Functional organization of the avian auditory field L

Summary The 2-deoxyglucose (2DG) autoradiographic method is used to analyse the functional organization of the auditory forebrain nucleus, field L, in parrots, ducks, pigeons, gulls and passerine birds. The data are compared to earlier studies in domestic and Guinea fowls. In all birds field L is a trilaminar structure, placed at the border between neostriatum mediale and caudale. The orientation and spatial extent within the forebrain, however, shows considerable variability. There is a close spatial relationship between field L and the overlying hyperstriatum ventrale, which is a secondary auditory center receiving input from field L. Stimulation with tones produces stripe like patterns of metabolic activity which are continuous across the layers of field L and the hyperstriatum ventrale. In all birds the position of the stripes in both areas shift in medio-lateral direction with decreasing tone frequency. In none of the birds the representation of frequencies above 3 kHz cover more than 20% of the neuronal space. Thus, high frequency hearing is underrepresented. Frequencies between 500 Hz and 3 kHz with somewhat variable representation, cover most of the neuronal space. Fowls and pigeons appear to have a low frequency specialization in field L.Abbreviations 2DG 2-deoxyglucose - FM frequency modulated     

Connectivity of the auditory forebrain nuclei in the Guinea Fowl (Numida meleagris)

Summary Injection of tritiated leucine and proline into the nucleus ovoidalis of the Guinea Fowl (Numida meleagris) produces terminal labeling in the palaeostriatum and in three adjacent zones (field L₁–L₃) of the auditory neostriatum (AN). L₂, situated between L₁ and L₃, receives the main input and corresponds to the former field L of Rose. These neuroanatomically defined zones of the auditory neostriatum are also characterized by differing properties of their neurons. Injection of radioactive material into the auditory neostriatum produces labeling of (i) a palaeostriatal, (ii) a ventral hyperstriatal, and (iii) an additional neostriatal area (Nd). Injection into the hyperstriatum ventrale reveals connections (i) to field L₂, (ii) to the palaeostriatum, (iii) to Nd, and (iv) to the archistriatum. After injection into the palaeostriatum, labeling can be observed (i) in the neostriatum dorsale, (ii) in the hyperstriatum ventrale, (iii) in the archistriatum, (iv) in the diencephalic nuclei, nucleus ansae lenticularis and nucleus spiriformis lateralis, and (v) in the mesencephalic nuclei, nucleus tegmenti pedunculo-pontinus and nucleus intercollicularis. These results show that a widespread connectivity exists among primary and presumably higher order auditory areas in the forebrain of birds. Connections also exist between these auditory areas and presumed vocal-motor areas (neostriatum dorsale, archistriatum, nucleus intercollicularis).Abbreviations A Archistriatum - AL Ansa lenticularis - AN Auditory neostriatum - Bas Nucleus basalis - CA Commissura anterior - Cb Cerebellum - CP Commissura posterior - DLP Nucleus dorsolateralis posterior thalami - DTh Dorsal thalamus - E Ectostriatum - EM Nucleus ectomamillaris - FA Tractus fronto-archistriatalis - FPL Fasciculus prosencephali lateralis - GLv Nucleus geniculatus lateralis, pars ventralis - HA Hyperstriatum accessorium - HD Hyperstriatum dorsale - HIS Hyperstriatum intercalatum superius - HV Hyperstriatum ventrale - HVc Hyperstriatum ventrale, pars caudale - I Injection site - ICo Nucleus intercollicularis - ICT Nucleus intercalatus thalami - Imc Nucleus isthmi, pars magnocellularis - Ipc Nucleus isthmi, pars parvocellularis - l₁, L₂, L₃ Auditory neostriatum: zones L₁, L₂, L₃ - LAD Lamina archistriatalis dorsalis - LH Lamina hyperstriatica - LMD Lamina medullaris dorsalis - LPO Lobus parolfactorius - M Mesencephalon - MLd Nucleus mesencephalicus lateralis, pars dorsalis - N Neostriatum - nAL Nucleus ansae lenticularis - Nc Neostriatum caudale - Nd Neostriatum dorsale - OM Tractus occipito-mesencephalicus - OMv Nucleus nervi oculomotorii, pars ventralis - Ov Nucleus ovoidalis - PA Palaeostriatum augmentatum - PP Palaeostriatum primitivum - PT Nucleus praetectalis - PVM Nucleus periventricularis magno-cellularis - RSd Nucleus reticularis superior, pars dorsalis - RSv Nucleus reticularis superior, pars ventralis - Rt Nucleus rotundus - SMe Stria medullaris - SpL Nucleus spiriformis lateralis - SpM Nucleus spiriformis medialis - SRt Nucleus subrotundus - TeO Tectum opticum - TOv Tractus ovoidalis - TPc Nucleus tegmenti pedunculo-pontinus - TrO Tractus opticus - TSM Tractus septo-mesencephalicus - Ve Ventricle The authors are indebted to Mrs. I. Röder and Mrs. M. Hansel for their aid in the preparation of the histological material and the illustrationsThis work was supported by the Deutsche Forschungsgemeinschaft, Sche 132/4     

