scholarly journals Intracortical circuits amplify sound-evoked activity in primary auditory cortex following systemic injection of salicylate in the rat

2012 ◽  
Vol 108 (1) ◽  
pp. 200-214 ◽  
Author(s):  
Daniel Stolzberg ◽  
Michael Chrostowski ◽  
Richard J. Salvi ◽  
Brian L. Allman
Keyword(s):  
Auditory Cortex ◽  
Field Potential ◽  
Primary Auditory Cortex ◽  
High Dose ◽  
Response Type ◽  
Cochlear Function ◽  
Systemic Injection ◽  
Sound Levels ◽  
Intracortical Circuits ◽  
Lower Amplitude

A high dose of sodium salicylate temporarily induces tinnitus, mild hearing loss, and possibly hyperacusis in humans and other animals. Salicylate has well-established effects on cochlear function, primarily resulting in the moderate reduction of auditory input to the brain. Despite decreased peripheral sensitivity and output, salicylate induces a paradoxical enhancement of the sound-evoked field potential at the level of the primary auditory cortex (A1). Previous electrophysiologic studies have begun to characterize changes in thalamorecipient layers of A1; however, A1 is a complex neural circuit with recurrent intracortical connections. To describe the effects of acute systemic salicylate treatment on both thalamic and intracortical sound-driven activity across layers of A1, we applied current-source density (CSD) analysis to field potentials sampled across cortical layers in the anesthetized rat. CSD maps were normally characterized by a large, short-latency, monosynaptic, thalamically driven sink in granular layers followed by a lower amplitude, longer latency, polysynaptic, intracortically driven sink in supragranular layers. Following systemic administration of salicylate, there was a near doubling of both granular and supragranular sink amplitudes at higher sound levels. The supragranular sink amplitude input/output function changed from becoming asymptotic at approximately 50 dB to sharply nonasymptotic, often dominating the granular sink amplitude at higher sound levels. The supragranular sink also exhibited a significant decrease in peak latency, reflecting an acceleration of intracortical processing of the sound-evoked response. Additionally, multiunit (MU) activity was altered by salicylate; the normally onset/sustained MU response type was transformed into a primarily onset response type in granular and infragranular layers. The results from CSD analysis indicate that salicylate significantly enhances sound-driven response via intracortical circuits.

scholarly journals Rat primary auditory cortex is tuned exclusively to the contralateral hemifield

2013 ◽  
Vol 110 (9) ◽  
pp. 2140-2151 ◽  
Author(s):  
Justin D. Yao ◽  
Peter Bremen ◽  
John C. Middlebrooks
Keyword(s):  
Auditory Cortex ◽  
Sound Source ◽  
Cortical Neurons ◽  
Free Field ◽  
Primary Auditory Cortex ◽  
Homogeneous Population ◽  
Spatial Sensitivity ◽  
Spatial Tuning ◽  
Sound Levels

The rat is a widely used species for study of the auditory system. Psychophysical results from rats have shown an inability to discriminate sound source locations within a lateral hemifield, despite showing fairly sharp near-midline acuity. We tested the hypothesis that those characteristics of the rat's sound localization psychophysics are evident in the characteristics of spatial sensitivity of its cortical neurons. In addition, we sought quantitative descriptions of in vivo spatial sensitivity of cortical neurons that would support development of an in vitro experimental model to study cortical mechanisms of spatial hearing. We assessed the spatial sensitivity of single- and multiple-neuron responses in the primary auditory cortex (A1) of urethane-anesthetized rats. Free-field noise bursts were varied throughout 360° of azimuth in the horizontal plane at sound levels from 10 to 40 dB above neural thresholds. All neurons encountered in A1 displayed contralateral-hemifield spatial tuning in that they responded strongly to contralateral sound source locations, their responses cut off sharply for locations near the frontal midline, and they showed weak or no responses to ipsilateral sources. Spatial tuning was quite stable across a 30-dB range of sound levels. Consistent with rat psychophysical results, a linear discriminator analysis of spike counts exhibited high spatial acuity for near-midline sounds and poor discrimination for off-midline locations. Hemifield spatial tuning is the most common pattern across all mammals tested previously. The homogeneous population of neurons in rat area A1 will make an excellent system for study of the mechanisms underlying that pattern.

