Uncertainty in predictions of forest carbon dynamics: separating driver error from model error.

We present an analysis of the relative magnitude and contribution of parameter and driver uncertainty to the confidence intervals on estimates of net carbon fluxes. Model parameters may be difficult or impractical to measure, while driver fields are rarely complete, with data gaps due to sensor failure and sparse observational networks. Parameters are generally derived through some optimization method, while driver fields may be interpolated from available data sources. For this study, we used data from a young ponderosa pine stand at Metolius, Central Oregon, and a simple daily model of coupled carbon and water fluxes (DALEC). An ensemble of acceptable parameterizations was generated using an ensemble Kalman filter and eddy covariance measurements of net C exchange. Geostatistical simulations generated an ensemble of meteorological driving variables for the site, consistent with the spatiotemporal autocorrelations inherent in the observational data from 13 local weather stations. Simulated meteorological data were propagated through the model to derive the uncertainty on the CO2 flux resultant from driver uncertainty typical of spatially extensive modeling studies. Furthermore, the model uncertainty was partitioned between temperature and precipitation. With at least one meteorological station within 25 km of the study site, driver uncertainty was relatively small ( 10% of the total net flux), while parameterization uncertainty was larger, 50% of the total net flux. The largest source of driver uncertainty was due to temperature (8% of the total flux). The combined effect of parameter and driver uncertainty was 57% of the total net flux. However, when the nearest meteorological station was > 100 km from the study site, uncertainty in net ecosystem exchange (NEE) predictions introduced by meteorological drivers increased by 88%. Precipitation estimates were a larger source of bias in NEE estimates than were temperature estimates, although the biases partly compensated for each other. The time scales on which precipitation errors occurred in the simulations were shorter than the temporal scales over which drought developed in the model, so drought events were reasonably simulated. The approach outlined here provides a means to assess the uncertainty and bias introduced by meteorological drivers in regional-scale ecological forecasting.

[Prognosis and treatment of Vernal keratoconjunctivitis in pediatric age: pilot study on 197 patients]. / Prognosi e trattamento della cheratocongiuntivite Vernal in età pediatricia: studio pilota su 197 pazienti.

AIM: Corticosteroids and high-concentrated cyclosporine eyedrops have been used for treatment of severe vernal keratoconjunctivitis (VKC) cases. The purpose of our study was to verify the efficacy of 1% topical cyclosporine in improving severe form of VKC in childhood and investigate for factors affecting the response to therapy. METHODS: We conducted an open trial involving 197 children with severe VKC, who received topical cyclosporine 1% for four months. Ocular subjective symptoms and objective signs were scored in all children at entry, two weeks and four months. Skin prick tests and microscope endothelial cells evaluation were also performed; serum IgE and cyclosporine levels were assessed. RESULTS: The mean score values for severity of subjective symptoms and objective signs were significantly decreased after 2 weeks, and 4 months, compared with those at entry (P<0.001) in all children. Cyclosporine serum levels were not detectable at the end of therapy, nor were endothelial corneal cells damaged. Patients who started the therapy at the beginning of the disease and/or received long-term regimen of treatment with cyclosporine had a faster improvement of ocular signs and symptoms, compared to all other patients. CONCLUSION: Our findings suggest that 1% cyclosporine concentration administrated topically at the beginning of the disease and for a long-term period might be the most effective treatment to control symptoms and local inflammation in severe forms of VKC in childhood.

Measurement of skin temperature after infrared laser stimulation.

OBJECTIVES: Several types of lasers are available for eliciting laser evoked responses (LEPs). In order to understand advantages and drawbacks of each one, and to use it properly, it is important that the pattern of skin heating is known and duly considered. This study was aimed at assessing the skin temperature during and immediately after irradiation with pulses by Nd:YAP and CO(2) lasers. MATERIALS AND METHODS: The back of the non-dominant hand was irradiated in 8 subjects. Temperatures were measured by a fast analogical pyrometer (5 ms response time). Stimuli were tested on natural colour (white) and blackened skin. RESULTS: Nd:YAP pulses yielded temperatures that were correlated with pulse energy, but not with pulse duration; much higher temperatures were obtained irradiating blackened skin than white skin (ranges 100-194 degrees C vs 35-46 degrees C). Temperature decay was extremely slow in white skin, reaching its basal value in more than 30 s. CO(2) pulses delivered with power of 3W and 6W yielded temperatures of 69-87 degrees C on white skin, and 138-226 degrees C on blackened skin. Temperature decay was very fast (4-8 ms). CONCLUSIONS: Differences in peak temperatures and decay times between lasers and tested conditions depend on energy and volume of heated skin. The highest temperatures are reached with lesser degree of penetration, as in the case of CO(2) laser and blackened skin. Taking into account the temperature decay time of the skin, the minimum interstimulus interval to get reliable LEPs should be no less than 10 s for Nd:YAP and 100 ms for CO(2) laser. Another important practical consequence of the heating pattern is that the Nd:YAP pulses will activate warmth receptors more easily than CO(2).