Immediate early gene response to hearing song correlates with receptive behavior and depends on dialect in a female songbird

Stimulus-induced expression of the immediate early gene ZENK (egr-1) in the songbird's auditory forebrain presumably depends on the behavioral significance of the stimulus. Few studies, however, have quantified both the ZENK and behavioral responses to a stimulus in the same individuals. We played conspecific male song of either hatch (local) or foreign dialect to female white-crowned sparrows (Zonotrichia leucophrys oriantha) and quantified both the auditory ZENK response and their behavioral response, which is known to depend on dialect. Birds hearing hatch dialect showed greater ZENK induction in the caudomedial hyperstriatum ventrale and the dorsal portion of the caudomedial neostriatum than birds hearing foreign dialect, supporting previous work showing a relationship between ZENK and salience of the stimulus. In the dorsal portion of the caudomedial neostriatum, ZENK induction was correlated with the amount of non-vocal courtship behavior; however, in the caudomedial hyperstriatum ventrale, ZENK induction was more highly correlated with the females' own vocal behavior and thus may have been partly self-induced. Some females sang and showed a male-like pattern of ZENK induction in their song systems. This study provides the first evidence that the ZENK response in a sensory area to a social stimulus is proportional to the animal's preference for the stimulus.     

Gap detection in the starling (Sturnus vulgaris)

Summary Gap-detection thresholds of single units were determined from auditory forebrain neurons of the awake starling. Nine different response types were statistically defined from the discharge pattern to a 400 ms broadband noise stimulus. The gap stimuli consisted of two broadband noise bursts which were separated by a gap ranging from 0.4 to 204.8 ms duration. The median minimumdetectable gap for 121 out of 145 units that had a significant threshold 204.8ms was 12.8 ms; 20% of the neurons showed thresholds between 0.4 and 3.2 ms. The neurons of the nine response types differed significantly in their minimum-detectable gaps; neurons with phasic-tonic and phasic excitation exhibited the best (i.e. shortest) minimum-detectable gaps. The neurons of the three different recording areas (field L, NCM and HV) were significantly different in their minimumdetectable gaps; field L neurons showed the best temporal resolution for gaps in broadband noise. Gap-detection thresholds are compared with psychophysical thresholds determined with the same stimuli and the relevance of forebrain units for temporal resolution is discussed.Abbreviations CS control stimulus - HV hyperstriatum ventrale - HVc hyperstriatum ventrale pars caudalis - NB noise burst - NCM neostriatum caudale pars medialis - NS noise stimulus - SGS standard gap series - TW time window     

Processing of frequency-modulated stimuli in the chick auditory cortex analogue: evidence for topographic representations and possible mechanisms of rate and directional sensitivity

