Magnetoencephalographic investigations of human primary auditory cortex responses to multiple amplitude modulated tones

Der zeitlichen Verläufe von Sprach- oder Musikklängen enthalten Amplitudenuktuationen mit unterschiedlichen Rhythmen die Träger der Information sind. Unsere Studie liefert wertvolle neue Erkenntnisse darüber, wie und in welcher Hirnregion komplexe Töne verarbeitet werden und mit anderen Komponenten des zentralen auditorischen Kortex interagieren. Die 40 Hz SSR hat sich dabei als wertvoller Parameter bei der Erforschung von Sprachverarbeitung und Störungen des zentralen Kortex erwiesen. Ein reiner Ton, mit zwei Sinusschwingungen von 38 und 40 Hz moduliert, wird wahrgenommen als eine 2 Hz Schwankung der Lautheit und eine Rauhigkeit, die den Modulationsfrequenzen bei 40 Hz entspricht. Korrespondierende SSRs bei 2, 38 und 40 Hz wurden mit dem MEG erfasst, das die Lokalisation überlappender Quellen im primären auditorischen Kortex ermöglichte. Der allgemeinere Fall mehrfacher AM Töne mit verschiedenen Trägerfrequenzen zeigte, dass die Antwort auf einen AM Ton unterdrückt wird, wenn ein zweiter AM Stimulus gleichzeitig dargeboten wird. Die Ergebnisse lassen eine zentrale Generierung der 40 Hz SSR annehmen

Perceptual organization of auditory streaming-task relies on neural entrainment of the stimulus-presentation rate: MEG evidence

Background: Humans are able to extract regularities from complex auditory scenes in order to form perceptually meaningful elements. It has been shown previously that this process depends critically on both the temporal integration of the sensory input over time and the degree of frequency separation between concurrent sound sources. Our goal was to examine the relationship between these two aspects by means of magnetoencephalography (MEG). To achieve this aim, we combined time-frequency analysis on a sensor space level with source analysis. Our paradigm consisted of asymmetric ABA-tone triplets wherein the B-tones were presented temporally closer to the first A-tones, providing different tempi within the same sequence. Participants attended to the slowest B-rhythm whilst the frequency separation between tones was manipulated (0-, 2-, 4- and 10-semitones). Results: The results revealed that the asymmetric ABA-triplets spontaneously elicited periodic-sustained responses corresponding to the temporal distribution of the A-B and B-A tone intervals in all conditions. Moreover, when attending to the B-tones, the neural representations of the A- and B-streams were both detectable in the scenarios which allow perceptual streaming (2-, 4- and 10-semitones). Alongside this, the steady-state responses tuned to the presentation of the B-tones enhanced significantly with increase of the frequency separation between tones. However, the strength of the B-tones related steady-state responses dominated the strength of the A-tones responses in the 10-semitones condition. Conversely, the representation of the A-tones dominated the B-tones in the cases of 2- and 4-semitones conditions, in which a greater effort was required for completing the task. Additionally, the P1 evoked fields’ component following the B-tones increased in magnitude with the increase of inter-tonal frequency difference. Conclusions: The enhancement of the evoked fields in the source space, along with the B-tones related activity of the time-frequency results, likely reflect the selective enhancement of the attended B-stream. The results also suggested a dissimilar efficiency of the temporal integration of separate streams depending on the degree of frequency separation between the sounds. Overall, the present findings suggest that the neural effects of auditory streaming could be directly captured in the time-frequency spectrum at the sensor-space level.<br

Modulations of neural activity in auditory streaming caused by spectral and temporal alternation in subsequent stimuli: a magnetoencephalographic study

