Biology subjects

Alter, K.

Publications and source records attributed to Alter, K..

8 recordsLinked to original sources

bioRxiv2025

Alterations in steady-state synchronisation between Acute and Chronic Tinnitus suggests reduction in both tinnitus and central gain.

The mechanism of tinnitus remains unclear as the generation and persistence of tinnitus is not widely understood. The acute tinnitus population serves as an ideal group for investigating the mechanisms behind the origin and persistence of tinnitus, from its initial onset to its subsequent chronification. One of the neural markers for measuring tinnitus such as neural synchrony or central gain is the Auditory Steady State Response (ASSR). The experiment was carried out on 39 participants with acute tinnitus (18 followed back six months post baseline), 30 with chronic tinnitus, and 27 controls. The results reveal that both cross sectionally and longitudinally, there were no significant differences in absolute amplitudes of ASSR across intensities and the slope of ASSR growth function between the groups. However, Controls tend to have an overall increase in ASSR amplitude when compared to Acute and Chronic Tinnitus which can be attributed to changes in neural synchronisation, attentional modulation, tinnitus-related distress, and diminished GABAergic inhibition coinciding with the presence of tinnitus. As there were no changes in the ASSR amplitude between Acute and Chronic Tinnitus or between Acute and Post Acute Tinnitus despite variations in distress and tinnitus loudness, we infer that auditory sensitivity/neural sensitvity is independent of the tinnitus.

neuroscience↗

bioRxiv2025

Perceptual Novelty in Tinnitus a Causative Factor for its Persistence. A Stimulus Novelty Based P300 Paradigm on Acute, Chronic, and Non-Tinnitus Controls

Our understanding of tinnitus pathophysiology may be greatly advanced by understanding how the condition evolves from its initial onset or acute stage to its chronic manifestation. Such a transition likely reflects dynamic neurophysiological changes within central auditory and non-auditory networks. Previous studies have highlighted that individuals with acute tinnitus tend to have increased activity in the regions of anterior cingulate cortex, inferior parietal lobe, and insula all of which are essential in constituting the salience network. We therefore aimed at tapping into the salience network of tinnitus through a novelty based P300 paradigm in individuals with Acute, Post Acute (six months follow up since tinnitus onset) Chronic, and Controls. Participants were presented with an auditory oddball paradigm comprising three deviant types: (1) novel environmental sounds, (2) low-frequency tonal deviants, and (3) high-frequency tonal deviants, embedded within a sequence of frequent standard tones. Our results indicate a significant drop in P300 amplitude during the Post Acute stage across the three deviant stimuli, highlighting the substantial influence of the anterior cingulate cortex/salience network in possible generation of tinnitus and inferior parietal lobe in the persistence of tinnitus.

neuroscience↗

bioRxiv2025

Evidence for a Transient State of Auditory Hypersensitivity During Initial Onset of Tinnitus, Evidenced by Intensity Dependence of the Auditory Evoked Potential (IDAEP)

Our understanding of tinnitus pathophysiology may be greatly advanced by understanding how the condition evolves from its initial onset or acute stage to its chronic manifestation. Such a transition likely reflects dynamic neurophysiological changes within central auditory and non-auditory networks. Our integrated model of tinnitus posits that sensory precision (sensory weighting) may be heightened during the acute stages of tinnitus to resolve degraded auditory input, but in chronic tinnitus, its role may diminish as plastic processes take over the percepts maintenance. Consequently, we hypothesize that bottom-up neural mechanisms linked to initiation of tinnitus, such as central gain and neural synchrony, are maximal around the time of tinnitus onset, but later subside by way of regression to the mean. We evaluated this hypothesis by measuring central auditory reactivity through the Intensity Dependence of Auditory Evoked Potential (IDAEP), a non-invasive index of higher-order inhibitory processing within the auditory system. A steeper IDAEP slope is associated with heightened sensory reactivity (higher sensitivity to changes in auditory stimuli), indicative of reduced central inhibition. Conversely, a shallower slope reflects greater inhibitory control. Studying a group with acute tinnitus (onset within six weeks), with a repeated assessment after six months from onset, we found an initially increased IDAEP slope in the acute stage, which had significantly reduced at follow-up, supporting our hypothesis that there is increased sensory reactivity during tinnitus onset, which need not persist in order for tinnitus to become chronic.

neuroscience↗

bioRxiv2024

Distinct profiles of tinnitus and hyperacusis in intensity deviant responses and auditory evoked potentials

ERPs in response to intensity deviant stimuli are assessed in four age and hearing matched groups of various combinations of tinnitus and hyperacusis (both conditions, one of the conditions, neither condition). Distinct profiles for tinnitus and hyperacusis are shown, as well as additional more nuanced interactions. This not only moves our understanding of each condition, but also speaks directly to possible mechanistic subtypes of tinnitus (and of hyperacusis) which might be disentangled through the cheap and available technique that is single-channel EEG. The current findings may also explain some discrepant findings in past literature.

neuroscience↗

bioRxiv2024

Intensity mismatch asymmetry in tinnitus: in which direction should participants pay attention?

