Victoria M Bajo
University of Oxford, DPAG, Department Member
Intracellular recordings in slice preparations of the basolateral amygdala were used to test which excitatory amino acid receptors mediate the excitatory postsynaptic potentials due to stimulation of the external capsule. These recordings... more
Intracellular recordings in slice preparations of the basolateral amygdala were used to test which excitatory amino acid receptors mediate the excitatory postsynaptic potentials due to stimulation of the external capsule. These recordings were also used to examine the action of muscarinic agonists on the evoked excitatory potentials. Intracellular recordings from amygdaloid pyramidal neurons revealed that carbachol (2-20 microM) suppressed, in a dose-dependent manner, excitatory postsynaptic responses evoked by stimulation of the external capsule (EC). This effect was blocked by atropine. The estimated effective concentration to produce half-maximal response (EC(50)) was 6.2 microM. Synaptic suppression was observed with no changes in the input resistance of the recorded cells, suggesting a presynaptic mechanism. In addition, the results obtained using the paired-pulse protocol provided additional support for a presynaptic action of carbachol. To identify which subtype of cholinergic receptors were involved in the suppression of the EPSP, four partially selective muscarinic receptor antagonists were used at different concentrations: pirenzepine, a compound with a similar high affinity for muscarinic M1 and M4 receptors; gallamine, a noncompetitive antagonist for M2; methoctramine, an antagonist for M2 and M4; and 4-diphenylacetoxy-N-methylpiperidine, a compound with similar high affinity for muscarinic receptors M1 and M3. None of them independently antagonized the suppressive effect of carbachol on the evoked EPSP completely, suggesting that more than one muscarinic receptor subtype is involved in the effect. These experiments provide evidence that in the amygdala muscarinic agonists block the excitatory synaptic response, mediated by glutamic acid, by acting on several types of presynaptic receptors.
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Research Interests: Art and Auditory Cortex
A unique feature of the auditory brainstem is the divergent/convergent nature of the path- ways from the auditory nerve to the inferior colliculus (IC, reviewed in Irvine, 1992). Some of the projections from the cochlear nucleus complex... more
A unique feature of the auditory brainstem is the divergent/convergent nature of the path- ways from the auditory nerve to the inferior colliculus (IC, reviewed in Irvine, 1992). Some of the projections from the cochlear nucleus complex to the IC are direct while others are indirect via the superior olivary complex and the nuclei of the lateral lemniscus (NLL). In these nuclei, sig- nificant monaural and binaural information are extracted from the auditory signal.
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For decades, the corticofugal descending projections have been anatomically well described but their functional role remains a puzzling question. In this review, we will first describe the contributions of neuronal networks in... more
For decades, the corticofugal descending projections have been anatomically well described but their functional role remains a puzzling question. In this review, we will first describe the contributions of neuronal networks in representing communication sounds in various types of degraded acoustic conditions from the cochlear nucleus to the primary and secondary auditory cortex. In such situations, the discrimination abilities of collicular and thalamic neurons are clearly better than those of cortical neurons although the latter remain very little affected by degraded acoustic conditions. Second, we will report the functional effects resulting from activating or inactivating corticofugal projections on functional properties of subcortical neurons. In general, modest effects have been observed in anesthetized and in awake, passively listening, animals. In contrast, in behavioral tasks including challenging conditions, behavioral performance was severely reduced by removing or transi...
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The non-lemniscal auditory cortex in ferrets: convergence of
Sensory disconnection from the environment is a hallmark of sleep and is crucial for sleep maintenance. It remains unclear, however, whether internally generated percepts—phantom percepts—may overcome such disconnection and, in turn, how... more
Sensory disconnection from the environment is a hallmark of sleep and is crucial for sleep maintenance. It remains unclear, however, whether internally generated percepts—phantom percepts—may overcome such disconnection and, in turn, how sleep and its effect on sensory processing and brain plasticity may affect the function of the specific neural networks underlying such phenomena. A major hurdle in addressing this relationship is the methodological difficulty to study sensory phantoms, due to their subjective nature and lack of control over the parameters or neural activity underlying that percept. Here, we explore the most prevalent phantom percept, subjective tinnitus—or tinnitus for short—as a model to investigate this. Tinnitus is the permanent perception of a sound with no identifiable corresponding acoustic source. This review offers a novel perspective on the functional interaction between brain activity across the sleep–wake cycle and tinnitus. We discuss characteristic fea...
