Autonomic changes with seizures correlate with postictal EEG suppression.

OBJECTIVE: Sudden unexpected death in epilepsy (SUDEP) poses a poorly understood but considerable risk to people with uncontrolled epilepsy. There is controversy regarding the significance of postictal generalized EEG suppression as a biomarker for SUDEP risk, and it remains unknown whether postictal EEG suppression has a neurologic correlate. Here, we examined the profile of autonomic alterations accompanying seizures with a wrist-worn biosensor and explored the relationship between autonomic dysregulation and postictal EEG suppression. METHODS: We used custom-built wrist-worn sensors to continuously record the sympathetically mediated electrodermal activity (EDA) of patients with refractory epilepsy admitted to the long-term video-EEG monitoring unit. Parasympathetic-modulated high-frequency (HF) power of heart rate variability was measured from concurrent EKG recordings. RESULTS: A total of 34 seizures comprising 22 complex partial and 12 tonic-clonic seizures from 11 patients were analyzed. The postictal period was characterized by a surge in EDA and heightened heart rate coinciding with persistent suppression of HF power. An increase in the EDA response amplitude correlated with an increase in the duration of EEG suppression (r = 0.81, p = 0.003). Decreased HF power correlated with an increase in the duration of EEG suppression (r = -0.87, p = 0.002). CONCLUSION: The magnitude of both sympathetic activation and parasympathetic suppression increases with duration of EEG suppression after tonic-clonic seizures. These results provide autonomic correlates of postictal EEG suppression and highlight a critical window of postictal autonomic dysregulation that may be relevant in the pathogenesis of SUDEP.

Biological stoichiometry of plant production: metabolism, scaling and ecological response to global change.

Biological stoichiometry theory considers the balance of multiple chemical elements in living systems, whereas metabolic scaling theory considers how size affects metabolic properties from cells to ecosystems. We review recent developments integrating biological stoichiometry and metabolic scaling theories in the context of plant ecology and global change. Although vascular plants exhibit wide variation in foliar carbon:nitrogen:phosphorus ratios, they exhibit a higher degree of 'stoichiometric homeostasis' than previously appreciated. Thus, terrestrial carbon:nitrogen:phosphorus stoichiometry will reflect the effects of adjustment to local growth conditions as well as species' replacements. Plant stoichiometry exhibits size scaling, as foliar nutrient concentration decreases with increasing plant size, especially for phosphorus. Thus, small plants have lower nitrogen:phosphorus ratios. Furthermore, foliar nutrient concentration is reflected in other tissues (root, reproductive, support), permitting the development of empirical models of production that scale from tissue to whole-plant levels. Plant stoichiometry exhibits large-scale macroecological patterns, including stronger latitudinal trends and environmental correlations for phosphorus concentration (relative to nitrogen) and a positive correlation between nutrient concentrations and geographic range size. Given this emerging knowledge of how plant nutrients respond to environmental variables and are connected to size, the effects of global change factors (such as carbon dioxide, temperature, nitrogen deposition) can be better understood.

The past and future influence of geographic information systems on hybrid zone, phylogeographic and speciation research.

Over the past two decades geographers have developed an increasingly sophisticated technology termed a geographic information system (GIS). A GIS has the ability to store, map and analyse spatial data. The powerful analytical capabilities of a GIS could serve to enhance our understanding of the spatial component of the evolutionary process. In particular, phylogeographers, hybrid zone and speciation researchers could benefit enormously from incorporating this sophisticated technology from the discipline of geography, as they have done so readily from other disciplines (e.g. genetics). Indeed, an increasing number of researchers in these fields are beginning to include GIS analyses into their research programmes. Some of this integration has taken the form of analysing the spatial relationship between populations and hybrid zones. Several other researchers have also begun to incorporate GIS into their work through the use of GIS-based niche models. These models estimate a multidimensional niche for a species using known geo-referenced populations and digital climate maps. Here, I review the recent integration of GIS and GIS-based predictive niche models into the above evolutionary sub-disciplines. I also describe evolutionary analyses that could be further enhanced through the implementation of GIS.

Gis-based niche models reveal unifying climatic mechanisms that maintain the location of avian hybrid zones in a North American suture zone.

The existence of suture zones in North America has recently been verified, yet the environmental factors responsible for the maintenance of their structure and position have remained undetermined. The Great Plains suture zone in the US is perhaps the most significant and broadly studied in North America. Numerous avian hybrid zones that cluster in this region have been extensively studied over the last half-century. A primary result of this work is that exogenous factors present in this region have promoted and maintained avian species divergence. Yet, to date the variables most important in the generation and the clustered positioning of these hybrid zones in relation to one another have not been determined. The present study aims to advance our understanding of this North American suture zone by using niche modelling to quantify which environmental variables are most important in its formation and maintenance. Through the generation of fundamental niches for four hybrids and their parental species, similarities linking the hybrid zones were uncovered. The results show that temperature holds this suture zone in position and also suggest that temperature played a primary role in promoting niche differentiation among these sister species pairs during Pleistocene glacial cycles.

Visual acuity recovery rates following cataract surgery and implantation of soft intraocular lenses.

To determine whether eyes receiving soft optic lens implants had faster visual recovery times than eyes receiving firm optic lens implants, we calculated the visual acuity recovery rates following our standard cataract operation. Visual acuity of 20/50 or better without correction was obtained in 31% of eyes on the first day following surgery, 55% at one week, 74% at three weeks, and 89% at six weeks and three months. Fifty best-case soft optic lens implant cases were reviewed and their visual recovery rates were calculated. There were no statistically significant differences in the visual acuities without correction at any follow-up point. There was a slightly significant difference at one week with correction and a significant difference at three weeks with correction favoring the soft lens/small incision group. Because optical correction is generally not provided on these visits, we conclude that soft lens implants with small incisions did not provide clinically significant improvement in visual acuity recovery over our standard cataract procedure.