What Reasons Lead Spanish Medical Students Not to Be in Favor of Organ Donation?

INTRODUCTION

Despite sensitization of medical students toward the donation of organs, a non-negligible percentage of students are not in favor of donation.

OBJECTIVE

To analyze the reasons of Spanish medical students who do not have a favorable attitude toward the donation of their own organs after death.

METHOD

The population under study is medical students in Spanish universities, using the database of the International Donor Collaborative Project, stratified by geographic area and academic year. The questionnaire completion was anonymous and self-administered. The study group is medical students with an unfavorable attitude toward organ donation. The assessment instrument used is a validated questionnaire of attitude toward the donation of organs for transplant, "PCID-DTO-Ríos." The reasons against the donation are valued in the questionnaire through a question.

RESULTS

Of the participants included in the PCID, students who are not in favor of organ donation were selected (n = 1899). Of them, 8.1% (n = 154) are against and 91.1% (n = 1745) are doubtful. The main reasons indicated are the fear of apparent death in 11.4% of respondents, fear of possible mutilation after donation in 11.1%, and religious reasons in 2.6%. Of those, 6.9% indicate other reasons but do not clearly specify the reasons, using words such as "fear" (2.5%) or "doubts about the process" (4.1%); 66.2% (n = 1257) indicated an "assertive refusal" ("I don't want to express my reasons").

CONCLUSION

Twenty percent of Spanish medical students are not in favor of donating their organs and are not in favor of showing their reasons.

Are Medical Students of Non-Spanish Nationality Studying in Spain as Sensitized to Transplantation as Those of Spanish Nationality?

INTRODUCTION

Awareness of organ donation among Spanish doctors and medical students is very positive. However, the emerging group of professionals of non-Spanish nationality studying in Spain has not been analyzed.

OBJECTIVE

To analyze the differences in the attitudes toward the different types of donation among medical students, according to their nationality.

METHODS

The population under study is medical students in Spanish universities using the database of the International Collaborative Donor Project, stratified by geographic area and academic year. Groups under study include students of non-Spanish nationality as group 1 (n = 1570) and students of Spanish nationality as Group 2 (n = 7705). Instruments are validated questionnaires of attitude toward donation "PCID-DTO-Ríos," "PCID-DVR-Ríos," "PCID-DVH-Ríos," and "PCID-XenoTx-Ríos."

RESULTS

The attitude toward the donation of own organs after death is similar in both groups (P = .703). Non-Spaniards are 79.2% in favor compared to 79.6% of Spaniards. Living kidney donation, both unrelated (33.3% vs 29.3% in favor; P = .001) and related (91.2% vs 89, 6% in favor; P = .047), is more favorable among non-Spanish students. There are no differences regarding non-related living liver donation (29.7% vs 29.3% in favor; P = .063), but there are differences in the results for related living liver donation (94.1% vs 88%; P < .001). The attitude toward xenotransplantation of organs is similar (80.8% vs 80.8%; P = .999).

CONCLUSIONS

Awareness of the donation of organs among Spanish medical students is similar to non-Spanish students studying in Spain, except the attitude toward living donation.

Information About Donation and Organ Transplantation Among Spanish Medical Students

INTRODUCTION

Health professionals are asked to promote health, especially organ transplantation; however, they do not always have specific training.

OBJECTIVE

To analyze information about donation and organ transplantation among Spanish medical students.

METHOD

The population under study is medical students in Spanish universities using the database of the International Donor Collaborative Project, stratified by geographic area and academic year (n = 9275). The instrument used is the attitude questionnaire for organ donation for "PCID-DTO-Ríos" transplantation, validated with an explained variance of 63.203% and α = 0.834. The Student t test was applied together with the χ² test, complemented by an analysis of the remainders, and Fisher's exact test was applied.

RESULTS

Of the students, 74% indicate that they have received information from university professors about organ transplant. Concerning specific issues with the donation, it is notable that only 66.7% (n = 6190) know and accept the concept of brain death as the death of a person. However, only 22% consider themselves as having good information, and 35.3% indicate that their information is scarce or void. Students indicate having received information about transplant from other extra-university sources, such as television and Internet (80.9%), books and magazines (73.2%), and the press (66.9%). From the information obtained in the sociofamilial field, 60.7% have obtained information from the family and 58.1% from friends. Of this information, 9% has been negative from friends, 7.5% from family, 6% from the Internet and television, and 4% from university professors.

CONCLUSION

Spanish medical students believe they have little information about organ transplantation and have received negative information.

A Multicentre and stratified study of the attitude of medical students towards organ donation in Spain

INTRODUCTION

Medical students represent a new generation of medical thought, and if they have a favourable attitude towards organ donation this will greatly encourage its promotion.

