Responses of Neurons in the Ventral Nucleus of the Lateral Lemniscus to Sinusoidally Amplitude Modulated Tones

2006 ◽  
Vol 96 (5) ◽  
pp. 2388-2398 ◽  
Author(s):  
Ranjan Batra
Keyword(s):  
Spontaneous Activity ◽  
Transfer Functions ◽  
Modulation Frequency ◽  
Auditory Pathway ◽  
Modulation Transfer ◽  
Lateral Lemniscus ◽  
Modulation Transfer Functions ◽  
Band Pass ◽  
Acoustic Space ◽  
Ventral Nucleus

Fluctuations in the amplitude of a sound play an important role in our perception of pitch and acoustic space, but their neural analysis has not been fully elucidated. The ventral nucleus of the lateral lemniscus (VNLL) has been implicated in the processing of such temporal features of a sound. This study examines responses of neurons in the VNLL of unanesthetized rabbits to sinusoidally amplitude modulated tones, a type of stimulus that has often been used to investigate encoding of temporal information. Modulation transfer functions of responses were calculated in two ways: based on discharge rates (rMTFs) and on synchronization to the envelope (tMTFs). Among the variety of rMTFs, two types were readily identifiable: flat and band-pass. The responses of neurons exhibiting these types of rMTF differed in several ways. Neurons with flat rMTFs typically had moderate rates of spontaneous activity, sustained responses to short tone bursts, and low-pass or band-pass tMTFs. Neurons with band-pass rMTFs typically had low spontaneous activity, onset responses to short tone bursts, and flat tMTFs. The vast majority synchronized strongly to the modulation envelope. The best modulation frequencies of neurons with band-pass rMTFs extended from 14 to 283 Hz. The presence of neurons with band-pass rMTFs in the VNLL suggests that this nucleus plays a role in converting the temporal code for modulation frequency used in lower structures into a rate-based code for use higher in the auditory pathway. The substantial number of neurons with more complex modulation transfer functions indicates that the VNLL has other functions.

scholarly journals Responses of Neurons in the Rat's Ventral Nucleus of the Lateral Lemniscus to Amplitude-Modulated Tones

2006 ◽  
Vol 96 (6) ◽  
pp. 2905-2914 ◽  
Author(s):  
Huiming Zhang ◽  
Jack B. Kelly
Keyword(s):  
Firing Rate ◽  
Transfer Functions ◽  
Modulation Frequency ◽  
Lateral Lemniscus ◽  
Low Pass ◽  
Band Pass ◽  
Contralateral Ear ◽  
Ventral Nucleus ◽  
Vector Strength ◽  
Onset Responses

Recordings were made from single neurons in the rat's ventral nucleus of the lateral lemniscus (VNLL) to determine responses to amplitude-modulated (AM) tones. The neurons were first characterized on the basis of their response to tone bursts presented to the contralateral ear and a distinction was made between those with transient onset responses and those with sustained responses. Sinusoidal AM tones were then presented to the contralateral ear with a carrier that matched the neuron's characteristic frequency (CF). Modulation transfer functions were generated on the basis of firing rate (MTFFR) and vector strength (MTFVS). Ninety-two percent of onset neurons that responded continuously to AM tones had band-pass MTFFRs with best modulation frequencies from 10 to 300 Hz. Fifty-four percent of sustained neurons had band-pass MTFFRs with best modulation frequencies from 10 to 500 Hz; other neurons had band-suppressed, all-pass, low-pass, or high-pass functions. Most neurons showed either band-pass or low-pass MTFVS. Responses were well synchronized to the modulation cycle with maximum vector strengths ranging from 0.37 to 0.98 for sustained neurons and 0.78 to 0.99 for onset neurons. The upper frequency limit for response synchrony was higher than that reported for inferior colliculus, but lower than that seen in more peripheral structures. Results suggest that VNLL neurons, especially those with onset responses to tone bursts, are sensitive to temporal features of sounds and narrowly tuned to different modulation rates. However, there was no evidence of a topographic relation between dorsoventral position along the length of VNLL and best modulation frequency as determined by either firing rate or vector strength.

