involving concussion education and training, and return-to-play protocols. Research design and methods: This study was guided by the Knowledge, Attitude and Practice (KAP) model of health knowledge to examine parents’ concussion literacy, and understanding of concussion education and training, and return-to-play protocols in youth sports. The mixed-method design involved 119 participants; that included in-person (n=8) and telephone (n=4) interviews, and web-based surveys administered through Mechanical Turk via Qualtrics (n=98). Main outcomes and results: Most respondents were not familiar with concussion protocols, but trusted coaches’ knowledge in return-to-play rules. More than half of the respondents report that the return-to-play concussion criteria have not been clearly explained to them. The majority of respondents were not familiar with the CDC’s ‘Heads Up’ online concussion training programme, nor were they familiar with any other educational/training tool. About one-fifth of the parents had conversations with a coach or medical staff about youth sport concussions. Conclusion: Parents have a general understanding of how to identify concussion symptoms, but lack knowledge of immediate steps to take following an incident other than seeking medical help.

Assessment of Anthropometric Measurements as Predictors of Car Seat Screening Failure

Objective The objective of this study was to determine whether anthropometric measurements such as head circumference (HC), body mass index (BMI), and body surface area (BSA) can predict car seat tolerance screen (CSTS) failure. We hypothesized that subjects with larger HC and lower BMI/BSA would have increased risk of failure. Study Design We performed retrospective medical record review of infants born in 2013 who qualified for CSTS due to being born preterm (< 37 weeks) or low birth weight (LBW). We performed bivariate analyses of clinical and demographic risk factors including anthropometrics to identify predictors of CSTS failure. Results In this study, 19 of 366 subjects failed their CSTS (5.3%). There were no significant differences in HC, length, BSA, BMI, or ratio of HC to length, BMI, or BSA between those who passed versus failed. On subgroup analysis of preterm infants, the significant predictor of failure was multiple gestation (p = 0.024). In the term LBW cohort, requiring nasal canula (NC) (p = 0.03) and having limited or no prenatal care (PNC) (p = 0.0006) were both significant predictors of failure. Conclusion Neither absolute measurements nor the ratios of HC to body measurements predicted CSTS outcome. Multiple gestation was a significant predictor of failure in preterm infants, while NC requirement and poor PNC were predictors in LBW term infants.