OBJECTIVE

To analyse the attitude of medical students in Spanish universities towards the donation of their own organs and to determine the factors affecting this attitude.

MATERIAL AND METHODS

Type of study: A sociological, interdisciplinary, multicentre, and observational study in Spain.

STUDY POPULATION

Students studying a degree in medicine enrolled in Spain (n = 34,000).

SAMPLE SIZE

A sample of 9598 students (confidence of 99% and precision of ±1%), stratified by geographical area and academic year. Instrument of measurement: A validated questionnaire of attitude towards organ donation and transplantation (PCID-DTO RIOS) was self-administered and completed anonymously.

RESULTS

The questionnaire completion rate was 95.7% (n = 9.275). 80% were in favour of donation, 2% against and 18% were undecided. The following main variables were related to a favourable attitude: being of the female sex (Odds Ratio = 1.739); being in the sixth year of the degree (OR = 2.506); knowing a donor (OR = 1.346); having spoken about the subject with one's family (OR = 2.132) and friends (OR = 1.333); having a family circle that is in favour, more specifically, having a father (OR = 1.841), mother (OR = 2.538) or partner in favour (OR = 2.192); being a blood donor (OR = 2.824); acceptance of the mutilation of the body if it were necessary (OR = 2.958); and being an atheist or an agnostic (OR = 1.766).

CONCLUSIONS

Spanish medical students generally have a favourable attitude towards organ donation, although 20% are not in favour.

Sensitization Toward Organ Donation Among Medical Students in Spanish Regions With More Than 50 Donors Per Million Population

The awareness of organ donation among health professionals is important at the time of transplant promotion. In this sense, the training and awareness of the professionals in training is fundamental.

OBJECTIVE

To analyze the differences in the attitude toward organ donation and the factors that condition it among medical students of regions with donation rates >50 donors per million population (pmp) with respect to those with rates <40 donor pmp.

METHOD

Population under study: medical students in Spanish universities. Database of the Collaborative International Donor Project, stratified by geographic area and academic course. The completion was anonymous and self-administered. Groups under study: Group 1 (n = 1136): students in universities of regions with >50 donors pmp. Group 2 (n = 2018): university students in regions with <40 donors pmp. Assessment instrument: attitude questionnaire for organ donation for transplant PCID-DTO-Ríos.

RESULTS

The attitude toward organ donation for transplantation is similar among students from the autonomous communities with >50 donors pmp and with <40 donors pmp. In group 1, 79% (n = 897) of students are in favor compared with 81% (n = 1625) of group 2 (P=.29). The psychosocial profile toward donation is similar in both groups relating to the following variables (P < .05): sex, having discussed transplantation with family and as a couple, considering the possibility of needing a transplant, involvement in prosocial activities, attitude toward the manipulation of corpses, knowledge of the brain death concept, and religion.

CONCLUSIONS

The awareness of organ donation in Spanish medical students is quite homogeneous and is not related to the local donation rates of each region.

Do Spanish Medical Students Understand the Concept of Brain Death?

Objective:

To analyze the level of understanding of the brain death concept among medical students in universities in Spain.

Methods:

This cross-sectional sociological, interdisciplinary, and multicenter study was performed on 9598 medical students in Spain. The sample was stratified by geographical area and academic year. A previously validated self-reported measure of brain death knowledge (questionnaire Proyecto Colaborativo Internacional Donante sobre la Donación y Transplante de Organos) was completed anonymously by students.

Results:

Respondents completed 9275 surveys for a completion rate of 95.7%. Of those, 67% (n = 6190) of the respondents understood the brain death concept. Of the rest, 28% (n = 2652) did not know what it meant, and the remaining 5% (n = 433) believed that it did not mean that the patient was dead. The variables related to a correct understanding of the concept were: (1) being older ( P < .001), (2) studying at a public university ( P < .001), (3) year of medical school ( P < .001), (4) studying at one of the universities in the south of Spain ( P = .003), (5) having discussed donation and transplantation with the family ( P < .001), (6) having spoken to friends about the matter ( P < .001), (7) a partner’s favorable attitude toward donation and transplantation ( P < .001), and (8) religious beliefs ( P < .001).

Conclusions:

Sixty-seven percent of medical students know the concept of brain death, and knowledge improved as they advanced in their degree.

