Lévy walkers inside spherical shells with absorbing boundaries: Towards settling the optimal Lévy walk strategy for random searches.

The Lévy flight foraging hypothesis states that organisms must have evolved adaptations to exploit Lévy walk search strategies. Indeed, it is widely accepted that inverse square Lévy walks optimize the search efficiency in foraging with unrestricted revisits (also known as nondestructive foraging). However, a mathematically rigorous demonstration of this for dimensions D≥2 is still lacking. Here we study the very closely related problem of a Lévy walker inside annuli or spherical shells with absorbing boundaries. In the limit that corresponds to the foraging with unrestricted revisits, we show that inverse square Lévy walks optimize the search. This constitutes the strongest formal result to date supporting the optimality of inverse square Lévy walks search strategies.

Effect of the search space dimensionality for finding close and faraway targets in random searches.

We investigate the dependence on the search space dimension of statistical properties of random searches with Lévy α-stable and power-law distributions of step lengths. We find that the probabilities to return to the last target found (P_{0}) and to encounter faraway targets (P_{L}), as well as the associated Shannon entropy S, behave as a function of α quite differently in one (1D) and two (2D) dimensions, a somewhat surprising result not reported until now. While in 1D one always has P_{0}≥P_{L}, an interesting crossover takes place in 2D that separates the search regimes with P_{0}>P_{L} for higher α and P_{0}

Landscape-scaled strategies can outperform Lévy random searches.

Information on the relevant global scales of the search space, even if partial, should conceivably enhance the performance of random searches. Here we show numerically and analytically that the paradigmatic uninformed optimal Lévy searches can be outperformed by informed multiple-scale random searches in one (1D) and two (2D) dimensions, even when the knowledge about the relevant landscape scales is incomplete. We show in the low-density nondestructive regime that the optimal efficiency of biexponential searches that incorporate all key scales of the 1D landscape of size L decays asymptotically as η_{opt}∼1/sqrt[L], overcoming the result η_{opt}∼1/(sqrt[L]lnL) of optimal Lévy searches. We further characterize the level of limited information the searcher can have on these scales. We obtain the phase diagram of bi- and triexponential searches in 1D and 2D. Remarkably, even for a certain degree of lack of information, partially informed searches can still outperform optimal Lévy searches. We discuss our results in connection with the foraging problem.

A novel integrative approach elucidates fine-scale dispersal patchiness in marine populations.

Dispersal is one of the main determining factors of population structure. In the marine habitat, well-connected populations with large numbers of reproducing individuals are common but even so population structure can exist on a small-scale. Variation in dispersal patterns between populations or over time is often associated to geographic distance or changing oceanographic barriers. Consequently, detecting structure and variation in dispersal on a fine-scale within marine populations still remains a challenge. Here we propose and use a novel approach of combining a clustering model, early-life history trait information from fish otoliths, spatial coordinates and genetic markers to detect very fine-scale dispersal patterns. We collected 1573 individuals (946 adults and 627 juveniles) of the black-faced blenny across a small-scale (2 km) coastline as well as at a larger-scale area (<50 kms). A total of 178 single nucleotide polymorphism markers were used to evaluate relatedness patterns within this well-connected population. In our clustering models we categorized SHORT-range dispersers to be potential local recruits based on their high relatedness within and low relatedness towards other spatial clusters. Local retention and/or dispersal of this potential local recruitment varied across the 2 km coastline with higher frequency of SHORT-range dispersers towards the southwest of the area for adults. An inverse pattern was found for juveniles, showing an increase of SHORT-range dispersers towards the northeast. As we rule out selective movement and mortality from one year to the next, this pattern reveals a complex but not full genetic mixing, and variability in coastal circulation is most likely the main driver of this fine-scale chaotic genetic patchiness within this otherwise homogeneous population. When focusing on the patterns within one recruitment season, we found large differences in temperatures (from approx. 17 °C to 25 °C) as well as pelagic larval duration (PLD) for juveniles from the beginning of the season and the end of the season. We were able to detect fine-scale differences in LONG-range juvenile dispersers, representing distant migrants, depending on whether they were born at the beginning of the season with a longer PLD, or at the end of the reproductive season. The ability to detect such fine-scale dispersal patchiness will aid in our understanding of the underlying mechanisms of population structuring and chaotic patchiness in a wide range of species even with high potential dispersal abilities.

