Experience-dependent Plasticity in the Adult Rat Auditory Cortex Induced by Passive Exposure to White Noise PDF Download
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Author: Maryse Thomas Publisher: ISBN: Category : Languages : en Pages :
Book Description
"The ability of the brain to change in response to its external environment is known as experience-dependent plasticity. Robust experience-dependent plasticity is typically restricted to early stages of life, when developing neural circuits are readily shaped by passive sensory experience. In the auditory system, for example, exposing juvenile but not adult rats to pure tones produces a functional over-representation of the tone frequency in the cortical tonotopic map. Recent studies have revealed the continued potential for passive experience to induce robust plasticity in the adult brain, however. In particular, chronic exposures to uninformative or disruptive sounds, such as white noise, have been shown to alter experience-dependent plasticity in the adult auditory cortex, returning the brain to a more plastic and juvenile state. This phenomenon provides an opportunity to study unprecedented cortical plasticity late in life, yet also reveals the brain’s vulnerability to abnormal sensory environments. Tackling both issues, the present thesis uses white noise as a tool to probe experience-dependent plasticity in the adult rat auditory cortex in three studies. In the first study, passive exposures to non-traumatic white noise of varying amplitude modulation depths are used to show the importance of salient temporal inputs for mature auditory function. Exposure to unmodulated but not modulated noise induces juvenile-like plasticity and frequency over-representation in response to a second exposure to pure tones, demonstrating that white noise triggers plasticity by masking temporal inputs from the environment. Since greater functional representation is generally thought to improve perceptual discrimination, the hypothesis that noise-induced plasticity could be used to improve adult perceptual learning is tested in the second study. Contrary to our expectations, sound-exposed animals were worse at discriminating the over-represented frequency, demonstrating that increased functional representation is not sufficient to improve discrimination. Finally, the third study investigates the possibility that changes in neural activity induced by noise exposure could be indicative of maladaptive plasticity leading to aberrant or unwanted perceptual consequences. Common neural and behavioral correlates of the auditory disorders tinnitus and hyperacusis were assessed in noise-exposed animals. Evidence of hyperacusis in exposed rats suggests that noise exposure opens windows of plasticity that may be understood as windows of vulnerability to maladaptive plastic changes. The results presented in this thesis help to elucidate the mechanisms and perceptual consequences of noise-induced plasticity in the adult rat auditory cortex. They describe the profound impact of noise on brain structure and function, advance our present understanding of experience-dependent plasticity in sensory circuits, and demonstrate how sensory environments may powerfully influence the brain throughout life"--
Author: Maryse Thomas Publisher: ISBN: Category : Languages : en Pages :
Book Description
"The ability of the brain to change in response to its external environment is known as experience-dependent plasticity. Robust experience-dependent plasticity is typically restricted to early stages of life, when developing neural circuits are readily shaped by passive sensory experience. In the auditory system, for example, exposing juvenile but not adult rats to pure tones produces a functional over-representation of the tone frequency in the cortical tonotopic map. Recent studies have revealed the continued potential for passive experience to induce robust plasticity in the adult brain, however. In particular, chronic exposures to uninformative or disruptive sounds, such as white noise, have been shown to alter experience-dependent plasticity in the adult auditory cortex, returning the brain to a more plastic and juvenile state. This phenomenon provides an opportunity to study unprecedented cortical plasticity late in life, yet also reveals the brain’s vulnerability to abnormal sensory environments. Tackling both issues, the present thesis uses white noise as a tool to probe experience-dependent plasticity in the adult rat auditory cortex in three studies. In the first study, passive exposures to non-traumatic white noise of varying amplitude modulation depths are used to show the importance of salient temporal inputs for mature auditory function. Exposure to unmodulated but not modulated noise induces juvenile-like plasticity and frequency over-representation in response to a second exposure to pure tones, demonstrating that white noise triggers plasticity by masking temporal inputs from the environment. Since greater functional representation is generally thought to improve perceptual