Serology and longevity of immunity against Echinococcus granulosus in sheep and llama induced by an oil-based EG95 vaccine

An oil-based formulation of the EG95 vaccine to protect grazing animals against infection with Echinococcus granulosus was formulated in Argentina. The efficacy of the vaccine was monitored by serology in sheep and llama (Lama glama) and was compared to the serology in sheep previously published using a QuilA-adjuvanted vaccine. Long-term efficacy was also tested in sheep by challenging with E. granulosus eggs of the G1 strain 4 years after the beginning of the trial. The serological results for both sheep and llama were similar to those described previously, except that there was a more rapid response after the first vaccination. A third vaccination given after 1 year resulted in a transient boost in serology that lasted for about 12 months, which was similar to results previously described. Sheep challenged after 4 years with three vaccinations presented 84·2% reduction of live cysts counts compared with control group, and after a fourth vaccination prior to challenge, this reduction was 94·7%. The oil-based vaccine appeared to be bio-equivalent to the QuilA vaccine.

[Brain death: is it an appropriate term?]

INTRODUCTION

Brain death is generally accepted as a concept to indicate death. It was introduced about 40 years ago, and it was considered the ideal situation for donation of organs.

METHODS

During this time, however, there have been problems in the understanding of this concept both in the medical profession and in the general population. University students from medical and non-medical schools were tested for their understanding of this concept.

RESULTS

Our results show that less than one third of the non-medical students identified brain death as death. The data from the medical students changed as they progressed through their studies, but only 2/3 of the graduating medical class believed that brain death is death.

CONCLUSION

Similar results have been seen in other universities around the world, and a renewed effort on the re-education of the concept of brain death may be worthwhile. Although we cannot extrapolate these results to the general population, the confusion is probably similar; hence an effort should be made to solve this problem.

[Brain oscillations: pathophysiological and potentially therapeutic role in some neurological and psychiatric diseases]

The terms "oscillations" or "oscillatory activity" are frequently used not only to define the rhythmic fluctuations of the postsynaptic potentials of a neuronal group (local field potentials) or a cortical region (EEG, MEG), but also to indicate the rhythmic discharge pattern of action potentials from a neuron or a small group of neurons. Oscillatory activity makes possible the synchronization of different neuronal groups from nearby or distant cortical regions that participate in the same motor, sensory or cognitive task. The presence of oscillatory activity is usually associated to the existence of synchronization, but both phenomena are not necessarily always equivalent. Abnormalities of oscillatory activities or synchronization within or between different brain structures have been described in several neurological and psychiatric diseases; these abnormalities might play a relevant pathophysiological role in Parkinson's disease (and other movement disorders), schizophrenia or epilepsy. This review discusses all these aspects, with emphasis on their potential role both as a basic mechanism in brain function and as a pathophysiological substrate for some of the symptoms and signs observed in several diseases.

Abnormalities in brain synchronization are correlated with cognitive impairment in multiple sclerosis

BACKGROUND

Cognitive functions are supported by brain networks and they are highly dependent on the integrity of long white matter tracts that mediate the information flow between such distant cortical areas. Brain damage in multiple sclerosis (MS) may produce cognitive impairment by preferentially damaging these tracts, thereby impairing brain synchrony. Auditory amplitude modulation following responses (AMFR), are oscillatory steady-state responses to rhythmic auditory stimuli that indirectly measure brain synchrony.

OBJECTIVE

To study the effect of MS lesions in brain synchrony and its relationship with cognitive function.

METHODS

We assessed the correlation between cognitive performance, as assessed with the brief repeatable battery-neuropsychology (BRB-N), and the AMFR in a group of 27 MS patients and 22 healthy controls.

RESULTS

The maximal AMFR frequency - but not the amplitude - in the 30-60 Hz range was lower in patients with cognitive impairment than in patients with no cognitive impairment or the healthy controls (39.79 Hz, 43.85 Hz, and 43.84 Hz, respectively, P < 0.05). Indeed, the frequency of the AMFR was negatively correlated with the scores obtained in verbal memory, attention, and executive function. The multiple regression analysis indicates that the AMFR was the best predictor of the BRB-N scores after controlling for potential confounding factors such as age, education, disability, and years of disease evolution.

CONCLUSIONS

These results suggest that the loss of synchronization in different central nervous system (CNS) pathways caused by demyelinating lesions might involve both the slowing of brain oscillatory activity and less efficient cognitive processing.

[Video-electroencephalography: a necessity]

The video-EEG is a common diagnostic tool nowadays. The technical achievements of the last decade have brought a simplification of the equipment required to obtain good quality recordings, with little more than a computer and a video camera being necessary. However, the medical and technical staff must be well trained to execute and interpret the study. It is very useful in the diagnosis of paroxysmal events, for the classification and characterization of epileptic seizures and to quantify epileptiform discharges. Due to the importance of a correct diagnosis to avoid mistreating many neurological patients, this tool should be accessible to clinicians. In spite of the advances of recent years, 20-30% of patients diagnosed with epilepsy are not really epileptic, a fact that it is excessive and unacceptable.