Active and reactive behaviour in human mobility: the influence of attraction points on pedestrians.

Human mobility is becoming an accessible field of study, thanks to the progress and availability of tracking technologies as a common feature of smart phones. We describe an example of a scalable experiment exploiting these circumstances at a public, outdoor fair in Barcelona (Spain). Participants were tracked while wandering through an open space with activity stands attracting their attention. We develop a general modelling framework based on Langevin dynamics, which allows us to test the influence of two distinct types of ingredients on mobility: reactive or context-dependent factors, modelled by means of a force field generated by attraction points in a given spatial configuration and active or inherent factors, modelled from intrinsic movement patterns of the subjects. The additive and constructive framework model accounts for some observed features. Starting with the simplest model (purely random walkers) as a reference, we progressively introduce different ingredients such as persistence, memory and perceptual landscape, aiming to untangle active and reactive contributions and quantify their respective relevance. The proposed approach may help in anticipating the spatial distribution of citizens in alternative scenarios and in improving the design of public events based on a facts-based approach.

Inferring Lévy walks from curved trajectories: A rescaling method.

An important problem in the study of anomalous diffusion and transport concerns the proper analysis of trajectory data. The analysis and inference of Lévy walk patterns from empirical or simulated trajectories of particles in two and three-dimensional spaces (2D and 3D) is much more difficult than in 1D because path curvature is nonexistent in 1D but quite common in higher dimensions. Recently, a new method for detecting Lévy walks, which considers 1D projections of 2D or 3D trajectory data, has been proposed by Humphries et al. The key new idea is to exploit the fact that the 1D projection of a high-dimensional Lévy walk is itself a Lévy walk. Here, we ask whether or not this projection method is powerful enough to cleanly distinguish 2D Lévy walk with added curvature from a simple Markovian correlated random walk. We study the especially challenging case in which both 2D walks have exactly identical probability density functions (pdf) of step sizes as well as of turning angles between successive steps. Our approach extends the original projection method by introducing a rescaling of the projected data. Upon projection and coarse-graining, the renormalized pdf for the travel distances between successive turnings is seen to possess a fat tail when there is an underlying Lévy process. We exploit this effect to infer a Lévy walk process in the original high-dimensional curved trajectory. In contrast, no fat tail appears when a (Markovian) correlated random walk is analyzed in this way. We show that this procedure works extremely well in clearly identifying a Lévy walk even when there is noise from curvature. The present protocol may be useful in realistic contexts involving ongoing debates on the presence (or not) of Lévy walks related to animal movement on land (2D) and in air and oceans (3D).

How landscape heterogeneity frames optimal diffusivity in searching processes.

Theoretical and empirical investigations of search strategies typically have failed to distinguish the distinct roles played by density versus patchiness of resources. It is well known that motility and diffusivity of organisms often increase in environments with low density of resources, but thus far there has been little progress in understanding the specific role of landscape heterogeneity and disorder on random, non-oriented motility. Here we address the general question of how the landscape heterogeneity affects the efficiency of encounter interactions under global constant density of scarce resources. We unveil the key mechanism coupling the landscape structure with optimal search diffusivity. In particular, our main result leads to an empirically testable prediction: enhanced diffusivity (including superdiffusive searches), with shift in the diffusion exponent, favors the success of target encounters in heterogeneous landscapes.

