Cells In Primary Auditory Cortex Research Articles

Age-related changes in excitatory and inhibitory intra-cortical circuits in auditory cortex of C57Bl/6 mice

A common impairment in aging is age-related hearing loss (presbycusis), which manifests as impaired spectrotemporal processing. Aging is accompanied by alteration in normal inhibitory (GABA) neurotransmission, and changes in excitatory (NMDA and AMPA) synapses in the auditory cortex (ACtx). However, the circuits affected by these synaptic changes remain unknown. Mice of the C57Bl/6J strain show premature age-related hearing loss and changes in functional responses in ACtx. We thus investigated how auditory cortical microcircuits change with age by comparing young (∼ 6 weeks) and aged (>1 year old) C57Bl/6J mice. We performed laser scanning photostimulation (LSPS) combined with whole-cell patch clamp recordings from Layer (L) 2/3 cells in primary auditory cortex (A1) of young adult and aged C57Bl/6J mice. We found that L2/3 cells in aged C57Bl/6J mice display functional hypoconnectivity of both excitatory and inhibitory circuits. Compared to cells from young C57Bl/6 mice, cells from aged C57Bl/6J mice have fewer excitatory connections with weaker connection strength. Whereas young adult and aged C57Bl/6J mice have similar amounts of inhibitory connections, the strength of local inhibition is weaker in the aged group. We confirmed these results by recording miniature excitatory (mEPSCs) and inhibitory synaptic currents (mIPSCs). Our results suggest a specific reduction in excitatory and inhibitory intralaminar cortical circuits in aged C57Bl/6J mice compared with young adult animals. We speculate that these unbalanced changes in cortical circuits contribute to the functional manifestations of age-related hearing loss.

Descending Projections from Extrastriate Visual Cortex Modulate Responses of Cells in Primary Auditory Cortex

Primary sensory cortical responses are modulated by the presence or expectation of related sensory information in other modalities, but the sources of multimodal information and the cellular locus of this integration are unclear. We investigated the modulation of neural responses in the murine primary auditory cortical area Au1 by extrastriate visual cortex (V2). Projections from V2 to Au1 terminated in a classical descending/modulatory pattern, with highest density in layers 1, 2, 5, and 6. In brain slices, whole-cell recordings revealed long latency responses to stimulation in V2L that could modulate responses to subsequent white matter (WM) stimuli at latencies of 5-20 ms. Calcium responses imaged in Au1 cell populations showed that preceding WM with V2L stimulation modulated WM responses, with both summation and suppression observed. Modulation of WM responses was most evident for near-threshold WM stimuli. These data indicate that corticocortical projections from V2 contribute to multimodal integration in primary auditory cortex.

Columnar transformation of neural response to time-varying sounds in auditory cortex

Event Abstract Back to Event Columnar transformation of neural response to time-varying sounds in auditory cortex Poppy Crum1* and Xiaoqin Wang1 1 Johns Hopkins School of Medicine , United States The neural representation of time-varying signals is of particular importance to our understanding of complex and biologically important sounds such as speech and music. How sub-cortical and cortical regions differentially encode temporal patterns of acoustic stimuli offers insight to the crucial properties of the stimulus being represented as well as the functional role of the neural region. It is well known that the neural representation of time-varying signals in most sub-cortical regions is time-locked to stimulus features. In contrast, previous studies of awake primate auditory cortex have shown both neurons with stimulus-synchronized phasic responses as well as neurons with non-synchronized tonic responses (Lu et al, 2001). Here, we show that in the awake marmoset monkey a central stage in the cortical transformation to a firing rate-based response occurs across the cortical laminae. Neurons in upper cortical laminae show both weaker synchronization than neurons in middle thalamo-recipient laminae (layer IIIb/IV), as well as a significant shift in the percentage of neurons responsive to time-varying sounds but having no clear time-locked response features. Moreover, when the percentage of cells in primary-auditory cortex showing non-synchronized, responses is compared with previous studies of lower and higher stages in the auditory pathway, the role of within column, cross-laminar transformations in forming or enhancing the non-synchronized response pattern is evident. Preliminary models are proposed of within-column shifts in inhibition and excitation to account for cross-laminar transformations from synchronized to non-synchronized response patterns. In our experiments, laminar location of single units was identified through registration with the current-source-density (CSD) measured within the same penetration. All measurements of the CSD were generated from local-field-potential (LFP) recordings made across depth and spanning the cortical laminae using the same tungsten electrode used to record single-unit responses. A shift to a firing rate-based representation of time varying signals in upper cortical laminae suggests a change in the stimulus features critical to encoding at successively higher processing stages in auditory cortex. Conference: Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010. Presentation Type: Poster Presentation Topic: Poster session II Citation: Crum P and Wang X (2010). Columnar transformation of neural response to time-varying sounds in auditory cortex. Front. Neurosci. Conference Abstract: Computational and Systems Neuroscience 2010. doi: 10.3389/conf.fnins.2010.03.00302 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 07 Mar 2010; Published Online: 07 Mar 2010. * Correspondence: Poppy Crum, Johns Hopkins School of Medicine, Baltimore, United States, poppy@jhmi.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Poppy Crum Xiaoqin Wang Google Poppy Crum Xiaoqin Wang Google Scholar Poppy Crum Xiaoqin Wang PubMed Poppy Crum Xiaoqin Wang Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Stimulus-invariant processing and spectrotemporal reverse correlation in primary auditory cortex

