An unusual primary presentation of myasthenia gravis

This patient presented with progressive eating difficulties, having been originally investigated for mechanical gastroenterological problems. Fruitless examinations led to referral to a tertiary oral medicine unit and a detailed review of his history, where the significance of progressive fatiguability during and after mastication became apparent in his dysphagia.The insidious onset contrasted with his more rapid decline in function between the initial examination and specialist electromyographic investigations, neurological admission and management. The dangers of fatigue and pharyngeal incompetence are of particular relevance to oral and maxillofacial clinicians.     

Task-dependent variability of Essential Tremor

IntroductionIn Essential Tremor (ET), tremor characteristics and the impairment caused by tremor may vary from task to task. A variability of tremor frequency between postural and kinetic tasks has been proposed in ET, suggesting either multiple central oscillating networks, or peripheral or proprioceptive feedback-mechanisms. This electrophysiological study aimed to assess tremor frequencies and amplitudes in tasks involving postural and kinetic tremor, and compare findings within and across tasks, to delineate physiological differences underlying individually affected manual tasks in ET.Methods40 ET patients were included in the study. Tremor was characterized clinically, as well as electrophysiologically using accelerometry and digitizing tablet tasks. Tremor amplitude measures and frequencies were extracted for tasks involving kinetic (digital spiral drawing, handwriting), as well as postural tremor. Tremor was compared between and within tasks.ResultsDigital spiral tremor frequencies were significantly higher compared to postural tremor frequencies, as measured by accelerometry, with a mean difference of >2 Hz (p < 0.001). Within-task variability of repeated digital spirals revealed a significant amplitude reduction over time in both hands (p < 0.001), with an up to 32% reduction compared to the first spiral.ConclusionET exhibited a frequency variability, which was dependent on activation condition, suggesting neurophysiologically distinct pathways between postural and kinetic tremor. The reduction of tremor amplitudes observed in repeated digital spiral drawing may be explained by a learning effect or adaptation, and should be considered as non-random factor of variability when using spirals in ET to assess effects of interventions.     

Visual attention: the past 25 years

This review focuses on covert attention and how it alters early vision. I explain why attention is considered a selective process, the constructs of covert attention, spatial endogenous and exogenous attention, and feature-based attention. I explain how in the last 25 years research on attention has characterized the effects of covert attention on spatial filters and how attention influences the selection of stimuli of interest. This review includes the effects of spatial attention on discriminability and appearance in tasks mediated by contrast sensitivity and spatial resolution; the effects of feature-based attention on basic visual processes, and a comparison of the effects of spatial and feature-based attention. The emphasis of this review is on psychophysical studies, but relevant electrophysiological and neuroimaging studies and models regarding how and where neuronal responses are modulated are also discussed.     

Parkin mutation and deep brain stimulation outcome

Patients with parkin mutations are expected to be good candidates for deep brain stimulation (DBS) because of an excellent levodopa response and frequent occurrence of levodopa-induced dyskinesia. However, there are insufficient data on surgical outcome in patients with parkin mutations. This study aimed to compare the outcome of subthalamic nucleus DBS in patients with early-onset Parkinson’s disease with and without parkin mutations. Fourteen patients with early-onset Parkinson’s disease who underwent bilateral subthalamic nucleus DBS surgery were screened for parkin mutations and assessed for surgical outcomes at baseline and 2–5 years after surgery. Three patients had homozygote/compound heterozygote mutations; two had single heterozygote mutations; and nine had no mutations. Patients with homozygote/compound heterozygote mutations were younger at disease onset and had longer disease duration than patients without a parkin mutation. Postoperatively, there were no significant differences in improvement on the Unified Parkinson’s Disease Rating Scale part II, III, and IV, or the reduction of levodopa equivalent daily doses between patients with and without parkin mutations. The therapeutic effect of DBS did not differ between patients with and without parkin mutations.     

Development of New Pharmacological Agents for Epilepsy: Lessons from the Kindling Model

Summary: The greatest value of the kindling model for new therapy of epilepsy almost certainly lies in elucidating the molecular basis of its development and persistence. Such an understanding may provide a foundation for therapies aimed at prevention or perhaps even cure of some forms of human epilepsy.     

