Análisis electroencefalográfico de la conectividad funcional en habituación por teoría de gráficas / Electroencephalographic analysis of the functional conectivity in habituation by graphics theory

Resumen Se ha propuesto, en la literatura de neurociencias, la hipótesis de que el cerebro funciona con base en redes glioneuronales, responsables de los procesos sensoriales, motores y cognitivos. La teoría de gráficas ofrece modelos matemáticos para describir estas redes complejas a partir de simples abstracciones: nodos y aristas. En este trabajo se plantea el uso de técnicas de procesamiento de señales para el análisis de la conectividad funcional entre ensambles neuronales a partir de medidas derivadas del EEG a través de la teoría de gráficas. Se describen los procedimientos para el análisis de la conectividad, desde el procesamiento y acondicionamiento de los registros, el cálculo de la densidad espectral en el EEG en banda ancha, la determinación de medidas de conectividad entre electrodos, y la estimación de parámetros de las redes complejas resultantes. Se analizó el EEG de 50 sujetos en intervalos de antes (Pre) y durante la fotoestimulación repetida (Rph). Con base en la significancia estadística de la respuesta durante Rph de desincronización/sincronización (D/S) en la banda alfa, y su extensión en las regiones corticales, los participantes se separaron en tres grupos: G1, G2 y G3. La pendiente de la regresión lineal D/S vs repetición en banda alfa, fue significativa en 16 de 16 regiones en G1, 12 de 16 en G2 y 5 de 16 en G3. La conectividad funcional siguió estos cambios mientras que en las bandas delta, theta y beta no se registraron modificaciones. D se relaciona con activación y la S con inhibición lo que apoya la hipótesis de la participación de alfa en el proceso cognitivo de habituación a la fotoestimulación.

Abstract The hypothesis that the brain works using glial-neuronal networks that are responsible for sensory, motor and cognitive processes has been proposed in the neuroscience literature. Graph theory offers mathematical models to describe these complex networks from simple abstractions such as nodes and connecting edges. In this work, usign signal processing techniques to the analysis of functional connectivity between neuronal emsembles derived from EEG measurements through theory graph. Procedures for the analysis of connectivity are described, from multichannel record processing and conditioning, computation of wideband power spectral density, determination of connectivity measures between electrodes, and parameter estimation of the resulting complex networks. EEG recordings from fifty subjects were analyzed in intervals before (pre) and during repeated photostimulation (Rph). Based on the statistical significance of the response during Rph, desynchronization/synchronization (D/S) in alfa band, and its wide distribution in corticals areas, the participants were divided into three groups: G1 , G2 and G3. The slope D/S in alfa band was significant in 16 of 16 regions (G1), 12 of 16 (G2) and 5 of 16 (G3). The functional connectivity depicted the same trend as these changes, whereas in the delta, theta and beta bands occurred no modifications. D is related to activation and S with inhibition, supporting the hypothesis of alfa-band's participation in the cognitive process of habituation to photostimulation.

[Efficiency of oxidant gas generator cells powered by electric or solar energy]. / Eficiencia de celdas generadoras de gases oxidantes alimentadas con energía eléctrica o solar.

Diseases caused by microbial contaminants in drinking water continue to be a serious problem in countries like Mexico. Chlorination, using chlorine gas or chlorine compounds, is one of the best ways to treat drinking water. However, difficulties in handling chlorine gas and the inefficiency of hypochlorite solution dosing systems--due to sociopolitical, economic, and cultural factors--have reduced the utility of these chlorination procedures, especially in far-flung and inaccessible rural communities. These problems led to the development of appropriate technologies for the disinfection of water by means of the on-site generation of mixed oxidant gases (chlorine and ozone). This system, called MOGGOD, operates through the electrolysis of a common salt solution. Simulated system evaluation using a hydraulic model allowed partial and total costs to be calculated. When powered by electrical energy from the community power grid, the system had an efficiency of 90%, and in 10 hours it was able to generate enough gases to disinfect about 200 m3 of water at a cost of approximately N$8 (US $1.30). When the electrolytic cell was run on energy supplied through a photoelectric cell, the investment costs were higher. A system fed by photovoltaic cells could be justified in isolated communities that lack electricity but have a gravity-fed water distribution system.

[Exercise test in young steers at 2800 M above sea level]. / Pruebas de esfuerzo en banda sin-fin en jóvenes a 2800 m SNM.

