Plasticity in the Auditory Cortex and Changes in Perceptual Discrimination After Nucleus Basalis Stimulation in Rats PDF Download

Author: Amanda Christine Reed
Publisher:
ISBN:
Category : Auditory pathways
Languages : en
Pages : 184

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Book Description
Humans and many other species have the capacity to learn and change their behavioral responses when they repeatedly practice a discrimination task. This change in behavior must be caused by changes in response properties of the nervous system. Understanding the relationship between learning and changes in neural responses has been an important field of study for the past twenty years. Numerous papers have observed correlations between plasticity in primary cortical areas and improved perceptual discrimination abilities, implying that this plasticity is the underlying cause of improved performance. However, a causal relationship cannot be proven unless plasticity is induced outside of a behavioral context. In the following dissertation I document the perceptual consequences of plasticity induced using stimulation of the nucleus basalis paired with auditory stimuli. The nucleus basalis is a deep-brain structure which releases acetylcholine onto the neocortex during behaviorally important events. Damage to this structure has been shown to impair both learning and plasticity, and stimulation during presentation of sensory stimuli produces plasticity which mimics the effects observed after behavioral training. We demonstrate for the first time that pairing nucleus basailis stimulation with a tone can alter learning and performance of a frequency discrimination task. We also document a pattern of plasticity after discrimination training and nucleus basalis stimulation which indicates that cortical plasticity in primary sensory areas may be important for learning but not performance of a discrimination task. Finally, we report a further possible source of cortical plasticity and behavioral improvement by showing that nucleus basalis-stimulation pairing can cause stimulus-specific plasticity in both primary and secondary cortical areas. The results of these studies reveal that cortical plasticity contributes to sensory discrimination and perceptual learning, and provide new insights about the relationship between cortical plasticity and continued performance of well-learned behavioral tasks.

Author: Michael P. Kilgard
Publisher:
ISBN:
Category :
Languages : en
Pages : 342

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Author: Hans Menning
Publisher: GRIN Verlag
ISBN: 3638340554
Category : Psychology
Languages : en
Pages : 128

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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: Vikram Jakkamsetti
Publisher:
ISBN:
Category : Auditory cortex
Languages : en
Pages : 182

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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: Hania Kover
Publisher:
ISBN:
Category :
Languages : en
Pages : 160

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Book Description
During an early epoch of development, the brain is highly adaptive to the stimulus environment. Repeatedly exposing young animals to a particular tone, for example, leads to an enlarged representation of that tone in primary auditory cortex. While the neural effects of simple, single-frequency tonal environments are well characterized, the principles that guide plasticity in complex tone environments, as well as the perceptual consequences of cortical plasticity, remain unclear. To address these questions, this dissertation documents the neural and perceptual effects of simple and complex manipulations to the early acoustic environment. First, I show that rearing rat pups in a multi-tone environment leads to complex primary cortical representational changes that are related to the statistical relationships between experienced sounds. Specifically, tones that occur together within short temporal sequences tend to be represented by the same groups of neurons, whereas tones that occur separately are represented separately. This suggests that the development of primary auditory cortical response properties is sensitive to higher-order statistical relationships between sounds. The observed neural changes are accompanied by perceptual changes. Discrimination ability for sounds that never occur together within temporal sequences is improved. Heightened perceptual sensitivity is correlated with heightened neuronal response contrasts. These results suggest that early experience-dependent neural changes can mediate perceptual changes that may be related to statistical learning. Finally, I develop and experimentally test a model of the relationship between cortical sensory representations and perception. The model suggests that cortical stimulus representations may function as the neural representation of previously encountered stimulus probabilities, and makes predictions about how changes in these representations should affect perception within a statistical inference framework. Preliminary behavioral results support the model predictions, suggesting that one function of early experience-dependent plasticity may be to internalize stimulus distributions to shape future perception and behavior.

Author: Jose Miguel Cisneros-Franco
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"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: Maryse Thomas
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"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: Laura Gillian Rosen
Publisher:
ISBN:
Category :
Languages : en
Pages : 152