[A retrospective study about 11 cases of Esthesioneuroblastomas treated in Hospital Santa Creu i Sant Pau between 2000 and 2008 and literature review]. / Estudio retrospectivo de 11 casos de estesioneuroblastomas tratados en el Hospital Santa Creu i Sant Pau entre los años 2000 y 2008 más revisión de la literatura.

INTRODUCTION. Esthesioneuroblastoma (ENB) is a very uncommon malignant tumor with a neuroectodermal origin that usually involves the anterior cranial fossa and nasal cavity. OBJECTIVES. To review our experience in the management of ENB and assess the validity of the histopathological diagnosis, modality of treatment and prognostic factors of the disease comparing our findings with the literature. METHODS. A retrospective study of 11 cases with the diagnosis of esthesioneuroblastoma treated in our hospital between 2000 and 2008. Statistical analysis was performed in search for prognostic factors. The bibliography about ENB published between 1990 and 2009 was reviewed RESULTS. There were 3 women and 8 men, with a mean age of 42 years old (range 20-71y). Their symptoms upon admission were nasal obstruction (81%), epistaxis (27%), visual loss (18%), headache and others. According to the Kadish Stage, 2 were stage B and 9 were stage C. Dulguerov and Calcaterra Classification was also used: 2 were T2, 3 were T3 and 6 were T4. The hystopathological result according to the Hyams classification was: 2 cases in stage I, 4 in stage II, 3 in stage III and 2 in stage IV. The two cases classified in stage IV changed the diagnosis to undifferenciate tumor in the second biopsy. A subcranial approach was performed in 8 cases combined with endonasal endoscopy to confirm the total removal, followed by radiotherapy in all and chemotherapy in one case, resulting on 62% (5 patients) being alive without disease, 12,5% (1 p) alive with disease, and 25% (2 p) dead of disease. Another patient was operated by a single endonasal endoscopic approach and a subtotal removal was achieved. This patient is alive without disease. The other 2 patients were treated by biopsy plus radiotherapy and chemotherapy, because they were considered unresectable, and one of them is alive with disease and the other one is dead of disease. Radiotherapy was performed in all cases and chemotherapy in 5 cases. The hystopathological grading system of Hyams was considered statistically significant as a prognostic factor of disease-free survival. CONCLUSIONS. When the hystopathological diagnosis of ENB is considered, the Hyams classification can be valid considering grade IV as an advanced stage that is sometimes difficult to differentiate from other undiferentiated tumors. The subcranial approach or craneofacial resection in advanced stages (Kadish C and some B) should be considered as the first treatment of choice. Radiotherapy is indicated in all cases and chemotherapy in selected cases. Hyams' classification was the only staging system that proved useful as a prognostic factor in our series.

Estudio retrospectivo de 11 casos de estesioneuroblastomas tratados en el Hospital Santa Creu i Sant Pau entre los años 2000 y 2008 más revisión de la literatura / A retrospective study about 11 cases of Esthesioneuroblastomas treated in Hospital Santa Creu i Sant Pau between 2000 and 2008 and literature review

Introducción. El estesioneuroblastoma (ENB) es un tumor maligno de origen neuroectodérmico poco habitual que afecta principalmente a la fosa craneal anterior y cavidad nasal. Objetivos. Revisar nuestra experiencia en el manejo de los ENB, evaluar la validez del diagnóstico anatomopatológico, el tipo de tratamiento y factores pronósticos de la enfermedad comparando nuestros hallazgos con los descritos en la literatura. Material y métodos. Estudio retrospectivo de 11 casos de ENB tratados en nuestro hospital en el periodo comprendido entre 2000 y 2008. Se realiza análisis estadístico sobre la existencia de factores pronósticos. Se revisa la bibliografía publicada sobre el ENB entre 1990 y 2009.Resultados. Se trataron 3 mujeres y 8 hombres, cuya edad media fue 42 años (rango 20-71 años). El síntoma inicial fue la obstrucción nasal (81%), epistaxis (27%), disminución de agudeza visual (18%), cefalea y otros. Según la clasificación de Kadish, 2 son estadío B y 9 estadío C; según la clasificación de Dulguerov, 2 son T2, 3 son T3 y 6 son T4. El resultado histológico según la clasificación de Hyams fue de 2 casos en grado I, 4 en grado II, 3 en grado III y 2 en grado IV. Dos de los casos inicialmente catalogados en grado IV cambiaron de diagnóstico en la segunda (..) (AU)

