Phase-Locked Responses to Pure Tones in the Auditory Thalamus

2007 ◽  
Vol 98 (4) ◽  
pp. 1941-1952 ◽  
Author(s):  
Mark N. Wallace ◽  
Lucy A. Anderson ◽  
Alan R. Palmer
Keyword(s):  
Guinea Pig ◽  
Inferior Colliculus ◽  
Phase Locking ◽  
Medial Geniculate Body ◽  
Low Frequency ◽  
Sine Wave ◽  
Temporal Coding ◽  
Auditory Thalamus ◽  
Medial Geniculate ◽  
The Brain

Accurate temporal coding of low-frequency tones by spikes that are locked to a particular phase of the sine wave (phase-locking), occurs among certain groups of neurons at various processing levels in the brain. Phase-locked responses have previously been studied in the inferior colliculus and neocortex of the guinea pig and we now describe the responses in the auditory thalamus. Recordings were made from 241 single units, 32 (13%) of which showed phase-locked responses. Units with phase-locked responses were mainly (82%) located in the ventral division of the medial geniculate body (MGB), and also the medial division (18%), but were not found in the dorsal or shell divisions. The upper limiting frequency of phase-locking varied greatly between units (60–1,100 Hz) and between anatomical divisions. The upper limit in the ventral division was 520 Hz and in the medial was 1,100 Hz. The range of steady-state delays calculated from phase plots also varied: ventral division, 8.6–14 ms (mean 11.1 ms; SD 1.56); medial division, 7.5–11 ms (mean 9.3 ms; SD 1.5). Taken together, these measurements are consistent with the medial division receiving a phase-locked input directly from the brain stem, without an obligatory relay in the inferior colliculus. Cells in both the ventral and medial divisions of the MGB showed a response that phase-locked to the fundamental frequency of a guinea pig purr and may be involved in analyzing communication calls.

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.

Temporal coding of envelopes and their interaural delays in the inferior colliculus of the unanesthetized rabbit

1989 ◽  
Vol 61 (2) ◽  
pp. 257-268 ◽  
Author(s):  
R. Batra ◽  
S. Kuwada ◽  
T. R. Stanford
Keyword(s):  
Inferior Colliculus ◽  
Phase Locking ◽  
Acoustic Stimulus ◽  
Low Frequency ◽  
Auditory Pathway ◽  
Temporal Coding ◽  
Time Of Arrival ◽  
Unanesthetized Rabbit ◽  
The Difference ◽  
Ipsilateral Stimulation

1. The difference in the time of arrival of a sound at the two ears can be used to locate its source along the azimuth. Traditionally, it has been thought that only the on-going interaural temporal disparities (ITDs) produced by sounds of lower frequency (approximately less than 2 kHz) could be used for this purpose. However, ongoing ITDs of low frequency are also produced by envelopes of amplitude-modulated (AM) tones. These ITDs can be detected and used to lateralize complex high-frequency sounds (1, 8, 12, 15, 22, 24, 26). Auditory neurons synchronize to the modulation envelope, but do so at progressively lower modulation frequencies at higher levels of the auditory pathway. Some neurons of the cochlear nucleus synchronize best to frequencies as high as 700 Hz, but those of the inferior colliculus (IC) exhibit their best synchrony below 200 Hz. Even though synchrony to higher modulation frequencies is reduced at higher levels of the auditory pathway, is information about ITDs retained? 2. We answered this question by extracellularly recording the responses of neurons in the IC of the unanesthetized rabbit. We used an unanesthetized preparation because anesthesia alters the responses of neurons in the IC to both monaurally presented tones and ITDs. The unanesthetized rabbit is ideal for auditory research. Recordings can be maintained for long periods, and the acoustic stimulus to each ear can be independently controlled. 3. We studied the responses of 89 units to sinusoidally AM tones presented to the contralateral ear. For each unit, we recorded the response at several modulation frequencies. The degree of phase locking to the envelope at each frequency was measured using the synchronization coefficient. Two measures were used to assess the range of modulation frequencies over which phase locking occurred. The "best AM frequency" was the frequency at which we observed the greatest phase locking. The "highest AM frequency" was the highest frequency at which significant phase locking (0.001 level) was observed. We could not assess synchrony to ipsilateral AM tones directly, because most units did not respond to ipsilateral stimulation. 4. We studied the sensitivity of 63 units to ITDs produced by the envelopes of AM tones. Sensitivity to ITDs was tested by presenting AM tones to the two ears that had the same carrier frequency, but modulation frequencies that differed by 1 Hz. Units that were sensitive to ITDs responded to this stimulus by varying their response rate cyclically at the difference frequency, i.e., 1 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)