Summary Responses of units in the auditory forebrain (field L/hyperstriatum ventrale-complex) of awake domestic chicks were studied to frequency-modulated (FM) signals and isointensity tone bursts, presented to the ear contralateral to the recording sites. FM signals, linear frequency sweeps in the range of 50 Hz to 10.25 kHz, differed in the rate of change of frequency (RCF) and in the direction of modulation. The majority of RCF response functions obtained could be classified as predominantly ascending and bell shaped. Best rates of change of frequency (BRCFs), assigned to these functions, covered a range of nearly 3 orders of magnitude. BRCFs of the same units for upward (positive BRCFs) and for downward modulations (negative BRCFs) were correlated. The lowest BRCF encountered among all units for a given isointensity ON-response bandwidth (F _on ) increased as a function of F _on . F _on was derived from the responses to tone bursts of various frequencies at 70 dB SPL. As F_ON tended to increase with the best frequency (BF) of units the lowest BRCF encountered among all units for a given BF also increased as a function of BF. Positive and negative BRCFs of a unit were also correlated with the slopes of onset latency-frequency relationships below and above BF, respectively. FM responses were optimal, when the frequency-specific latency differences at a given unit were compensated by the direction and rate of frequency change in the signal. FM-directional sensitivity varied with BF. Most units with BFs below about 2 kHz preferred upward modulations, while those with BFs above 2 kHz preferred downward modulations. Directional preference and sensitivity correlated with asymmetric distributions of inhibitory sidebands around BF, as derived from the analysis of OFF-responses. Maximum directional sensitivity for a given BRCF increased with BRCF. BRCF and FM-directional sensitivity were topographically organized on neuronal planes harboring units with similar BFs (isofrequency planes). Highest BRCFs were observed in the input-layer L₂ of field L. BRCF declined along a rostrocaudal isofrequency axis in all 4 subdivisions of the auditory forebrain. Similarly, response strength shifted from rostral to caudal as a function of RCF. FM-directional sensitivity was organized in a subdivision-specific fashion. Units in the input-layer of field L (L₂), and even more so in the hyperstriatum ventrale, were fairly insensitive to the direction of modulation, whereas units in the postsynaptic layers of field L (L₁ and L₃) exhibited higher degrees of directional sensitivity. Directional sensitivity also declined along the rostrocaudal isofrequency axis of field L. Two simple models of connectivity in the chick auditory forebrain are presented, which could be sufficient to explain these results. One is based on a tonotopic arrangement of afferent synapses on dendrites and somata of units in L₂, the other on local lateral inhibition in the postsynaptic layers of field L.Abbreviations BF best frequency (kHz) - BRCF best rate of change of frequency (kHz/s) - DS index of FM-directional sensitivity - F _on ON-response bandwidth (kHz) - F _off OFF-response bandwidth (kHz) - FM frequency modulation - RCF rate of change of frequency (kHz/s)     

鸽丘脑听觉中继核团传出神经投射的研究

应用神经示踪物生物素标记的葡聚糖对环鸽丘脑听觉中继核团的传出神经投射进行了研究。结果发现：（１）丘脑卵圆核的传出纤维投射至端脑新纹状体内侧的Ｌ２听区;（２）卵圆核壳的传出纤维投射至Ｌ１、Ｌ３和部分Ｌ２听区,在Ｌ区周围亦存在许多标记终末;（３）尾侧卵圆核壳的传出投射参与了卵圆核壳的形成并发出二束纤维分别投射至下丘脑腹内侧核和端脑新纹状体Ｌ区外侧的旁听区。本实验结果首次揭示在鸟类丘脑听中继核团、端脑新     

Field-specific responses in the auditory cortex of the unanaesthetized Mongolian gerbil to tones and slow frequency modulations

Responses of multi-units in the auditory cortex (AC) of unanaesthetized Mongolian gerbils to pure tones and to linearly frequency modulated (FM) sounds were analysed. Three types of responses to pure tones could be clearly distinguished on the basis of spectral tuning properties, response latencies and overall temporal response pattern. In response to FM sweeps these three types discharged in a temporal pattern similar to tone responses. However, for all type-1 units the latencies of some phasic response components shifted systematically as a function of range and/or speed of modulation. Measurements of response latencies to FMs revealed that such responses were evoked whenever the modulation reached a particular instantaneous frequency (F_i). Effective F_i was: (1) independent of modulation range and speed, (2) always reached before the modulation arrived at a local maximum of the frequency response function (FRF) and consequently differed for downward and upward sweeps, and (3) was correlated with the steepest slope of that FRF maximum. The three different types of units were found in discrete and separate fields or regions of the AC. It is concluded that gross temporal response properties are one of the key features distinguishing auditory cortical regions in the Mongolian gerbil. Accepted: 13 August 1997     