CCD imaging of the electrical activity in the leech nervous system.

A single ganglion of the nervous system of the leech Hirudo medicinalis was isolated. One or both roots emerging from each side of the ganglion were sucked into suction pipettes used either for extracellular stimulation or for recording the gross electrical activity. The ganglion was stained with the fluorescence voltage sensitive dye Di-4-Anepps. The fluorescence was measured with a nitrogen cooled CCD camera. Our recording system allowed us to measure in real time slow optical signals corresponding to changes in light intensity of at least 5/1000. These signals were caused by the direct polarization of neuronal structures, the afterhyperpolarization or the afterdischarge induced by a prolonged stimulation. When images were acquired at fixed times, several of them could be averaged and optical signals of at least 2/1000 could be reliably measured. These optical signals originated from well identified neurons, such as T, P and N sensory neurons. By taking images at different times and at different focal planes, electrical events could be followed at a temporal resolution of 50 Hz. The three dimensional dynamics of electrical events, initiated by a specific stimulation, was imaged and the spread of excitation among leech neurons was followed. When two roots were selectively stimulated, their neuronal interactions could be imaged and the linear and non-linear terms of the interaction could be characterized.

Eye closure affects flash VEP latency in dementia.

In a group of 27 demented patients (21 with DAT and 6 with MID) with normal pattern VEP (PVEP), the latencies of the main flash VEP (FVEP) components (P1, N2, P2 and N3) were assessed both with open and closed eyes. At variance from controls, demented patients showed that both P2 and N3 components are significantly delayed with closed eyes while neither P1 nor N2 timings are affected. Control studies ruled out the possibility that such an outcome might depend on a defective pupillary responsiveness and/or an impaired sensitivity to luminance changes. On these grounds it is suggested that the effect of mode of stimulation on FVEP latency in demented patients is more likely to depend on "central" than on "peripheral" mechanisms. The dependence of latency changes on closure of the eyes seems to negate the direct effect of lesions upon visual structures and suggests an impairment of the modulatory action of non-visual afferents upon the activity of the visual cortex.

Response of arm flexor muscles to magnetic and electrical brain stimulation during shortening and lengthening tasks in man.

1. The responses of the brachioradialis and biceps brachii muscles to non-invasive magnetic and electrical stimulation of the human motor cortex have been investigated during performance of different tasks. 2. Both muscles were simultaneously active during elbow flexor isometric torque, or forearm flexion lifting a weight (shortening contraction), or extension breaking the fall of the weight (lengthening contraction). The forearm extensor triceps brachii muscle was not engaged in any task. By using different weights, comparable levels of EMG activity were obtained in the same muscle across tasks. 3. Both magnetic (7 subjects) and electrical (3 subjects) brain stimulation (at about 1.5 times the motor threshold) produced larger responses during shortening, and smaller responses during lengthening, in the brachioradialis muscle with respect to isometric contractions, in spite of equal background EMG levels. Responses evoked in the biceps brachii by either stimulation mode were smaller during lengthening but not significantly enhanced during shortening. No consistent differences in the task-related modulation of the responses were present between electrical or magnetic stimulations. No significant changes in the evoked responses occurred during passive elbow flexion or extension. 4. In three subjects, the H reflex was evoked in the brachioradialis by stimulation of the radial nerve during performance of the same tasks. The pattern of task-related modulation of the reflex amplitude paralleled that obtained for brain stimulation. 5. The opposite modulation induced by the shortening and lengthening tasks both in magnetically and electrically evoked motor responses, and in the H reflex, suggests that task-related changes in excitability of the cortical neurones play a minor role.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemisphere asymmetry in decision making abilities. An experimental study in unilateral brain damage.