Background: The aim of the present study was to identify a specific neuronal correlate underlying the preattentive auditory stream segregation of subsequent sound patterns alternating in spectral or temporal cues. Fifteen participants with normal hearing were presented with series’ of two consecutive ABA auditory tone-triplet sequences, the initial triplets being the Adaptation sequence and the subsequent triplets being the Test sequence. In the first experiment, the frequency separation (delta-f) between A and B tones in the sequences was varied by 2, 4 and 10 semitones. In the second experiment, a constant delta-f of 6 semitones was maintained but the Inter-Stimulus Intervals (ISIs) between A and B tones were varied. Auditory evoked magnetic fields (AEFs) were recorded using magnetoencephalography (MEG). Participants watched a muted video of their choice and ignored the auditory stimuli. In a subsequent behavioral study both MEG experiments were replicated to provide information about the participants’ perceptual state. Results: MEG measurements showed a significant increase in the amplitude of the B-tone related P1 component of the AEFs as delta-f increased. This effect was seen predominantly in the left hemisphere. A significant increase in the amplitude of the N1 component was only obtained for a Test sequence delta-f of 10 semitones with a prior Adaptation sequence of 2 semitones. This effect was more pronounced in the right hemisphere. The additional behavioral data indicated an increased probability of two-stream perception for delta-f = 4 and delta-f = 10 semitones with a preceding Adaptation sequence of 2 semitones. However, neither the neural activity nor the perception of the successive streaming sequences were modulated when the ISIs were alternated. Conclusions: Our MEG experiment demonstrated differences in the behavior of P1 and N1 components during the automatic segregation of sounds when induced by an initial Adaptation sequence. The P1 component appeared enhanced in all Test-conditions and thus demonstrates the preceding context effect, whereas N1 was specifically modulated only by large delta-f Test sequences induced by a preceding small delta-f Adaptation sequence. These results suggest that P1 and N1 components represent at least partially-different systems that underlie the neural representation of auditory streaming

Spatial distribution of beef cattle on a New Zealand hill country farm: monitoring the use of streams and wet areas

Grazing livestock are an important source of contamination of freshwater, particularly when they have direct access to streams. Cattle in particular contribute to riparian habitat deterioration through stream bank destruction and direct defecation and urination in streams. Exclusion of stock or planting of riparian areas, are the most common catchment management methods used to protect waterways. Given the relatively low returns from beef and sheep farming, both of these strategies are very expensive and often logistically prohibitive in steep hill county landscapes. Despite this, policy trends indicate that fencing of streams in agricultural catchments may become mandatory in the future. It is important that we understand how much time cattle spend in and around hill country streams and wet areas (wetlands and hill side seeps), in order to quantify the likely environmental benefits from such policies. The current study examined cattle movement data obtained using Global Positioning System (GPS) collars from experiments undertaken at Massey University’s hill country research farm, Tuapaka, near Palmerston North, to investigate the amount of time cattle spent in and around streams and wet areas. Animal movement data were collected over seven grazing events, in three winter periods (2012, 2013 and 2015). Permanent streams and wet areas were identified using a digital elevation model derived from 1m LiDAR data, aerial RGB images and RTK measurements. Cattle spent 3.3 – 6% (48 – 86 min/day) of their day in streams and wet areas consistently across the 7 data collections. Cattle spent more time in streams and wet areas during the afternoon. There are differences in the median amount of time individual animals spend in non-risk areas. Further research is necessary to evaluate how we can influence the amount of time cattle spend in riparian areas on hill country and how stream bank behaviour varies at different times of the year