discrimination, the hypothesis that noise-induced plasticity could be used to improve adult perceptual learning is tested in the second study. Contrary to our expectations, sound-exposed animals were worse at discriminating the over-represented frequency, demonstrating that increased functional representation is not sufficient to improve discrimination. Finally, the third study investigates the possibility that changes in neural activity induced by noise exposure could be indicative of maladaptive plasticity leading to aberrant or unwanted perceptual consequences. Common neural and behavioral correlates of the auditory disorders tinnitus and hyperacusis were assessed in noise-exposed animals. Evidence of hyperacusis in exposed rats suggests that noise exposure opens windows of plasticity that may be understood as windows of vulnerability to maladaptive plastic changes. The results presented in this thesis help to elucidate the mechanisms and perceptual consequences of noise-induced plasticity in the adult rat auditory cortex. They describe the profound impact of noise on brain structure and function, advance our present understanding of experience-dependent plasticity in sensory circuits, and demonstrate how sensory environments may powerfully influence the brain throughout life"--
Author: Jennifer Lauren Hogsden Robinson Publisher: ISBN: Category : Languages : en Pages : 232
Book Description
Synaptic plasticity reflects the capacity of synapses to undergo changes in synaptic strength and connectivity, and is highly regulated by age and sensory experience. This thesis focuses on the characterization of synaptic plasticity in the primary auditory cortex (A1) of rats throughout development and following sensory deprivation. Initial experiments revealed an age-dependent decline in plasticity, as indicated by reductions in long-term potentiation (LTP). The enhanced plasticity of juvenile rats appeared to be mediated by NR2B subunits of the N-methyl-d-aspartate receptor (NMDAR), as NR2B antagonist application reduced LTP to adult-like levels in juveniles, yet had no effect in adults. The importance of sensory experience in mediating plasticity was revealed in experiments using white noise exposure, which is a sensory deprivation technique known to arrest cortical development in A1. Notably, adult rats reared in continuous white noise maintained more juvenile-like levels of LTP, which normalized upon subsequent exposure to an unaltered acoustic environment. The white noise-induced LTP enhancements also appeared to be mediated by NR2B subunits, as NR2B antagonists reversed these LTP enhancements in white noise-reared rats. Given the strong influence that sensory experience exerts on plasticity, additional experiments examined the effect of shorter episodes of white noise exposure on LTP in adult rats. Exposure to white noise during early postnatal life appeared to "prime" A1 for subsequent exposure in adulthood, resulting in enhanced LTP. The necessity of early-life exposure was evident, as repeated episodes of white noise in adulthood did not enhance plasticity. In older rats that typically no longer express LTP in A1, pharmacological methods to enhance plasticity were explored. Moderate LTP was observed in older rats with cortical zinc application, which may act through its antagonism of NR2A subunits of the NMDAR. Additionally, current source density and cortical silencing analyses were conducted to characterize the distinct peaks of field postsynaptic potentials recorded in A1, with the earlier and later peaks likely representing thalamocortical and intracortical synapses, respectively. Together, this thesis emphasizes the critical role of sensory experience in determining levels of cortical plasticity, and demonstrates strategies to enhance plasticity in the mature auditory cortex.
Author: Vikram Jakkamsetti Publisher: ISBN: Category : Auditory cortex Languages : en Pages : 182
Book Description
In an adult rat, we paired acoustic input with injections of Rolipram-a drug that increases cortical cAMP levels and observed that Rolipram increased the length of the cortex activated by the paired tone and induced primary cortex neurons to become more selective to the paired tone. In the third part of the dissertation I explored induction of experience-dependent plasticity using modulation of attentional mechanisms. It has been previously demonstrated that paying attention to a tone for a tone discrimination task stimulates the nucleus basalis to release cortical acetylcholine which activates muscarinic M1 receptors to increase the representation of that tone in the primary auditory cortex. We paired acoustic input with injections of M1 agonist Cevemiline and observed an increase in the length of the cortex corresponding to the acoustic input. The experiments in this dissertation attempt to understand experience dependent brain changes and use current understanding of the mechanisms of experience dependent plasticity to research drugs that could help improve neuronal processing for neuronal disorders.