THE AFFERENT PATH OF THE MILK-EJECTION REFLEX IN THE BRAIN OF THE GUINEA-PIG

1967 ◽  
Vol 38 (3) ◽  
pp. 337-349 ◽  
Author(s):  
J. S. TINDAL ◽  
G. S. KNAGGS ◽  
A. TURVEY
Keyword(s):  
Guinea Pig ◽  
Medial Geniculate Body ◽  
Pituitary Stalk ◽  
Medial Lemniscus ◽  
Milk Ejection ◽  
Major Pathway ◽  
Ventral Thalamus ◽  
Medial Geniculate ◽  
Milk Ejection Reflex ◽  
The Brain

SUMMARY The afferent path of the milk-ejection reflex has been studied in the brain of the lactating guinea-pig in light pentobarbitone anaesthesia. Square-wave pulses were applied between an indifferent electrode in the scalp and a monopolar electrode inserted stereotaxically in the brain. The brain was transected at the mid-cerebellar level to eliminate activation of the sympathetico-adrenal system, and milk-ejection pressure was monitored to detect release of neurohypophysial hormone(s). The afferent path of the reflex in the caudal midbrain was very compact and lay in the lateral tegmentum. More rostrally, milk-ejection responses were obtained from the tectum and mesencephalic central grey, but the major pathway remained in the lateral tegmentum and passed forward to lie ventromedial to the medial geniculate body, after which it divided into two components which we have termed the dorsal and ventral paths. The dorsal path traversed dorsomedially across the brainstem to reach the parafascicular thalamic nucleus, the extreme rostral central grey and the periventricular region at the meso-diencephalic boundary, and then continued forward to reach the pituitary stalk and the medial and dorsal hypothalamus. The ventral path traversed ventromedially to enter the subthalamus and then the lateral hypothalamus, in which it passed both to the rostral basal diencephalon and to the pituitary stalk. In the diencephalon, milk-ejection responses were obtained after stimulation of part of the ventral thalamus, the lateral, dorsal and anterior hypothalamic areas, the dorsomedial, ventromedial, arcuate, supraoptic and paraventricular nuclei, and the pituitary stalk. It is suggested from these findings that in the guinea-pig the suckling stimulus ascends by the spinothalamic system, and continues rostrally to relay with the medial and ventral thalamus, the dorsal longitudinal fasciculus and the medial forebrain bundle. Other ascending pathways in the medial lemniscus and mammillary peduncle may also be involved, but appear to be of only minor significance.

scholarly journals Is GABA neurotransmission enhanced in auditory thalamus relative to inferior colliculus?

2014 ◽  
Vol 111 (2) ◽  
pp. 229-238 ◽  
Author(s):  
Rui Cai ◽  
Bopanna I. Kalappa ◽  
Thomas J. Brozoski ◽  
Lynne L. Ling ◽  
Donald M. Caspary
Keyword(s):  
Inferior Colliculus ◽  
Chloride Channel ◽  
Single Unit ◽  
Ex Vivo ◽  
Medial Geniculate Body ◽  
Gamma Aminobutyric Acid ◽  
Auditory Thalamus ◽  
Medial Geniculate

