Intracellular Recording Reveals Temporal Integration in Inferior Colliculus Neurons of Awake Bats

2007 ◽  
Vol 97 (2) ◽  
pp. 1368-1378 ◽  
Author(s):  
S. V. Voytenko ◽  
A. V. Galazyuk
Keyword(s):  
Inferior Colliculus ◽  
Temporal Integration ◽  
Myotis Lucifugus ◽  
Central Nucleus ◽  
Intracellular Recordings ◽  
Auditory Pathways ◽  
Postsynaptic Potentials ◽  
Sound Levels ◽  
Wide Range ◽  
Little Brown Bats

The central nucleus of the inferior colliculus (IC) is a major integrative center in the central auditory system. It receives information from both the ascending and descending auditory pathways. To determine how single IC neurons integrate information over a wide range of sound frequencies and sound levels, we examined their intracellular responses to frequency-modulated (FM) sounds in awake little brown bats ( Myotis lucifugus). Postsynaptic potentials were recorded in response to downward FM sweeps of the range typical for little brown bats (80–20 kHz) and to three FM subcomponents (80–60, 60–40, and 40–20 kHz). The majority of recorded neurons responded to the 80- to 20-kHz downward FM sweep with a complex response. In this response an initial hyperpolarization was followed by depolarization with or without spike followed by hyperpolarization. Intracellular recordings in response to three FM subcomponents revealed that these neurons receive excitatory and inhibitory inputs from a wide range of sound frequencies. One third of IC neurons performed nearly linear temporal summation across a wide range of sound frequencies, whereas two thirds of IC neurons exhibited nonlinear summation with different degrees of nonlinearity. Some IC neurons showed different latencies of postsynaptic potentials in response to different FM subcomponents. Often responses to the later FM subcomponent occurred before responses to the earlier ones. This phenomenon may be responsible for response selectivity of IC neurons to FM sweeps.

Coactivation of different neurons within an isofrequency lamina of the inferior colliculus elicits enhanced auditory cortical activation

2012 ◽  
Vol 108 (4) ◽  
pp. 1199-1210 ◽  
Author(s):  
Roger Calixto ◽  
Minoo Lenarz ◽  
Anke Neuheiser ◽  
Verena Scheper ◽  
Thomas Lenarz ◽  
...  
Keyword(s):  
Inferior Colliculus ◽  
Temporal Integration ◽  
Three Dimensional ◽  
Primary Auditory Cortex ◽  
Cortical Activation ◽  
Central Nucleus ◽  
Speech Understanding ◽  
Auditory Midbrain ◽  
Temporal Cues ◽  
Multiple Regions

The phenomenal success of the cochlear implant (CI) is attributed to its ability to provide sufficient temporal and spectral cues for speech understanding. Unfortunately, the CI is ineffective for those without a functional auditory nerve or an implantable cochlea required for CI implementation. As an alternative, our group developed and implanted in deaf patients a new auditory midbrain implant (AMI) to stimulate the central nucleus of the inferior colliculus (ICC). Although the AMI can provide frequency cues, it appears to insufficiently transmit temporal cues for speech understanding. The three-dimensional ICC consists of two-dimensional isofrequency laminae. The single-shank AMI only stimulates one site in any given ICC lamina and does not exhibit enhanced activity (i.e., louder percepts or lower thresholds) for repeated pulses on the same site with intervals <2–5 ms, as occurs for CI pulse or acoustic click stimulation. This enhanced activation, related to short-term temporal integration, is important for tracking the rapid temporal fluctuations of a speech signal. Therefore, we investigated the effects of coactivation of different regions within an ICC lamina on primary auditory cortex activity in ketamine-anesthetized guinea pigs. Interestingly, our findings reveal an enhancement mechanism for integrating converging inputs from an ICC lamina on a fast scale (<6-ms window) that is compromised when stimulating just a single ICC location. Coactivation of two ICC regions also reduces the strong and long-term (>100 ms) suppressive effects induced by repeated stimulation of just a single location. Improving AMI performance may require at least two shanks implanted along the tonotopic gradient of the ICC that enables coactivation of multiple regions along an ICC lamina with the appropriate interstimulus delays.

Immediate Changes in Tuning of Inferior Colliculus Neurons Following Acute Lesions of Cat Spiral Ganglion

2002 ◽  
Vol 87 (1) ◽  
pp. 434-452 ◽  
Author(s):  
Russell L. Snyder ◽  
Donal G. Sinex
Keyword(s):  
Inferior Colliculus ◽  
Spiral Ganglion ◽  
Primary Auditory Cortex ◽  
Compound Action Potential ◽  
Central Nucleus ◽  
Auditory Information ◽  
Cells Of Origin ◽  
Wide Range ◽  
Before And After ◽  
Evoked Compound Action Potential