Introduction. Esthesioneuroblastoma (ENB) is a very uncommon malignant tumor with a neuroectodermal origin that usually involves the anterior cranial fossa and nasal cavity. Objectives. To review our experience in the management of ENB and assess the validity of the histopathological diagnosis, modality of treatment and prognostic factors of the disease comparing our findings with the literature. Methods. A retrospective study of 11 cases with the diagnosis of esthesioneuroblastoma treated in our hospital between 2000 and 2008. Statistical analysis was performed in search for prognostic factors. The bibliography about ENB published between 1990 and 2009 (..) (AU)

Optimising the success of random destructive searches: Lévy walks can outperform ballistic motions.

We re-evaluate the long standing and widely held belief that ballistic movements (i.e. straight-lines movements) outperform Lévy walks when searching for targets that once located are not revisited. The belief stems from the results of analyses of one-dimensional searches, analyses which have not accounted for the fact that target numbers can be continually depleted during the search process. This is a crucial oversight because continual depletion promotes the searching efficiencies of some Lévy walks above that of ballistic motion. The continual depletion effect is not so important for two- and three-dimensional searches. Nevertheless, we show that Lévy walks and ballistic movements can be equally or almost equally effective when searching within two- and three-dimensional environments for randomly and sparsely distributed targets or when searching for targets that are occasionally concealed. We also show that Lévy walks are advantageous when searching for targets that can occasionally evade capture. These situations represent common predator-prey interactions in which predators are involved in 'imperfect destructive' searches. Our model suggests that accounting for coevolutionary arms races at the predator-prey detection/reaction scales can explain to some extent Lévy walk searching patterns of predators at larger scales. This result provides new insights into the Lévy walk movement patterns of some destructive foragers.

The influence of turning angles on the success of non-oriented animal searches.

Animal searches cover a full range of possibilities from highly deterministic to apparently completely random behaviors. However, even those stochastic components of animal movement can be adaptive, since not all random distributions lead to similar success in finding targets. Here we address the general problem of optimizing encounter rates in non-deterministic, non-oriented searches, both in homogeneous and patchy target landscapes. Specifically, we investigate how two different features related to turning angle distributions influence encounter success: (i) the shape (relative kurtosis) of the angular distribution and (ii) the correlations between successive relative orientations (directional memory). Such influence is analyzed in correlated random walk models using a proper choice of representative turning angle distributions of the recently proposed Jones and Pewsey class. We consider the cases of distributions with nearly the same shape but considerably distinct correlation lengths, and distributions with same correlation but with contrasting relative kurtosis. In homogeneous landscapes, we find that the correlation length has a large influence in the search efficiency. Moreover, similar search efficiencies can be reached by means of distinctly shaped turning angle distributions, provided that the resulting correlation length is the same. In contrast, in patchy landscapes the particular shape of the distribution also becomes relevant for the search efficiency, specially at high target densities. Excessively sharp distributions generate very inefficient searches in landscapes where local target density fluctuations are large. These results are of evolutionary interest. On the one hand, it is shown that equally successful directional memory can arise from contrasting turning behaviors, therefore increasing the likelihood of robust adaptive stochastic behavior. On the other hand, when target landscape is patchy, adequate tumbling may help to explore better local scale heterogeneities, being some details of the shape of the distribution also potentially adaptive.