Oscillatory changes related to the forced termination of a movement

OBJECTIVE

Stimulus-induced movements are accompanied by a definite pattern of oscillatory changes, that include a frontal 15 Hz synchronization, a central peri-movement desynchronization, and a contralateral beta rebound after the movement. Our aim was to study the oscillatory changes related to the forced termination of a single complex motor program (signature) and compare them with those observed after the normal termination of the movement.

METHODS

Fifty-eight reference-free EEG channels were analyzed in 10 healthy subjects. A 2000 Hz tone (S1, go signal) indicated the subject to begin to write his/her complete signature. A second 2000 Hz tone 0.8 s afterwards (50% probability: S2, stop signal) indicated the subject to stop immediately. Movement-related energy changes were evaluated by means of time-frequency (Gabor) transforms.

RESULTS

A frontal 15 Hz synchronization was observed after S1, but not after S2. The amplitude of the post-movement beta increase was significantly lower when the movement was abnormally terminated (p=0.005), while the peri-movement decrease was similar.

CONCLUSIONS

The forced termination of a motor program reduces significantly the amplitude of the post-movement beta increment, conserving its temporal pattern. Also, the presence of the 15 Hz frontal synchronization only after S1, together with the results of previous studies, suggests that the frontal mechanisms involved in go/no go and stop signals are very different.

SIGNIFICANCE

Our results indicate that the beta rebound is an active process, independent of the peri-movement beta decrease, which is influenced by how the movement is terminated.

[Polysomnography in the neurology patient]

The polysomnography is a standardized diagnostic tool in neurology. It is used to study sleep structure and can diagnose many sleep disorders. Since this test is not always adequately available as it is a complex test that requires a qualified team and staff, its most necessary and urgent indications should be stressed in order to thus avoid the waiting lists. In this paper we review the primary indications of the nocturnal sleep studies in the different groups of neurological disorders. We review the bibliography, selecting the papers that help to specify when the polysomnographic study would be indicated and those situations in which it may be indispensable or urgent.

Chirp-evoked potentials in the awake and anesthetized rat. A procedure to assess changes in cortical oscillatory activity

Steady-state potentials are oscillatory responses generated by rhythmic stimulation of a sensory pathway. The frequency of the response, which follows the frequency of stimulation and potentially indicates the preferential working frequency of the auditory neural network, is maximal at a stimulus rate of 40 Hz for auditory stimuli in humans, but may be different in other species. Our aim was to explore the responses to different frequencies in the rat. The stimulus was a tone modulated in amplitude by a sinusoid with linearly-increasing frequency from 1 to 250 Hz ("chirp"). Time-frequency transforms were used for response analysis in 12 animals, awake and under ketamine/xylazine anesthesia. We studied whether the responses were due to increases in amplitude or to phase-locking phenomena, using single-sweep time-frequency transforms and inter-trial phase analysis. A progressive decrease in the amplitude of the response was observed from the maximal values (around 15 Hz) up to the limit of the test (250 Hz). The high-frequency component was mainly due to phase-locking phenomena with a smaller amplitude contribution. Under anesthesia, the amplitude and phase-locking of lower frequencies (under 100 Hz) decreased, while the phase-locking over 200 Hz increased. In conclusion, amplitude-modulation following responses differ between humans and rats in response range and frequency of maximal amplitude. Anesthesia with ketamine/xylazine modifies differentially the amplitude and the phase-locking of the responses. These findings should be taken into account when assessing the changes in cortical oscillatory activity related to different drugs, in healthy rodents and in animal models of neurodegenerative diseases.

Late Pleistocene and Holocene environmental history of the Iguala Valley, Central Balsas Watershed of Mexico

The origin of agriculture was a signal development in human affairs and as such has occupied the attention of scholars from the natural and social sciences for well over a century. Historical studies of climate and vegetation are closely associated with crop plant evolution because they can reveal the ecological contexts of plant domestication together with the antiquity and effects of agricultural practices on the environment. In this article, we present paleoecological evidence from three lakes and a swamp located in the Central Balsas watershed of tropical southwestern Mexico that date from 14,000 B.P. to the modern era. [Dates expressed in B.P. years are radiocarbon ages. Calibrated (calendar) ages, expressed as cal B.P., are provided for dates in the text.] Previous molecular studies suggest that maize (Zea mays L.) and other important crops such as squashes (Cucurbita spp.) were domesticated in the region. Our combined pollen, phytolith, charcoal, and sedimentary studies indicate that during the late glacial period (14,000-10,000 B.P.), lake beds were dry, the climate was cooler and drier, and open vegetational communities were more widespread than after the Pleistocene ended. Zea was a continuous part of the vegetation since at least the terminal Pleistocene. During the Holocene, lakes became important foci of human activity, and cultural interference with a species-diverse tropical forest is indicated. Maize and squash were grown at lake edges starting between 10,000 and 5,000 B.P., most likely sometime during the first half of that period. Significant episodes of climatic drying evidenced between 1,800 B.P. and 900 B.P. appear to be coeval with those documented in the Classic Maya region and elsewhere, showing widespread instability in the late Holocene climate.