GABAergic Disinhibition Affects Responses of Bat Inferior Collicular Neurons to Temporally Patterned Sound Pulses

1998 ◽  
Vol 79 (5) ◽  
pp. 2303-2315 ◽  
Author(s):  
Yong Lu ◽  
Philip H.-S. Jen ◽  
Min Wu
Keyword(s):  
Transfer Functions ◽  
Average Rate ◽  
Free Field ◽  
Response Repetition ◽  
Modulation Transfer ◽  
Modulation Transfer Functions ◽  
Low Pass ◽  
Band Pass ◽  
Inferior Collicular ◽  
Sound Pulses

Lu, Yong, Philip H.-S. Jen, and Min Wu. GABAergic disinhibition affects responses of bat inferior collicular neurons to temporally patterned sound pulses. J. Neurophysiol. 79: 2303–2315, 1998. Using the big brown bat, Eptesicus fuscus, as a model mammalian auditory system, we studied the effect of GABAergic disinhibition by bicuculline on the responses of inferior collicular (IC) neurons to temporally patterned trains of sound pulses delivered at different pulse repetition rates (PRRs) under free-field stimulation conditions. All 66 neurons isolated from eight bats either discharged one to two impulses (phasic on responders, n = 41, 62%), three to eight impulses (phasic bursters, n = 19, 29%), or many impulses throughout the entire duration of the stimulus (tonicresponders, n = 6, 9%). Whereas 50 neurons responded vigorously to frequency-modulated (FM) pulses, 16 responded poorly ornot at all to FM pulses. Bicuculline application increased the number of impulses of all 66 neurons in response to 4 ms pulses by 15–1,425%. The application also changed most phasic on responders into phasic bursters or tonic responders, resulting in 12 (18%) phasic on responders, 34 (52%) phasic bursters, and 20 (30%) tonic responders. Response latencies of these neurons were either shortened ( n = 25, 38%) by 0.5–6.0 ms, lengthened ( n = 9, 14%) by 0.5–2.5 ms or not changed ( n = 32, 48%) on bicuculline application. Each neuron had a highest response repetition rate beyond which the neuron failed to respond. Bicuculline application increased the highest response repetition rates of 62 (94%) neurons studied. The application also increased the highest 100% pulse-locking repetition rates of 21 (32%) neurons and facilitated 27 (41%) neurons in response to more pulses at the same PRR than predrug conditions. According to average rate-based modulation transfer functions (average rate MTFs), all 66 neurons had low-pass filtering characteristics both before and after bicuculline application. According to total discharge rate-based modulation transfer functions (total rate MTFs), filtering characteristics of these neurons can be described as band-pass ( n = 52, 79%), low-pass ( n = 12, 18%), or high-pass ( n = 2, 3%) before bicuculline application. Bicuculline application changed the filtering characteristics of 14 (21%) neurons. According to synchronization coefficient-based modulation transfer functions, filtering characteristics of these neurons can be described as low-pass ( n = 41, 62%), all-pass ( n = 11, 17%), band-suppression ( n = 7, 10.5%), and band-suppression–band-pass filters ( n = 7, 10.5%). Bicuculline application changed filtering characteristics of 19 (29%) neurons.