System-specific distribution of zinc in the chick brain

Summary The brain of young domestic chicks was investigated using a Timm sulfide silver method. Serial Vibratome sections were analyzed under the light microscope, and the localization of zinc-positive structures in selected areas was determined at the ultrastructural level. Both strong and differential staining was visible in the avian telencephalon whereas most subtelencephalic structures showed a pale reaction. The highest staining intensity was found in the nonprimary sensory regions of the telencephalon such as the hyperstriatum dorsale, hyperstriatum ventrale, hippocampus, palaeostriatum augmentatum, lobus parolfactorius and caudal parts of neostriatum. There was an overall gradient of staining intensity in neostriatal areas from rostral to caudal with the heaviest zinc deposits in the caudal neostriatum. Primary sensory projection areas, such as the ectostriatum (visual), hyperstriatum intercalatum superius (visual), nucleus basalis (beak representation), the input layer L₂ of the auditory field L and the somatosensory area rostral to field L were selectively left unstained. Fiber tracts throughout the brain were free of zinc deposits except for glial cells. In electron micrographs of stained regions, silver grains were localized in some presynaptic boutons of asymmetric synapses (Gray type I), within the cytoplasm of neuronal somata and sporadically in the nucleus. The possible involvement of zinc in synaptic transmission and other processes is discussed.Abbreviations for Anatomical Structures used in the Text and Figures Ac Nucleus accumbens - Ad Archistriatum dorsale - Ai Archistriatum intermedium - Am Archistriatum mediale - Ap Archistriatum posterior - APH Area parahippocampalis - BAS Nucleus basalis - BO Bulbus olfactorius - Cb Cerebellum; - CbI Nucleus cerebellaris internus - CbM Nucleus cerebellaris intermedius - CDL Area corticoidea dorsolateralis - CPi Cortex piriformis - CT Commissura tectalis - DMP Nucleus dorsomedialis posterior thalami - E Ectostriatum - H Hyperstriatum - HA Hyperstriatum accessorium - HD Hyperstriatum dorsale - HIS Hyperstriatum intercalatum superius - Hp Hippocampus - HV Hyperstriatum ventrale - ICo Nucleus intercollicularis - Ipc Nucleus isthmi, pars parvocellularis - L Lingula - L _{1, 2, 3} Field L - La Nucleus laminaris - LFM Lamina frontalis suprema - LFS Lamina frontalis superior - LH Lamina hyperstriatica - LMD Lamina medullaris dorsalis - LNH Rostrolateral neostriatum/Hyperstriatum ventrale - LPO Lobus parolfactorius - M Medulla - MLd Nucleus mesencephalicus lateralis, pars dorsalis - MNH Rostromedial neostriatum/Hyperstriatum ventrale - N Neostriatum - NC Neostriatum caudale - NEB Nucleus of ectostriatal belt - NHA Nucleus of HA - PA Palaeostriatum augmentatum - Pap Nucleus papillioformis - PL Nucleus pontis lateralis - PP Palaeostriatum primitivum - RP Nucleus reticularis pontis caudalis - Rt Nucleus rotundus - S Nucleus septalis - SS Somatosensory area - TeO Tectum opticum - Tn Nucleus taeniae - TPO Area temporoparieto-occipitalis - V Ventricle - Va Vallecula     

Role of a species-specific acoustic environment in the development of hearing in nestlings

Main parameters were studied of the acoustic evoked potentials (EPs) from L field of the caudal neostriatum of altricial nestlings of 2-8 days to pure tones in the range of species-specific signals. It has been established that auditory EPs to the tones of different frequencies differ by the terms of appearance and the degree of maturity. At every of the revealed stages of the auditory ontogenesis, including the stage of completely formed auditory sensitivity, such parameters of auditory EPs, as latencies of different phases, amplitude-temporal pattern and the course of recovery curve are different for the tones of different frequencies. The earliest to appear are the responses to the tones 0.2-4.0 kHz, corresponding to the energy of alimentary signals. Responses to tones of higher frequencies corresponding to the spectrum of other species-specific signals appear later, but the speed of their formation is higher than in the responses to the tones of low frequencies. It is suggested that the higher speed of sensitivity maturation in the high-frequency region is determined by ecologically conditioned afferentation, the function of which is fulfilled by nestlings own vocalization.     