Among its different activities the Mexican Health Ministry (SSA) promotes: 1) the specification of biological standards for the Mexican population; 2) mechanisms for early detection of physiopathological changes and 3) development of the appropriate technology as a basis for primary health care. As part of this program we studied a random sample of students at the "Colegio de Bachilleres" of Cuajimalpa a suburban area of Mexico City, situated at 2800 m above sea level, part of the equipment used was produced at the Center for Development and Technological Applications (CE-DAT), an agency of SSA. Height, weight, heart rate (HR), systolic and diastolic blood pressures (SBP/DBP) were measured at rest in sitting position, standing up and walking on a treadmill. The results show a population with similar physical characteristics to those described for other populations in Mexico, with HR values within a homogeneous distribution, except for three subjects with rates larger than 2 standard deviations (SD). At standing up, women showed an orthostatic reflex of 27 beats/min and men of 22 beats/min. At the beginning of the exercise, the HR curve becomes more homogeneous, showing a discrete ascending slope with a low correlation coefficient, suggesting low physical capacity of the studied population. As exercise continued, some subjects showed a low increment of HR, giving values differing by 2 SD. Five women and three men had resting SBP values lying 2 SD out of the mean values of the sample. During exercise, SBP increases 28 mmHg as average. Notwithstanding the low cardiac response, the time spent on the treadmill lies within the levels considered as good and, even, excellent, on the table of the National Institute of Cardiology. We discuss new procedures to analyze instantaneously the HR and the pressoreceptor reflex as well as their functional significance.

[Evaluation of heart rate and blood pressure in residents of Milpa Alta, D.F]. / Evaluación de la frecuencia cardiaca y presión arterial en habitantes de Milpa Alta, D.F.

Both the altitude of Mexico City (D.F.) and the increase in atmospheric pollutants make it important to establish parameters of comparison for cardiovascular variables, such as heart rate (HR) and blood pressure (BP). The epidemiological transition occurring in Mexico is increasing the need for human and physical resources at the first level of health care in order to perform early diagnoses of cardiovascular disorders among the population. Heart rate, systolic and diastolic blood pressures (SBP, DBP) were recorded under diverse conditions (seated, standing, performing 30 sit-ups, and then standing and seated after the sit-ups) in 235 inhabitants of Milpa Alta (a suburb of Mexico City). The procedures and equipment used were designed and produced at the Center for Development and Technological Applications, Ministry of Health. The following results were found: HR decreases with age and body surface. Likewise, the HR increase due to exercise is lower with increasing age and larger body surface and its return to resting levels is slower. SBP and DBP magnitude is directly related to body surface. In women an increase of body weight was found to be significantly related to a higher SBP. The orthostatic reflex (OR) decreases with age and body surface. The descending slope is higher in women than in men. We propose that the study of OR could provide better information for predicting cardiovascular changes. The described procedures can be performed with the physical and human resources available at the Health Centers. The extension of this type of applied research to first level health care centers would allow the country to respond efficiently to the epidemiological transition.

Installation of a water disinfection system in a Mexico City hospital.

With a view to evaluating a small-scale water disinfection system based on production and application of oxidizing gases, the level of equivalent residual chlorine and the degree of contamination by fecal and total coliform bacteria was assessed at various points in the drinking water system of a Mexico City hospital before and after installation of the disinfection equipment. Tests done in May and June 1989, prior to installation of the equipment, showed that residual chlorine concentrations were lower than the national standard in most of the samples and that a sizable portion of these samples were also contaminated with fecal and total coliform concentrations exceeding national standards. After installation of the disinfection system at the main inflow to the hospital's drinking water supply in August 1989, the equivalent residual chlorine concentrations were found adequate and no coliform bacteria were detected. These results indicate that the oxidant mixture generated by the newly installed system was effectively disinfecting the water.