Author: Hans Menning Publisher: GRIN Verlag ISBN: 3638340554 Category : Psychology Languages : en Pages : 128
Book Description
Doctoral Thesis / Dissertation from the year 2002 in the subject Psychology - Biological Psychology, grade: magna cum laude, University of Münster (Institute for Experimental Audiology), language: English, abstract: The motivation for this thesis came from the intriguing idea that we continuously restructure our brain through everyday learning. How can this highly complex, highly adaptive “learning device” change and reorganize itself all the time while keeping the illusion that we are constantly “ourselves”? The question is, whether learning has the power to trigger functional and structural changes in the brain. Several levels of thinking are involved in an interdisciplinary way. Thus, on a psychological level, 3 major topics enter this work: learning, memory and preconscious or pre-attentive perception and processing of information. Pre-attentive perception means that the subjects' attention and awareness is not mirrored in the neuronal response at a great deal. Learning is involved in this study as an improving discrimination of fine frequency and word duration differences; the latter was examined in a group of native and non-native speakers. Memory is referred to as sensory memory, a short-time memory trace that is established through the repetition of the same “standard” stimulus. In the auditory modality this has been termed “echoic memory”. A long, repetitive training engraves deep “traces” into the memory. The lifelong training of one’s native language results in a very fast and highly automated long-term memory access. On a neurophysiological level the main topics are plasticity and the reorganization of the underlying representational brain areas. Plastic changes on a molecular, synaptic and neuronal level and reorganization of cortical “maps” have been demonstrated abundantly in animal studies. On a physical level the measured magnetic fields and the calculation of the source parameters of their underlying neural generators are discussed in the light of the neurophysiological and psychological phenomena. Therefore, the aim of this dissertation thesis was, to transfer the insights of animal plasticity research onto the human brain and to draw a connection line between discrimination learning and the underlying neurophysiological changes. In a second step, these effects of discrimination learning are tested on speech perception.
Author: Publisher: ISBN: Category : Languages : en Pages : 140
Book Description
Neocortical architecture is established by both intrinsic, genetic factors and experience- dependent factors. Postnatal sensory experience plays a significant role in the maturation and refinement of cortical sensory fields, such as the primary auditory cortex (A1). In this thesis, I investigated the effects of manipulating postnatal acoustic experience on the functional and morphological properties of neurons in the thalamocortical auditory pathway of adult rats. In Experiment 1, I used two converging electrophysiological techniques to determine the effects of patterned acoustic deprivation (through exposure to continuous, moderate-level white noise; cWN) on the functional properties of neurons in the central auditory system. In Experiment 2, I used Golgi-Cox staining to visualize morphological correlates of experience-dependent changes in neuron functioning. Long- and short-term plasticity mediate synaptic strengthening in sensory cortices in response to postnatal sensory experience. I assessed levels of long-term plasticity (using long- term potentiation; LTP) and short-term plasticity (using paired-pulse facilitation/depression; PPF/PPD) in vivo (under deep urethane anesthesia) in the A1 of normally reared rats and rats reared in the absence of patterned acoustic input through cWN exposure. Rats reared under cWN showed significantly greater LTP of field postsynaptic potentials (fPSPs) for thalamocortical, but not intracortical synapses in A1 compared to age-matched controls, indicative of immature, more plastic synaptic connectivity. Both groups showed similar, moderate levels of PPD (across interstimulus intervals ranging from 25 to 1000 ms) prior to LTP induction. Across groups, PPD was significantly enhanced after LTP induction, indicative of a presynaptic component of thalamocortical LTP in A1. I also assessed the morphology of layer II/III pyramidal neurons in A1 using Golgi-Cox staining and two-dimensional neuron reconstruction. Morphological features, including dendritic length, arbor complexity, and spine density, did not differ significantly between rats reared under cWN and age-matched controls. Rats reared under cWN showed a significantly greater proportion of filopodia to mature spines on apical dendrites compared to age-matched controls. Together, these data indicate that patterned acoustic experience results in a reduction of plasticity in A1, indicative of more mature, hard-wired synaptic connectivity. Furthermore, LTP in A1 in vivo is mediated in part by presynaptic mechanisms, such as increases in transmitter release probability at thalamocortical synapses.