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To form a coherent representation of the environment, the brain must integrate information across different senses. Such multisensory convergence is widespread at the level of the cortex, where it is thought to arise primarily from... more
To form a coherent representation of the environment, the brain must integrate information across different senses. Such multisensory convergence is widespread at the level of the cortex, where it is thought to arise primarily from corticocortical connections. Much less is known about the role of subcortical circuits in shaping the multisensory properties of cortical neurons. We show that sound-evoked activity in the mouse auditory cortex is widely suppressed by whisker stimulation. This suppression depends on the primary somatosensory cortex (S1), but surprisingly is implemented through a circuit linking S1 and the auditory thalamocortical system via the auditory midbrain. We also show that an additional, direct pathway exists from S1 to the medial sector of auditory thalamus, which facilitates auditory responses in neurons that do not project to the auditory cortex. The thalamus thus occupies a pivotal role in integrating multisensory signals by somatosensory top-down control of a...
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Neural adaptation enables sensory information to be represented optimally in the brain despite large fluctuations over time in the statistics of the environment. Auditory contrast gain control represents an important example, which is... more
Neural adaptation enables sensory information to be represented optimally in the brain despite large fluctuations over time in the statistics of the environment. Auditory contrast gain control represents an important example, which is thought to arise primarily from cortical processing. We find, however, that neurons in both the auditory thalamus and midbrain of mice show robust contrast gain control, and that this is implemented independently of cortical activity. Although neurons at each level exhibit contrast gain control to similar degrees, adaptation time constants become longer at later stages of the processing hierarchy, resulting in progressively more stable representations. We also show that auditory discrimination thresholds in human listeners compensate for changes in contrast, and that the strength of this perceptual adaptation can be predicted from physiological measurements. Contrast adaptation is therefore a robust property of both the subcortical and cortical auditor...
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doi: 10.3389/fncir.2013.00029 Patterns of convergence in the central nucleus of the inferior colliculus of the Mongolian gerbil: organization of inputs from the superior olivary complex in the low frequency representation
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doi: 10.3389/fnsys.2014.00188 Descending projections from auditory cortex to excitatory and inhibitory cells in the nucleus of the brachium of the inferior colliculus
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Los nucleos del lemnisco lateral (lln) son los nucleos menos conocidos de la via auditiva. Para conocer los limites de los lln, asi como su morfologia neuronal, hemos utilizado en 10 ratas albinas, el metodo de nisal y posterior analisis... more
Los nucleos del lemnisco lateral (lln) son los nucleos menos conocidos de la via auditiva. Para conocer los limites de los lln, asi como su morfologia neuronal, hemos utilizado en 10 ratas albinas, el metodo de nisal y posterior analisis morfometrico. En los lln distinguimos un nucleo dorsal (dll) y un nucleo ventral (vll). El limite entre ambos lo constituye la lamina de los lln, zona donde se produce un entrecruzamiento de fibras del ll, en lln describimos 6 tipos neuronales morfologica y estadisticamente diferentes. Hemos inyectado iontoforeticamente el trazador anterogrado pha-l, en los lln de 15 ratas para conocer las proyecciones referentes de estos nucleos. Asi, dll proyecta al dll contralateral a traves de la comisura de probst, al nucleo central y corteza externa del coliculo inferior (ic) bilateralmente (bl), a la corteza dorsal del ic ipsilateral (il), e ipsilateralmente al coliculo superior (sc), a la division medial del cuerpo geniculado medial (mg), y al complejo oliva...