Medición de la frecuencia cardiaca y presión arterial en habitantes del Ajusco, Tlalpan, Distrito Federal, México, utilizando equipo CEDAT / Measurement of cardiac frecuency and blood lpressure in a district of Mexico City

Para mejorar los procedimientos de atención de la salud cardiovascular en México es indispensable que en los centros de salud puedan hacer mediciones precisas con aparatos adecuados y se cuente con valores estándar de la población. Se analizaron en 102 personas la frecuencia cardiaca (FC), presión arterial sistólica (PAS) y presión arterial diastólica (PAD) en situasión de reposo sentados, parados, haciendo 30 sentadillas y nuevamente en reposo, parados y sentados. Se encontró una relación directa entre la magnitud de FC y PA con la supérficie corporal y con la edad cronológica. El reflejo ortostático va disminuyendo en relación con el incremento de años de vida. El ejercicio físico incrementó la FC, PAS y PAD que vuelve a disminuir en los siguientes cuatro a ocho minutos consecutivos al ejercicio en las personas en las tres primeras décadas de vida, mientras que en las otras dos no regresa, dentro de este tiempo, a los valores previos. Este decremento de RO es más pronunciado en los hombres que en las mujeres, aunque las cifras de PA son mayores en mujeres en las dos últimas décadas estudiadas. La distribución de los datos parece seguir la curva de distribución normal y queda dentro de lo descrito para altitudes sobre el nivel del mar menores que la ciudad de México. Al implantar los sistemas de medición que se describen en este trabajo, se podrán detectar al inicio los procesos patológicos que afecten la actividad cardiaca y la presión arterial, en situasiones de alteración del ambiente

To improve theprocedures for cardiovascular health care in Mexico it is necessary to be able to perform accurate measurements of the cardiovascular parameters with appropriate equipment and to count with standard values for the Mexican population at the primary health level. Cardiac frequency (CF), systolic arterial pressure (DAP) and diastolic arterial pressure (DAP) were analyzed in 02 consenting volunteers under resting (seated) and standing conditions as well as during excercise (30 sitting), and again after excercise under resurge conditions. A direct relation was found between CF, SAP and DAP with body surface and age. The orthostatic reflex (OR) diminished with age. Excercise increased FC, PAS and PAD, which decreased four-eight minutes after completing the excercise in those subjetcs under 30 years of age, where as in those aged 30 to 50 years these parameters did not return to their previous values. The RO decrement is more pronounced in men, although arterial pressure values ar higher in women aged 30 to 50 years. Data followed normal distribution curve, agreeing with the data re ported for altitudes lower than that of Mexico City. Implementing the measurement systems described in thi paper will allow early detection of pathology that migh affect cardiac activity and arterial pressure that could b, related to environmental pollution at the first level o medical attention.

[Measurement of heart rate and blood pressure in the population of Ajusco, Tlalpan, Federal District, Mexico, using CEDAT equipment]. / Medición de la frecuencia cardiaca y presión arterial en habitantes del Ajusco, Tlalpan, Distrito Federal, México, utilizando equipo CEDAT.

To improve the procedures for cardiovascular health care in Mexico it is necessary to be able to perform accurate measurements of the cardiovascular parameters with appropriate equipment and to count with standard values for the Mexican population at the primary health level. Cardiac frequency (CF), systolic arterial pressure (SAP) and diastolic arterial pressure (DAP) were analyzed in O2 consenting volunteers under resting (seated) and standing conditions as well as during exercise (30 sitting), and again after exercise under resurge conditions. A direct relation was found between CF, SAP and DAP with body surface and age. The orthostatic reflex (OR) diminished with age. Exercise increased FC, PAS and PAD, which decreased four-eight minutes after completing the exercise in those subjects under 30 years of age, where as in those aged 30 to 50 years these parameters did not return to their previous values. The RO decrement is more pronounced in men, although arterial pressure values are higher in women aged 30 to 50 years. Data followed a normal distribution curve, agreeing with the data reported for altitudes lower than that of Mexico City. Implementing the measurement systems described in this paper will allow early detection of pathology that might affect cardiac activity and arterial pressure that could be related to environmental pollution at the first level of medical attention.

[The evaluation of the integral water treatment system of a general hospital in Mexico City]. / Evaluación del sistema integral para tratamiento del agua en un hospital general de la Ciudad de México.