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Book Description
Plasticity of synapses is not static across the lifespan. As the brain matures and ages, the ability of neurons to undergo structural and functional change becomes more limited. Further, there are a number of modulatory factors that influence the expression of synaptic plasticity. Here, three approaches were taken to examine and manipulate plasticity in the auditory thalamocortical system of rats. Using an in vivo preparation, long-term potentiation (LTP) and paired pulse (PP) responses were used as measures of long- and short-term plasticity, respectively. First, the effect of intracortical zinc application in the primary auditory cortex (A1) on LTP was examined. Following theta burst stimulation (TBS) of the medial geniculate nucleus (MGN), juvenile and middle-age rats, but not young adults, showed greater levels of LTP with zinc application relative to age-matched control animals. Next, PP responses were examined between rats reared in unaltered acoustic conditions and those reared in continuous white noise (WN) from postnatal day (PD) 5 to PD 50-60 (i.e., subjected to patterned sound deprivation). Rats reared in WN demonstrated less PP depression relative to controls, indicating that WN rearing alters short-term thalamocortical synaptic responses. Furthermore, control males showed no change in PP response following LTP induction, indicating a postsynaptic locus of LTP, whereas increased PP depression following LTP induction was seen in WN animals, suggestive of a presynaptic involvement in LTP. Finally, differences in plasticity between male and female rats were investigated, and the result of early WN exposure on both sexes was examined. Males and females did not show consistent differences in LTP expression; however WN exposure appeared to affect LTP of females less than their male counterparts. PP responses were then compared between WN-reared males and females, and no difference was found. This indicates that short-term plastic properties of auditory thalamocortical synapses between the sexes do not differ, even though plasticity on a longer time scale following sensory deprivation does indicate some difference. Together, the experiments summarized here identify some of the important factors that contribute to the regulation of short- and long-term synaptic plasticity in the central auditory system of the mammalian brain.

Author: Heesoo Kim
Publisher:
ISBN:
Category :
Languages : en
Pages : 94

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Book Description
The early acoustic environment plays a crucial role in how the brain represents sounds and how language phonemes are perceived. Human infants are born with the capacity to distinguish phonemes from virtually all languages, but very quickly change their perceptual ability to match that of their primary language. This has been described as the Perceptual Magnet Effect in humans, where phoneme tokens are perceived to be more similar than they physically are, leading to decreased discrimination ability. Early development is marked by distinct critical periods, when cortical regions are highly plastic and particularly sensitive to sensory input. These lasting alterations in cortical sensory representation may directly impact the perception of the external world. My thesis is comprised of three different studies, all of which investigate the role of the developmental acoustic environment on cortical representation and the behavioral consequence of altered cortical representation. Passive exposure to pure-tone pips during the auditory critical period can lead to over-representation of the exposure tone frequency in the primary auditory cortex (A1) of rats. This over-representation is associated with decreased discrimination ability of that frequency, similar to the Perceptual Magnet Effect in humans. Another hallmark of human language is categorical perception. Using a computational model of A1, I show that certain representation patterns (which may be achieved with passive exposure to two distinct pure-tone pips) in A1 can lead to categorical perception in rats. This suggests that cortical representation may be a mechanism that drives categorical perception. Rodents are socially vocal animals whose con-specific calls are often presented in bouts in the ultrasonic frequency range. These calls are vocalized at ethologically relevant repetition rates. I show that pure-tone pips that are presented at the ethological repetition rate (but not slower or faster rates) during the auditory critical period lead to over-representation of the pure-tone frequency. A certain subclass of ultrasonic vocalizations, the pup isolation calls, occurs during the auditory critical period. I show that there is over representation of ultrasonic vocalization frequencies in the rat A1. This preferential representation is experience-dependent and is associated with higher discrimination ability.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 298

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Book Description
Synaptic plasticity (long-term potentiation, LTP and long-term depression, LTD) plays an important role in processes of learning and memory formation. In order to provide a link between these neurophysiological and cognitive processes the following experiments were performed using behavioral, electrophysiological, and pharmacological in vivo methods in order to describe synaptic plasticity in the adult rat visual system after learning a simple visual discrimination task. Initially, a novel method is described providing a simple and noninvasive means to restrict visual input. Using a harness and face-mask for monocular occlusion, rats were trained in a monocular visual discrimination task using a Y-shaped water maze. Following learning, assessment of synaptic plasticity in the thalamocortical visual pathway found both general (changes in short-term plasticity in both cerebral hemispheres) and localized changes (greater LTP levels in the hemisphere contralateral to the open eye). The enhanced LTP in the primary visual cortex (V1) was blocked by an NR2B antagonist, suggesting that training resulted in changes in NMDA receptor expression or functioning. Next, the effectiveness of LTD stimulation protocols to elicit synaptic depression under in vivo conditions were assessed. Of several single-pulse induction protocols tested, only strong low frequency burst stimulation (SLFS) produced significant, but transient (~20 min) depression in V1 (not affected by blockade of NMDA or metabotrobic glutamate receptors). These data highlight the resistance of the thalamocortical visual system to undergo synaptic depression in vivo. To examine whether learning alters LTD induction, SLFS was delivered to the thalamocortical visual pathway or the V1-perirhinal cortex pathway following visual discrimination. Neither pathway exhibited changes in LTD following training, suggesting that the learning-induced LTP facilitation reflects an expansion of the synaptic modification range. Finally, the role of different populations of NMDA receptors (cortical vs. thalamic) in LTP induction in naïve and visually trained rats was examined. Surprisingly, naïve rats do not require activation of cortical NMDA receptors to express LTP, while LTP in trained rats involved the activation of both thalamic and cortical NMDA receptors. In summary, this thesis provides novel evidence for a metaplastic, training-induced up-regulation of LTP mechanisms in the thalamocortical visual system of adult rats.