Investigating the build-up of precedence effect using reflection masking

The auditory processing level involved in the build‐up of precedence [Freyman et al., J. Acoust. Soc. Am. 90, 874–884 (1991)] has been investigated here by employing reflection masked threshold (RMT) techniques. Given that RMT techniques are generally assumed to address lower levels of the auditory signal processing, such an approach represents a bottom‐up approach to the buildup of precedence. Three conditioner configurations measuring a possible buildup of reflection suppression were compared to the baseline RMT for four reflection delays ranging from 2.5–15 ms. No buildup of reflection suppression was observed for any of the conditioner configurations. Buildup of template (decrease in RMT for two of the conditioners), on the other hand, was found to be delay dependent. For five of six listeners, with reflection delay=2.5 and 15 ms, RMT decreased relative to the baseline. For 5‐ and 10‐ms delay, no change in threshold was observed. It is concluded that the low‐level auditory processing involved in RMT is not sufficient to realize a buildup of reflection suppression. This confirms suggestions that higher level processing is involved in PE buildup. The observed enhancement of reflection detection (RMT) may contribute to active suppression at higher processing levels

Sound processing in the mouse auditory cortex: organization, modulation, and transformation

The auditory system begins with the cochlea, a frequency analyzer and signal amplifier with exquisite precision. As neural information travels towards higher brain regions, the encoding becomes less faithful to the sound waveform itself and more influenced by non-sensory factors such as top-down attentional modulation, local feedback modulation, and long-term changes caused by experience. At the level of auditory cortex (ACtx), such influences exhibit at multiple scales from single neurons to cortical columns to topographic maps, and are known to be linked with critical processes such as auditory perception, learning, and memory. How the ACtx integrates a wealth of diverse inputs while supporting adaptive and reliable sound representations is an important unsolved question in auditory neuroscience. This dissertation tackles this question using the mouse as an animal model. We begin by describing a detailed functional map of receptive fields within the mouse ACtx. Focusing on the frequency tuning properties, we demonstrated a robust tonotopic organization in the core ACtx fields (A1 and AAF) across cortical layers, neural signal types, and anesthetic states, confirming the columnar organization of basic sound processing in ACtx. We then studied the bottom-up input to ACtx columns by optogenetically activating the inferior colliculus (IC), and observed feedforward neuronal activity in the frequency-matched column, which also induced clear auditory percepts in behaving mice. Next, we used optogenetics to study layer 6 corticothalamic neurons (L6CT) that project heavily to the thalamus and upper layers of ACtx. We found that L6CT activation biases sound perception towards either enhanced detection or discrimination depending on its relative timing with respect to the sound, a process that may support dynamic filtering of auditory information. Finally, we optogenetically isolated cholinergic neurons in the basal forebrain (BF) that project to ACtx and studied their involvement in columnar ACtx plasticity during associative learning. In contrast to previous notions that BF just encodes reward and punishment, we observed clear auditory responses from the cholinergic neurons, which exhibited rapid learning-induced plasticity, suggesting that BF may provide a key instructive signal to drive adaptive plasticity in ACtx

Music and language comprehension in the brain

Contains fulltext : 166652.pdf (publisher's version ) (Open Access)Radboud University, 10 februari 2017Promotor : Hagoort, P. Co-promotor : Willems, R.M.236 p

Sound processing in the mouse auditory cortex: organization, modulation, and transformation