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central auditory system. Sensory thalamic structures show high levels of non-desensitizing extrasynaptic GABAA receptors (GABAARs) and a reduction in the redundancy of coded information. The present study compared the inhibitory potency of GABA acting at GABAARs between the inferior colliculus (IC) and the medial geniculate body (MGB) using quantitative in vivo, in vitro, and ex vivo experimental approaches. In vivo single unit studies compared the ability of half maximal inhibitory concentrations of GABA to inhibit sound-evoked temporal responses, and found that GABA was two to three times ( P < 0.01) more potent at suppressing MGB single unit responses than IC unit responses. In vitro whole cell patch-clamp slice recordings were used to demonstrate that gaboxadol, a δ-subunit selective GABAAR agonist, was significantly more potent at evoking tonic inhibitory currents from MGB neurons than IC neurons ( P < 0.01). These electrophysiological findings were supported by an in vitro receptor binding assay which used the picrotoxin analog [3H]TBOB to assess binding in the GABAAR chloride channel. MGB GABAARs had significantly greater total open chloride channel capacity relative to GABAARs in IC ( P < 0.05) as shown by increased total [3H]TBOB binding. Finally, a comparative ex vivo measurement compared endogenous GABA levels and suggested a trend towards higher GABA concentrations in MGB than in IC. Collectively, these studies suggest that, per unit GABA, high affinity extrasynaptic and synaptic GABAARs confer a significant inhibitory GABAAR advantage to MGB neurons relative to IC neurons. This increased GABA sensitivity likely underpins the vital filtering role of auditory thalamus.

off Responses in the Auditory Thalamus of the Guinea Pig

2002 ◽  
Vol 88 (5) ◽  
pp. 2377-2386 ◽  
Author(s):  
Jufang He
Keyword(s):  
Guinea Pig ◽  
Frequency Tuning ◽  
Medial Geniculate Body ◽  
Noise Burst ◽  
Border Region ◽  
Tuning Curves ◽  
Auditory Thalamus ◽  
Auditory Responses ◽  
Medial Geniculate ◽  
The Mean

on and off auditory responses were examined in the medial geniculate body (MGB) of the guinea pig. Single- and multiunit recordings were carried out on 12 anesthetized animals, and noise-burst or pure-tone stimuli were applied to the ear contralateral to the recording hemisphere. One hundred and thirty-fiveoff or on-off neurons and 160 onneurons were studied, and the tuning curves of 21 on-off oroff neurons were examined from various nuclei of the MGB. The mean minimum threshold of the off responses (40.8 ± 20.0 dB SPL, mean ± SD; range: 0–80 dB SPL) was significantly higher than that of the on responses (28.5 ± 17.6 dB SPL, range: 0–60 dB SPL; n = 17, P < 0.001). Of 10 on-off neurons that showed identifiable tuning frequencies for both on andoff responses, 7 showed a higher off thanon best frequency (BF), 2 showed the same BF for bothon and off, and only 1 showed a slightly loweroff than on BF. Most off responses sampled from the borders of the ventral (MGv) and the rostromedial (MGrm) nuclei of the MGB showed single-peaked tuning curves, similar to those of the on responses in the MGv. The neurons located in the shell (MGs) and dorsal (MGd) nuclei of the MGB showed complicated—either multi-peaked or broad—tuning curves. Alloff responses showed long-duration-selectivity for acoustic stimuli: the mean half-maximum duration was 116.5 ± 114.8 ms ( n = 19, range: 27–411 ms). The latencies of 135off responses were studied in various divisions of the MGB. The ventral border region of MGv showed the shortest latency, followed by the dorsal border region of the MGv, the MGrm, and the caudomedial nucleus (MGcm) of the MGB. The posterior nucleus of the thalamus (Po), the MGd, and the MGs showed much longer mean latencies of >30 ms ( P < 0.05 compared with the border regions of the MGv, ANOVA), with Po showing the greatest mean latency of 60.3 ms and the greatest deviation of 25.5 ms). The latency of the offresponse (29.0 ± 14.0 ms, n = 135) was significantly greater than that of the on response (15.6 ± 9.6 ms, n = 160, P < 0.001). The present results provide valuable information about the threshold, frequency tuning characteristics, minimal response latency, and duration selectivity of off neurons in the auditory thalamus.

scholarly journals Postnatal development of synaptic properties of the GABAergic projection from the inferior colliculus to the auditory thalamus

2013 ◽  
Vol 109 (12) ◽  
pp. 2866-2882 ◽  
Author(s):  
Yamini Venkataraman ◽  
Edward L Bartlett
Keyword(s):  
Inferior Colliculus ◽  
Temporal Processing ◽  
Brain Slices ◽  
Critical Time ◽  
Membrane Properties ◽  
Auditory Temporal Processing ◽  
Postsynaptic Potentials ◽  
Auditory Thalamus ◽  
Inhibitory Postsynaptic Potentials ◽  
Medial Geniculate

