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PubMed1985

Acoustic chiasm II: Anatomical basis of binaurality in lateral superior olive of cat.

The afferent projections to the lateral superior olive (LSO) were examined with horseradish peroxidase, horseradish peroxidase-wheat germ agglutinin conjugate, 125I-wheat germ agglutinin and tritiated leucine autoradiograhy, anterograde axonal degeneration, and 14C-2-deoxyglucose methods. The pathway to the ipsilateral LSO orginates in the spherical cells in anteroventral cochlear nucleus. Although some of the fibers pass above the lateral nucleus of the trapezoid body, most pass below it and turn at right angles to enter the LSO either directly through its ventral, lateral, or dorsal borders, or through its ventral or dorsal hilus. They end in unpolarized terminal fields throughout the LSO. Most if not all of these fibers are true collaterals of axons continuing across the midline in the trapezoid body. Verifying Held's (1893) finding of a major direct projection from the cochlear nucleus to the contralateral medial nucleus of the trapezoid body (MTB) and Rasmussen's ('46) finding of a major projection from the MTB to the LSO, the present results illustrate that this two-neuron pathway probably supplies all but a very small component of the relatively direct input to the LSO from the contralateral ear. This pathway originates in the globular cells of the ventral cochlear nucleus and relays mostly though not exclusively through the "principal cells" in the more rostral parts of the MTB. It terminates mostly in perisomal endings in unpolarized fields throughout the LSO, though most heavily within the (high frequency) medial and middle limbs and less heavily in the LSO's (low frequency) lateral limb. In addition to this indirect pathway, there is a small direct pathway to the contralateral LSO as suggested by Goldberg and Brown ('69) and Warr ('72, '82). This direct pathway to the contralateral LSO, like the direct ipsilateral pathway, probably originates in the spherical cell region of the ventral cochlear nucleus, crosses the midline in the trapezoid body, and terminates in a small circumscribed area within the LSO's ventromedial (high frequency) area. The 2-deoxyglucose method applied to cats in which the ipsilateral and contralateral pathways have been surgically isolated shows that each of the pathways converging on the LSO is topographically and tonotopically organized with the ipsilateral and the combined contralateral terminations in strict tonotopic register.

Animals↗
PubMed1993

Frequency organization of the dorsal cochlear nucleus in cats.

Sensory epithelia are often spatially reiterated throughout their representation in the central nervous system. Differential expression of this representation can reveal specializations of the organism's behavioral repertoire. For example, the nature of the central representation of sound frequency in the auditory system has provided important clues in understanding ecological pressures for acoustic processing. In this context, we used electrophysiological techniques to map the frequency organization of the dorsal cochlear nucleus in nine cats. Frequency responses were sampled in increments of 100-200 microns along electrode tracks that entered the dorsomedial border of the nucleus and exited at the ventrolateral border. Electrode tracks were oriented parallel to the long (or strial) axis of the nucleus so that each penetration sampled neural responses for most of the cat's audible frequencies and remained in or near the pyramidal cell layer for several millimeters. Nearly identical distance versus frequency relationships were obtained for different rostral-caudal locations within the same cat as well as for different cats. Frequency responses systematically decreased from above 50 kHz at the most dorsomedial locations in the nucleus to below 1 kHz in the most ventrolateral regions. The rate of frequency change was roughly three times greater in high frequency regions than in low frequency regions. In addition, the highest pyramidal cell density and longest rostral-caudal axis was observed for the middle third of the dorsal-ventral axis of the nucleus. As a result, roughly half of all pyramidal cells responded to frequencies between 8-30 kHz. The representation of neural tissue for these frequencies may be related to the importance of spectral cues in sound locations.

Animals↗
PubMed1995

Development of ectopic projections from the ventral cochlear nucleus to the superior olivary complex induced by neonatal ablation of the contralateral cochlea.