The effects attention has on intensity deviant Mismatch Negativity responses is an unknown factor in basic sensory neuroscience. It would be useful to understand how attention would affect responses to intensity deviants compared to each other (upward vs downward), and compared to other sensory dimensions such as frequency. Overall, previous research indicates that attention may modulate neuronal gain in healthy participants and change the amplitudes of evoked responses, and may mainly affect the responses to regularly repeating (standard) stimuli rather than deviants. Gain may respond differently in participants with tinnitus and/or hyperacusis under the same conditions compared to controls. Overall, results of the passive task condition were consistent with previous research. Auditory attention magnified MMN in response to upward deviants, while visual attention attenuated it in both control and tinnitus groups. However, auditory attention selectively enhanced downward deviant MMN in the tinnitus group (compared to passive attention). Using the auditory attention paradigm may be advantageous in MMN studies on tinnitus/hyperacusis because the observed differences would be particularly large.

neuroscience↗

bioRxiv2024

Effects of the overall paradigm context on intensity deviant responses in healthy subjects

Three experiments have been carried out to explore Mismatch Negativity responses to intensity deviants in a roving intensity deviant paradigm in control and tinnitus groups. The first experiment used interspersed blocks of two tinnitus-like frequencies set by each participant with tinnitus, which were usually around 1/3 of an octave apart. On the other hand, two later studies used interspersed blocks tones at tinnitus-like frequencies and at 1 kHz. This was the only difference in the paradigms used, however, there were differences in the patterns displayed by the control group in the first study compared to the other two. Three groups of healthy controls were recruited to measure responses to intensity deviants when different frequencies were used for the alternating blocks. For one group, the whole experiment was set at a single frequency; for the next, blocks were played at 6 kHz and at a frequency 1/3 octave below 6 kHz (small difference); the last group was presented with blocks that had tones at 6 kHz and 1 kHz frequencies (large difference). Overall, the Mismatch Negativity responses in the small difference group were opposite to the large difference and the single frequency group. It would be useful to see whether these results generalise to other experiment designs such as attended and ignored stimulus conditions, different stimulus durations, non-isochronous, or paradigms with frequency deviants.

neuroscience↗

bioRxiv2023

Acclimation Capacity to Global Warming of Amphibians and Freshwater Fishes: Drivers, Patterns, and Data Limitations

Amphibians and fishes play a central role in shaping the structure and function of freshwater environments. These organisms have a limited capacity to disperse across different habitats and the thermal buffer offered by freshwater systems is small. Understanding determinants and patterns of their physiological sensitivity across life history is, therefore, imperative to predicting the impacts of climate change in freshwater systems. Based on a systematic literature review including 345 experiments with 998 estimates on 96 amphibian (Anura/Caudata) and 93 freshwater fish species (Teleostei), we conducted a quantitative synthesis to explore phylogenetic, ontogenetic, and biogeographic (thermal adaptation) patterns in upper thermal tolerance (CTmax) and thermal acclimation capacity (Acclimation Response Ratio, ARR) as well as the influence of the methodology used to assess these thermal traits using a conditional inference tree analysis. We found globally consistent patterns in CTmax and ARR, with phylogeny (taxa/order), experimental methodology, climatic origin, and life stage as significant determinants of thermal traits. The analysis demonstrated that CTmax does not primarily depend on the climatic origin but on experimental acclimation temperature and duration, and life stage. Higher acclimation temperatures and longer acclimation times led to higher CTmax values, whereby Anuran larvae revealed a higher CTmax than older life stages. The ARR of freshwater fishes was more than twice that of amphibians. Differences in ARR between life stages were not significant. In addition to phylogenetic differences, we found that ARR also depended on acclimation duration, ramping rate, and adaptation to local temperature variability. However, the amount of data on early life stages is too small, methodologically inconsistent, and phylogenetically unbalanced to identify potential life cycle bottlenecks in thermal traits. We therefore propose methods to improve the robustness and comparability of CTmax/ARR data across species and life stages, which is crucial for the conservation of freshwater biodiversity under climate change.

ecology↗

bioRxiv2018

Extrinsic and Intrinsic Dynamics in Movement Intermittency

What determines how we move in the world? Motor neuroscience often focusses either on intrinsic rhythmical properties of motor circuits or extrinsic sensorimotor feedback loops. Here we show that the interplay of both intrinsic and extrinsic dynamics is required to explain the intermittency observed in continuous tracking movements. Using spatiotemporal perturbations in humans, we demonstrate that apparently discrete submovements made 2-3 times per second reflect constructive interference between motor errors and continuous feedback corrections that are filtered by intrinsic circuitry in the motor system. Local field potentials in monkey motor cortex revealed characteristic signatures of a Kalman filter giving rise to both low-frequency cortical cycles during movement, and delta oscillations during sleep. We interpret these results within the framework of optimal feedback control, and suggest that the intrinsic rhythmicity of motor cortical networks reflects an internal model of external dynamics which is used for state estimation during feedback-guided movement.

neuroscience↗