Sound frequency representation in primary auditory cortex is level tolerant for moderately loud, complex sounds

2011 ◽  
Vol 106 (2) ◽  
pp. 1016-1027 ◽  
Author(s):  
Martin Pienkowski ◽  
Jos J. Eggermont
Keyword(s):  
Auditory Cortex ◽  
Field Potential ◽  
Primary Auditory Cortex ◽  
Sound Level ◽  
Sound Frequency ◽  
Frequency Resolution ◽  
Neural Population ◽  
Complex Sounds ◽  
Individual Unit ◽  
Nonlinear Processing

The distribution of neuronal characteristic frequencies over the area of primary auditory cortex (AI) roughly reflects the tonotopic organization of the cochlea. However, because the area of AI activated by any given sound frequency increases erratically with sound level, it has generally been proposed that frequency is represented in AI not with a rate-place code but with some more complex, distributed code. Here, on the basis of both spike and local field potential (LFP) recordings in the anesthetized cat, we show that the tonotopic representation in AI is much more level tolerant when mapped with spectrotemporally dense tone pip ensembles rather than with individually presented tone pips. That is, we show that the tuning properties of individual unit and LFP responses are less variable with sound level under dense compared with sparse stimulation, and that the spatial frequency resolution achieved by the AI neural population at moderate stimulus levels (65 dB SPL) is better with densely than with sparsely presented sounds. This implies that nonlinear processing in the central auditory system can compensate (in part) for the level-dependent coding of sound frequency in the cochlea, and suggests that there may be a functional role for the cortical tonotopic map in the representation of complex sounds.

scholarly journals Level dependence of spatial processing in the primate auditory cortex

2012 ◽  
Vol 108 (3) ◽  
pp. 810-826 ◽  
Author(s):  
Yi Zhou ◽  
Xiaoqin Wang
Keyword(s):  
Auditory Cortex ◽  
Sound Field ◽  
Primary Auditory Cortex ◽  
Neural Mechanism ◽  
Stimulus Level ◽  
Sound Level ◽  
Broadband Noise ◽  
Spatial Tuning ◽  
Sound Levels ◽  
Tuning Width

Sound localization in both humans and monkeys is tolerant to changes in sound levels. The underlying neural mechanism, however, is not well understood. This study reports the level dependence of individual neurons' spatial receptive fields (SRFs) in the primary auditory cortex (A1) and the adjacent caudal field in awake marmoset monkeys. We found that most neurons' excitatory SRF components were spatially confined in response to broadband noise stimuli delivered from the upper frontal sound field. Approximately half the recorded neurons exhibited little change in spatial tuning width over a ∼20-dB change in sound level, whereas the remaining neurons showed either expansion or contraction in their tuning widths. Increased sound levels did not alter the percent distribution of tuning width for neurons collected in either cortical field. The population-averaged responses remained tuned between 30- and 80-dB sound pressure levels for neuronal groups preferring contralateral, midline, and ipsilateral locations. We further investigated the spatial extent and level dependence of the suppressive component of SRFs using a pair of sequentially presented stimuli. Forward suppression was observed when the stimuli were delivered from “far” locations, distant to the excitatory center of an SRF. In contrast to spatially confined excitation, the strength of suppression typically increased with stimulus level at both the excitatory center and far regions of an SRF. These findings indicate that although the spatial tuning of individual neurons varied with stimulus levels, their ensemble responses were level tolerant. Widespread spatial suppression may play an important role in limiting the sizes of SRFs at high sound levels in the auditory cortex.