The ability of an animal to localize a sound in space requires the precise innervation of the superior olivary complex by the ventral cochlear nuclei on each side of the lower brainstem. This precise pattern of innervation could require an immutable recognition of appropriate targets by afferent processes arising from these nuclei. This possibility was investigated by destroying one cochlea of gerbil pups (Meriones unguiculatus) on the second postnatal day and assessing the projections from the ventral cochlear nucleus (VCN) on the unablated side to the superior olivary complex during the subsequent 2 weeks and after the animals had reached maturity. A crystal of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was inserted into VCN on the unablated side in animals ranging in age from 3 to 14 days. To assess the permanence of any altered pattern of innervation, horseradish peroxidase was injected into VCN on the unablated side in adult, neonatally ablated animals. Finally, electrophysiological responses to acoustic stimuli delivered to the ear on the unablated side were recorded in the superior olivary complex of adult animals to assess whether altered innervation patterns were functional. Normative data were derived from our accompanying study of the development of VCN projections to the superior olivary complex in normal gerbils (Kil et al., this issue). Whereas VCN normally projects to the lateral aspect of the ipsilateral medial superior olive and to the medial aspect of the contralateral medial superior olive in control animals, in experimental animals VCN on the unablated side projects to both sides of these nuclei. Whereas in the gerbil, VCN normally projects only to the hilar area and to the ventrolateral limb of the contralateral lateral superior olive, in experimental animals VCN on the unablated side projects throughout this nucleus. This induced projection is specific in that the efferents to each limb of the contralateral nucleus are linked to the normal projection to the homotopic region of the ipsilateral nucleus. Whereas VCN innervates the contralateral medial nucleus of the trapezoid body in control animals, in experimental animals VCN on the unablated side provides calyces of Held in the ipsilateral nucleus as well. The induced projections to these three major subnuclei of the superior olivary complex first appear within 24 hours of the cochlear ablation and continue to develop over at least the subsequent 11 days. Thus, prior to the day when the cochlea becomes functional, VCN has established specific ectopic projections to loci normally innervated by VCN on the ablated side.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1995

Topographical organization of the motoneuron pools that innervate the muscles of the pinna of the cat.

The topographical organization of the 22 motoneuron pools that innervate the pinna muscles of the cat was examined by injecting the B-subunit of cholera toxin conjugated to horseradish peroxidase into individual muscles. All 22 pools are found in the facial nucleus, organized as rostro-caudally oriented columns, and arranged according to the action of the muscles they innervate. Pools innervating muscles that pull the pinna dorsally are located in the dorsal two thirds of the medio-dorsal subdivision, and those innervating muscles that pull the pinna ventrally are located in the ventral one half of the nucleus. Motoneurons innervating muscles that pull the pinna cranially are located laterally, those that pull the pinna caudally are located medio-ventrally, and those that change the shape of the pinna are located along the entire dorso-ventral extent in the center of the medio-dorsal subdivision. This topographical layout is consistent with the somatotopic organization of the entire facial nucleus as demonstrated in a variety of species.

Animals↗
PubMed1989

Stimulus duration and repetition rate influence newborns' head orientation toward sound.

Three experiments evaluated the effects of stimulus duration and repetition rate on newborns' head orientation responses. In Experiment 1, 28 infants turned toward a 20-sec continuous rattle sound but not toward 14- and 500-msec rattle sounds. Signal energy as a possible explanation for the infants' difficulty orienting toward brief sounds was explored in Experiment 2. Twenty neonates did not turn toward a single 90 dB, 14-msec rattle sound, although a longer duration (10 sec) sound containing less energy (70 dB) did elicit reliable head orientation. In Experiment 3, 16 neonates heard trains of repeated 14-msec rattle sounds (2/sec, 1.3/sec, and 1/sec) lasting 10 sec as well as a 10-sec continuous rattle sound. They turned toward the most rapidly repeating brief sound and the continuous one, while the slowly repeating sounds elicited little head movement in any direction. These results suggest that newborns' head orientation is selectively deficient for brief sounds, that the difficulty does not result from lessened energy in the brief sounds, and that the efficacy of repeated brief sounds depends upon their repetition rates.

Analysis of Variance↗
PubMed2003

Tonotopic cortical representation of periodic complex sounds.