The Mexican Health Office (SSA) promotes the use and progeny of the appropriate technology for the bacteriological quality evaluation and disinfect the water by means of the in situ progeny of the clorus and ozonus gases when needed, for the human consumption in suburban and rural communities. The clorus water disinfecting conventional methods by many reasons are useless, even in urbanized cities. CEDAT has built and design a group of apparatus, called: "Water treatment whole equipment for small communities", and it's build up by: Membrane Filter, Double Chamber Incubator, ultraviolet Light Sterilizer and a clorus and ozonus progenic gas electrolytic cell with CA and CD power box and a Venturi Tube. The electrolytic cell raw material is the sodium chlorine (salt) water mixed. The evaluation of these equipment was made at the Manuel Gea González Medical Doctor General Hospital. During 38 days there was a daily measure of chlorine sewage in six different parts of the hospital. It was used the cellulose membrane filter technic with a 0.45 mm porus and a sowing in M-Endo and M-FC Broth cultivation was in a 37 and 44 centigrade incubation. The first 10 days chlorine sewage was found, the last 28 weren't measurable. Total coliforms in 23 of 42, 7 days samples and excrement coliforms in 5 of 18, 3 days samples, were developed during the 38 days period. The electrolytic cell was settled for the water gas measure up in its way to the reservoir. Afterwards chlorine sewage was measured from 0.2 mg/l to 1 mg/l in all the sample parts. No germ kind was discovered during the 10 days sampling.(ABSTRACT TRUNCATED AT 250 WORDS)

[Quality of potable water and incidence of gastroenteritis in 2 cities in the state of Sonora, Mexico]. / Calidad del agua potable e incidencia de gastroenteritis en dos ciudades del estado de Sonora, México.

Based on the fact that drinking-water is of great significance in the transmission of infectious diseases, the incidence of diarrheal disorders was examined in two cities similar in their demographic composition and in their use of health services, but not in the quality of the drinking-water supply. In Navojoa, a city with high incidence of diarrheal diseases (116/1000 pop. in 1985), high rates of drinking-water contamination with fecal coliforms were found (43% of water samples); on the contrary, in Ciudad Obregón, a city with lower rates of diarrheal diseases (49/1000 pop. in 1985), drinking-water contamination with fecal coliforms was also comparatively lower (only 6% of water samples). These data illustrate the need to promote the implementation of drinking-water treatment in those places with signs of fecal contamination and high incidence of diarrheal diseases. To this regard, the General Direction for Research and Technological Development of the Ministry of Health has promoted the development of a chlorination equipment, useful mainly in rural areas, where biological contamination is usually high. These and similar procedures for water treatment should be considered as effective means to decrease the incidence of diarrheal diseases.

[Removal of arsenic from water for human consumption in homes in rural communities in the Comarca Lagunera, Mexico]. / Remoción del arsénico del agua para consumo humano en domicilios de comunidades rurales de la Comarca Lagunera, México.

This paper presents the results of an intradomiciliary procedure for arsenic removal from water, by means of flocculation with ferric sulphate. The reaction was carried out in a specifically designed tank with a manual agitator (reactor) installed in a vertical support. The salts to flocculate were handed in two small envelopes, whose contents were added independently, agitating the water and letting it settle for two to three hours. Water is decanted by opening a faucet connected to the inferior part of the recipient. Ten families of the states of Durango and Coahuila (the Comarca Lagunera) were selected. Samples of water were taken before and after the treatment. In 70 percent of these samples the arsenic removal was total, and in the remaining 30 percent the removal was superior to 93 percent. The arsenic removal of water in the domicile was very effective, for which it is suggested as a palliative method for those groups with higher levels of exposition.

Lever pressing and active avoidance conditioning after electrolytic lesions of the entopeduncular nucleus in cats.

Several authors have shown that CN participates in the acquisition of motor conditioned responses (MCR), probably as the integrating structure. Most of CN's efferent fibers in the cat end in the entopeduncular nucleus (EPN), therefore the command for the motor pattern could be exerted through EPN, representing part of the efferent link of the neuronal circuitry involved in MCR. Thirty-two cats were trained to avoid actively an electrical stimulus when a series of flashes appeared, and to press a lever to obtain 0.5 ml of milk. After the cats reached the learning criterion for both responses, electrolytic lesions of the entopeduncular nucleus or internal capsule (IC) were made bilaterally. When the cats recovered their normal motor behavior, the conditioned sessions were resumed once a day, for 45-50 days. Both learning responses disappeared (p less than 0.01) in those animals with the largest EPN lesions. In contrast, for small EPN lesions, learned responses were absent only during the first 3 or 4 sessions, and then the level of responses increased each day. However, it never reached that of sham lesioned cats. On the other hand, IC lesioned cats showed no statistical differences with respect to sham lesioned animals. These data support the participation of EPN in the motor circuitry responsible for MCR.

Caudate unit activity and somal diameters in intact and nigral lesioned cats.