Author: Jose Miguel Cisneros-Franco Publisher: ISBN: Category : Languages : en Pages :
Book Description
"Neuroplasticity refers to the brain’s ability to modify its connections and function in response to experience. This experience-dependent plasticity is necessary for the acquisition of new abilities during early development or in adult life, and plays a crucial role in recovery after a neurological injury. During early developmental epochs known as critical periods (CPs), passive experience alone can have profound and long-lasting effects in cortical sensory representations. In contrast, plasticity in the adult brain occurs almost exclusively in the context of perceptual learning (PL); i.e., the process whereby attention and repetition lead to long-lasting improvements in stimulus detection or sensory discrimination.Whether it occurs as a result of passive experience, PL, or other experimental interventions, cortical plasticity ultimately entails a change in activity patterns driven by a shift in the local levels of excitation and inhibition. And although cortical inhibitory interneurons constitute a clear minority compared to the number of excitatory neurons, they are instrumental in regulating both juvenile and adult experience-dependent plasticity. This thesis consists of three experimental studies that addressed critical and interrelated knowledge gaps regarding the inhibitory regulating mechanisms of experience-dependent plasticity, both in the context of changes in the environment and during PL. Using the rat primary auditory cortex (A1) as a model, we combined electrophysiological, anatomical, chemogenetic, and behavioral methodologies to address each study’s main hypotheses. In the first study we examined the role of inhibition in A1 plasticity across the lifespan. We found that reduced cortical inhibition in older adults was associated with an increased but poorly regulated plasticity when compared to younger adults. In older brains, however, changes elicited by auditory stimulation and training were rapidly lost, suggesting that such increased plasticity might be detrimental, as the older brains were unable to consolidate these changes. Importantly, increasing inhibition artificially with clinically available drugs restored the stability of sensory representations and improved the retention of plastic changes associated with PL.In the second study, we turned our attention to parvalbumin-positive (PV+) cells, the most common type of inhibitory neurons in the brain. Bidirectional manipulation of PV+ cell activity affected neuronal spectral and sound intensity selectivity, and, in the case of PV+ interneuron inactivation, was mirrored by anatomical changes in PV and associated perineuronal net expression. In addition, we showed that the inactivation of PV+ interneurons is sufficient to reinstate CP plasticity in the adult auditory cortex. In the third study, we investigated the role of PV+ cells in auditory PL. As previously reported in other cortical areas, training was associated with a transient downregulation of PV expression during early stages of training. We then examined the effects of prolonged PV+ cell manipulation throughout the training period. Our results suggest that, although reduced PV+ cell function may facilitate early training-related modifications in cortical circuits, a subsequent increase in PV+ cell activity is needed to prevent further plastic changes and consolidate learning. Taken together, our findings underscore the importance of sustained inhibitory neurotransmission in ensuring high fidelity discrimination of sensory inputs and in maintaining the stability of sensory representations. Our behavioral studies further suggest that such stability is necessary for the consolidation of complex skills that are built on basic sensory representations. Finally, the experimental work presented in this thesis also highlights the potential of pharmacological and chemogenetic approaches for harnessing cortical plasticity with the ultimate goal of aiding recovery from brain injury or disease"--
Author: Jacob J. Bollinger Publisher: ISBN: Category : Languages : en Pages : 374
Book Description
These data demonstrate that the adult auditory cortex retains the capacity for receptive field, tonotopic-map, and response profile plasticity and that stimulus-paired LC activity plays an important role in remodeling the adult brain.
Author: Maryse Thomas
Author: Maryse Thomas
Author: Jennifer Lauren Hogsden Robinson
Author: Vikram Jakkamsetti
Author: Theodore M. Moallem
Author: Hans Menning
Author: Raluca Moucha
Author: 
Author: Jose Miguel Cisneros-Franco
Author: Jacob J. Bollinger
Author: Nick Swindale