Intracortical Pathways Determine Breadth of Subthreshold Frequency Receptive Fields in Primary Auditory Cortex

2004 ◽  
Vol 91 (6) ◽  
pp. 2551-2567 ◽  
Author(s):  
Simranjit Kaur ◽  
Ronit Lazar ◽  
Raju Metherate
Keyword(s):  
Receptive Field ◽  
Auditory Cortex ◽  
Receptive Fields ◽  
Field Potential ◽  
Primary Auditory Cortex ◽  
Response Threshold ◽  
Complex Stimuli ◽  
Cortical Receptive Fields ◽  
Local Field Potential Lfp ◽  
Integrated Responses

To examine the basis of frequency receptive fields in auditory cortex (ACx), we have recorded intracellular (whole cell) and extracellular (local field potential, LFP) responses to tones in anesthetized rats. Frequency receptive fields derived from excitatory postsynaptic potentials (EPSPs) and LFPs from the same location resembled each other in terms of characteristic frequency (CF) and breadth of tuning, suggesting that LFPs reflect local synaptic (including subthreshold) activity. Subthreshold EPSP and LFP receptive fields were remarkably broad, often spanning five octaves (the maximum tested) at moderate intensities (40–50 dB above threshold). To identify receptive-field features that are generated intracortically, we microinjected the GABAA receptor agonist muscimol (0.2–5.1 mM, 1–5 μl) into ACx. Muscimol dramatically reduced LFP amplitude and reduced receptive-field bandwidth, implicating intracortical contributions to these features but had lesser effects on CF response threshold or onset latency, suggesting minimal loss of thalamocortical input. Reversal of muscimol's inhibition preferentially at the recording site by diffusion from the recording pipette of the GABAA receptor antagonist picrotoxin (0.01–100 μM) disinhibited responses to CF stimuli more than responses to spectrally distant, non-CF stimuli. We propose that thalamocortical and intracortical pathways preferentially contribute to responses evoked by CF and non-CF stimuli, respectively, and that intracortical projections linking frequency representations determine the breadth of receptive fields in primary ACx. Broad, subthreshold receptive fields may distinguish ACx from subcortical auditory relay nuclei, promote integrated responses to spectrotemporally complex stimuli, and provide a substrate for plasticity of cortical receptive fields and maps.

scholarly journals Network Architecture, Receptive Fields, and Neuromodulation: Computational and Functional Implications of Cholinergic Modulation in Primary Auditory Cortex

2006 ◽  
Vol 96 (6) ◽  
pp. 2972-2983 ◽  
Author(s):  
Gabriel Soto ◽  
Nancy Kopell ◽  
Kamal Sen
Keyword(s):  
Auditory Cortex ◽  
Cortical Neurons ◽  
Network Architecture ◽  
Frequency Tuning ◽  
Receptive Fields ◽  
Primary Auditory Cortex ◽  
Physiological Data ◽  
Cholinergic Modulation ◽  
Tuning Curves ◽  
Intracortical Circuits

Two fundamental issues in auditory cortical processing are the relative importance of thalamocortical versus intracortical circuits in shaping response properties in primary auditory cortex (ACx), and how the effects of neuromodulators on these circuits affect dynamic changes in network and receptive field properties that enhance signal processing and adaptive behavior. To investigate these issues, we developed a computational model of layers III and IV (LIII/IV) of AI, constrained by anatomical and physiological data. We focus on how the local and global cortical architecture shape receptive fields (RFs) of cortical cells and on how different well-established cholinergic effects on the cortical network reshape frequency-tuning properties of cells in ACx. We identify key thalamocortical and intracortical circuits that strongly affect tuning curves of model cortical neurons and are also sensitive to cholinergic modulation. We then study how differential cholinergic modulation of network parameters change the tuning properties of our model cells and propose two different mechanisms: one intracortical (involving muscarinic receptors) and one thalamocortical (involving nicotinic receptors), which may be involved in rapid plasticity in ACx, as recently reported in a study by Fritz and coworkers.

scholarly journals Decoding sound level in the marmoset primary auditory cortex

2017 ◽  
Vol 118 (4) ◽  
pp. 2024-2033 ◽  
Author(s):  
Wensheng Sun ◽  
Ellisha N. Marongelli ◽  
Paul V. Watkins ◽  
Dennis L. Barbour
Keyword(s):  
Auditory Cortex ◽  
Auditory System ◽  
Primary Auditory Cortex ◽  
Sound Level ◽  
Central Auditory System ◽  
Sound Perception ◽  
Neuron Populations ◽  
Sound Levels ◽  
Real Neuron