Most of the sounds that are biologically relevant are complex periodic sounds, i.e., they are made up of harmonics, whose frequencies are integer multiples of a fundamental frequency (Fo). The Fo of a complex sound can be varied by modifying its periodicity frequency; these variations are perceived as the pitch of the voice or as the note of a musical instrument. The center frequency (CF) of peaks occurring in the audio spectrum also carries information, which is essential, for instance, in vowel recognition. The aim of the present study was to establish whether the generators underlying the 100 m are tonotopically organized based on the Fo or CF of complex sounds. Auditory evoked neuromagnetic fields were recorded with a whole-head magnetoencephalography (MEG) system while 14 subjects listened to 9 different sounds (3 Fo x 3 CF) presented in random order. Equivalent current dipole (ECD) sources for the 100 m component show an orderly progression along the y-axis for both hemispheres, with higher CFs represented more medially. In the right hemisphere, sources for higher CFs were more posterior, while in the left hemisphere they were more inferior. ECD orientation also varied as a function of the sound CF. These results show that the spectral content CF of the complex sounds employed here predominates, at the latency of the 100 m component, over a concurrent mapping of their periodic frequency Fo. The effect was observed both on dipole placement and dipole orientation.

Acoustic Stimulation↗
PubMed2004

Different areas of human non-primary auditory cortex are activated by sounds with spatial and nonspatial properties.

In humans, neuroimaging studies have identified the planum temporale to be particularly responsive to both spatial and nonspatial attributes of sound. However, a functional segregation of the planum temporale along these acoustic dimensions has not been firmly established. We evaluated this scheme in a factorial design using modulated sounds that generated a percept of motion (spatial) or frequency modulation (nonspatial). In addition, these sounds were presented in the context of a motion detection and a frequency-modulation detection task to investigate the cortical effects of directing attention to different perceptual attributes of the sound. Motion produced stronger activation in the medial part of the planum temporale and frequency-modulation produced stronger activation in the lateral part of the planum temporale, as well as an additional non-primary area lateral to Heschl's gyrus. These separate subregions are consistent with the notion of divergent processing streams for spatial and nonspatial auditory information. Activation in the superior parietal cortex, putatively involved in the spatial pathway, was dependent on the task of motion detection and not simply on the presence of acoustic cues for motion. This finding suggests that the listening task is an important determinant of how the processing stream is engaged.

Acoustic Stimulation↗
PubMed2004

Nonlinearity of FMRI responses in human auditory cortex.

An investigation was made into the nature of the nonlinearity observed in auditory functional magnetic resonance imaging (fMRI) experiments associated with increases in total duration of acoustic imaging noise [e.g., Edmister et al., 1999; Shah et al., 1999]. A two-stimulus, four-condition paradigm was used to evaluate four acoustic conditions involving: (1) the presence or absence of a desired broadband music stimulus; and (2) two possible durations of trains of acoustic noise associated with image acquisition. Responses observed while increasing the duration of acoustic imaging noise were consistent with previous work (Talavage et al. [1999]: Hum Brain Mapp7:79-88) but the response to combined stimulation did not exhibit variation as a function of the acoustic imaging noise duration. These results suggest that spectral overlap of the stimuli produced colocalized responses that did not add linearly. This conclusion has implications for conducting both blocked and rapid-presentation event-related auditory fMRI experiments. The cortical activity induced by the stimulus may not reflect the activation, in spatial extent or magnitude of signal change, occurring in the absence of other acoustic noise.

Acoustic Stimulation↗
PubMed1996

Mineral anisotropy in mineralized tissues is similar among species and mineral growth occurs independently of collagen orientation in rats: results from acoustic velocity measurements.