DINAMICA PIEȚEI FORȚEI DE MUNCĂ ÎN BULGARIA

BACKGROUND. Bulgaria, as many countries in the world is experiencing a critical period for the health workforce. The shortage of qualified nurses is one of the biggest obstacles for improving the health-system performance. Lack of strategic planning based on profound market research and elaboration of scientifically based prognosis further deteriorate the current nursing labor market disequilibrium. THE AIM of the study is to explore the main factors influencing the nursing market disequilibrium in Bulgaria and to make an evidence-based forecast of the future needs for nurses in order to suggest relevant workforce development strategies. MATERIAL AND METHODS. The study employs a combination of sociological and statistical methods. The analysis is based on the official statistical data on Bulgarian nursing personnel up to 2012. Primary information is collected through self-administered questionnaires distributed among 337 practicing nurses from April 2007 to December 2012. Data are processed with the packages MS Office Excel 2010 and SPSS v. 13. RESULTS. Results indicate that a decrease in the demand for nursing labour caused large staff layoffs during the first stage of the restructuring period (1990-2000) followed by a severe drop in the number of nurses due to emigration and exodus from the profession. There are also educational and qualification problems along with unattractiveness of the nursing practice due to high workload and low remuneration. With the mean age of 49 severe nursing workforce’s deficit is expected in 10-15 years due to retirement. According to our estimations the deficit of nurses will account for 3162 specialists by 2030. CONCLUSION. The Bulgarian nursing labor market disequilibrium is due to long-term structural imbalances. As the market mechanism is unable to attain equilibrium Bulgarian government should be urgently involved in workforce planning and initiate actions and strategies for producing and retaining the highly qualified nurse professionals in Bulgaria.   Key words: nursing workforce market, Bulgaria, disequilibrium, factors.  CONTEXT. Similar multor state, Bulgaria traversează, de asemenea, o perioadă critică &icirc;n ceea ce privește piața forței de muncă din sănătate. Lipsa de asistente medicale calificate este unul dintre cele mai mari obstacole pentru &icirc;mbunătățirea performanței sistemului de sănătate. Lipsa planificării strategice bazată pe cercetare amănunțită a pieței și lipsa prognozelor și proiecțiilor bazate pe argumente științifice conduc la dezechilibrul existent pe piața muncii asistentelor medicale, existent la momentul actual. SCOPUL studiului este de a explora factorii principali care influențează dezechilibrul de pe piața muncii asistentelor medicale &icirc;n Bulgaria și de a face prognoze, bazate pe dovezi, ale nevoilor viitoare de asistente medicale, &icirc;n scopul de a sugera strategii viitoare de dezvoltare a forței de muncă. MATERIAL ȘI METODE. Studiul&nbsp; de față abordează o combinație de metode sociologice și statistice.&nbsp; Analiza are la bază date statistice oficiale privind personalul medical din Bulgaria, date disponibile inclusiv pentru anul 2012. Informatiile primare au fost colectate cu ajutorul unor chestionare auto-administrate, distribuite unui număr de 337 asistente medicale practicante, &icirc;n perioada aprilie 2007 - decembrie 2012. Datele sunt prelucrate cu pachetele de analiză MS Office Excel 2010 și SPSS v. 13. REZULTATE. Rezultatele indică faptul că scăderea cererii pentru asistentele medicale a cauzat&nbsp; disponibilizările masive din timpul primei etape a perioadei de restructurare 1990-2000, urmată de o scădere severă a numărului de asistente medicale din cauza emigrării și exodul profesional. Există probleme educațiomale și de calificare, alături de lipsa de atractivitate a practicii de asistentă medicală din cauza volumului mare de muncă și a nivelului redus de salarizare. Cu o medie crescută a v&acirc;rstei asistentelor medicale, de 49 de ani,&nbsp; un deficit sever este așteptat &icirc;n următorii 10+15 ani, din cauza fenomenului de pensionare. Conform estimărilor noastre, deficitul de asistente medicale, p&acirc;nă &icirc;n anul 2030, va fi de 3162 de specialiști. CONCLUZII. Dezechilibrul numeric de asistente medicale de pe piața forței de muncă din sănătate este cauza unor dezechilibre structurale pe termen lung. Cum mecanismul piaței nu este &icirc;n măsură să rezolve acest dezechilibru, guvernul din Bulgaria va trebui urgent să&nbsp; se implice &icirc;n planificarea forței de muncă și să inițieze acțiuni și strategii de creare și menținere a asistentelor medicale calificate, &icirc;n Bulgaria. &nbsp;Cuvinte cheie: piața forței de muncă, asistente medicale, dezechilibru, factori frenatori, Bulgaria &nbsp