Hyperleptinaemia, respiratory drive and hypercapnic response in obese patients

Leptin is a powerful stimulant of ventilation in rodents. In humans, resistance to leptin has been consistently associated with obesity. Raised leptin levels have been reported in subjects with sleep apnoea or obesity-hypoventilation syndrome. The aim of the present study was to assess, by multivariate analysis, the possible association between respiratory centre impairment and levels of serum leptin. In total, 364 obese subjects (body mass index >or=30 kg.m(-2)) underwent the following tests: sleep studies, respiratory function tests, baseline and hypercapnic response (mouth occlusion pressure (P(0.1)), minute ventilation), fasting leptin levels, body composition and anthropometric measures. Subjects with airways obstruction on spirometry were excluded. Out of the 346 subjects undergoing testing, 245 were included in the current analysis. Lung volumes, age, log leptin levels, end-tidal carbon dioxide tension, percentage body fat and minimal nocturnal saturation were predictors for baseline P(0.1). The hypercapnic response test was performed by 186 subjects; log leptin levels were predictors for hypercapnic response in males, but not in females. Hyperleptinaemia is associated with a reduction in respiratory drive and hypercapnic response, irrespective of the amount of body fat. These data suggest the extension of leptin resistance to the respiratory centre.

[Classification of sleep disorders]

Sleep disorders are frequent processes, both as a symptom associated with other diseases and as independent disorders. However, only in the last 4 decades has Sleep medicine gained its position among the medical specialties. In fact, it was only in these years that significant advances were obtained in the study of the etiology and treatment of these disorders. Similarly, the different classifications have been evolving over the years. First, they were based upon the clinical symptom; later on, more emphasis was given to the diseases. Finally, in 2005, the new classification was once again based on the symptoms. More than 90 disorders are listed in this latest classification, and an attempt is made to include the symptoms and the diseases of sleep, as well as those in which sleep disorders are fundamental. It is essential to have a clear idea of this complete classification of sleep disorders in order to deal with these patients appropriately.

High frequency oscillations in the somatosensory evoked potentials (SSEP's) are mainly due to phase-resetting phenomena

A small series of high frequency oscillations (HFOs) overlapping the earliest part of the N20 wave can be observed in the somatosensory evoked potentials (SSEPs) of normal subjects. We tried to elucidate whether these high frequency components are mainly due to phase-resetting phenomena, to the emergence of new oscillations related to the stimuli, or to a combination of both. Averaged median-nerve SSEPs from seven healthy subjects were studied by means of time-frequency analysis. The presence of new oscillatory activities was evaluated by averaging the energy of the single-trial time-frequency transforms in the HFOs range (400-1000 Hz). To study phase-resetting phenomena, we measured inter-trial coherence (ITC) in the same frequency range. A marked inter-trial coherence related to the HFOs was found, whereas energy changes (related to the emergence of new oscillations) were minimal. The combination of these three different approaches suggests that the HFOs are mainly due to resettings of the ongoing EEG activity originated in response to the stimuli. The emergence of new activities does not seem to be a relevant mechanism in the formation of these components.

Study of microvessel density and the expression of the angiogenic factors VEGF, bFGF and the receptors Flt-1 and FLK-1 in benign, premalignant and malignant prostate tissues

PURPOSE

Vascular endothelial growth factor (VEGF) is an angiogenic factor that stimulates endothelial cell growth and enhances vascular permeability. VEGF exerts its action by binding to the specific cell surface receptors, fms-like tyrosine kinase 1 (Flt-1) and fetal liver kinase 1 (FLK/KDR). In tumor angiogenesis, Vascular endothelial growth factor stimulates endothelial cells to produce Basic fibroblastic growth factor (bFGF), which further enhances angiogenic activity. Very little information on the expression of VEGF, bFGF, and the receptors Flt-1 and FLK/KDR is available. Herein, we evaluate the expression of these angiogenic factors and receptors in normal prostate, high grade prostate intraepithelial neoplasia (HGPIN) and prostatic cancer (CaP).

MATERIALS AND METHODS

58 selected surgical specimens exhibiting areas of normal prostate, HGPIN, and CaP were evaluated for microvessel density, and for VEGF, bFGF, Flt-1 and FLK/KDR protein expression by immunohistochemistry. Results were correlated with pathological data.