It has been reported that the mineral crystals in long bones have their c-axis aligned with the bone axis, presumably because collagen fibrils in bone also align with the bone axis. However, the predominant collagen orientation in bone often does not appear to be aligned with the mineral crystals, especially in rat primary bone. We hypothesized that mineral orientation in bone is not necessarily related to collagen orientation. An acoustic microscope was used to measure elastic constants of mineralized tissues from rat, cow, monkey, and human bone, and mineralized turkey leg tendon (MTLT). Measurements were made before and after demineralization with 10% ethylenediaminetetraacetic acid (EDTA) or decollagenization with 7% sodium hypochlorite. The elastic anisotropy ratio (AR) was defined as the ratio of the elastic coefficient in the longitudinal direction to the elastic coefficient in the transverse direction. Anisotropy ratios of mineralized tissues were not affected by formalin fixation or plastic embedding. An evaluation of tissues from the different species showed that the AR after decollagenization was not significantly different (p > 0.4, analysis of variance) among the groups, while AR after demineralization varied from 1.04 (rat bone) to 1.51 (MTLT). There was no correlation between AR after demineralization and AR after decollagenization (r = 0.13, p = 0.5). This showed that the elastic anisotropy of collagen is more variable than mineral anisotropy in bone and MTLT. Another experiment showed that mineralization of turkey leg tendon changes the elasticity of the collagen matrix, making it less anisotropic. A final, prospective experiment was performed in which tibiae of rats were subjected to mechanical loading for 16 weeks. After 12 days, new periosteal woven bone was observed on the tibiae and, after 16 weeks, this new bone was consolidated and mineralized. Mineral in the newly formed woven bone was virtually isotropic (AR = 1.07) after 12 days of loading, then became more anisotropic (AR = 1.52) after 16 weeks of mechanical loading, as the mineral density of the new bone increased. This increase in anisotropy of bone mineral occurred even though the collagen matrix was woven and had no measureable fibril orientation. We conclude that (1) collagen anisotropy and mineral anisotropy are not necessarily correlated in mineralized tissues, (2) mineralization can affect the collagen matrix elasticity of mineralized tissues, and (3) an organized mineral structure can form in the absence of an organized collagen matrix.

Acoustics↗
PubMed2004

Processing of auditory information in insects.

Insects exhibit an astonishing diversity in the design of their ears and the subsequent processing of information within their auditory pathways. The aim of this review is to summarize and compare the present concepts of auditory processing by relating behavioral performance to known neuronal mechanisms. We focus on three general aspects, that is frequency, directional, and temporal processing. The first part compares the capacity (in some insects high) for frequency analysis in the ear with the rather low specificity of tuning in interneurons by looking at Q10dB values and frequency dependent inhibition of interneurons. Since sharpening of frequency does not seem to be the prime task of a set of differently tuned receptors, alternative hypotheses are discussed. Moreover, the physiological correspondence between tonotopic projections of receptors and dendritic organization of interneurons is not in all cases strong. The second part is concerned with directional hearing and thus with the ability for angular resolution of insects. The present concepts, as derived from behavioral performances, for angular resolution versus lateralization and serial versus parallel processing of directional and pattern information can be traced to the thoracic level of neuronal processing. Contralateral inhibition, a mechanism for enhancing directional tuning, appears to be most effective in parallel pathways, whereas in serial processing it may have detrimental effects on pattern processing. The third part, after some considerations of signal analysis in the temporal domain, demonstrates that closely related species often use different combinations of temporal parameters in their recognition systems. On the thoracic level, analysis of temporal modulation functions and effects of inhibition on spiking patterns reveals relatively simple processing, whereas brain neurons may exhibit more complex properties.

Acoustic Stimulation↗
PubMed2003

Prolonged response to calling songs by the L3 auditory interneuron in female crickets (Acheta domesticus): intracellular evaluation.

The L3 auditory interneuron in female Acheta domesticus, produces two different responses to the male calling song: an immediate response and a prolonged response. The prolonged response exhibited spiking activity and a correlated prolonged depolarization, both of which are clearly seen in intracellular recordings. The morphology revealed by intracellular staining was clearly the L3 neuron. The amplitude of the prolonged depolarization associated with the prolonged response increased with increases in sound intensity, resulting in increased spiking rates. Both depolarization and sound presentation increased the spiking rate and the slope of pre-potentials (thus leading to spiking threshold more quickly). Injecting hyperpolarizing current had the expected opposite effect. The effects of positive current injection and sound presentation were additive, resulting in spiking rates that were approximately double the rates in response to sound alone. Short postsynaptic potentials (PSPs), whose duration ranged from 15-60 ms, which may lead to action potentials were also observed in all recordings and summated with the prolonged depolarization, increasing the probability of spiking.

Animal Communication↗
PubMed2003

Prolonged response to calling songs by the L3 auditory interneuron in female crickets (Acheta domesticus): possible roles in regulating phonotactic threshold and selectiveness for call carrier frequency.

