Spectrotemporal receptive fields of neurons in cochlear nucleus of guinea pig

Spectrotemporal receptive fields (STRFs) [Hermes et al., Hear. Res. 5, 147-178, 1981] for neurons in the cochlear nuclei (CN) of guinea pig were estimated. Sixteen periodic segments of bandlimited, synthesized noise evoked replicable, distinctive period histograms for spike discharges. All driven units in the major divisions of the CN having their characteristic frequency (CF) within the noise bandlimits had unique STRFs for a given intensity of noise stimulation. The STRF maximum corresponded to the unit's CF, and details of the STRF patterns differed over CN divisions and response classes derived from tonebursts. The sizes of features in STRFs from this mammal appeared significantly smaller in their temporal and spectral extents than those reported in the torus semicircularis of an amphibian and were roughly comparable to the few units reported from cat ventral CN [Eggermont et al., Quart. Rev. Biophys. 16, 341-414, 1983], STRFs, as they are presently obtained, provide useful insight into some aspects of afferent processing and perhaps connectivity, but their interpretation is specific to the level of stimulation and limited by the need to choose a specific energy distribution to represent the stimulus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29402/1/0000475.pd

Loss of auditory sensitivity from inner hair cell synaptopathy can be centrally compensated in the young but not old brain

AbstractA dramatic shift in societal demographics will lead to rapid growth in the number of older people with hearing deficits. Poorer performance in suprathreshold speech understanding and temporal processing with age has been previously linked with progressing inner hair cell (IHC) synaptopathy that precedes age-dependent elevation of auditory thresholds. We compared central sound responsiveness after acoustic trauma in young, middle-aged, and older rats. We demonstrate that IHC synaptopathy progresses from middle age onward and hearing threshold becomes elevated from old age onward. Interestingly, middle-aged animals could centrally compensate for the loss of auditory fiber activity through an increase in late auditory brainstem responses (late auditory brainstem response wave) linked to shortening of central response latencies. In contrast, old animals failed to restore central responsiveness, which correlated with reduced temporal resolution in responding to amplitude changes. These findings may suggest that cochlear IHC synaptopathy with age does not necessarily induce temporal auditory coding deficits, as long as the capacity to generate neuronal gain maintains normal sound-induced central amplitudes

Bilateral Dorsal Cochlear Nucleus Lesions Prevent Acoustic-Trauma Induced Tinnitus in an Animal Model

Animal experiments suggest that chronic tinnitus (“ringing in the ears”) may result from processes that overcompensate for lost afferent input. Abnormally elevated spontaneous neural activity has been found in the dorsal cochlear nucleus (DCN) of animals with psychophysical evidence of tinnitus. However, it has also been reported that DCN ablation fails to reduce established tinnitus. Since other auditory areas have been implicated in tinnitus, the role of the DCN is unresolved. The apparently conflicting electrophysiological and lesion data can be reconciled if the DCN serves as a necessary trigger zone rather than a chronic generator of tinnitus. The present experiment used lesion procedures identical to those that failed to decrease pre-existing tinnitus. The exception was that lesions were done prior to tinnitus induction. Young adult rats were trained and tested using a psychophysical procedure shown to detect tinnitus. Tinnitus was induced by a single unilateral high-level noise exposure. Consistent with the trigger hypothesis, bilateral dorsal DCN lesions made before high-level noise exposure prevented the development of tinnitus. A protective effect stemming from disruption of the afferent pathway could not explain the outcome because unilateral lesions ipsilateral to the noise exposure did not prevent tinnitus and unilateral lesions contralateral to the noise exposure actually exacerbated the tinnitus. The DCN trigger mechanism may involve plastic circuits that, through loss of inhibition, or upregulation of excitation, increase spontaneous neural output to rostral areas such as the inferior colliculus. The increased drive could produce persistent pathological changes in the rostral areas, such as high-frequency bursting and decreased interspike variance, that comprise the chronic tinnitus signal