Neural coding of speech sound in the telencephalic auditory area of the mynah bird

Summary The responses of neurons in field L in the auditory neostriatum of the mynah bird, Gracula religiosa, were recorded during presentation of intact or manipulated mimic voices. A typical mimic voice konnichiwa elicited responses in most of the neurons. Neurons in the input layer (L2) of field L showed many peaks on peristimulus time histograms while those in other layers (L1 and L3) exhibited only one or two peaks. Several neurons in L1 and L3 responded only to the affricative consonant /t/ in the intact mimic voices. They did not respond to the affricative consonant in the isolated segment or to the one in the playbacked voice in reverse. Forty-five percent of the neurons (33/ 73) decreased in firing rates at the affricative consonant in the isolated segment compared with in the intact voice. Some of these neurons, in which neither the affricative consonant in the isolated segment nor bursts of noise alone elicited responses, exhibited clear phasic responses to /t/ in the case when bursts of noise with particular central frequencies preceded the affricative consonant. The responsiveness of these neurons appears to receive temporal facilitation. These results suggest that these neurons code the temporal relationship of speech sound.Abbreviations HVc hyperstriatum ventrale, pars caudale - TFN temporally facilitated neuron - TSN temporally suppressed neuron     

Ontogenesis of the alpha2-adrenergic receptor system in the hypothalamo-limbic system of the Pekin duck

The development of the central nervous α₂-adrenergic system in the duck was studied by semiquantitative autoradiography at the ontogenetic stages embryonic days 20 (E20) and 27 (E27) and postnatal days 3 (P3) and 14 (P14) by using the monoradioiodinated α₂-agonist clonidine ([¹²⁵I]CLO) as radioligand. All structures endowed with α₂-adrenoceptors in the adult animal were specifically labeled with [¹²⁵I]CLO by E20. A detailed analysis of the binding capacity for [¹²⁵I]CLO was performed for parts of several functional systems: hypothalamic structures (nucleus inferior hypothalami, nucleus magnocellularis preopticus, nucleus paraventricularis), limbic system (habenula, nucleus septalis lateralis, nucleus striae terminalis), circumventricular organs (organum pineale, organum subfornicale, plexus choroidei ventriculi tertii and ventriculi lateralis), visual system (hyperstriatum accessorium, nucleus reticularis superior, tectum opticum), and associative cortex (hyperstriatum ventrale). Except for the nucleus inferior hypothalami and the plexus choroideus ventriculi lateralis, all structures showed a perinatal (E27–P3) maximum of α₂-adrenoceptor-binding capacity with a subsequent decline to values of prehatching stages. This uniform expression pattern of α₂-adrenoceptors indicates that the days around hatching are a critical period for the development of the adrenergic system in the brain of the duck. Received: 21 March 1996 / Accepted: 4 July 1996     

Influence of experience on the representation of the “mothering call” in frontoparietal and auditory cortex of pups of the rodent Octodon degus : FDG mapping

Several types and subtypes of vocalizations which have a behavioral impact on degu pups were identified. Among these the complex “mothering call” which is exclusively uttered by females and first during extensive nursing periods in the nest is a candidate for filial learning. In ¹⁴C-2-fluoro-2-deoxyglucose (FDG) experiments two-weeks-old pups raised by normal mothers showed higher metabolic activity in somatosensory frontoparietal and frontal cortex upon play back of a mothering call than pups raised by muted mothers. It is suggested that pups learn to associate the mothering call with close body contact with their mother early in life. In addition, FDG representation of the call, of its components and of tone and noise stimuli were studied in degu auditory cortex. Five fields and some aspects of tonotopic organization were identified. The mothering call activated all fields, but with more spatial extent of labeling in normally raised pups. A rostral field was activated by play-back of the mothering call, noise, and two-tone sequences, but hardly by single-frequency tones and the narrow-band component of the mothering call. Accepted: 13 August 1997     

Distribution of GABAergic perikarya and terminals in the centers of the higher auditory pathway of the chicken