[Current management of arteriovenous malformations. Retrospective study of 31 cases and literature review]. / Manejo actual de las malformaciones arteriovenosas. Estudio retrospectivo de 31 casos y revisión de la literatura.

OBJECTIVE: To establish some therapeutic criteria about the treatment of AVMs of III, IV and V grade of Spetzler and Martin and to analyse the results in the subgroup of preoperative embolization plus surgery. METHODS: We perform a retrospective analysis of a group of 31 patients with arteriovenous malformations (AVMs) treated in our center between 1999 and 2004. There were 19 women and 12 men, with a mean age of 31.6 years old (range, 1-62a). Their symptoms upon admission were intracranial hemorrhage in 77.4%, seizures in 12.9%, headache, ischemic event and incidental finding in 3.2% each group. Diagnostic angiography was performed in 29 cases and anatomopathologic diagnostic in 2 cases. The malformations were classified with Spetzler and Martin Grading Scale, in 10.3% grade I, 24.1% grade II, 37.9% grade III, 24.1% grade IV and 3.4% grade V. Patients were classified in 6 subgroups of treatment (surgery, embolization, radiosurgery, embolization plus surgery, embolization plus radiosurgery and conservative treatment). RESULTS: AVMs grade III, IV and V (19 patients) were treated with surgery (6 cases), embolization plus surgery (5 cases), but also other kind of treatments (embolization alone, radiosurgery and conservative) were used. Functional results in these groups of patients were 36.8% (7 cases) with no symptoms or slights symptoms (modified Rankin 0-1), 52.6% (10 cases) minor disability (mRankin 2), 5.3% (1 case) moderate disability and 5.3% (1 case) mortality. We observe a high rate of postembolization hemorrhage in the group of patients in which the combination of preoperative embolization plus surgery was used. In these cases, early surgery was performed with a good functional recovery. There was one case of postoperative mortality. CONCLUSION: We should consider some factors like the natural history, clinical presentation (hemorrhage), angiographic features (deep arterial supply, aneurisms), Spetzler and Martin Grading and the clinical condition of the patient before treating a cerebral AVM. In the subgroup of treatment with embolization plus surgery, we recommend to achieve a subtotal preoperative embolization > 50%, not to obliterate more than 50% in one session, to perform staged embolization waiting from 4 to 6 weeks between procedures, and from 1 to 3 weeks between the last embolization and surgery.

Manejo actual de las malformaciones arteriovenosas. Estudio retrospectivo de 31 casos y revisión de la literatura / Actual Management of arteriovenous malformations. Retrospective study of 31 cases and literature review

Objetivos. Establecer unos criterios terapéuticos en las malformaciones arterio venosas (MAVs) grados III,IV y V de Spetzler y Martin y análisis de resultados en el subgrupo de tratamiento con embolización más cirugía. Material y métodos. Estudio retrospectivo de 31pacientes con MAVs cerebrales tratados en nuestro servicio entre 1999 y 2004. Se trata de 19 mujeres y 12 hombres, con una edad media de 31,6 años (rango de 1 a 62a).La forma de presentación fue en un 77,4% hemorragiaintracraneal, en un 12,9% crisis comicial y en un 3,2%cefalea, infarto isquémico y hallazgo casual en cada uno de ellos. En 29 casos se realizó arteriografía diagnóstica y en 2 casos el diagnóstico fue anatomo-patológico. Según la clasificación de Spetzler y Martin, 10,3%fueron de Grado I, 24,1% de Grado II, 37,9% de GradoIll, 24,1% de Grado IV y 3,4% de Grado V. Se clasificaron en 6 grupos según el tratamiento realizado (cirugía, embolización, radiocirugía, embolización más cirugía, embolización más radiocirugía y tratamiento conservador).Resultados. Las MAVs grado III, IV y V (19 pacientes)fueron tratadas en su mayoría por cirugía (6 casos) y embolización más cirugía (5 casos) pero también se utilizaron otras modalidades de tratamiento (embolización, radiocirugía y conservador). Los resultados funcionales de estos 3 subgrupos muestra un 36,8% (7 casos) de asintomáticos o con mínimos síntomas (Rankin m 0-1),un 52,6% (10 casos) de discapacidad leve pero independientes(Rankin m=2), un 5,3% (1 caso) de moderada discapacidad (Rankin m=3), y un 5,3% (1 caso)de mortalidad. En el manejo combinado embolización más cirugía de malformaciones complejas, se observa un alto porcentaje de sangrado postembolización que motivó cirugía precoz con buen resultado funcional. Hubo un caso de mortalidad postquirúrgica. Conclusiones. En el tratamiento de las MAVs cerebralesse debe tener en cuenta factores como la historia natural, la forma de presentación (hemorragia), las características angioestructurales (presencia de aporte arterial profundo, aneurismas), la escala de Spetzler y Martin y el estado clínico del paciente. En el tratamiento con embolización más cirugía es recomendable obtener una embolización prequirúrgica subtotal > 50%, no ocluir más del 50% por sesión, mantener un intervalo entre sesiones de embolización entre4 y 6 semanas y un intervalo entre última embolización y cirugía entre 1 y 3 semanas