L3, an auditory interneuron in the prothoracic ganglion of female crickets (Acheta domesticus) exhibited two kinds of responses to models of the male's calling song (CS): a previously described, phasically encoded immediate response; a more tonically encoded prolonged response. The onset of the prolonged response required 3-8 sec of stimulation to reach its maximum spiking rate and 6-20 sec to decay once the calling song ceased. It did not encode the syllables of the chirp. The prolonged response was sharply selective for the 4-5 kHz carrier frequency of the male's calling songs and its threshold tuning matched the threshold tuning of phonotaxis, while the immediate response of the same neuron was broadly tuned to a wide range of carrier frequencies. The thresholds for the prolonged response covaried with the changing phonotactic thresholds of 2- and 5-day-old females. Treatment of females with juvenile hormone reduced the thresholds for both phonotaxis and the prolonged response by equivalent amounts. Of the 3 types of responses to CSs provided by the ascending L1 and L3 auditory interneurons, the threshold for L3's prolonged response, on average, best matched the same females phonotactic threshold. The prolonged response was stimulated by inputs from both ears while L3's immediate response was driven only from its axon-ipsilateral ear. The prolonged response was not selective for either the CS's syllable period or chirp rate.

Analysis of Variance↗
PubMed1999

Selective visual and auditory attention toward utterances-a PET study.

The purpose of this study was to reveal functional areas of the brain modulating processing of selective auditory or visual attention toward utterances. Regional cerebral blood flow was measured in six normal volunteers using positron emission tomography during two selective attention tasks and a control condition. The auditory task activated the auditory, inferior parietal, prefrontal, and anterior cingulate cortices. The visual task activated the visual association, inferior parietal, and prefrontal cortices. Both conditions activated the same area in the superior temporal sulcus. During the visual task, deactivation was observed in the auditory cortex. These results indicate that there exists a modality-dependent selective attention mechanism which activates or deactivates cortical areas in different ways.

Adolescent↗
PubMed1999

Auditory attention to space and frequency activates similar cerebral systems.

PET was used to test the hypothesis that similar neural systems are involved in attending to spectral and to spatial features of sounds. In each of four conditions subjects heard tones varying randomly in frequency and location and responded to either the low- or the high-frequency stimuli, ignoring location, or to stimuli on the left or right, ignoring frequency. In comparison to a silent baseline, CBF increases were observed in auditory cortex bilaterally and in the right superior parietal, right dorsolateral frontal, and right premotor regions, with no modulation as a function of attentional condition. Analysis of regional covariation indicated a coordinated CBF response between the right parietal region and the right frontal and middle temporal regions. The data imply that auditory attention engages a network of right-hemisphere cortical regions for both spatial location and tonal frequency and support a model whereby auditory attention operates at a level at which separate features have been integrated into a unitary representation.

Adult↗
PubMed2001

Evidence for dissociation of spatial and nonspatial auditory information processing.

Several lines of evidence suggest that visual information processing is segregated into the ventral "what" and dorsal "where" pathways. But the question whether information processing in the auditory system is also parceled to spatial and nonspatial domains remains open. In the present study, we performed simultaneous EEG and MEG recordings during auditory location and pitch delayed matching-to-sample tasks to find out whether working memory processing of the auditory stimulus attribute affects the transient components of the evoked potentials. In both tasks, identical blocks of tone stimuli of one of two frequencies were presented in one of two locations; the only difference between the tasks was the instruction to attend either to the frequency or to the location. In the match condition, the N1 latency was shorter and the N1m amplitude larger in the location task compared to the pitch task. Furthermore, the right-hemisphere generator of N1m elicited in the match condition of the location task was situated significantly medially to the N1m generator in the match condition of the pitch task. Latency and amplitude task-related differences in the N1/N1m components as well as the source location differences indicate at least partial segregation of neuronal mechanisms involved in working memory processing of spatial and nonspatial auditory information.

Adult↗
PubMed2002

Segregated processing of auditory motion and auditory location: an ERP mapping study.