Summary The distribution of presumed GABAergic neurons and axon terminals in nuclei of the higher auditory pathway of the chicken was investigated by immunocytochemical methods employing antisera to the rate-limiting enzyme of GABA synthesis, glutamic acid decarboxylase, and to GABA. In the mesencephalic auditory center (MLD) about 20% of the cells reveal immunoreactivity. In contrast, the thalamic relay station nucleus ovoidalis is devoid of immunostained somata. This nucleus contains a high density of punctate immunoreactive structures presumed to be GABAergic axon terminals. In the auditory forebrain center field L and the auditory portions of the hyperstriatum ventrale, up to 8% of the cells were immunopositive. These neurons were significantly smaller than estimated from measurements of the overall cell population in these nuclei. From the two-dimensional arrangement of immunopositive neurons it is suggested that the GABAergic system in the avian auditory telencephalon consists of two separate groups of neurons: one subgroup mediating local inhibitory interactions, the other responsible for lateral inhibition between different frequency representations.This work was supported by the Deutsche Forschungsgemeinschaft (SFB 45)     

Effects of frequency of the tones on auditory event related potentials in monkeys (Macaca fuscata) under various hypobaric hypoxia conditions of simulated high altitudes

Changes in auditory event related potentials (ERPs) as a function of frequency of tones ranging from 500 Hz to 8,000 Hz were examined under various hypobaric hypoxia conditions of simulated high altitudes up to 6,000 m. A sequence of P₁-N₁-P₂ components, corresponding to those of the human subject, was observed with the monkey's ERPs. These component amplitudes changed as a function of frequency of tone. The relationship revealed an inverted U curve with a maximum amplitude at a tone of 2,000 Hz. The following results under hypoxia were noted: marked reduction of amplitude in ERPs induced by hypoxia linked only to a tone's particular frequency, especially for 2,000 Hz. The delay of latency in the respective components of the ERPs was dependent on the degree of hypoxia. These findings seem to suggest the anatomical bases of the neural generators contributing to each component of the ERPs. This work was supported by the Cooperation Research Program, Primate Research Institute, Kyoto University.     

Neural response to bird’s own song and tutor song in the zebra finch field L and caudal mesopallium

Neurons in the song system nuclei of songbirds exhibit a strong preference for the sound of the birds own song relative to that of conspecific songs. This selectivity is observed in the high vocal center and the nucleus interface of the nidopallium, two song nuclei that receive input from the birds auditory system. To investigate the role of the auditory system in generating the selective responses observed in the song system, we recorded auditory responses in the zebra finch primary auditory forebrain, field L, and in a secondary auditory area, the caudal mesopallium. Field L and caudal mesopallium project directly or indirectly to the high vocal center and nucleus interface of the nidopallium and are presumed to provide substantial auditory input to the song system. We found that, on average, neurons in field L and caudal mesopallium did not show positive selective responses for the birds own song or tutor song relative to conspecific song. Moreover, there were no particular sub-areas in the auditory telencephalon that were relatively more selective than the average. The selectivity for the birds own song would therefore be restricted to song nuclei and would arise in one processing step, potentially found at the interface between the auditory and the song systems.Abbreviations BOS birds own song - CM caudal mesopallium (older term: caudal hyperstriatum ventrale or cHV) - Con conspecific song - HVC high vocal center - LMAN lateral magnocellular nucleus of the anterior nidopallium (older term: lateral magnocellular nucleus of the anterior neostriatum) - LPS pallial-subpallial lamina (older term: lamina medularis dorsalis or LMD) - NCM caudal medial nidopallium (older term: caudo-medial neostriatum) - NIf nucleus interface of the nidopallium (older term: nucleus interface of the neostriatum) - RA robust nucleus of arcopallium (older term: robust nucleus of the archistriatum) - Rev reverse BOS - Revorder reverse order of BOS - Uva nucleus uvaeformis of the thalamusNew avian brain terminology has been used in this paper (). Older terms are given in parentheses in the list of abbreviations     

Neural adaptation to tone sequences in the songbird forebrain: patterns, determinants, and relation to the build-up of auditory streaming

Neural responses to tones in the mammalian primary auditory cortex (A1) exhibit adaptation over the course of several seconds. Important questions remain about the taxonomic distribution of multi-second adaptation and its possible roles in hearing. It has been hypothesized that neural adaptation could explain the gradual “build-up” of auditory stream segregation. We investigated the influence of several stimulus-related factors on neural adaptation in the avian homologue of mammalian A1 (field L2) in starlings (Sturnus vulgaris). We presented awake birds with sequences of repeated triplets of two interleaved tones (ABA–ABA–…) in which we varied the frequency separation between the A and B tones (ΔF), the stimulus onset asynchrony (time from tone onset to onset within a triplet), and tone duration. We found that stimulus onset asynchrony generally had larger effects on adaptation compared with ΔF and tone duration over the parameter range tested. Using a simple model, we show how time-dependent changes in neural responses can be transformed into neurometric functions that make testable predictions about the dependence of the build-up of stream segregation on various spectral and temporal stimulus properties.     

