New thin-film surface electrode array enables brain mapping with high spatial acuity in rodents

In neuroscience, single-shank penetrating multi-electrode arrays are standard for sequentially sampling several cortical sites with high spatial and temporal resolution, with the disadvantage of neuronal damage. Non-penetrating surface grids used in electrocorticography (ECoG) permit simultaneous recording of multiple cortical sites, with limited spatial resolution, due to distance to neuronal tissue, large contact size and high impedances. Here we compared new thin-film parylene C ECoG grids, covering the guinea pig primary auditory cortex, with simultaneous recordings from penetrating electrode array (PEAs), inserted through openings in the grid material. ECoG grid local field potentials (LFP) showed higher response thresholds and amplitudes compared to PEAs. They enabled, however, fast and reliable tonotopic mapping of the auditory cortex (place-frequency slope: 0.7 mm/octave), with tuning widths similar to PEAs. The ECoG signal correlated best with supragranular layers, exponentially decreasing with cortical depth. The grids also enabled recording of multi-unit activity (MUA), yielding several advantages over LFP recordings, including sharper frequency tunings. ECoG first spike latency showed highest similarity to superficial PEA contacts and MUA traces maximally correlated with PEA recordings from the granular layer. These results confirm high quality of the ECoG grid recordings and the possibility to collect LFP and MUA simultaneously

Die intracochleär gemessene CAP-Hörschwelle beim Meerschweinchen - Hinweise für einen apikalen Hörverlust nach Elektrodeninsertion

Einleitung: Die elektroakustische Stimulation ermöglicht die Nutzung eines Resthörvermögens bei der Cochlea Implantation. Voraussetzung ist, dass atraumatische Elektroden und Insertionstechniken zur Anwendung kommen. Dies wird in der Realität nur uneinheitlich erreicht. Ziel dieser tierexperimentellen Studie war es daher, bei hörenden Meerschweinchen Hörschwellen nach Elektrodeninsertion zu bestimmen, um so das Ausmaß eines Elektrodentraumas einzuschätzen.Methoden: Bei 10 Meerschweinchen (n=20) erfolgte über eine Cochleostomie die komplette Insertion einer vorgefertigten 6-Kontakt-Cochlea-Implantat-Elektrode (MedEl, Österreich) in Vollnarkose. Anschließend wurde in einem Frequenzbereich von 1 bis 32 kHz bei 0 bis 90 dB SPL akustisch stimuliert und gleichzeitig über die einliegenden Kontakte neurale Aktionspotentiale (CAP) abgeleitet.Ergebnisse: Im Vergleich zu Tieren ohne Elektrodeninsertion zeigte sich in diesem Kollektiv eine Verschlechterung der CAP-Hörschwellen. Insbesondere im Frequenzbereich unterhalb von 12 kHz lag dieser Hörverlust zwischen 20 bis 50 dB. Dieser Bereich liegt apikal der Elektrodenspitze und enthält die Region des besten Hörens (8 bis 12 kHz). Hingegen zeigten sich die Hörschwellen oberhalb von 12 kHz unverändert im Vergleich zu den Kontrolltieren.Schlussfolgerungen: Während sich im tonotopen Bereich der liegenden Elektrode die Hörschwelle unverändert zeigte, fiel sie apikal der Elektrodenspitze signifikant ab. Diese Beobachtung weist darauf hin, dass nicht ein 'direktes' Trauma, sondern eher ein 'indirektes' Trauma durch Flüssigkeitsverschiebungen oder einen Okklusionseffekt der Scala tympani ursächlich für einen Schwellenabfall ist.Unterstützt durch: MED-ELDer Erstautor gibt keinen Interessenkonflikt an

Anomalies of attenuation and phase velocity of surface acoustic waves in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7‒δ</Subscript> thin films in the vicinity of T<Subscript>c</Subscript>

PACS. 62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances , - 73.50.Rb Acoustoelectric and magnetoacoustic effects , - 74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation,

Optoacoustic effect is responsible for laser-induced cochlear responses

Optical stimulation of the cochlea with laser light has been suggested as an alternative to conventional treatment of sensorineural hearing loss with cochlear implants. The underlying mechanisms are controversially discussed: The stimulation can either be based on a direct excitation of neurons, or it is a result of an optoacoustic pressure wave acting on the basilar membrane. Animal studies comparing the intra-cochlear optical stimulation of hearing and deafened Guinea pigs have indicated that the stimulation requires intact hair cells. Therefore, optoacoustic stimulation seems to be the underlying mechanism. The present study investigates optoacoustic characteristics using pulsed laser stimulation for in vivo experiments on hearing Guinea pigs and pressure measurements in water. As a result, in vivo as well as pressure measurements showed corresponding signal shapes. The amplitude of the signal for both measurements depended on the absorption coefficient and on the maximum of the first time-derivative of laser pulse power (velocity of heat deposition). In conclusion, the pressure measurements directly demonstrated that laser light generates acoustic waves, with amplitudes suitable for stimulating the (partially) intact cochlea. These findings corroborate optoacoustic as the basic mechanism of optical intra-cochlear stimulation

Food and fitness: associations between crop yields and life-history traits in a longitudinally monitored pre-industrial human population

Severe food shortage is associated with increased mortality and reduced reproductive success in contemporary and historical human populations. Studies of wild animal populations have shown that subtle variation in environmental conditions can influence patterns of mortality, fecundity and natural selection, but the fitness implications of such subtle variation on human populations are unclear. Here, we use longitudinal data on local grain production, births, marriages and mortality so as to assess the impact of crop yield variation on individual age-specific mortality and fecundity in two pre-industrial Finnish populations. Although crop yields and fitness traits showed profound year-to-year variation across the 70-year study period, associations between crop yields and mortality or fecundity were generally weak. However, post-reproductive individuals of both sexes, and individuals of lower socio-economic status experienced higher mortality when crop yields were low. This is the first longitudinal, individual-based study of the associations between environmental variation and fitness traits in pre-industrial humans, which emphasizes the importance of a portfolio of mechanisms for coping with low food availability in such populations. The results are consistent with evolutionary ecological predictions that natural selection for resilience to food shortage is likely to weaken with age and be most severe on those with the fewest resources