Thirty control subjects and 60 unilateral brain-damaged patients, 30 with left hemisphere (LH) damage and 30 with right hemisphere (RH) disease, underwent a disjunctive 4-choice reaction time study. Speed of reaction (as defined by the reciprocal of reaction time (RT), movement time (MT) and total response time (TRT] and accuracy of response (as represented by the sum of errors in selecting the correct response key) were investigated comparatively as a function of side of lesion and of performance on Raven's Coloured Progressive Matrices (PM47). In contrast to movement speed (1/MT), reaction speed (1/RT) as well as total response speed (1/TRT) showed a lesion effect independent of side of damage. Conversely, accuracy was differentially impaired, LH damage being associated with a significantly higher number of errors. Speed and accuracy had different relationships with the performance on the PM47 in the two hemisphere groups. Speed was affected in parallel with changes in PM47 performance both in the LH and in RH groups, whereas accuracy was altered only in LH patients. It was concluded that speed of motor reaction is affected by unilateral brain lesions irrespective of their side, whereas decision making processes, as expressed by accuracy of response, seem to be specifically impaired by LH damage.

Variability of light-evoked response pattern and morphological characterization of amacrine cells in goldfish retina.

Amacrine cells of the goldfish retina were characterized electrophysiologically and subsequently labelled by intracellular injection of horseradish peroxidase. An attempt was made to broaden the electrophysiological classification of the cells. Light-evoked sustained amacrine cell responses were divided into two subtypes depending on colour opponency. Colour-coded responses (red/depolarizing and green/hyperpolarizing) were found to arise in amacrine cells possessing highly polarized dendritic fields; the dendrites were monostratified in the proximal half (sublamina b) of the inner plexiform layer. Non-colour-opponent sustained responses also arose in monostratified units, but the level of dendritic ramification was in sublamina a or b (hyperpolarizing or depolarizing units, respectively). Transient (ON-OFF) responses were associated mainly with bi- or multi-stratified or diffuse amacrine cells. Some variability was observed in the sizes of the dendritic fields in different sublaminae. There was a tendency for units with brisk components of responses to be narrowly stratified in the inner plexiform layer. Some units possessed "distant" dendrites. Several aspects of structure-function correlation in amacrine cells are discussed.

Impaired habituation of long-latency stretch reflexes of the wrist muscles in Huntington's disease.

Electromyographic responses to sudden wrist extension were recorded from the forearm and finger flexor muscles in 10 patients with Huntington's disease (HD) and in 10 normal controls. Stretch reflexes were characterized by a short-latency (SL) and a long-latency (LL) component both in patients and controls. Latency, duration, and size of the SL component were not different in the two groups, whereas the LL component was delayed in latency and reduced in size in HD patients. Increasing the stretch repetition rate from 0.1 to 0.4 cycles/s did not affect the SL component of either group, whereas the LL stretch reflex was reduced in size and duration in normal controls, but not in HD patients. These findings suggest an impairment of the "gain" mechanisms of the sole LL component, responsible for a desaturation of this component. This study supports the hypothesis that LL stretch reflexes are mediated by a transcortical long loop, possibly damaged in HD.

Electrical stimulation of the motor tracts in cervical spondylosis.

Motor action potentials evoked by percutaneous electrical stimulation of the scalp and of the cervical (or lumbar) vertebral region were recorded from the biceps, thenar and tibialis anterior muscles in 30 patients with cervical spondylosis. Twelve normal controls were matched for age and height. Abnormalities of central motor conduction (absence or increased central delay of cortical responses) for at least one muscle were observed in all (but one) the patients with myelopathy alone or combined with radiculopathy. An increase in latency of the responses evoked by cervical stimulation occurred in 40% of patients with radiculopathy or myelo-radiculopathy. Changes of motor conduction occurred even in the absence of abnormalities of somatosensory evoked potentials, while the opposite was never observed. Direct stimulation of the motor tracts may be of value in the functional assessment of the motor pathways in cervical spondylosis.

Parietal and prerolandic somatosensory evoked responses in carotid artery reversible ischemic attacks (RIA).

Somatosensory potentials evoked by median nerve stimulation were recorded bilaterally from the prerolandic and parietal scalp in 36 patients with reversible ischemic attacks in one carotid artery distribution. Responses recorded from the affected and unaffected hemisphere were compared. SEP abnormalities were observed over the affected hemisphere in 22 subjects (61.1%), irrespective of number and/or duration of episodes, and appeared selectively correlated to their clinical features. SEP studies proved to be more sensitive than conventional EEG recordings and are suitable for evaluation of the functional impairment of specific cerebral areas following transient cerebral ischemia. The occurrence of SEP abnormalities in RIA may represent an unfavourable sign, being more frequent in patients with evidence of internal carotid artery disease.

Electrophysiological detection of "silent" plaques in the optic pathways.