Neurons that respond favorably to a particular sound level have been observed throughout the central auditory system, becoming steadily more common at higher processing areas. One theory about the role of these level-tuned or nonmonotonic neurons is the level-invariant encoding of sounds. To investigate this theory, we simulated various subpopulations of neurons by drawing from real primary auditory cortex (A1) neuron responses and surveyed their performance in forming different sound level representations. Pure nonmonotonic subpopulations did not provide the best level-invariant decoding; instead, mixtures of monotonic and nonmonotonic neurons provided the most accurate decoding. For level-fidelity decoding, the inclusion of nonmonotonic neurons slightly improved or did not change decoding accuracy until they constituted a high proportion. These results indicate that nonmonotonic neurons fill an encoding role complementary to, rather than alternate to, monotonic neurons. NEW & NOTEWORTHY Neurons with nonmonotonic rate-level functions are unique to the central auditory system. These level-tuned neurons have been proposed to account for invariant sound perception across sound levels. Through systematic simulations based on real neuron responses, this study shows that neuron populations perform sound encoding optimally when containing both monotonic and nonmonotonic neurons. The results indicate that instead of working independently, nonmonotonic neurons complement the function of monotonic neurons in different sound-encoding contexts.

scholarly journals Nicotinic neuromodulation in auditory cortex requires MAPK activation in thalamocortical and intracortical circuits

2012 ◽  
Vol 107 (10) ◽  
pp. 2782-2793 ◽  
Author(s):  
Irakli Intskirveli ◽  
Raju Metherate
Keyword(s):  
Auditory Cortex ◽  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Current Source ◽  
Primary Auditory Cortex ◽  
Mek Inhibitor ◽  
Mitogen Activated Protein Kinase ◽  
Evoked Responses ◽  
Intracortical Circuits ◽  
Sensory Evoked

Activation of nicotinic acetylcholine receptors (nAChRs) by systemic nicotine enhances sensory-cognitive function and sensory-evoked cortical responses. Although nAChRs mediate fast neurotransmission at many synapses in the nervous system, nicotinic regulation of cortical processing is neuromodulatory. To explore potential mechanisms of nicotinic neuromodulation, we examined whether intracellular signal transduction involving mitogen-activated protein kinase (MAPK) contributes to regulation of tone-evoked responses in primary auditory cortex (A1) in the mouse. Systemic nicotine enhanced characteristic frequency (CF) tone-evoked current-source density (CSD) profiles in A1, including the shortest-latency (presumed thalamocortical) current sink in layer 4 and longer-latency (presumed intracortical) sinks in layers 2–4, by increasing response amplitudes and decreasing response latencies. Microinjection of the MAPK kinase (MEK) inhibitor U0126 into the thalamus, targeting the auditory thalamocortical pathway, blocked the effect of nicotine on the initial (thalamocortical) CSD component but did not block enhancement of longer-latency (intracortical) responses. Conversely, microinjection of U0126 into supragranular layers of A1 blocked nicotine's effect on intracortical, but not thalamocortical, CSD components. Simultaneously with enhancement of CF-evoked responses, responses to spectrally distant (nonCF) stimuli were reduced, implying nicotinic “sharpening” of frequency receptive fields, an effect also blocked by MEK inhibition. Consistent with these physiological results, acoustic stimulation with nicotine produced immunolabel for activated MAPK in A1, primarily in layer 2/3 cell bodies. Immunolabel was blocked by intracortical microinjection of the nAChR antagonist dihydro-β-erythroidine, but not methyllycaconitine, implicating α4β2*, but not α7, nAChRs. Thus activation of MAPK in functionally distinct forebrain circuits—thalamocortical, local intracortical, and long-range intracortical—underlies nicotinic neuromodulation of A1.

