Zi-Ying Fu

The auditory response properties of single-on and double-on responders in the inferior colliculus of the leaf-nosed bat, Hipposideros armiger.

The present study examines the response properties of neurons in the central nucleus of the inferior colliculus (IC) of the CF-FM (constant frequency-frequency-modulated) bat, Hipposideros armiger using CF, FM and CF-FM sounds as stimuli. All 169 IC neurons recorded are tonotopically organized along the dorsoventral axis of the IC. Collicular neurons have V-shaped or upper-threshold frequency tuning curves. Those neurons tuned at the predominant second harmonic have extremely sharp frequency tuning curves and low minimum thresholds. Collicular neurons typically discharge impulses to both CF and FM sounds. However, when stimulated with CF-FM sounds, most (76%) neurons only discharge impulses to the onset of CF-FM sounds (single-on responders). The remaining neurons (24%) discharge impulses to both CF and FM components (double-on responders) of CF-FM sounds. The double-on responders have higher minimum threshold and longer latency to the FM component than to the CF component of CF-FM sounds. Our data show that the FM component of the CF-FM sounds contributes significantly in shaping the discharge pattern, latency and number of impulses of IC neurons. The present study suggests that using CF-FM sounds to study auditory response properties of the CF-FM bat may be essential for a better understanding of echo analysis by the CF-FM in the real world. Because the double-on responders have shorter response latency than single-on responders, we speculate that these two types of responders may be best suited for echo analysis during different phases of hunting.

Bilateral Collicular Interaction: Modulation of Auditory Signal Processing in Amplitude Domain

In the ascending auditory pathway, the inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from many lower auditory nuclei, intrinsic projections within the IC, contralateral IC through the commissure of the IC and from the auditory cortex. All these connections make the IC a major center for subcortical temporal and spectral integration of auditory information. In this study, we examine bilateral collicular interaction in modulating amplitude-domain signal processing using electrophysiological recording, acoustic and focal electrical stimulation. Focal electrical stimulation of one (ipsilateral) IC produces widespread inhibition (61.6%) and focused facilitation (9.1%) of responses of neurons in the other (contralateral) IC, while 29.3% of the neurons were not affected. Bilateral collicular interaction produces a decrease in the response magnitude and an increase in the response latency of inhibited IC neurons but produces opposite effects on the response of facilitated IC neurons. These two groups of neurons are not separately located and are tonotopically organized within the IC. The modulation effect is most effective at low sound level and is dependent upon the interval between the acoustic and electric stimuli. The focal electrical stimulation of the ipsilateral IC compresses or expands the rate-level functions of contralateral IC neurons. The focal electrical stimulation also produces a shift in the minimum threshold and dynamic range of contralateral IC neurons for as long as 150 minutes. The degree of bilateral collicular interaction is dependent upon the difference in the best frequency between the electrically stimulated IC neurons and modulated IC neurons. These data suggest that bilateral collicular interaction mainly changes the ratio between excitation and inhibition during signal processing so as to sharpen the amplitude sensitivity of IC neurons. Bilateral interaction may be also involved in acoustic-experience-dependent plasticity in the IC. Three possible neural pathways underlying the bilateral collicular interaction are discussed.

Bilateral collicular interaction: Modulation of auditory signal processing in frequency domain

In the ascending auditory pathway, the inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from a variety of lower auditory nuclei, intrinsic projections within the IC, contralateral IC through the commissure of the IC and the auditory cortex. All these connections make the IC a major center for subcortical temporal and spectral integration of auditory information. In this study, we examine bilateral collicular interaction in the modulation of frequency-domain signal processing of mice using electrophysiological recording and focal electrical stimulation. Focal electrical stimulation of neurons in one IC produces widespread inhibition and focused facilitation of responses of neurons in the other IC. This bilateral collicular interaction decreases the response magnitude and lengthens the response latency of inhibited IC neurons but produces an opposite effect on the response of facilitated IC neurons. In the frequency domain, the focal electrical stimulation of one IC sharpens or expands the frequency tuning curves (FTCs) of neurons in the other IC to improve frequency sensitivity and the frequency response range. The focal electrical stimulation also produces a shift in the best frequency (BF) of modulated IC (ICMdu) neurons toward that of electrically stimulated IC (ICES) neurons. The degree of bilateral collicular interaction is dependent upon the difference in the BF between the ICES neurons and ICMdu neurons. These data suggest that bilateral collicular interaction is a part of dynamic acoustic signal processing that adjusts and improves signal processing as well as reorganizes collicular representation of signal parameters according to the acoustic experience.