RESULTS

There was a statistically significant increase in the microvessel density and in the expression of the angiogenic factors VEGF, bFGF and the receptors FLK/KDR and Flt-1, in the premalignant and malignant tissues in comparison with normal prostatic glands. Microvessel density also correlated with higher Gleason grade, pathological stage and the expression of the receptors FLK/KDR and Flt-1.

CONCLUSIONS

The "initiation switch" of angiogenesis was observed to be an early event consistent with the recruitment of new vasculature into high grade PIN lesions and it increased in the progression of prostatic cancer.

Imitating versus non-imitating movements: Differences in frontal electroencephalographic oscillatory activity

Non phase-locked oscillatory changes were studied in seven healthy volunteers during two different reaction time movement paradigms, in which the stimulus was a wrist movement (either extension or flexion) performed by another person seated in front of the subject (examiner). In the first paradigm (imitation), the subject was instructed to perform the same movement observed. In the second paradigm (non-imitation), the subject was instructed to perform the opposite movement (flexion when an extension was observed, and vice-versa). Changes in the 7-37 Hz range band were determined by means of Gabor transforms. A frontal energy increase (event-related synchronization, ERS) around 15 Hz could be observed in the frontal region after the examiner's movement; this frontal ERS was significantly larger in the non-imitation paradigm. A typical alpha and beta movement-related event-related desynchronization/synchronization (ERD/ERS) pattern was also observed in both paradigms in the central region. The beta-ERD was significantly larger in the imitation paradigm. Our results show that the motor preparation mechanisms involved in an imitated and a non-imitated movement are different.

Alpha and beta changes in cortical oscillatory activity in a go/no go randomly-delayed-response choice reaction time paradigm

OBJECTIVE

Predictable movements induce oscillatory changes over the contralateral motor cortex that begin before the movement, but their significance has not been fully established. We studied non-phase-locked changes in cortical oscillatory activity in a S1-centred double-stimulus go/no go paradigm with random interstimulus interval.

METHODS

About 58 reference-free EEG channels were analyzed by means of Gabor transforms in a group of 10 healthy subjects. A 2000 Hz tone (S1go, 84% probability) indicated the subject to make a brisk wrist extension after a second 2000 Hz tone (S2go). The S1-S2 interval was either 1.5, 3 or 4.5 s. A 1000 Hz tone (S1 no go, 16% probability) indicated the subject not to move (and wait for another S1 tone).

RESULTS

A frontal 15 Hz synchronization was observed after S1 in all conditions. No further significant changes were observed in the no go condition. A small pre-S2 alpha and beta desynchronization could be observed only in the 3 and 4.5s-interval go conditions, being larger in the latter.

CONCLUSIONS

These results suggest that the predictability of the timing of a movement influences the appearance of the pre-movement oscillatory changes; not only motor planning (the 'go' decision) is necessary, but also an estimation of when to move.

SIGNIFICANCE

Our findings provide new insight on the relationship between the decision-making process, movement, and cortical oscillatory activity.

[Mathematical analyses in the study of electroencephalographic signals]

AIM

The principal mathematical techniques applied to the EEG are reviewed.

DEVELOPMENT

After the introduction of digital EEG, new mathematical tools have been developed for the EEG analysis. Nowadays there are several techniques that analyse the EEG signal in different ways, getting a better understanding of the EEG: development of new montages; artifact removal; analysis in time domain, phase coherence and synchrony; source analysis; epileptic seizures detection and prediction; superposition of electrical activity and other neuroimaging techniques. Although they have demonstrated their efficacy, the comparison between them is not always easy.

CONCLUSIONS

The development of mathematical tools for EEG analysis has improved the knowledge of the electric cerebral activity in normal and pathological conditions. They study many different aspects of the EEG signal. Their continuous development will produce an increase the knowledge of the normal and pathological cerebral functions.

[Independent Components Analysis (ICA) in the study of electroencephalographic signals]

Independent Component Analysis (ICA) is a mathematical tool able to separate complex signals in statistically independent components. It solves the blind source separation problem (BSS). The EEG satisfies most of the assumptions of ICA, so it may be an adequate signal for ICA for its use. In this paper we review the method and the applications of ICA in EEG. The studied applications are: a) artifacts removal; b) source estimation of spikes; c) analysis of seizures. Several studies have demonstrated that ICA is useful to remove artifacts from contaminated EEG records without distorting cerebral activity. It is able to decompose epileptic discharges and seizures in independent spatio-temporal components. In combination with techniques of source localisation, as dipole modelling, ICA improves the localization of the epileptic focus. Finally, we discuss the future role of ICA in the study of epileptic patients.