In previous studies, we demonstrated that acute lesions the spiral ganglion (SG), the cells of origin of the auditory nerve (AN), change the frequency organization of the inferior colliculus central nucleus (ICC) and primary auditory cortex (AI). In those studies, we used a map/re-map approach and recorded the tonotopic organization of neurons before and after restricted SG lesions. In the present study, response areas (RAs) of ICC multi-neuronal clusters were recorded to contralateral and ipsilateral tones after inserting and fixing-in-place tungsten microelectrodes. RAs were recorded from most electrodes before, immediately (within 33–78 min) after, and long(several hours) after restricted mechanical lesions of the ganglion. Each SG lesion produced a “notch” in the tone-evoked compound action potential (CAP) audiogram corresponding to a narrow range of lesion frequencies with elevated thresholds. Responses of contralateral IC neurons, which responded to these lesion frequencies, underwent an elevation in threshold to the lesion frequencies with either no change in sensitivity to other frequencies or with dramatic decreases in threshold to lesion-edge frequencies. These changes in sensitivity produced shifts in characteristic frequency (CF) that could be more than an octave. Thresholds at these new CFs matched the prelesion thresholds of neurons tuned to the lesion-edge frequencies. Responses evoked by ipsilateral tones delivered to the intact ear often underwent complementary changes, i.e., decreased thresholds to lesion frequency tones with little or no change in sensitivity to other frequencies. These results indicate that responses of IC neurons are produced by convergence of auditory information across a wide range of AN fibers and that the acute “plastic” changes reported in our previous studies occur within 1 h of an SG lesion.

AMPA and NMDA Receptors Regulate Responses of Neurons in the Rat's Inferior Colliculus

2001 ◽  
Vol 86 (2) ◽  
pp. 871-880 ◽  
Author(s):  
Huiming Zhang ◽  
Jack B. Kelly
Keyword(s):  
Nmda Receptors ◽  
Inferior Colliculus ◽  
Ampa Receptors ◽  
Action Potentials ◽  
Drug Application ◽  
Pronounced Effect ◽  
Central Nucleus ◽  
Wide Range ◽  
Ampa And Nmda Receptors ◽  
Excitatory Responses

The contribution of N-methyl-d-aspartate (NMDA) and AMPA receptors to auditory responses in the rat's inferior colliculus was examined by recording single-unit activity before, during, and after local iontophoretic application of receptor-specific antagonists. Tone bursts and sinusoidal amplitude modulated sounds were presented to one ear, and recordings were made from the contralateral central nucleus of inferior colliculus (ICC). The receptor specific antagonists, (±)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) for NMDA receptors and 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX) for AMPA receptors, were released at the recording site through a multi-barreled pipette. For most neurons, either CPP or NBQX alone resulted in a reversible reduction in the number of action potentials evoked by tonal stimulation. For neurons with an onset response pattern, NBQX either completely eliminated or greatly reduced the number of action potentials. CPP also reduced the number of action potentials but had a less pronounced effect than NBQX. For neurons with a sustained firing pattern, NBQX reduced the total number of action potentials, but had a preferential effect on the early part (first 10–20 ms) of the response. CPP also resulted in a reduction in the total number of action potentials, but had a more pronounced effect on the later part (>20 ms) of the response. These results indicate that both AMPA and NMDA receptors contribute to sound evoked excitatory responses in the ICC. They have a selective influence on early and late components of tone-evoked responses. Both receptor types are involved in generating excitatory responses across a wide range of sound pressure levels as indicated by rate level functions obtained before and during drug application. In addition, both CPP and NBQX reduced responses to sinusoidal amplitude modulated sounds. The synchrony of firing to the modulation envelope as measured by vector strength at different rates of modulation was not greatly affected by either CPP or NBQX in spite of the decrease in firing rate.

scholarly journals Transformation of spatial sensitivity along the ascending auditory pathway

2015 ◽  
Vol 113 (9) ◽  
pp. 3098-3111 ◽  
Author(s):  
Justin D. Yao ◽  
Peter Bremen ◽  
John C. Middlebrooks
Keyword(s):  
Inferior Colliculus ◽  
Primary Auditory Cortex ◽  
Noise Burst ◽  
Auditory Pathway ◽  
Sound Level ◽  
Central Nucleus ◽  
Sound Location ◽  
Spatial Sensitivity ◽  
Sound Levels ◽  
Medial Geniculate

Locations of sounds are computed in the central auditory pathway based primarily on differences in sound level and timing at the two ears. In rats, the results of that computation appear in the primary auditory cortex (A1) as exclusively contralateral hemifield spatial sensitivity, with strong responses to sounds contralateral to the recording site, sharp cutoffs across the midline, and weak, sound-level-tolerant responses to ipsilateral sounds. We surveyed the auditory pathway in anesthetized rats to identify the brain level(s) at which level-tolerant spatial sensitivity arises. Noise-burst stimuli were varied in horizontal sound location and in sound level. Neurons in the central nucleus of the inferior colliculus (ICc) displayed contralateral tuning at low sound levels, but tuning was degraded at successively higher sound levels. In contrast, neurons in the nucleus of the brachium of the inferior colliculus (BIN) showed sharp, level-tolerant spatial sensitivity. The ventral division of the medial geniculate body (MGBv) contained two discrete neural populations, one showing broad sensitivity like the ICc and one showing sharp sensitivity like A1. Dorsal, medial, and shell regions of the MGB showed fairly sharp spatial sensitivity, likely reflecting inputs from A1 and/or the BIN. The results demonstrate two parallel brainstem pathways for spatial hearing. The tectal pathway, in which sharp, level-tolerant spatial sensitivity arises between ICc and BIN, projects to the superior colliculus and could support reflexive orientation to sounds. The lemniscal pathway, in which such sensitivity arises between ICc and the MGBv, projects to the forebrain to support perception of sound location.