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The precise encoding of temporal features of auditory stimuli by the mammalian auditory system is critical to the perception of biologically important sounds, including vocalizations, speech, and music. In this study, auditory... more
The precise encoding of temporal features of auditory stimuli by the mammalian auditory system is critical to the perception of biologically important sounds, including vocalizations, speech, and music. In this study, auditory gap-detection behavior was evaluated in adult pigmented ferrets (Mustelid putorius furo) using bandpassed stimuli designed to widely sample the ferret's behavioral and physiological audiogram. Animals were tested under positive operant conditioning, with psychometric functions constructed in response to gap-in-noise lengths ranging from 3 to 270 ms. Using a modified version of this gap-detection task, with the same stimulus frequency parameters, we also tested a cohort of normal-hearing human subjects. Gap-detection thresholds were computed from psychometric curves transformed according to signal detection theory, revealing that for both ferrets and humans, detection sensitivity was worse for silent gaps embedded within low-frequency noise compared with hi...
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Despite numerous studies of auditory cortical processing in the ferret (Mustela putorious), very little is known about the connections between the different regions of the auditory cortex that have been characterised cytoarchitectonically... more
Despite numerous studies of auditory cortical processing in the ferret (Mustela putorious), very little is known about the connections between the different regions of the auditory cortex that have been characterised cytoarchitectonically and physiologically. We examined the distribution of retrograde and anterograde labelling after injecting tracers into one or more regions of ferret auditory cortex. Injections of different tracers at frequency-matched locations in the core areas, the primary auditory cortex (A1) and anterior auditory field (AAF), of the same animal revealed the presence of reciprocal connections with overlapping projections to and from discrete regions within the posterior pseudosylvian and suprasylvian fields (PPF and PSF), suggesting that these connections are frequency specific. In contrast, projections from the primary areas to the anterior dorsal field (ADF) on the anterior ectosylvian gyrus were scattered and non-overlapping, consistent with the non-tonotopi...
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The role of auditory cortex in sound localization and its recalibration by experience was explored by measuring the accuracy with which ferrets turned toward and approached the source of broadband sounds in the horizontal plane. In one... more
The role of auditory cortex in sound localization and its recalibration by experience was explored by measuring the accuracy with which ferrets turned toward and approached the source of broadband sounds in the horizontal plane. In one group, large bilateral lesions were made of the middle ectosylvian gyrus, where the primary auditory cortical fields are located, and part of the anterior and/or posterior ectosylvian gyrus, which contain higher-level fields. In the second group, the lesions were intended to be confined to primary auditory cortex (A1). The ability of the animals to localize noise bursts of different duration and level was measured before and after the lesions were made. A1 lesions produced a modest disruption of approach-to-target responses to short-duration stimuli (<500 ms) on both sides of space, whereas head orienting accuracy was unaffected. More extensive lesions produced much greater auditory localization deficits, again primarily for shorter sounds. In thes...
Research Interests: Psychology, Electrophysiology, Magnetoencephalography, Neurophysiology, Medicine, and 15 moreLearning, Cues, Female, Animals, Male, Neuronal Plasticity, Head Movements, Neural pathways, Auditory Cortex, Ferrets, Sound Localization, Acoustic Stimulation, Psychomotor Performance, Psychology and Cognitive Sciences, and Medical and Health Sciences
Research Interests: Neuroscience, Cognitive Science, Algorithms, Information Theory, Electroencephalography, and 15 moreVisual Cortex, Evoked Potentials, Cerebral Cortex, Multisensory Integration, Animals, Visual, Parietal Lobe, Visual Fields, Ferret, Cross-modal Processing, Auditory Cortex, Ferrets, Neurosciences, Acoustic Stimulation, and photic stimulation
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cholinergic basal forebrain in the ferret and its inputs to the auditory cortex
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Neural adaptation enables sensory information to be represented optimally in the brain despite large fluctuations over time in the statistics of the environment. Auditory contrast gain control represents an important example, which is... more
Neural adaptation enables sensory information to be represented optimally in the brain despite large fluctuations over time in the statistics of the environment. Auditory contrast gain control represents an important example, which is thought to arise primarily from cortical processing. Here we show that neurons in the auditory thalamus and midbrain of mice show robust contrast gain control, and that this is implemented independently of cortical activity. Although neurons at each level exhibit contrast gain control to similar degrees, adaptation time constants become longer at later stages of the processing hierarchy, resulting in progressively more stable representations. We also show that auditory discrimination thresholds in human listeners compensate for changes in contrast, and that the strength of this perceptual adaptation can be predicted from physiological measurements. Contrast adaptation is therefore a robust property of both the subcortical and cortical auditory system a...