The incidence of a delayed P100 component of the VEP after checkerboard stimulation in probable or possible multiple sclerosis (MS) without history, signs or symptoms of optic neuritis is not significantly different from that found in other neurological disorders in which the visual system is unaffected. This reduces the diagnostic validity of a delayed P100 as evidence of "silent" plaques in the optic pathway, at least in suspected MS. The use of grating increases the VEP sensitivity in the MS group, but it still leaves more than a 30% chance of error in attributing a delayed P100 to a demyelinating disorder. In this respect the discordant behaviour of checkerboard and grating responses may represent a useful clue.

Electrophysiological analysis of motor control in patients with vascular hemichorea.

An EMG analysis of motor control was performed in 4 patients with unilateral choreic movements of sudden onset, 3 of whom presented CT scan evidence of lacunar infarcts involving the contralateral striatum. The choreic dyskinesias were correlated with EMG bursts of variable duration occurring with a random order of activation. Ballistic elbow flexion movements were performed with a normal triphasic EMG pattern, but both size and duration of the first agonist burst were increased on the affected side. Abnormalities of cerebral somatosensory evoked responses were observed in 3 patients on stimulation of the side with choreic movements.

Blocking of the squid axon K+ channel by noxiustoxin: a toxin from the venom of the scorpion Centruroides noxius.

We have studied the selective effects of noxiustoxin (NTX), a fraction of the venom of the scorpion Centruroides noxius, on the K currents of perfused squid giant axons using the voltage-clamp technique. At concentrations below 1.5 microM, NTX blocked K currents in a voltage-independent manner, with little effect on their turning-on and turning-off kinetics. Above 1.5 microM, the block by NTX became voltage-dependent and could be partially removed by repetitive pulsing and strong depolarizations. Long repolarizations and more negative holding potentials favoured the slow restoration of channel block. Reduction of K currents by internally perfusing the fibers with solutions of low K+ concentration (200 mM), affected very little the removal of NTX-block during repetitive pulsing, suggesting that block removal depended on membrane potential and not on outward movements of K+ ions through open channels. In high extracellular K+ (300 mM) the blocking action of NTX was reduced and the instantaneous I-V characteristics showed a marked outward rectification. At 20 microM NTX, inward tail currents measured on step repolarizations to -70 mV were fully blocked, suggesting a direct interaction of the toxin with the open channel. The effects of the total venom Centruroides noxius Hoffmann was also studied. External application of 0.25 mg/ml of the venom caused a marked reduction of both Na and K currents, an effect similar to that of other scorpion venoms.

A microcomputer-based system for data acquisition and analysis of step-like current jumps due to the opening of single ionic channels in model membranes.

At the cell surface, passive transport is controlled by membrane proteins forming hydrophilic pores (or channels) which span the hydrophobic core of the lipid bilayer. Gating mechanisms determine the occurrence of very small and fast step-like current jumps. We developed an intelligent system to acquire and to analyze signals due to the opening and closing of ionic single channels. A specific algorithm allows us to recognize channel current transitions and to discard false events due to noise peaks or to unwelcome fluctuations of the signal. Statistics of the single channel amplitude and mean life-time can be performed. We report the results obtained from analyzing the characteristics of the gramicidin A single channel in phosphatidylserine model membranes. Mean current values of 2.08 +/- 0.01 pA and life-times of 101 +/- 3 ms. were measured at 100mV applied potentials in KC1 100mM solution.

Simple reaction-time changes in patients with unilateral brain damage.

Changes of simple visual reaction time were analysed in two groups of unilateral brain-damaged patients in order to evaluate to what extent properties of lesions, clinical parameters and experimental variables might influence speed of motor response. The results confirmed that brain damage, independent of its side, produces a retardation of speed. However, the two hemispheric groups differed in so far as volume of damage had a different bearing depending on side of lesion. In spite of such a difference the presence of a general interaction between size of damage and rate of progression of lesion was noted in both the hemispheres, reminiscent of Jackson's concept of 'lesion momentum'. Aphasia was related to a significant retardation of speed in left-hemisphere-diseased patients, although a specific effect of the disturbance of language could not be demonstrated. Experimental variables such as warned vs unwarned stimulation did not affect significantly the performance of brain-damaged patients.

VEP changes in Parkinson's disease are stimulus dependent.

Two stimulus configurations (gratings and checkerboards) have been presented to a series of consecutive patients with the aim of exploring VEP changes in Parkinson's disease. The outcome turned out to be quite different according to the stimulus employed. Specifically, grating pattern produced a high diagnostic yield as opposite to checkerboard, which did not reveal substantial modifications of the latency of the VEP major positive peak with respect to a control group. This finding raises problems as to the characteristics of visual changes associated with Parkinson's disease.