[Ictal asystolia in the differential diagnosis of dizziness]

Frequently, epileptic seizures are accompanied by changes in the heart rate. They are usually transient and irrelevant for the patient's symptoms and the patient recorders his usually baseline rhythm in second or a few minutes. In this report we present a case of a patient diagnosed previously of epilepsy who presented episodes of dizziness and presyncope. During the video-EEG study we recorded one of these spells. The diagnosis of this spell was a focal seizure associated with asystole: the seizure was almost asymptomatic, and only when the asystole developed (40 seconds after the EEG ictal changes) the patient complained about dizziness. Recovery was fast, but treatment with pacemaker must be considered.

Frontal and central oscillatory changes related to different aspects of the motor process: a study in go/no-go paradigms

We studied alpha and beta EEG oscillatory changes in healthy volunteers during two different auditory go/no-go paradigms, in order to investigate their relationship with different components of the motor process. In the first paradigm (S2-centered), the initial tone (S1) was constant (warning), and the second tone (S2) indicated the subject whether to move or not. In the second paradigm (S1-centered), S1 indicated whether to move or not, while S2 just indicated the timing of the movement. A medial frontal beta energy increase was found in all conditions after the stimulus that forces the subject to decide whether to move or not (S1 or S2 depending on the paradigm). In both go conditions, a central alpha and beta energy decrease began after the go decision, reaching minimum values during the movement; it was followed by a beta post-movement increase, limited to the central contralateral area. In the no-go conditions, a marked fronto-central beta synchronization appeared after the decision not to move. In conclusion, our study was able to dissociate the beta oscillatory changes related to movement preparation and execution (central decrease/increase) from those associated with decision-making (medial frontal increase) and motor inhibition (fronto-central increase).

[The obstructive sleep apnoea syndrome in obesity: a conspirator in the shadow]

The obstructive sleep apnoea syndrome (OSAS) is caused by upper airway collapse during sleep. These episodes are associated with recurrent oxyhaemoglobin desaturations and arousals which lead to disruption of the sleep pattern and cognitive deterioration. Factors such as age, male sex, menopause, tobacco and alcohol consumption and anatomic abnormalities are demonstrated risk factors for OSAS development. Obesity, specially of abdominal type, is also a very strong predictor of OSAS, increasing the risk of apnoea by ten times. OSAS prevalence may reach 80% and 50% en males and females with morbid obesity respectively. OSAS induces sympathoexcitation, insulin resistance, renin-angiotensin system activation, oxidative stress, endothelial dysfunction, hypercoagulability and reduction of fibrinolysis leading to hypertension and increased cardiovascular risk. The best diagnostic procedure is polysomnography. Obesity treatment is followed by a dramatic improvement in OSAS. Weight loss of 10% results in reductions of apnoea index by 26%. Application of a positive pressure system is a very effective treatment for OSAS which reduces the apnoea index and improves cardiovascular risk and cognitive impairment.

Potentials evoked by chirp-modulated tones: a new technique to evaluate oscillatory activity in the auditory pathway

OBJECTIVE

Steady-state potentials are oscillatory responses generated by a rhythmic stimulation of a sensory pathway. The frequency of the response, which follows the frequency of stimulation, is maximal at a stimulus rate of 40 Hz for auditory stimuli. The exact cause of these maximal responses is not known, although some authors have suggested that they might be related to the 'working frequency' of the auditory cortex. Testing of the responses to different frequencies of stimulation may be lengthy if a single frequency is studied at a time. Our aim was to develop a fast technique to explore the oscillatory response to auditory stimuli, using a tone modulated in amplitude by a sinusoid whose frequency increases linearly in frequency ('chirp') from 1 to 120 Hz.

METHODS

Time-frequency transforms were used for the analysis of the evoked responses in 10 subjects. Also, we analyzed whether the peaks in these responses were due to increases of amplitude or to phase-locking phenomena, using single-sweep time-frequency transforms and inter-trial phase analysis.

RESULTS

The pattern observed in the time-frequency transform of the chirp-evoked potential was very similar in all subjects: a diagonal band of energy was observed, corresponding to the frequency of modulation at each time instant. Two components were present in the band, one around 45 Hz (30-60 Hz) and a smaller one between 80 and 120 Hz. Inter-trial phase analysis showed that these components were mainly due to phase locking phenomena.

CONCLUSIONS

A simultaneous testing of the amplitude-modulation-following oscillatory responses to auditory stimulation is feasible using a tone modulated in amplitude at increasing frequencies. The maximal energies found at stimulation frequencies around 40 Hz are probably due to increased phase-locking of the individual responses.

Gamma-band phase clustering and photosensitivity: is there an underlying mechanism common to photosensitive epilepsy and visual perception?