Modulation Transfer Functions

1990 ◽  
Vol 33 (2) ◽  
pp. 390-397 ◽  
Author(s):  
Diane M. Scott ◽  
Larry E. Humes
Keyword(s):  
Transfer Functions ◽  
Modulation Frequency ◽  
Normal Hearing ◽  
Probe Method ◽  
Lowpass Filter ◽  
Modulation Transfer ◽  
Probe Tone ◽  
Modulation Transfer Functions ◽  
Cutoff Frequencies ◽  
Factors Influencing

Modulation transfer functions (MTFs) were measured with three different psychoacoustical paradigms in the same normal-hearing subjects. In the temporal-probe method, the threshold of a 4-ms probe tone (frequencies of 1000 and 4000 Hz) was measured at various envelope phases within a 100% sinusoidally amplitude-modulated (SAM) noise at modulation frequencies from 2 to 256 Hz. For the derived-MTF method, the threshold of a 500-ms tone at 1000 and 4000 Hz was measured in the same noise at the same modulation frequencies. For the modulation-detection paradigm, modulation thresholds were measured as a function of modulation frequency for bandpass filtered SAM noise centered at 1000 and 4000 Hz. MTFs with lowpass shapes were observed with all three methods. Differences were observed in the cutoff frequencies and/or attenuation rates when the data were fitted with lowpass filter transfer functions. Factors influencing those differences are discussed.

scholarly journals Amplitude modulation encoding in the auditory cortex: comparisons between the primary and middle lateral belt regions

2020 ◽  
Vol 124 (6) ◽  
pp. 1706-1726
Author(s):  
Jeffrey S. Johnson ◽  
Mamiko Niwa ◽  
Kevin N. O’Connor ◽  
Mitchell L. Sutter
Keyword(s):  
Auditory Cortex ◽  
Amplitude Modulation ◽  
Neural Activity ◽  
Transfer Functions ◽  
Modulation Frequency ◽  
Modulation Transfer ◽  
Modulation Transfer Functions ◽  
A1 Neurons ◽  
Two Populations

ML neurons synchronized less than A1 neurons, consistent with a hierarchical temporal-to-rate transformation. Both A1 and ML had a class of modulation transfer functions previously unreported in the cortex with a low-modulation-frequency (MF) peak, a middle-MF trough, and responses similar to unmodulated noise responses at high MFs. The results support a hierarchical shift toward a two-pool opponent code, where subtraction of neural activity between two populations of oppositely tuned neurons encodes AM.

Intracellular Responses of Neurons in the Mouse Inferior Colliculus to Sinusoidal Amplitude-Modulated Tones

2009 ◽  
Vol 101 (4) ◽  
pp. 2002-2016 ◽  
Author(s):  
H.-R. Geis ◽  
J. G. G. Borst
Keyword(s):  
Membrane Potential ◽  
Inferior Colliculus ◽  
Transfer Functions ◽  
Modulation Frequency ◽  
Modulation Transfer ◽  
Postsynaptic Potentials ◽  
Low Pass ◽  
Band Pass ◽  
Brief Tones ◽  
High Pass

Changes in the temporal envelope are important defining features of natural acoustic signals. Many cells in the inferior colliculus (IC) respond preferentially to certain modulation frequencies, but how they accomplish this is not yet clear. We therefore made whole cell patch-clamp recordings in the IC of anesthetized mice while presenting sinusoidal amplitude-modulated (SAM) tones. The relation between the number of evoked spikes and modulation frequency was used to construct rate modulation transfer functions (rMTFs). We observed different types of rate tuning, including band-pass (16%), band-reject (13%), high-pass (6%), and low-pass (6%) tuning. In the high-pass rMTF neurons and some of the low-pass rMTF neurons, the tuning characteristics appeared to be already present in the inputs. In both band-pass and band-reject rMTF neurons, the nonlinear relation between membrane potential and spike probability ensured preferential spiking during only a small part of the modulation period. Band-pass rMTF neurons had rapidly rising excitatory postsynaptic potentials, allowing good phase-locking to brief tones and intermediate modulation frequencies. At low modulation frequencies, adaptation of their spike threshold contributed to the onset response. In contrast, band-reject rMTF neurons responded with small excitatory or inhibitory postsynaptic potentials to brief tones. In these cells, a power law could describe the supralinear relation between average membrane potential and spike rate. Differences in timing of synaptic input and presence or absence of spike adaptation therefore define band-pass and band-reject rate tuning to SAM tones in the mouse IC.

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