Cellular Mechanisms of Epilepsy and Potential New Treatment Strategies

Summary: Over the last 15 years, neurobiologists have begun to unravel the cellular mechanisms that underlie epileptiform activity. Such investigations have two main objectives: (I) to develop new methods for treating, "curing" or preventing epilepsy; and (2) to learn more about the normal functioning of the human brain at the cellular/ molecular and the neurological/psychological levels by analyzing abnormal brain functioning. The electroencephalogram (EEG) spike is a marker for the hyperexcitable cortex and arises in or near an area with a high epileptogenic potential. The depolarizing shift (DS) that underlies the interictal discharge (ID) appears to be generated by a combination of excitatory synaptic currents and intrinsic voltagedependent membrane currents. The hyperpolarization that follows the DS (post-DS HP) limits ID duration, determines ID frequency, and prevents ID deterioration into seizures. The disappearance of the post-DS HP in some models is related to the onset of seizures and the spread of epileptifonn activity. During the transition to seizures , the usually self-limited ID spreads in time and anatomical space. Several processes may intervene in the pathophysioogical dysfunction. These include enhancing GABA-mediated inhibition, dampening NMDA-mediated excitability, interfering with specific Ca²⁺ currents in central neurons, and perhaps stimulating "gating" pathways.     

Pathophysiology of cytotoxic drug-induced emesis: far from crystal-clear

Both radiotherapy and chemotherapy for cancer are capable of causing severe nausea and vomiting, which formerly often interfered with the patient's compliance to treatment. The basic pathway and pharmacological mechanisms involved in this are still poorly understood. The recent discovery, however, that 5-HT₃ receptor antagonists can prevent or greatly reduce chemotherapy-induced emesis led to a re-evaluation of the sequence of events occurring in the protective emetic reflex, which are reviewed in this paper. The vomiting centre co-ordinates the incoming and outgoing information, and is thought to be represented by complex interactions between different adjacent areas in the brainstem. Whether the main role in the emetic reflex arch is accomplished by either the central part (chemoreceptor trigger zone) or the peripheral part (gastro-intestinal tract) needs further confirmation. A more important role, however, of the vagal nerve and the gastro-intestinal tract is generally accepted. The neurotransmitter serotonin (5-HT) appears to play a major role in chemotherapy-induced emesis via the 5-HT receptor. These indications could form the basis for further investigations into the involvement of other neurotransmitters, and the character of their interactions.     

Anatomic basis of chronic perineal pain: role of the pudendal nerve

Summary Our anatomic findings have led us to define conflictual relations that may be encountered in their course by the pudendal n. and its branches. Starting from the clinical study of a group of patients suffering from chronic perineal pain in the seated position, we have defined, beginning with the cadaver, three possible conflictual settings: in the constriction between the sacrotuberal and sacrospinal ligaments; in the pudenal canal of Alcock; and during the straddling of the falciform process of the sacrotuberal ligament by the pudendal n. and its branches. Consequently, considering so-called idiopathic perineal pain as an entrapment syndrome, the clinical and neurophysiologic arguments and infiltration tests have led us to define a surgical strategy which has currently given 70% of good results in 170 operated patients. Earlier diagnosis should improve on this.

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Bases anatomiques des algies périnéales chroniques : rôle du nerf pudendal

Résumé Des constatations anatomiques nous ont conduits à définir des situations conflictuelles que peuvent rencontrer dans leur trajet le n. pudendal et ses branches. C'est à partir de l'étude clinique d'une population de patients souffrant d'algies périnéales chroniques, lors de la position assise que nous avons défini sur cadavre d'abord les conflits possibles au nombre de trois : -dans la pince ligamentaire entre le ligament sacrotubéral et le sacro-épineux ; - dans le canal pudendal d'Alcock ; - lors du chevauchement du processus falciforme du ligament sacro-tubéral par le nerf ou ses branches. Considérant dès lors certaines algies périnéales dites essentielles comme un syndrome canalaire, les arguments cliniques, neurophysiologiques, les tests aux infiltrations, nous ont fait définir une stratégie chirurgicale qui actuellement sur 170 patients opérés apporte 70 % de bons résultats. Un diagnostic plus précoce devrait encore les améliorer.

     

A signal averaging program

The article describes the hardware and software required for an inexpensive signal averaging system.     

Effect of galanin and enterostatin on sympathetic nerve activity to interscapular brown adipose tissue

The effects of galanin and enterostatin on sympathetic activity have been examined in rats using electrophysiological techniques. Galanin, in doses of 25–300 pmol, and enterostatin, in doses of 0.5–10 nmol, were injected into the third ventricle of anesthetized male Sprague-Dawley rats in 1-μl volumes. Galanin produced a dose-dependent suppression (ranging between 20 and 80%) of sympathetic firing rate of nerves innervating interscapular brown adipose tissue. In rats fed a chow diet, injection of enterostatin produced only a transient 10% rise in firing rate which returned to baseline within 10–15 min. In contrast, animals fed a high-fat diet showed a dose-dependent increase in firing rate lasting for 60 min. The results of this experiment are consistent with the hypothesis that food intake and sympathetic nervous system activity have a reciprocal relationship. The implications of this relationship are discussed.