Objective. To stablish some therapeutic criteria about the treatment of AVMs of III, IV and V grade of Spetzler and Martin and to analyse the results in the subgroup of preoperative embolization plus surgery. Methods. We perform a retrospective analysis of a group of 31 patients with arteriovenous malformations(AVMs) treated in our center between 1999 and 2004.There were 19 women and 12 men, with a mean age of 31,6 years old (range, 1-62a). Their symptoms upon admission were intracranial hemorrhage in 77,4%, seizures in 12,9%, headache, ischemic event and incidental finding in 3,2% each group. Diagnostic angiography was performed in 29 cases and anatomopathologic diagnosticin 2 cases. The malformations were classified with Spetzler and Martin Grading Scale, in 10,3% grade I,24,1% grade II, 37,9% grade III, 24,1% grade IV and3,4% grade V. Patients were classified in 6 subgroups of treatment (surgery, embolization, radiosurgery, embolizationplus surgery, embolization plus radiosurgery and conservative treatment).Results. AVMs grade III, IV and V (19 patients) were treated with surgery (6 cases), embolization plus surgery(5 cases), but also other kind of treatments (embolization alone, radiosurgery and conservative) were used. Functional results in these groups of patients were36,8% (7 cases) with no symptoms or slights symptoms(modified Rankin 0-1), 52,6% (10 cases) minor disability(mRankin 2), 5,3% (1 case) moderate disability and 5,3% (1 case) mortality. We observe a high rate of postembolization hemorrhage in the group of patients in which the combination of preoperative embolization plus surgery was used. In these cases, early surgery was performed with a good functional recovery. There was one case of postoperative mortality. Conclusion. We should considerer some factors likethe natural history, clinical presentation (hemorrhage),angiographic features (deep arterial supply, aneurisms), Spetzler and Martin Grading and the clinical condition of the patient before treating a cerebral AVM. In the subgroup of treatment with embolization plus surgery, we recommend to achieve a subtotal preoperative embolization > 50%, not to obliterate more than50% in one session, to perform staged embolization waiting from 4 to 6 weeks between procedures, and from 1 to 3 weeks between the last embolization and surgery

Determinants of neurosurgical outcome in pituitary tumors.