Neuromagnetic evidence for early auditory restoration of fundamental pitch

Background

Understanding the time course of how listeners reconstruct a missing fundamental component in an auditory stimulus remains elusive. We report MEG evidence that the missing fundamental component of a complex auditory stimulus is recovered in auditory cortex within 100 ms post stimulus onset.

Methodology

Two outside tones of four-tone complex stimuli were held constant (1200 Hz and 2400 Hz), while two inside tones were systematically modulated (between 1300 Hz and 2300 Hz), such that the restored fundamental (also knows as “virtual pitch”) changed from 100 Hz to 600 Hz. Constructing the auditory stimuli in this manner controls for a number of spectral properties known to modulate the neuromagnetic signal. The tone complex stimuli only diverged on the value of the missing fundamental component.

Principal Findings

We compared the M100 latencies of these tone complexes to the M100 latencies elicited by their respective pure tone (spectral pitch) counterparts. The M100 latencies for the tone complexes matched their pure sinusoid counterparts, while also replicating the M100 temporal latency response curve found in previous studies.

Conclusions

Our findings suggest that listeners are reconstructing the inferred pitch by roughly 100 ms after stimulus onset and are consistent with previous electrophysiological research suggesting that the inferential pitch is perceived in early auditory cortex.     

Response properties of auditory activated cells in the occipital cortex of the blind mole rat: an electrophysiological study

Previous studies have demonstrated that despite its blindness, the subterranean blind mole rat (Spalax ehrenbergi) possesses a noticeable lateral geniculate nucleus and a typical cyto-architectural occipital cortex that are reciprocally connected. These two areas, as revealed by the metabolic tracer 2-deoxyglucose, are activated by auditory stimuli. Using single unit recordings, we show that about 57% of 325 cells located within the occipital cortex of anesthetized mole rats responded to at least one of the following auditory stimuli — white noise, pure tones, clicks, and amplitude modulated tones — with the latter two being the most effective. About 85% of cells driven by either contralateral or ipsilateral stimulation also responded to binaural stimulation; about 13% responded only to binaural stimulation; and 2% were driven exclusively by contralateral stimulation. Comparing responsiveness and response strength to these three modes of stimulation revealed a contralateral predominance. Mean latency (±SD) of ipsilateral and contralateral responses were 48.5±32.6 ms and 33.5±9.4 ms, respectively. Characteristic frequencies could be divided into two distinct subgroups ranging between 80 and 125 Hz and between 2,500 and 4,400 Hz, corresponding to the most intensive spectral components of the vibratory intraspecific communication signals and airborne vocalizations.Abbreviations BMF best modulation frequency - CF characteristic frequency - 2-DG 2-deoxyglucose - dLGN dorsal lateral geniculate nucleus - IC inferior colliculus - LGN lateral geniculate nucleus - OC occipital cortex - MTF modulation transfer function - SAM sinusoidally amplitude modulation - SC superior colliculus     

Hearing in the FM-bat Phyllostomus discolor: a behavioral audiogram

Absolute auditory thresholds of six adult lesser spear-nosed bats Phyllostomus discolor (Chiroptera, Phyllostomidae) were determined in a two-alternative forced-choice procedure. Behavioral responses to pure tone stimuli could be elicited throughout the tested frequency range of 5–142 kHz. The shape of the average audiogram is characterized by two sensitivity peaks and a pronounced increase of thresholds around 55 kHz, and towards the limits of the tested frequency range. The spectral extent of both sensitivity peaks shows a close relation to the bandwidth of two types of species-specific vocalizations. The first low threshold area (> 10 and < 55 kHz) of the audiogram seems perfectly adapted to the directive call used for intraspecific communication, whereas the second sensitivity peak, centered around 85 kHz, covers most of the bandwidth of the species' echolocation calls.Abbreviations CF constant frequency - FM frequency modulation - l left - r right - SPL Sound pressure level