The spectrotemporal receptive field (STRF) provides a versatile and integrated, spectral and temporal, functional characterization of single cells in primary auditory cortex (AI). In this paper, we explore the origin of, and relationship between, different ways of measuring and analyzing an STRF. We demonstrate that STRFs measured using a spectrotemporally diverse array of broadband stimuli-such as dynamic ripples, spectrotemporally white noise, and temporally orthogonal ripple combinations (TORCs)-are very similar, confirming earlier findings that the STRF is a robust linear descriptor of the cell. We also present a new deterministic analysis framework that employs the Fourier series to describe the spectrotemporal modulations contained in the stimuli and responses. Additional insights into the STRF measurements, including the nature and interpretation of measurement errors, is presented using the Fourier transform, coupled to singular-value decomposition (SVD), and variability analyses including bootstrap. The results promote the utility of the STRF as a core functional descriptor of neurons in AI.

A biophysical model of frequency-sweep selectivity in primary auditory cortex

Cells in primary auditory cortex respond preferably to frequency sweeps of a certain rate and direction. In a model by Fishbach et al. [J. Neurophysiol. 90 (2003) 3663–3678], direction selective cells emerged through patterned thalamocortical projections. The thalamic inputs to the auditory cortex were modeled as time-varying firing rates without explicit spikes. We investigate the biophysical constraints for the emergence of direction selectivity using a model that includes spiking thalamic neurons. We find that directional selectivity can still be achieved for a broad range of parameter values using an architecture similar to that proposed previously for visual cortex models. Furthermore, recurrent connections could improve the directional selectivity of the neurons.

Temporal Nonlinearity During Recovery From Sequential Inhibition by Neurons in the Cat Primary Auditory Cortex

Auditory stimuli occur most often in sequences rather than in isolation. It is therefore necessary to understand how responses to sounds occurring in sequences differ from responses to isolated sounds. Cells in primary auditory cortex (AI) respond to a large set of binaural stimuli when presented in isolation. The set of responses to such stimuli presented at one frequency comprises a level response area. A preceding binaural stimulus can reduce the size and magnitude of level response areas of AI cells. The present study focuses on the effects of the time interval between a preceding stimulus and the stimuli of a level response area in pentobarbital-anesthetized cats. After the offset of a preceding stimulus, the ability of AI cells to respond to succeeding stimuli varies dynamically in time. At short interstimulus intervals (ISI), a preceding stimulus can completely inhibit responses to succeeding stimuli. With increasing ISIs, AI cells respond first to binaural stimuli that evoke the largest responses in the control condition, i.e., not preceded by a stimulus. Recovery rate is nonlinear across the level response area; responses to these most-effective stimuli recover to 70% of control on average 187 ms before responses to other stimuli recover to 70% of their control sizes. During the tens to hundreds of milliseconds that a level response area is reduced in size and magnitude, the selectivity of AI cells is increased for stimuli that evoke the largest responses. This increased selectivity results from a temporal nonlinearity in the recovery of the level response area which protects responses to the most effective binaural stimuli. Thus in a sequence of effective stimuli, a given cell will respond selectively to only those stimuli that evoke a strong response when presented alone.

The cellular origin of corticofugal projections to the superior olivary complex in the rat

Corticofugal pathways originating in auditory cortex innervate most subcortical auditory nuclei in the ascending pathway [ Auditory Neurosci. 1 (1995) 287–308; J. Comp. Neurol. 371 (1996) 15–40]. Our goal is to determine if these projections arise from the same neurons or if different neurons project to each of the separate structures. We also seek to identify the layers and fields of auditory cortex from which these neurons originate. In the present study, we answer these questions with respect to the projections to the superior olivary complex (SOC). Fluorescent retrograde tracers, Fast Blue (FB) or Diamidino Yellow (DiY), were injected into the SOC and the pattern of labeled cells was determined in temporal neocortex. We also injected FB into the granule cell domain (GCD) of the cochlear nucleus. Cortical projections to the GCD derive exclusively from layer V pyramidal cells in primary auditory cortex [ Brain Res. 706 (1996) 97–102]. Thus the pattern of labeling produced by injections in the GCD provided a reference for interpreting the labeling after SOC injections. Layer V pyramidal cells project to the SOC, and these neurons were distributed bilaterally in primary and secondary areas of auditory cortex. The projections to the SOC from primary auditory cortex are predominantly uncrossed, whereas those from secondary auditory cortex are nearly equal for the two hemispheres. In animals that received injections of FB in the GCD and DiY in the SOC, cells labeled by each injection had a different laminar distribution and very few cells were double labeled. These data suggest that the cortical pathways ending in the cochlear nucleus and SOC are largely independent. We discuss the implications of these findings with respect to the multifunctional nature of the SOC in brainstem auditory processing.