The auditory system begins with the cochlea, a frequency analyzer and signal amplifier with exquisite precision. As neural information travels towards higher brain regions, the encoding becomes less faithful to the sound waveform itself and more influenced by non-sensory factors such as top-down attentional modulation, local feedback modulation, and long-term changes caused by experience. At the level of auditory cortex (ACtx), such influences exhibit at multiple scales from single neurons to cortical columns to topographic maps, and are known to be linked with critical processes such as auditory perception, learning, and memory. How the ACtx integrates a wealth of diverse inputs while supporting adaptive and reliable sound representations is an important unsolved question in auditory neuroscience. This dissertation tackles this question using the mouse as an animal model. We begin by describing a detailed functional map of receptive fields within the mouse ACtx. Focusing on the frequency tuning properties, we demonstrated a robust tonotopic organization in the core ACtx fields (A1 and AAF) across cortical layers, neural signal types, and anesthetic states, confirming the columnar organization of basic sound processing in ACtx. We then studied the bottom-up input to ACtx columns by optogenetically activating the inferior colliculus (IC), and observed feedforward neuronal activity in the frequency-matched column, which also induced clear auditory percepts in behaving mice. Next, we used optogenetics to study layer 6 corticothalamic neurons (L6CT) that project heavily to the thalamus and upper layers of ACtx. We found that L6CT activation biases sound perception towards either enhanced detection or discrimination depending on its relative timing with respect to the sound, a process that may support dynamic filtering of auditory information. Finally, we optogenetically isolated cholinergic neurons in the basal forebrain (BF) that project to ACtx and studied their involvement in columnar ACtx plasticity during associative learning. In contrast to previous notions that BF just encodes reward and punishment, we observed clear auditory responses from the cholinergic neurons, which exhibited rapid learning-induced plasticity, suggesting that BF may provide a key instructive signal to drive adaptive plasticity in ACtx

The effects of emotionally salient unimodal and multimodal stimuli on low-level visual perception

Sensory information can both impair and enhance low-level visual feature processing, and this can be significantly modulated depending on the whether this information matches the visual sensory modality. Emotionally significant visual and auditory stimuli can have opposing effects on attention. While task-irrelevant emotionally salient visual stimuli can often impair task attention, task-irrelevant emotionally salient auditory stimuli have been shown to enhance aspects of attention. To date, no study has directly compared how emotionally salient information presented to different sensory modalities can affect low-level vision. Using Gabor patches of differing contrasts to measure the threshold of visual perception, we hypothesized that emotionally salient visual stimuli would impair low-level vision, while emotionally salient auditory stimuli would enhance low-level vision. We found that sensory modulation may be dependant on matched sensory domain presentation, as visual emotional stimuli impaired low-level vision, but emotional auditory stimuli did not affect low-level vision

An experimental examination of psychophysical methods for studying the perception of binaural repetitive transients

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Cortical state dynamics during sensory decision-making

Cortical states, defined as the dynamics of cortical neural activity on the timescale of seconds or more, vary during different behavioural states. Originally associated mainly with the sleep-wake cycle, it is now recognised that cortical states present subtle changes during waking that reflect the cognitive and behavioural demands an individual is pursuing. Therefore, it has been suggested that attention leads to a desynchronised cortical state, characterised by the absence of low frequency oscillations, which is thought to improve the information processing of the object of interest and thereby improve performance in attention demanding tasks. To maximise the beneficial effects of desynchronisation, it has been proposed that this state should occur locally, as this may spot-light the attended feature. I investigated this hypothesis by asking whether attending to a specific sensory modality leads to local desynchronisation of the sensory cortex of the modality being used. I trained mice to perform visual and auditory decision making tasks, and assessed cortical state through spectral analysis of widefield calcium signals. Genetically encoded calcium indicators were expressed in cortical excitatory neurons, and their activity was imaged simultaneously across cortex while the animals were performing the different tasks. Cortical states correlated with task engagement rather than with task performance, and this effect was global. Unexpectedly, the biggest desynchronisation was seen in somatosensory cortex in all tasks, and there was along lasting effect of reward. These effects could not be explained by movement or pupil diameter, a commonly used measure of arousal. Furthermore, desynchronisation correlated with reaction time. Thus, variations in cortical state closely relate to changes in task engagement, demands and outcome. This suggests that desynchronization is not a causal effect of attention that improves performance, but instead may be a cognitive state related to preparing rapid and coordinated responses to sensory stimuli