Recent studies have revealed a distinct cortical network activated during the analysis of sounds' spatial properties. Whether common brain regions in this auditory where pathway are involved in both auditory motion and location processing is unresolved. We investigated this question with multichannel auditory evoked potentials (AEPs) in 11 subjects. Stimuli were binaural 500-ms white noise bursts. Interaural time differences (ITD) created the sensation of moving or stationary sounds within each auditory hemifield, and subjects discriminated either their position or direction of motion in a blocked design. Scalp potential distributions (AEP maps) differentiated electric field configurations across stimulus classes. The initial approximately 250-ms poststimulus yielded common topographies for both stimulus classes and hemifields. After approximately 250-ms, moving and stationary sounds engaged distinct cortical networks at two time periods, again with no differences observed between hemifields. The first ( approximately 250- to 350-ms poststimulus onset) was during stimulus presentation, and the second ( approximately 550- to 900-ms poststimulus onset) occurred after stimulus offset. Distributed linear inverse solutions of the maps over the 250- to 350-ms time period revealed not only bilateral inferior frontal activation for both types of auditory spatial processing, but also strong right inferior parietal activation in the case of auditory motion discrimination. During the later 550-to 900-ms time period, right inferior parietal and bilateral inferior frontal activity was again observed for moving sounds, whereas strong bilateral superior frontal activity was seen in the case of stationary sounds. Collectively, the evidence supports the existence of partly segregated networks within the auditory where pathway for auditory location and auditory motion processing.

Acoustic Stimulation↗
PubMed1996

Effects of sound direction on the processing of amplitude-modulated signals in the frog inferior colliculus.

Single-unit recordings were made from 143 neurons in the frog (Rana p. pipiens) inferior colliculus (IC) to investigate how free-field sound direction influenced neural responses to sinusoidal-amplitude-modulated (SAM) tone and/or noise. Modulation transfer functions (MTFs) were derived from 3 to 5 sound directions within 180 degrees of frontal field. Five classes of MTF were observed: low-pass, high-pass, band-pass, multi-pass, and all-pass. For 64% of IC neurons, the MTF class remained unchanged when sound direction was shifted from contralateral 90 degrees to ipsilateral 90 degrees. However, the MTFs of more than half of these neurons exhibited narrower bandwidths when the loudspeaker was shifted to ipsilateral azimuths. There was a decrease in the cut-off frequency for neurons possessing low-pass MTFs, an increase in cut-off frequency for neurons showing high-pass MTFs, or a reduction in the pass-band for neurons displaying bandpass MTFs. These results suggest that sound direction can influence amplitude modulation (AM) frequency tuning of single IC neurons. Since changes in periodicity of SAM tones alter both the temporal parameters of sounds as well as the sound spectrum, we examined whether directional effects on spectral selectivity play a role in shaping the observed direction-dependent AM selectivity. The directional influence on AM selectivity to both SAM tone and SAM noise was measured in 62 neurons in an attempt to gain some insight into the mechanisms that underlie directionally-induced changes in AM selectivity. Direction-dependent changes in the shapes of the tone and noise derived MTFs were different for the majority of IC neurons (55/62) tested. These data indicate that a spectrally-based and a temporally-based mechanism may be responsible for the observed results.

Acoustic Stimulation↗
PubMed1996

Serially homologous ears perform frequency range fractionation in the praying mantis, Creobroter (Mantodea, Hymenopodidae).

Unlike most praying mantises that have a single region of auditory sensitivity, species in the genus Creobroter have equally sensitive hearing at 2-4 and at 25-50 kHz and and are relatively insensitivity at 10-15 kHz- they have a W-shaped audiogram. Ultrasonic sensitivity originates from an auditory organ in the ventral midline of the metathorax that closely resembles the ear of other mantises. Ablation experiments demonstrate that low frequency sensitivity derives from a serially homologous mesothoracic auditory organ. Extracellular recordings suggest that these two ears operate largely, if not entirely, independently of one another in the thorax. The low frequency response has a longer latency, more action potentials per stimulus, and different patterns of change with increasing SPL than the high frequency response. Separate interneurons mediate responses in the two frequency ranges, but our evidence suggests that they are two serially homologous sets of cells. Neither auditory organ shows any physiological evidence of directional sensitivity. Ultrasound triggers a set of behaviors in flying hymenopodid mantises much like those in other mantises, but the behavioral significance of low frequency hearing in these animals is still unknown.

Acoustic Stimulation↗