Hechavarria, J. | Search bioRxiv

bioRxiv2024

Stimulus-specific processing of auditory deviants and repetitive stimulus sequences in the human brainstem

Auditory deviance detection, the neural process by which unexpected stimuli are identified within repetitive acoustic environments, is crucial for survival. While this phenomenon has been extensively studied in the cortex, recent evidence indicates that it also occurs in subcortical regions, including the inferior colliculus (IC). However, compared to animal studies, research on subcortical deviance detection in humans is often constrained by methodological limitations, leaving several important questions unanswered. This study aims to overcome some of these limitations by employing auditory brainstem responses (ABRs) to investigate the earliest neural correlates of deviance detection in humans, with a focus on the IC. We presented healthy participants of either sex with low- and high-frequency chirps in an oddball paradigm and observed significant deviance detection effects in the ABR, specifically when low-frequency chirps were used as deviants within a context of high-frequency standards. These effects manifested as larger and faster ABRs to deviant stimuli, with the strongest responses occurring at higher stimulation rates. Our findings suggest that the human IC exhibits rapid, stimulus-specific deviance detection with differential modulation of response amplitude and latency. The data indicate that the temporal dynamics of novelty detection in humans align well with the data reported in animals, helping to bridge the gap between animal and human research. By uncovering previously unknown characteristics of subcortical deviance detection in humans, this study highlights the value of ABR recordings with excellent temporal resolution in investigating subcortical deviance detection processes. Significance statementAuditory deviance detection enables the brain to identify unexpected stimuli in a repetitive environment, but its subcortical mechanisms in humans remain comparatively underexplored. Using auditory brainstem responses (ABRs), our study reveals two key findings about deviance detection in the human inferior colliculus (IC). First, we show subcortical deviance detection at latencies under 10 ms, bridging a longstanding gap between human and animal research. Second, deviance detection in the IC is rapid, emerging within three or fewer standard repetitions, with differential modulation of ABR amplitude and latency. These findings improve our understanding of the temporal dynamics of auditory processing in the human IC and highlight the value of ABR recordings in studying subcortical deviance detection mechanisms.

neuroscience↗

bioRxiv2022

A neuron model with unbalanced synaptic weights explains asymmetric effects of ketamine in auditory cortex

Although new advances in neuroscience allow the study of vocal communication in awake animals, substantial progress in the processing of vocalizations has been made from brains of anaesthetized preparations. Thus, understanding how anaesthetics affect neuronal responses is of paramount importance. Here, we used electrophysiological recordings and computational modelling to study how the auditory cortex of bats responds to vocalizations under anaesthesia and in wakefulness. We found that multifunctional neurons that process echolocation and communication sounds were affected by ketamine anaesthesia in a manner that could not be predicted by known anaesthetic effects. In wakefulness, acoustic contexts (preceding echolocation or communication sequences) led to stimulus-specific suppression of lagging sounds, accentuating neuronal responses to sound transitions. However, under anaesthesia, communication contexts (but not echolocation) led to a global suppression of responses to lagging sounds. Such asymmetric effect was dependent on the frequency composition of the contexts and not on their temporal patterns. We constructed a neuron model that could replicate the data obtained in vivo. In the model, anaesthesia modulates spiking activity in a channel-specific manner, decreasing responses of cortical inputs tuned to high-frequency sounds and increasing adaptation in the respective cortical synapses. Combined, our findings obtained in vivo and in silico reveal that ketamine anaesthesia does not reduce uniformly the neurons responsiveness to low and high frequency sounds. This effect depends on combined mechanisms that unbalance cortical inputs and ultimately affect how auditory cortex neurons respond to natural sounds in anaesthetized preparations.

neuroscience↗