Biology subjects

Koeppl, C.

Publications and source records attributed to Koeppl, C..

5 recordsLinked to original sources

bioRxiv2024

Auditory perception and neural representation of temporal fine structure are impaired by age but not by cochlear synaptopathy

Age-related hearing loss is a complex phenomenon. The earliest-onset degenerative event is the gradual loss of neural connections between cochlea and auditory brainstem. To probe for perceptual deficits that might arise from this loss, cochlear synaptopathy was induced pharmacologically in young-adult gerbils, which were then tested in a challenging listening task for the perception of temporal fine structure. Treated gerbils behaved no differently than normal-hearing, young-adult animals. In contrast, old gerbils, which typically express many cochlear and central-neural pathologies, showed impaired perception. To probe for the underlying mechanisms, single-unit responses were obtained from the auditory nerve to the same test stimuli. Responses from old gerbils showed no impairment in temporal locking to the stimulus fine structure. However, responses were significantly more driven by slower temporal fluctuations of the stimulus envelope, suggesting that the central auditory system may be unable to extract the relevant information for discrimination from such altered inputs.

neuroscience↗

bioRxiv2024

Single neuron contributions to the auditory brainstem EEG

The auditory brainstem response (ABR) is an acoustically evoked EEG potential that is an important diagnostic tool for hearing loss, especially in newborns. The ABR originates from the response sequence of auditory nerve and brainstem nuclei, and a click-evoked ABR typically shows three positive peaks ( waves) within the first six milliseconds. However, an assignment of the waves of the ABR to specific sources is difficult, and a quantification of contributions to the ABR waves is not available. Here, we exploit the large size and physical separation of the barn owl first-order cochlear nucleus magnocellularis (NM) to estimate single-cell contributions to the ABR. We simultaneously recorded NM neurons spikes and the EEG in owls of both sexes, and found that {gtrsim} 5, 000 spontaneous single-cell spikes are necessary to isolate a significant spike-triggered average response at the EEG electrode. An average single-neuron contribution to the ABR was predicted by convolving the spike-triggered average with the cells peri-stimulus time histogram. Amplitudes of predicted contributions of single NM cells typically reached 32.9 {+/-} 1.1 nV (mean {+/-} SE, range: 2.5 - 162.7 nV), or 0.07 {+/-} 0.02% (median {+/-} SE; range from 0.01% to 1%) of the ABR amplitude. The time of the predicted peak coincided best with the peak of the ABR wave II, independent of the click sound level. Our results suggest that individual neurons contributions to an EEG can vary widely, and that wave II of the ABR is shaped by NM units. Significance statementThe auditory brainstem response (ABR) is a scalp potential used for the diagnosis of hearing loss, both clinically and in research. We investigated the contribution of single action potentials from auditory brainstem neurons to the ABR and provide direct evidence that action potentials recorded in a first order auditory nucleus, and their EEG contribution, coincide with wave II of the ABR. The study also shows that the contribution of single cells varies strongly across the population.

neuroscience↗

bioRxiv2023

Differences in the neural representation of binaural sound localization cues in the auditory midbrain of chicken and barn owl

The sound localisation behaviour of the nocturnally hunting barn owl and its underlying neural computations is a textbook example of neuroethology. Differences in sound timing and level at the two ears are integrated in a series of well characterised steps, from brainstem to inferior colliculus, resulting in a topographical neural representation of auditory space. It remains an important question of brain evolution how this specialised case derived from a more plesiomorphic pattern. The present study is the first to match physiology and anatomical subregions in the non-owl avian inferior colliculus. Single-unit responses in the chicken inferior colliculus were tested for selectivity to different frequencies and to the binaural difference cues. Their anatomical origin was reconstructed with the help of electrolytic lesions and immunohistochemical identification of different subregions of the inferior colliculus, based on previous characterisations in owl and chicken. In contrast to barn owl, there was no distinct differentiation of responses in the different subregions. We found neural topographies for both binaural cues but no evidence for a coherent representation of auditory space. The results are consistent with previous work in pigeon inferior colliculus and chicken higher-order midbrain and suggest a plesiomorphic condition of multisensory integration in the midbrain that is dominated by lateral panoramic vision.

neuroscience↗

bioRxiv2023

Experience-Dependent Plasticity in Nucleus Laminaris of the Barn Owl

Barn owls experience increasing interaural time differences (ITDs) during development, because their head width more than doubles in the month after hatching. We therefore hypothesized that their ITD detection circuit might be modified by experience. To test this, we raised owls with unilateral ear inserts that delayed and attenuated the acoustic signal, then measured the ITD representation in the brainstem nucleus laminaris (NL) when they were adult. The ITD circuit is composed of delay line inputs to coincidence detectors, and we predicted that plastic changes would lead to shorter delays in the axons from the manipulated ear, and complementary shifts in ITD representation on the two sides. In owls that received ear inserts starting around P14, the maps of ITD shifted in the predicted direction, but only on the ipsilateral side, and only in those tonotopic regions that had not experienced auditory stimulation prior to insertion. The contralateral map did not change. Experience-dependent plasticity of the ITD circuit occurs in NL, and our data suggest that ipsilateral and contralateral delays are independently regulated. Thus, altered auditory input during development leads to long-lasting changes in the representation of ITD. Significance StatementThe early life of barn owls is marked by increasing sensitivity to sound, and by increasing ITDs. Their prolonged post-hatch development allowed us to examine the role of altered auditory experience on the development of ITD detection circuits. We raised owls with a unilateral ear insert and found that their maps of ITD were altered by experience, but only in those tonotopic regions that had not experienced auditory stimulation prior to insertion. Thus experience-induced plasticity allows the sound localization circuits to be customized to individual characteristics, such as the size of the head, and potentially to compensate for natural conductive hearing losses.

neuroscience↗

bioRxiv2019

Internally coupled middle ears enhance the range of interaural time differences heard by the chicken

Interaural time differences (ITD) are one of several principle cues for localizing sounds. However, ITD are in the sub-millisecond range for most animals. Because the neural processing of such small ITDs pushes the limit of temporal resolution, the precise ITD-range for a given species and its usefulness - relative to other localization cues - was a powerful selective force in the evolution of the neural circuits involved. Birds and other non-mammals have internally coupled middle ears working as pressure-difference receivers that may significantly enhance ITD, depending on the precise properties of the interaural connection. Here, the extent of this internal coupling was investigated in chickens, specifically under the same experimental conditions as typically used in neurophysiology of ITD-coding circuits, i.e. with headphone stimulation. Cochlear microphonics (CM) were recorded simultaneously from both ears of anesthetized chickens under monaural and binaural stimulation, using pure tones from 0.1 to 3 kHz. Interaural transmission peaked at 1.5 kHz at a loss of only -5.5 dB; the mean interaural delay was 264 s. CM amplitude strongly modulated as a function of ITD, confirming significant interaural coupling. The \"ITD heard\" derived from the CM phases in both ears showed enhancement, compared to the acoustic stimuli, by a factor of up to 1.8. However, the closed sound delivery systems impaired interaural transmission at low frequencies (< 1 kHz). We identify factors that need to be considered when interpreting neurophysiological data obtained under these conditions, and relating them to the natural free-field condition.\n\nSummary statementThe interaural time differences that chickens can use for sound localization are significantly greater than their small head size suggests. Closed-system sound stimulation can, however, produce complex artefacts.

neuroscience↗