OBJECTIVE: Neurosurgery is one of the main therapies for pituitary tumors; optimising outcome is highly desirable for the patient and the health system. We have analysed predictors of outcome in surgically treated pituitary adenomas operated in this centre. DESIGN AND PATIENTS: A total of 289 patients underwent neurosurgery for a pituitary tumor, by the same two neurosurgeons, between 1982 and 2001. Their records were examined to find predictors of post-surgical outcome. Thirty-eight percent were males, with a median age of 40.8 (8-82.7) yr; 51.9% had been operated since 1992, 92.2% by the transsphenoidal route. Most tumors (70.2%) were macroadenomas; 28.4% were non-functioning, 27.3% secreted PRL, 26.3% GH of which 14 (4.8%) also secreted PRL, 17.3% ACTH, 0.3% FSH and 0.3% TSH. RESULTS: A stepwise, forward logistic regression analysis revealed tumor size as the only significant predictor of radiological cure [odds ratio (OR) for macroadenoma 0.16 vs microadenoma, p=0.0005]. Hormonally, PRL-secretion by the tumor was a predictor of poor prognosis (OR 3.29 for cure of non-PRL-secreting tumors, p=0.005), as was tumor size (OR 0.45 for cure of macroadenomas, p=0.005). Considering simultaneous radiological and hormonal remission, tumor size (OR 0.35 for macroadenoma, p=0.0002), and operation date (OR 0.40 for up to 1991, p=0.0002) were the only significant predictors. CONCLUSIONS: PRL secretion, tumor size and operation date are the main predictors of neurosurgical outcome in pituitary tumors, the latter suggesting that neurosurgical experience plays an important role.

Necessary criterion for distinguishing true superdiffusion from correlated random walk processes.

A difficulty in interpreting phenomena related to anomalous diffusion concerns how to identify scale invariant superdiffusive from Markovian correlated random walk processes. Here we propose a criterion that can distinguish between these two kinds of random walks and describe its usefulness in interpreting real data. To do so, we estimate the correlation time tau of the orientation persistence of a general correlated random walk. If the experimentally observed random walk appears diffusive on scales larger than tau, then the data cannot support the possibility of superdiffusion. We argue that the criterion is a necessary but not sufficient condition for establishing true superdiffusive behavior.

[Intraoperative neurophysiological monitoring of brain stem in a case of cavernoma in the pons]. / Monitorización neurofisiológica intraoperatoria del tronco del encéfalo en un caso de cavernoma en protuberancia.

Neurophysiological monitoring during surgery to avoid damaging of eloquent brain areas is a useful tool. We are performing intraoperative neurophysiological test to locate motor, sensitive and speech areas with cortical stimulation and cranial nerves during cerebellopontine cranial base surgery. Neurophysiological monitoring during brain stem surgery has been less described. Brain stem surgery implies a careful selection of patients for surgery given the high risk of morbidity and mortality. For this reason, conservative treatment is usually indicated when an asymptomatic cavernoma is incidentally found. Instead, when bleeding or neurological deficit appear, operative treatment may be indicated and then the goal of surgery is to avoid the disability linked to the natural history. We present the case of a 29 year old woman with diagnosis of multiple cavernomas. She was admitted at our hospital because she presented weakness and sensitive disturbance of left limbs and dizziness. The CT scan and MRI showed a pontine haemorrhage caused by a cavernous hemangioma. We operated her on using neurophysiological monitoring of VII, VIII, X and XII cranial nerves with electromyographic recordings. Postoperative disability could be reduced with a better knowledge of entry zone into the brain stem and early physiotherapy.

Monitorización neurofisiológica intraoperatoria del tronco del encéfalo en un caso de cavernoma en protuberancia / Intraoperative neurophysiological monitoring of brain stem in a case of cavernoma in the pons