Visual projections routed to the auditory pathway in ferrets: receptive fields of visual neurons in primary auditory cortex

How does cortex that normally processes inputs from one sensory modality respond when provided with input from a different modality? We have addressed such a question with an experimental preparation in which retinal input is routed to the auditory pathway in ferrets. Following neonatal surgical manipulations, a specific population of retinal ganglion cells is induced to innervate the auditory thalamus and provides visual input to cells in auditory cortex (Sur et al., 1988). We have now examined in detail the visual response properties of single cells in primary auditory cortex (A1) of these rewired animals and compared the responses to those in primary visual cortex (V1) of normal animals. Cells in A1 of rewired animals differed from cells in normal V1: they exhibited larger receptive field sizes and poorer visual responsivity, and responded with longer latencies to electrical stimulation of their inputs. However, striking similarities were also found. Like cells in normal V1, A1 cells in rewired animals exhibited orientation and direction selectivity and had simple and complex receptive field organizations. Furthermore, the degree of orientation and directional selectivity as well as the proportions of simple, complex, and nonoriented cells found in A1 and V1 were very similar. These results have significant implications for possible commonalities in intracortical processing circuits between sensory cortices, and for the role of inputs in specifying intracortical circuitry.

Three-dimensional analysis of auditory-evoked potentials in rat neocortex

1. A 8 X 8-channel microelectrode array was used to map epicortical field potentials evoked by bilaterally presented click stimuli from a 8 X 8-mm2 area in the right parietotemporal neocortex of four rats. In two rats, a 16-channel microelectrode array was also inserted into primary auditory cortex to record the laminar profile of auditory evoked potentials (AEP). 2. The epicortical responses began with a positive-negative fast wave followed by a positive-negative slow wave, similar to the previously reported P1, N1, P2, N2 complex. Topographical distributions of the potentials at the peak of each of these waves were distinct, suggesting that they were produced by separate but overlapping populations of cells. 3. Laminar recording revealed the asynchronous participation of supragranular and infragranular pyramidal cells in the generation of the evoked-response complex. The surface-recorded P1 was primarily produced by supragranular cells and the N1, by infragranular cells. The P2 and N2 were produced by temporally overlapping contributions from both cell groups. 4. We conclude that middle-latency components of the AEP complex are produced by both sequential and parallel activation of subpopulations of pyramidal cells in primary auditory cortex.

Acoustic response characteristics of neurons in nonspecific areas of cat cerebral cortex

1. Acoustic properties of single neurons in pericruciate, anterior lateral, and medial suprasylvian "association" areas were studied in chloralose-anesthetized cats using sealed stimulating systems incorporating probe microphone assemblies. 2. A total of 652 cells were isolated. Approximately 70% of the cells in each area were responsive to acoustic stimulation, and the majority of these cells were also driven by visual and/or somatosensory stimulation. 3. Association cortex neurons responded to tone- or noise-burst stimulation with an onset response of 16--50 ms latency. The onset response was found to be followed by a long period of suppression in those cases in which spontaneous activity was sufficiently high for this to be detected. 4. The majority of 56 units for which detailed frequency-tuning data were obtained had broad, irregular tuning curves extending over 5--6 octaves or more. A small proportion of association cortex cells exhibited sharp tuning comparable to that obtained in control recordings from cells in primary auditory cortex (AI). Although a number of broadly tuned units were rather insensitive, many cells--both broadly and sharply tuned--were of comparable sensitivity to AI cells. 5. Of the association cortex cells examined for binaural properties, 95% received excitatory input from each ear, and the dominant mode of binaural interaction in these cells was one of occlusion. The occurrence of occlusion at suprathreshold intensities reflected a tendency for monoaural and binaural intensity functions to asymptote at the same level. 6. The broad tuning, lability, and polysensory convergence exhibited by association cortex cells are similar to those of the so-called auditory lemniscal adjunct system. However, the binaural properties of association cells differ significantly from those of both the lemniscal line and adjuct components of the auditory pathway. 7. The homogeneity of acoustic and polysensory input to the three association fields is compatible with their input being derived from the single subcortical nonspecific projection system (reticular formation and medial/intralaminar thalamus) postulated by previous investigators. However, both neuroanatomical and neurophysiological evidence suggest that the lemniscal adjunct system and certain areas of periauditory cortex might also contribute to this input.