In a search for morphofunctional relationships in the head of the caudate nucleus (CN), we recorded extracellular unit activity in intact cats and in cats that had received bilateral injections of 6-OHDA into the substantia nigra (SN) 30 days previously. Only units firing spontaneously and continuously for 2 min were studied. In dorsal regions, potentials were small and iterative at almost constant intervals; the somal diameters were relatively small. In the ventrolateral region, potentials were bigger and appeared in bursts; somal diameters were significantly larger (p less than 0.05). For the centromedial region a histogram of numbers of neurons as a function of diameters revealed a Gaussian distribution extending from small to large neurons. Most dorsal neurons increased their firing rate to radial nerve, visual, SN, and/or nucleus centralis medialis (NCM) stimulation. Ventral neurons usually responded with excitation followed by long lasting inhibition, particularly to SN and NCM stimulation. A few neurons responded to all four inputs and some showed long-lasting potentiation in response to low frequency stimulation, suggesting a more general function. Greatest convergence (65%) was found for NCM and SN inputs. In lesioned cats, there was no SN driving, NCM's inhibitory actions almost disappeared, and the excitatory action of the other stimuli was reduced.

Electrophysiological correlates among the radial nerve, the caudate and the entopeduncular nuclei in cats.

The entopeduncular nucleus (EPN), as the medial part of the globus pallidum, has been considered the efferent structure of the striatum. Based on this, we decided to study its possible somatosensory projections and the electrophysiological relationship with the caudate nucleus (CN). Radial nerve stimulation produced evoked responses (ER) in CN and EPN. The ERs recorded in EPN are of shorter latencies (11 msec) than those in CN (23 msec). Electrical stimulation of CN elicited ERs in EPN. These ERs are bigger when the stimulation sites coincide with the regions of CN where somatic stimulation also elicited ERs. The same regions of CN yielding ERs by somatic stimulation respond to EPN stimulation. The ERs recorded in EPN by radial nerve stimulation diminished when the CN was stimulated 7 msec after the radial nerve, while other intervals were less effective. The results show that the radial nerve probably has direct ipsi and contralateral projections to the EPN and a bidirectional connection between EPN and CN. We suggest a feedback response of EPN to CN stimulation, an arrangement which would be the functional basis for the central motor regulation.

Effects of general anesthesia, neodecortication and spreading depression upon somatic evoked responses in caudate and entopeduncular nuclei, and their electrophysiological correlates in cats.

The electrophysiological relationship among an afferent somatic input (radial nerve), the caudate and the entopeduncular nuclei was studied in intact animals under chloralose anesthesia and in decorticated ones. The results confirm the hypothesis that the cerebral cortex is not essential to record somatic evoked responses in both nuclei, nor for the reciprocal responses in these nuclei when one of them is stimulated, suggesting the existence of direct somatic projections to these nuclei from the subcortical structures. On the other hand, the spreading depression by microinjection of KCl 3M into the CN does not modify the ERs in EPN, but the spreading depression in EPN does modify the CN response. Thus, the somatic projection to EPN seems to course directly from the thalamus or the reticular formation but not through the CN. The results suggest a reciprocal influence of the outflow structure (EPN) upon the higher level (CN), in which the inferior structure is modifying the excitability of the higher one.

Modification of motor activity, passive avoidance conditioning and evoked potentials by microinjections of strychnine in both caudate nuclei in cats.

Passive avoidance conditioning (PAC) seems to depend on inhibitory actions within the caudate nucleus (CN). Thus topical application of strychnine could block these influences. In cats, with permanently implanted cannulae in the head of the CN, bilateral microinjections of 100 micrograms of strychnine produced a stereotyped behavior of grooming and running with the extremities flexed to dark places. When placed into a two compartment chamber for a PAC acquisition they would not move from the dark compartment to the illuminated one. After decreasing the illumination some cats crossed and the acquisition test was performed. Twenty four hours later they showed the learned response. A second retention test was not modified by another strychnine application. These results contrast with those obtained by picrotoxin microinjections which disrupt the retention of a PAC. However, strychnine affects the evoked potentials (EP) recorded in CN by n. centralis medialis (NCM) stimulation by decreasing a positive peak, which probably represents post-synaptic inhibition and increasing the late positive component. In the lateral geniculate body strychnine affected a late positive wave and in the occipital cortex it increased the initial negative peaks and decreased the late positive ones of the potentials evoked by flash stimulation. These findings suggest a more suitable role of the CN in the regulation of visual information, which is probably related with the attention processes.