Local neuronal circuits that may shape the discharge patterns of inferior collicular neurons

The discharge patterns of neurons in auditory centers encode information about sounds. However, few studies have focused on the synaptic mechanisms underlying the shaping of discharge patterns using intracellular recording techniques. Here, we investigated the discharge patterns of inferior collicular (IC) neurons using intracellular recordings to further elucidate the mechanisms underlying the shaping of discharge patterns. Under in vivo intracellular recording conditions, recordings were obtained from 66 IC neurons in 18 healthy adult mice (Mus musculus, Km) under free fi eld-stimulation. Fiftyeight of these neurons fi red bursts of action potentials (APs) to auditory stimuli and the remaining eight just generated local responses such as excitatory (n = 4) or inhibitory (n = 4) postsynaptic potentials. Based on the APs and subthreshold responses, the discharge patterns were classifi ed into seven types: phasic (24/58, 41.4%), phasic burst (8/58,13.8%), pauser (4/58, 6.9%), phasic-pauser (1/58, 1.7%), chopper (2/58, 3.4%), primary-like tonic (14/58, 24.1%) and sound-induced inhibitory (5/58,8.6%). We concluded that (1) IC neurons exhibit at least seven distinct discharge patterns; (2) inhibition participates in shaping the discharge pattern of most IC neurons and plays a role in sculpting the pattern, except for the primary-like tonic pattern which was not shaped by inhibition; and (3) local neural circuits are the likely structural basis that shapes the discharge patterns of IC neurons and can be formed either in the IC or in lower-level auditory structures.

Modulation of amplitude sensitivity by bilateral collicular interaction among different frequency laminae.

In the ascending auditory pathway, the commissure of the inferior colliculus (IC) interconnects the two ICs and may therefore mediate bilateral collicular interaction during sound processing. In this study, we show that electrically stimulates one IC produces facilitation or suppression of acoustically evoked response of neurons in the other IC. The facilitated IC neurons (14%) are located in bilateral corresponding frequency laminae while the suppressed IC neurons (86%) are widespreadly located in bilateral different frequency laminae. Whereas induced facilitation increases the dynamic range but decreases the slope of the rate-amplitude function of modulated IC neurons, induced suppression produces the opposite effect. As a result, bilateral collicular facilitation increases the sensitivity of modulated IC neurons to a wider range of sound amplitude while bilateral collicular suppression improves the sensitivity of modulated IC neurons to minor change in sound amplitude over a narrower range of sound amplitude. The degree of suppression is significantly greater for suppressed IC neurons located in bilateral corresponding frequency laminae than in non-corresponding frequency laminae. We suggest that bilateral collicular interaction through the commissure of the IC may play a role in modulation of amplitude sensitivity and in shaping the binaural property of IC neurons.

Sexual dimorphism in echolocation pulse parameters of the CF-FM bat, Hipposideros pratti

BackgroundPrevious studies of sexual dimorphism in the echolocation pulses of the constant frequency-frequency modulating (CF-FM) bat have been mainly concentrated on the difference in the frequency of the CF component of the predominant second harmonic while neglected other pulse parameters. However, recent studies have shown that other pulse parameters of the predominant second harmonic are also biologically significant to the bat hunting. To complement and advance these studies, we have examined sexual dimorphism of multiple parameters (e.g., duration, frequency, bandwidth of the FM component, and repetition rate of emitted pulses) of the echolocation pulses of the CF-FM bat, Hipposideros pratti.ResultsOur studies of the predominant second harmonic show that on average the male bat has higher frequency of the CF component, wider FM bandwidth, and higher pulse repetition rate while the female bat has longer duration of the CF and FM components.ConclusionsThese observations suggest that bats may potentially use this sexual dimorphism in echolocation pulse parameters for social communication and species and sex identification.