Electrophysiological correlates of selective attention: A lifespan comparison

<p>Abstract</p> <p>Background</p> <p>To study how event-related brain potentials (ERPs) and underlying cortical mechanisms of selective attention change from childhood to old age, we investigated lifespan age differences in ERPs during an auditory oddball task in four age groups including 24 younger children (9–10 years), 28 older children (11–12 years), 31 younger adults (18–25), and 28 older adults (63–74 years). In the Unattend condition, participants were asked to simply listen to the tones. In the Attend condition, participants were asked to count the deviant stimuli. Five primary ERP components (N1, P2, N2, P3 and N3) were extracted for deviant stimuli under Attend conditions for lifespan comparison. Furthermore, Mismatch Negativity (MMN) and Late Discriminative Negativity (LDN) were computed as difference waves between deviant and standard tones, whereas Early and Late Processing Negativity (EPN and LPN) were calculated as difference waves between tones processed under Attend and Unattend conditions. These four secondary ERP-derived measures were taken as indicators for change detection (MMN and LDN) and selective attention (EPN and LPN), respectively. To examine lifespan age differences, the derived difference-wave components for attended (MMN and LDN) and deviant (EPN and LPN) stimuli were specifically compared across the four age groups.</p> <p>Results</p> <p>Both primary and secondary ERP components showed age-related differences in peak amplitude, peak latency, and topological distribution. The P2 amplitude was higher in adults compared to children, whereas N2 showed the opposite effect. P3 peak amplitude was higher in older children and younger adults than in older adults. The amplitudes of N3, LDN, and LPN were higher in older children compared with both of the adult groups. In addition, both P3 and N3 peak latencies were significantly longer in older than in younger adults. Interestingly, in the young adult sample P3 peak amplitude correlated positively and P3 peak latency correlated negatively with performance in the Identical Picture test, a marker measure of fluid intelligence.</p> <p>Conclusion</p> <p>The present findings suggest that patterns of event-related brain potentials are highly malleable within individuals and undergo profound reorganization from childhood to adulthood and old age.</p

Good vibrations, bad vibrations: Oscillatory brain activity in the attentional blink

The attentional blink (AB) is a deficit in reporting the second (T2) of two targets (T1, T2) when presented in close temporal succession and within a stream of distractor stimuli. The AB has received a great deal of attention in the past two decades because it allows to study the mechanisms that influence the rate and depth of information processing in various setups and therefore provides an elegant way to study correlates of conscious perception in supra-threshold stimuli. Recently evidence has accumulated suggesting that oscillatory signals play a significant role in temporally coordinating information between brain areas. This review focuses on studies looking into oscillatory brain activity in the AB. The results of these studies indicate that the AB is related to modulations in oscillatory brain activity in the theta, alpha, beta, and gamma frequency bands. These modulations are sometimes restricted to a circumscribed brain area but more frequently include several brain regions. They occur before targets are presented as well as after the presentation of the targets. We will argue that the complexity of the findings supports the idea that the AB is not the result of a processing impairment in one particular process or brain area, but the consequence of a dynamic interplay between several processes and/or parts of a neural network

Electrical Brain Responses to an Auditory Illusion and the Impact of Musical Expertise

The presentation of two sinusoidal tones, one to each ear, with a slight frequency mismatch yields an auditory illusion of a beating frequency equal to the frequency difference between the two tones; this is known as binaural beat (BB). The effect of brief BB stimulation on scalp EEG is not conclusively demonstrated. Further, no studies have examined the impact of musical training associated with BB stimulation, yet musicians' brains are often associated with enhanced auditory processing. In this study, we analysed EEG brain responses from two groups, musicians and non-musicians, when stimulated by short presentation (1 min) of binaural beats with beat frequency varying from 1 Hz to 48 Hz. We focused our analysis on alpha and gamma band EEG signals, and they were analysed in terms of spectral power, and functional connectivity as measured by two phase synchrony based measures, phase locking value and phase lag index. Finally, these measures were used to characterize the degree of centrality, segregation and integration of the functional brain network. We found that beat frequencies belonging to alpha band produced the most significant steady-state responses across groups. Further, processing of low frequency (delta, theta, alpha) binaural beats had significant impact on cortical network patterns in the alpha band oscillations. Altogether these results provide a neurophysiological account of cortical responses to BB stimulation at varying frequencies, and demonstrate a modulation of cortico-cortical connectivity in musicians' brains, and further suggest a kind of neuronal entrainment of a linear and nonlinear relationship to the beating frequencies