Short Term Depression Unmasks the Ghost Frequency

Short Term Plasticity (STP) has been shown to exist extensively in synapses throughout the brain. Its function is more or less clear in the sense that it alters the probability of synaptic transmission at short time scales. However, it is still unclear what effect STP has on the dynamics of neural networks. We show, using a novel dynamic STP model, that Short Term Depression (STD) can affect the phase of frequency coded input such that small networks can perform temporal signal summation and determination with high accuracy. We show that this property of STD can readily solve the problem of the ghost frequency, the perceived pitch of a harmonic complex in absence of the base frequency. Additionally, we demonstrate that this property can explain dynamics in larger networks. By means of two models, one of chopper neurons in the Ventral Cochlear Nucleus and one of a cortical microcircuit with inhibitory Martinotti neurons, it is shown that the dynamics in these microcircuits can reliably be reproduced using STP. Our model of STP gives important insights into the potential roles of STP in self-regulation of cortical activity and long-range afferent input in neuronal microcircuits

Spectrotemporal response properties of neurons in the guinea pig dorsal cochlear nucleus to stimulation with periodic wideband noise.

Spectrotemporal receptive field (STRF) analysis was used to study neural response properties in guinea pig dorsal cochlear nucleus (DCN) for acoustic stimulation with periodic, wideband noises. The approach estimated the average time-frequency patterns of energy fluctuations in the stimuli associated with neural firing, but without the restrictions of standard reverse-correlation methods (i.e., not limited to phaselocked units). The STRF patterns consisted of high-energy peak regions, and occasionally low energy trough areas, where the frequency associated with the maximum peak was correlated with the unit's best frequency (BF). Two major STRF pattern classes were characteristic of particular unit response types for toneburst stimulation (peristimulus time histogram classification): a single, long-duration peak region was seen for most pauser/buildups; while choppers usually exhibited multiple bands (combinations of peaks, or peaks and troughs), spaced at regular time intervals. These STRF patterns are described in the first of three reports forming the body of this work. The second report focuses on the unique temporal response properties evoked in DCN units by the noise stimulation. Many pauser/buildups and chopper-types exhibiting temporally complex STRF patterns also had discharge periodicities in response to noise stimulation. Two categories of periodicities were observed: the first reflected synchronization to particular phases of individual frequency components in the noise; the second was a lower-frequency periodicity, similar to the "intrinsic oscillations" observed with amplitude-modulated stimuli for the same unit classes. The third study focused on frequency selectivity properties of unit noise responses in the presence of continuous tone maskers. Dependent on masker frequency and intensity, the tonal maskers had variable effects on discharge rate, from complete rate suppression to partial summation, with greatest masking observed for maskers of moderate intensities at BF. Addition of the masker tones also caused a loss of temporal patterning in the period histograms and STRF patterns. The periodic noise stimuli and this spectrotemporal analysis provided information about unit responses to complex signals beyond those available from more traditional methods.Ph.D.Physiological AcousticsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105339/1/9123972.pdfDescription of 9123972.pdf : Restricted to UM users only

A spectrotemporal analysis of DCN single unit responses to wideband noise in guinea pig

Spectrotemporal receptive fields (STRFs) were estimated for chopper and pauser units recorded in guinea pig dorsal cochlear nucleus (DCN). Sixteen wideband, periodic noise stimuli, represented as time-frequency surfaces of energy density, were crosscorre-lated in time with the unit's corresponding period histograms to determine if specific energy patterns tended to precede spike occurrence. The STRFs obtained were unique to the DCN, as compared to the ventral cochlear nucleus (VCN) [Clopton and Backoff. 1991, Hear. Res. 52, 329-344] in their degree of temporal and spectral complexity. Certain unit response types, classified from their peristimulus-time histograms (PSTHs) to tonebursts, were associated with distinctive patterns in the STRFs. All STRFs had at least one region of elevated energy density (peak region) closely preceding spike occurrence, which may reflect a short-pathway, primary excitatory input (or inputs) to the neuron. In addition, some units displayed low-energy regions (troughs) with greater temporal precedences on their STRFs, particularly when higher stimulus intensities were used. This analysis approach appears to have potential for investigating functional neural connectivity and predicting responses to novel complex stimuli, although specific implementations of the technique impose limitations on the interpretation of results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29340/1/0000407.pd