The function of offset neurons in auditory information processing

Offset neurons which respond to the termination of the sound stimulation may play important roles in auditory temporal information processing, sound signal recognition, and complex distinction. Two additional possible mechanisms were reviewed: neural inhibition and the intrinsic conductance property of offset neuron membranes. The underlying offset response was postulated to be located in the superior paraolivary nucleus of mice. The biological significance of the offset neurons was discussed as well.

Post-spike hyperpolarization participates in the formation of auditory behavior-related response patterns of inferior collicular neurons in Hipposideros pratti

To probe the mechanism underlying the auditory behavior-related response patterns of inferior collicular neurons to constant frequency-frequency modulation (CF-FM) stimulus in Hipposideros pratti, we studied the role of post-spike hyperpolarization (PSH) in the formation of response patterns. Neurons obtained by in vivo extracellular (N=145) and intracellular (N=171) recordings could be consistently classified into single-on (SO) and double-on (DO) neurons. Using intracellular recording, we found that both SO and DO neurons have a PSH with different durations. Statistical analysis showed that most SO neurons had a longer PSH duration than DO neurons (p<0.01). These data suggested that the PSH directly participated in the formation of SO and DO neurons, and the PSH elicited by the CF component was the main synaptic mechanism underlying the SO and DO response patterns. The possible biological significance of these findings relevant to bat echolocation is discussed.

Association of the C47T polymorphism in superoxide dismutase gene 2 with noise-induced hearing loss: a meta-analysis.

INTRODUCTION Currently, there is limited information about the relationship between manganese superoxide dismutase (sod2) c47t polymorphism and susceptibility to noise-induced hearing loss (NIHL). OBJECTIVE The aim of this meta-analysis was to clarify the association between SOD2 C47T polymorphism and NIHL. METHODS A search in PubMed and Web of Science was performed to collect data. All full-text, English-written studies containing sufficient and complete case-and-control data about the relationship between SOD2 C47T polymorphism and NIHL were included. Three eligible studies, comprising 1094 subjects, were identified. pooled odds ratios (ORs) and 95% confidence intervals (CI) were calculated to evaluate the strength of the association between SOD2 C47T polymorphism and NIHL. RESULTS No significant association between C47T polymorphism and risk of NIHL was found with the following combinations: T vs. C (OR=0.83; 95% CI=0.63-1.09); TT vs. CC (OR=0.49; 95% CI=0.22-1.09); CT vs. CC (OR=0.54; 95% CI=0.25-1.17); TT vs. CC+CT (OR=0.82; 95% CI=0.50-1.32); CC vs. TT+TC (OR=0.49; 95% CI=0.23-1.04). However, in subgroup analysis, a significant association was found for TT vs. CC+CT (OR=0.77; 95% CI=0.42-1.41) in the Chinese population. CONCLUSION The present meta-analysis suggests that SOD2 C47T polymorphism is significantly associated with increased risk of NIHL in the Chinese population. Further large and well-designed studies are needed to confirm this association.

Plastic Change in the Auditory Minimum Threshold Induced by Intercollicular Effects in Mice

In the auditory pathway, the commissure of the inferior colliculus (IC) interconnects the two ICs on both sides of the dorsal midbrain. This interconnection could mediate an interaction between the two ICs during sound signal processing. The intercollicular effects evoked by focal electric stimulation for 30 min could inhibit or facilitate auditory responses and induce plastic changes in the response minimum threshold (MT) of IC neurons. Changes in MT are dependent on the best frequency (BF) and MT difference. The MT shift is larger in IC neurons with BF differences ≤2 kHz than in those with BF differences >2 kHz. Moreover, MTs that shift toward electrically stimulated IC neurons increase with the increasing MT difference between the two ICs. The shift in MT lasts for a certain period of time and then returns to previous levels within ~150 min. The collicular interactions are either reciprocal or unilateral under alternate stimulating and recording conditions in both ICs. Our results suggest that intercollicular effects may be involved in the acoustic experience-dependent plasticity of the MT of IC neurons.