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Ray Guillery was a neuroscientist known primarily for his ground-breaking studies on the development of the visual pathways and subsequently on the nature of thalamocortical processing loops. The legacy of his work, however, extends well... more
Ray Guillery was a neuroscientist known primarily for his ground-breaking studies on the development of the visual pathways and subsequently on the nature of thalamocortical processing loops. The legacy of his work, however, extends well beyond the visual system. Thanks to Ray Guillery's pioneering anatomical studies, the ferret has become a widely used animal model for investigating the development and plasticity of sensory processing. This includes our own work on the auditory system, where experiments in ferrets have revealed the role of sensory experience during development in shaping the neural circuits responsible for sound localization, as well as the capacity of the mature brain to adapt to changes in inputs resulting from hearing loss. Our research has also built on Ray Guillery's ideas about the possible functions of the massive descending projections that link sensory areas of the cerebral cortex to the thalamus and other subcortical targets, by demonstrating a ro...
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Feedback signals from the primary auditory cortex (A1) can shape the receptive field properties of neurons in the ventral division of the medial geniculate body (MGBv). However, the behavioral significance of corticothalamic modulation is... more
Feedback signals from the primary auditory cortex (A1) can shape the receptive field properties of neurons in the ventral division of the medial geniculate body (MGBv). However, the behavioral significance of corticothalamic modulation is unknown. The aim of this study was to elucidate the role of this descending pathway in the perception of complex sounds. We tested the ability of adult female ferrets to detect the presence of a mistuned harmonic in a complex tone using a positive conditioned go/no-go behavioral paradigm before and after the input from layer VI in A1 to MGBv was bilaterally and selectively eliminated using chromophore-targeted laser photolysis. MGBv neurons were identified by their short latencies and sharp tuning curves. They responded robustly to harmonic complex tones and exhibited an increase in firing rate and temporal pattern changes when one frequency component in the complex tone was mistuned. Injections of fluorescent microbeads conjugated with a light-sen...
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The harmonic structure of sounds is an important grouping cue in auditory scene analysis. The ability of ferrets to detect mistuned harmonics was measured using a go/no-go task paradigm. Psychometric functions plotting sensitivity as a... more
The harmonic structure of sounds is an important grouping cue in auditory scene analysis. The ability of ferrets to detect mistuned harmonics was measured using a go/no-go task paradigm. Psychometric functions plotting sensitivity as a function of degree of mistuning were used to evaluate behavioral performance using signal detection theory. The mean (± standard error of the mean) threshold for mistuning detection was 0.8 ± 0.1 Hz, with sensitivity indices and reaction times depending on the degree of mistuning. These data provide a basis for investigation of the neural basis for the perception of complex sounds in ferrets, an increasingly used animal model in auditory research.
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Sound localization is a computational process accomplished along the auditory pathway. Once the acoustic information received at each ear is analyzed independently (monaural cues) and comparatively (binaural cues), those cues are... more
Sound localization is a computational process accomplished along the auditory pathway. Once the acoustic information received at each ear is analyzed independently (monaural cues) and comparatively (binaural cues), those cues are integrated to generate a coherent spatial percept. Using adult ferrets trained by positive conditioning in a spatial task, we aimed to study the role of the auditory cortex in the ability to localize sounds under both normal hearing and monaurally occluded conditions, the latter of which requires a reinterpretation of the values of the localization cues. Sound localization deficits were found after lesion or inactivation of the different auditory cortical regions, thereby indicating their participation in spatial processing. The differential impairments found in the approach-to-target and in the head movement responses reveal the complex relationship between cortex and midbrain which are putatively responsible for the voluntary and reflexive aspects of loca...