La introducción del control neurofisiológico intraoperatorio ha conseguido minimizar el riesgo funcional quirúrgico en lesiones localizadas en áreas cerebrales funcionales. En la actualidad realizamos control neurofisiológico intraoperatorio para localizar el área motora o sensitiva y el área del lenguaje mediante estimulación cortical, así como de los pares craneales en cirugía del ángulo ponto cerebeloso. La monitorización neurofisiológica durante cirugía del tronco del encéfalo y fosa romboidea está menos instaurada. La cirugía del tronco del encéfalo implica una cuidadosa selección de los pacientes, dado el alto riesgo de morbilidad y mortalidad asociadas. Por esta razón, los cavernomas de esta región suelen ser tratados de manera conservadora cuando se trata de un hallazgo casual o no son sintomáticos. Sin embargo, la presencia de un sangrado o afectación neurológica inducen a tomar una decisión quirúrgica, dada la mala evolución natural. Presentamos el caso de una mujer de 29 años, diagnosticada de cavernomas múltiples, que ingresó por cuadro de debilidad motora y déficit sensitivo en hemicuerpo izquierdo. Se realizó TC craneal y RM que mostraba hemorragia protuberancial y se practicó una craniectomía infratentorial y resección de la lesión vascular por línea media, con control neurofisiológico intraoperatorio del VII, VIII, X y XII pares craneales con lectura electromiográfica. El control neurofisiológico ayudó a decidir el punto de acceso a la lesión que no afloraba a la superficie, minimizar las secuelas postoperatorias y pronosticar precozmente los déficits asociados con el fin de iniciar una rehabilitación precoz

Neurophysiological monitoring during surgery to avoid damaging of eloquent brain areas is a useful tool. We are performing intraoperative neurophysiological test to locate motor, sensitive and speech areas with cortical stimulation and cranial nerves during cerebellopontine cranial base surgery. Neurophysiological monitoring during brain stem surgery has been less described. Brain stem surgery implies a careful seleccion of patients for surgery given the high risk of morbidity and mortality. For this reason, conservative treatment is usually indicated when an asymptomatic cavernoma is incidentally found. Instead, when bleeding or neurological deficit appear, operative treatment may be indicated and then the goal of surgery is to avoid the disability linked to the natural history. We present the case of a 29 years old woman with diagnosis of multiple cavernomas. She was admitted at our hospital because she presented weakness and sensitive disturbance of left limbs and dizziness. The CT scan and MRI showed a pontine haemorrhage caused by a cavernous hemangioma. We operated her on using neurophysiological monitoring of VII, VIII, X and XII cranial nerves with electromyographic recordings. Postoperative disability could be reduced with a better knowledge of entry zone into the brain stem and early physiotherapy

Role of food partitioning in structuring the zooplankton community in mountain lakes.

Trophic-niche differentiation is often cited as a main factor in structuring zooplankton assemblages, although field evidence for this is rarely presented. The study was based on a survey of 29 Pyrenean lakes with altitudes ranging between 1,875 and 2,990 m carried out during July and August 2000. Because of the oligotrophic nature of these lakes, we aimed to confirm that food partitioning is a major factor in shaping zooplankton assemblages. We analysed the amino acid composition of six cladocera and seven copepod species. A discriminant analysis showed that each species could be distinguished according to its amino acid composition. A negative relationship between amino acid differentiation and co-occurrence among the cladocera and cyclopoid copepod was observed. In contrast, calanoids did not show any relationship and were characterised by a high amino acid differentiation between species. As the differences in the amino acid composition among zooplankton species indicate distinct food sources, the relationship found indicates that trophic-niche differentiation plays a key role in determining the assemblage of these zooplankton communities. Therefore exploitative competition, either at present or in the past by driving co-evolutionary histories, has been a significant factor in structuring the cladocera and cyclopoid communities in these oligotrophic lakes.

Optimizing the encounter rate in biological interactions: Lévy versus Brownian strategies.

An important application involving two-species reaction-diffusion systems relates to the problem of finding the best statistical strategy for optimizing the encounter rate between organisms. We investigate the general problem of how the encounter rate depends on whether organisms move in Lévy or Brownian random walks. By simulating a limiting generalized searcher-target model (e.g., predator-prey, mating partner, pollinator-flower), we find that Lévy walks confer a significant advantage for increasing encounter rates when the searcher is larger or moves rapidly relative to the target, and when the target density is low.