scholarly journals Neural Response Properties of Primary, Rostral, and Rostrotemporal Core Fields in the Auditory Cortex of Marmoset Monkeys

2008 ◽  
Vol 100 (2) ◽  
pp. 888-906 ◽  
Author(s):  
Daniel Bendor ◽  
Xiaoqin Wang
Keyword(s):  
Auditory Cortex ◽  
Auditory Processing ◽  
Transfer Functions ◽  
Primary Auditory Cortex ◽  
Modulation Transfer ◽  
Response Properties ◽  
Sound Levels ◽  
Pure Tones ◽  
Functional Pathway ◽  
Marmoset Monkeys

The core region of primate auditory cortex contains a primary and two primary-like fields (AI, primary auditory cortex; R, rostral field; RT, rostrotemporal field). Although it is reasonable to assume that multiple core fields provide an advantage for auditory processing over a single primary field, the differential roles these fields play and whether they form a functional pathway collectively such as for the processing of spectral or temporal information are unknown. In this report we compare the response properties of neurons in the three core fields to pure tones and sinusoidally amplitude modulated tones in awake marmoset monkeys ( Callithrix jacchus). The main observations are as follows. ( 1) All three fields are responsive to spectrally narrowband sounds and are tonotopically organized. ( 2) Field AI responds more strongly to pure tones than fields R and RT. ( 3) Field RT neurons have lower best sound levels than those of neurons in fields AI and R. In addition, rate-level functions in field RT are more commonly nonmonotonic than in fields AI and R. ( 4) Neurons in fields RT and R have longer minimum latencies than those of field AI neurons. ( 5) Fields RT and R have poorer stimulus synchronization than that of field AI to amplitude-modulated tones. ( 6) Between the three core fields the more rostral regions (R and RT) have narrower firing-rate–based modulation transfer functions than that of AI. This effect was seen only for the nonsynchronized neurons. Synchronized neurons showed no such trend.

scholarly journals Simultaneous auditory agnosia: Systematic description of a new type of auditory segregation deficit following a right hemisphere lesion

2020 ◽  
Author(s):  
Emma Holmes ◽  
Nattawan Utoomprurkporn ◽  
Chandrashekar Hoskote ◽  
Jason D. Warren ◽  
Doris-Eva Bamiou ◽  
...  
Keyword(s):  
Auditory Cortex ◽  
Young Patient ◽  
Right Hemisphere ◽  
Causal Explanation ◽  
Primary Auditory Cortex ◽  
List Type ◽  
Cochlear Function ◽  
Speech In Noise ◽  
Auditory Agnosia ◽  
Music Streaming

AbstractWe investigated auditory processing in a young patient who experienced a single embolus causing an infarct in the right middle cerebral artery territory. This lead to damage to auditory cortex including planum temporale that spared medial Heschl’s gyrus, and included damage to the posterior insula and inferior parietal lobule. She first reported difficulty hearing all sounds, which fully recovered within days, but she subsequently reported chronic difficulties with segregating speech from noise and segregating elements of music. Clinical tests showed no evidence for abnormal cochlear function. Follow-up tests confirmed difficulties with auditory segregation in her left ear that spanned multiple domains, including speech-in-noise and music streaming. Testing with a stochastic figure-ground task—a way of estimating generic acoustic foreground and background segregation—demonstrated that this was also abnormal. This is the first demonstration of an acquired deficit in the segregation of complex acoustic patterns due to cortical damage, which we argue is a causal explanation for the symptomatic deficits in the segregation of speech and music. These symptoms are analogous to the visual symptom of simultaneous agnosia. Consistent with functional imaging studies on normal listeners, the work implicates non-primary auditory cortex. Further, the work demonstrates a (partial) lateralisation of the necessary anatomical substrate for segregation that has not been previously highlighted.HighlightsRare case of auditory agnosia in a young patient with a right-hemisphere infarctDamage affecting non-primary auditory cortex, but sparing primary auditory cortexGeneralised auditory segregation deficit, revealed by auditory figure-ground taskThis explains segregation deficits for speech-in-noise and music streamingThe deficit affects stimuli presented on the left

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