Single-Unit Responses in the Inferior Colliculus of Decerebrate Cats II. Sensitivity to Interaural Level Differences

1999 ◽  
Vol 82 (1) ◽  
pp. 164-175 ◽  
Author(s):  
Kevin A. Davis ◽  
Ramnarayan Ramachandran ◽  
Bradford J. May
Keyword(s):  
Frequency Response ◽  
Inferior Colliculus ◽  
Free Field ◽  
Central Nucleus ◽  
Type I ◽  
Discharge Rates ◽  
Ipsilateral Stimulation ◽  
Interaural Level Differences ◽  
Type V ◽  
Decerebrate Cats

Single units in the central nucleus of the inferior colliculus (ICC) of unanesthetized decerebrate cats can be grouped into three distinct types (V, I, and O) according to the patterns of excitation and inhibition revealed in contralateral frequency response maps. This study extends the description of these response types by assessing their ipsilateral and binaural response map properties. Here the nature of ipsilateral inputs is evaluated directly using frequency response maps and compared with results obtained from methods that rely on sensitivity to interaural level differences (ILDs). In general, there is a one-to-one correspondence between observed ipsilateral input characteristics and those inferred from ILD manipulations. Type V units receive ipsilateral excitation and show binaural facilitation (EE properties); type I and type O units receive ipsilateral inhibition and show binaural excitatory/inhibitory (EI) interactions. Analyses of binaural frequency response maps show that these ILD effects extend over the entire receptive field of ICC units. Thus the range of frequencies that elicits excitation from type V units is expanded with increasing levels of ipsilateral stimulation, whereas the excitatory bandwidth of type I and O units decreases under the same binaural conditions. For the majority of ICC units, application of bicuculline, an antagonist for GABAA-mediated inhibition, does not alter the basic effects of binaural stimulation; rather, it primarily increases spontaneous and maximum discharge rates. These results support our previous interpretations of the putative dominant inputs to ICC response types and have important implications for midbrain processing of competing free-field sounds that reach the listener with different directional signatures.

Phase-Locked Responses to Pure Tones in the Inferior Colliculus

2006 ◽  
Vol 95 (3) ◽  
pp. 1926-1935 ◽  
Author(s):  
Liang-Fa Liu ◽  
Alan R. Palmer ◽  
Mark N. Wallace
Keyword(s):  
Guinea Pig ◽  
Inferior Colliculus ◽  
Phase Locking ◽  
Single Units ◽  
Central Nucleus ◽  
Dorsal Cortex ◽  
Upper Limits ◽  
Ascending Pathways ◽  
Pure Tones ◽  
The Brain

In the auditory system, some ascending pathways preserve the precise timing information present in a temporal code of frequency. This can be measured by studying responses that are phase-locked to the stimulus waveform. At each stage along a pathway, there is a reduction in the upper frequency limit of the phase-locking and an increase in the steady-state latency. In the guinea pig, phase-locked responses to pure tones have been described at various levels from auditory nerve to neocortex but not in the inferior colliculus (IC). Therefore we made recordings from 161 single units in guinea pig IC. Of these single units, 68% (110/161) showed phase-locked responses. Cells that phase-locked were mainly located in the central nucleus but also occurred in the dorsal cortex and external nucleus. The upper limiting frequency of phase-locking varied greatly between units (80−1,034 Hz) and between anatomical divisions. The upper limits in the three divisions were central nucleus, >1,000 Hz; dorsal cortex, 700 Hz; external nucleus, 320 Hz. The mean latencies also varied and were central nucleus, 8.2 ± 2.8 (SD) ms; dorsal cortex, 17.2 ms; external nucleus, 13.3 ms. We conclude that many cells in the central nucleus receive direct inputs from the brain stem, whereas cells in the external and dorsal divisions receive input from other structures that may include the forebrain.

Elevated mercury exposure and neurochemical alterations in little brown bats (Myotis lucifugus) from a site with historical mercury contamination

Ecotoxicology ◽  
2012 ◽  
Vol 21 (4) ◽  
pp. 1094-1101 ◽  
Author(s):  
Dong-Ha Nam ◽  
David Yates ◽  
Pedro Ardapple ◽  
David C. Evers ◽  
John Schmerfeld ◽  
...  
Keyword(s):  
Mercury Exposure ◽  
Myotis Lucifugus ◽  
Mercury Contamination ◽  
A Site ◽  
Little Brown Bats
Sign in / Sign up

Export Citation Format

Share Document