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The activity elicited by electrical stimulation of the cochlea in the auditory pathway was assessed in an animal model of cochlear implants on the basis of the induction of the immediate early gene c-fos and single neuron recordings.... more
The activity elicited by electrical stimulation of the cochlea in the auditory pathway was assessed in an animal model of cochlear implants on the basis of the induction of the immediate early gene c-fos and single neuron recordings. Electrical stimulation of the cochlea induced Fos-like immunoreactivity in the cochlear nucleus, mainly in its dorsal nucleus, in the superior olivary complex, in the lateral lemniscus, but not in the central nucleus of the inferior colliculus, the main relay nucleus in the auditory midbrain. However, single unit recordings from the inferior colliculus, ipsilateral and contralateral to the electrically stimulated cochlea, showed clear responses of single neurons, reminiscent of those elicited by acoustic stimulation. These findings provide immunocytochemical and electrophysiological evidence that the various nuclei of the auditory pathway are activated by electrical stimulation of the cochlea.
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The aim of the present study was to characterize the discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the rat. In the absence of acoustic stimulation, two types of spontaneous discharge... more
The aim of the present study was to characterize the discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the rat. In the absence of acoustic stimulation, two types of spontaneous discharge patterns were observed: units tended to fire in a bursting or in a nonbursting mode. The distribution of units in the DNLL based on spontaneous firing rate followed a rostrocaudal gradient: units with high spontaneous rates were most commonly located in the rostral part of the DNLL, whereas in the caudal part units had lower spontaneous discharge rates. The most common response pattern of DNLL units to 200 ms binaural noise bursts contained a prominent onset response followed by a lower but steady-state response and an inhibitory response in the early-off period. Thresholds of response to noise bursts were on average higher for DNLL units than for units recorded in the inferior colliculus under the same experimental conditions. The DNLL units were arranged according to a mediolateral sensitivity gradient with the lowest threshold units in the most lateral part of the nucleus. In the rat, as in other mammals, the most common DNLL binaural input type was an excitatory response to contralateral ear stimulation and inhibitory response to ipsilateral ear stimulation (EI type). Pure tone bursts were in general a more effective stimulus compared to noise bursts. Best frequency (BF) was established for 97 DNLL units and plotted according to their spatial location. The DNLL exhibits a loose tonotopic organization, where there is a concentric pattern with high BF units located in the most dorsal and ventral parts of the DNLL and lower BF units in the middle part of the nucleus.
Research Interests: Cognitive Science, Animal Behavior, Noise, Animals, Neurons, and 13 moreSteady state, Rats, Wistar Rats, Auditory Threshold, Action Potentials, Single Unit Recording, Neurosciences, Extracellular Space, Inferior Colliculus, Spontaneous Activity, Functional Laterality, Brain stem, and Acoustic Stimulation
The harmonic structure of sounds is an important grouping cue in auditory scene analysis. The ability of ferrets to detect mistuned harmonics was measured using a go/no-go task paradigm. Psychometric functions plotting sensitivity as a... more
The harmonic structure of sounds is an important grouping cue in auditory scene analysis. The ability of ferrets to detect mistuned harmonics was measured using a go/no-go task paradigm. Psychometric functions plotting sensitivity as a function of degree of mistuning were used to evaluate behavioral performance using signal detection theory. The mean (± standard error of the mean) threshold for mistuning detection was 0.8 ± 0.1 Hz, with sensitivity indices and reaction times depending on the degree of mistuning. These data provide a basis for investigation of the neural basis for the perception of complex sounds in ferrets, an increasingly used animal model in auditory research.