Photosensitive epilepsy (PSE) is the most common form of human reflex epilepsy, appearing in up to 10% of epileptic children. It also offers a highly reproducible model to investigate whether changes in neuronal activity preceding the transition to an epileptic photoparoxysmal response (PPR) may be detected. We studied 10 patients with idiopathic PSE (eight female, mean age 26 years, range 9-51 years) using magnetoencephalography. In addition, we also studied the responses of five normal controls (mean age 24 years, age range 9-35 years) and three non-photosensitive epileptic patients (mean age 10 years, range 8-11 years). Spectral analysis of the MEG signals recorded during intermittent photic stimulation revealed relevant information in the phase spectrum. To quantify this effect, we introduced a second order response feature of the stimulus-triggered visual response preceding the PPR: the phase clustering index, which measures how close the phases of successive periods are grouped for each frequency component for all periods of the stimuli applied. We recorded a total of 86 PPRs, including several absence seizures, in nine of the 10 patients. We found that an enhancement of phase synchrony in the gamma-band (30-120 Hz), harmonically related to the frequency of stimulation, preceded the stimulation trials that evolved into PPRs, and differed significantly from that encountered in trials not followed by PPR or in control subjects. This novel finding leads us to postulate that a pathological deviation of normally occurring synchronization of gamma oscillations, underlying perceptional processes, mediates the epileptic transition in PSE.

Movement-related changes in cortical oscillatory activity in ballistic, sustained and negative movements

We studied movement-related EEG oscillatory changes in the alpha, beta and low-gamma frequency bands in three different paradigms of movement, namely ballistic, sustained, and negative (muscle relaxation). A time-frequency analysis of non-phase-locked activity in the 7-47 Hz range was performed on movement-centred EEG sweeps using wavelet filters and Gabor transforms. All three movements were accompanied by a decrease in beta activity that began contralaterally about 1.5 s prior to the onset of movement but that extended to both sides near the beginning of the movement. This decrease was followed by a rebound after the end of the movement in the ballistic and negative movements. A decrease was also seen in the alpha band during the three paradigms, which began later (1 s before movement) and lasted longer. An increase in gamma activity was only seen during ballistic and sustained movements, while a decrease in gamma energy was observed during negative movements. It was concluded that changes in the beta band of the EEG before movement are related to the preparation for the movement, but an important afferent component may be present in the later changes. Gamma band activity may be just involved in the execution of the movement, related to muscle contraction.

Beta electroencephalograph changes during passive movements: sensory afferences contribute to beta event-related desynchronization in humans

Non-phase-locked beta oscillatory changes during passive movements were studied in six healthy volunteers, and compared with those observed in a similar group during ballistic movements. Passive movements consisted of brisk wrist extensions done with the help of a pulley system. Changes in the beta band were determined by means of wavelet and Gabor transforms, and compared statistically with a pre-movement period. In this paradigm, a marked beta energy loss (event-related desynchronization, ERD) was present after the beginning of the movement, followed by a beta energy increase (event-related synchronization, ERS). The ERD/ERS was similar to that observed during ballistic movements, but without pre-movement components. Although both changes were maximal in the contralateral central electrode, the beta ERD showed a more bilateral topography. These findings suggest that afferent proprioceptive inputs may play a role in the final part of the beta ERD observed during voluntary movements.

[Postictal paralysis during video-EEG monitoring studies]

OBJECTIVE

To know the frequency of Todd s paralysis during the video EEG monitoring studies, to investigate in its pathophysiology, and to confirm its value to localise the epileptic focus.

PATIENTS AND METHODS

We reviewed 114 monitoring studies, in 102 patients.

RESULTS

Sixty patients had epileptic seizures. An obvious paresis was noted in four seizures of two patients (3 and 1, respectively). Both patients had frontal epilepsy. During the paralysis, in the first patient the EEG showed ictal discharges on the contralateral centrotemporal area. In the second patient, the EEG demonstrated slow waves in the contralateral frontal region. The ictal onset was contralateral to the paresis in all cases. No patient with pseudoseizures had paralysis.

CONCLUSIONS

Postconvulsive paralysis are not frequent in video EEG monitoring studies. However, if present it points out to a contralateral seizure onset. In our series it happened in patients with frontal seizures. The EEG may help to clarify if it correspond to a true postictal phenomenon or to a ictal paralysis.

[Vagal stimulation in the treatment of epilepsy]

INTRODUCTION

The vagal nerve stimulation is a new technique for the treatment of drug resistant epilepsies.

DEVELOPMENT

In 1997, it was approved in United States by the FDA to be used in adults with refractory focal epilepsies not candidates for epilepsy surgery. Its mechanism of action is unknown. The results in the controlled studies indicated a decrease of 30 50% in the seizure frequency in around 50% of the patients. Although more experience is needed to corroborate these results, it seems reasonable as a treatment for patients with difficult epilepsies, especially when the response to the antiepileptic drugs is poor or they are producing secondary effects, and the resection of the focus is not possible.