The development of auditory temporal processing is important for processing complex sounds as well as for acquiring reading and language skills. Neuronal properties and sound processing change dramatically in auditory cortex neurons after the onset of hearing. However, the development of the auditory thalamus or medial geniculate body (MGB) has not been well studied over this critical time window. Since synaptic inhibition has been shown to be crucial for auditory temporal processing, this study examined the development of a feedforward, GABAergic connection to the MGB from the inferior colliculus (IC), which is also the source of sensory glutamatergic inputs to the MGB. IC-MGB inhibition was studied using whole cell patch-clamp recordings from rat brain slices in current-clamp and voltage-clamp modes at three age groups: a prehearing group [ postnatal day (P)7–P9], an immediate posthearing group (P15–P17), and a juvenile group (P22–P32) whose neuronal properties are largely mature. Membrane properties matured substantially across the ages studied. GABAA and GABAB inhibitory postsynaptic potentials were present at all ages and were similar in amplitude. Inhibitory postsynaptic potentials became faster to single shocks, showed less depression to train stimuli at 5 and 10 Hz, and were overall more efficacious in controlling excitability with age. Overall, IC-MGB inhibition becomes faster and more precise during a time period of rapid changes across the auditory system due to the codevelopment of membrane properties and synaptic properties.

Modulatory Effect of Cortical Activation on the Lemniscal Auditory Thalamus of the Guinea Pig

2002 ◽  
Vol 88 (2) ◽  
pp. 1040-1050 ◽  
Author(s):  
Jufang He ◽  
Yan-Qin Yu ◽  
Ying Xiong ◽  
Tsutomu Hashikawa ◽  
Ying-Shing Chan
Keyword(s):  
Guinea Pig ◽  
Auditory Cortex ◽  
Firing Pattern ◽  
Inhibitory Effect ◽  
Electrical Activation ◽  
Facilitatory Effect ◽  
Thalamic Neurons ◽  
Auditory Thalamus ◽  
Medial Geniculate ◽  
Corticofugal Modulation

In the present study, we investigated the point-to-point modulatory effects from the auditory cortex to the thalamus in the guinea pig. Corticofugal modulation on thalamic neurons was studied by electrical activation of the auditory cortex. The modulation effect was sampled along the frontal or sagittal planes of the auditory thalamus, focusing on the ventral division (MGv) of the medial geniculate body (MGB). Electrical activation was targeted at the anterior and dorsocaudal auditory fields, to which the MGv projects and from which it assumptively receives reciprocal projections. Of the 101 MGv neurons examined by activation of the auditory cortex through passing pulse trains of 100–200 μA current into one after another of the three implanted electrodes (101 neurons × 3 stimulation sites = 303 cases), 208 cases showed a facilitatory effect, 85 showed no effect, and only 10 cases (7 neurons) showed an inhibitory effect. Among the cases of facilitation, 63 cases showed a facilitatory effect >100%, and 145 cases showed a facilitatory effect from 20–100%. The corticofugal modulatory effect on the MGv of the guinea pig showed a widespread, strong facilitatory effect and very little inhibitory effect. The MGv neurons showed the greatest facilitations to stimulation by the cortical sites, with the closest correspondence in BF. Six of seven neurons showed an elevation of the rate-frequency functions when the auditory cortex was activated. The comparative results of the corticofugal modulatory effects on the MGv of the guinea pig and the cat, together with anatomical findings, hint that the strong facilitatory effect is generated through the strong corticothalamic direct connection and that the weak inhibitory effect might be mainly generated via the interneurons of the MGv. The temporal firing pattern of neuronal response to auditory stimulus was also modulated by cortical stimulation. The mean first-spike latency increased significantly from 15.7 ± 5.3 ms with only noise-burst stimulus to 18.3 ± 4.9 ms ( n = 5, P < 0.01, paired t-test), while the auditory cortex was activated with a train of 10 pulses. Taking these results together with those of previous experiments conducted on the cat, we speculate that the relatively weaker inhibitory effect compared with that in the cat could be due to the smaller number of interneurons in the guinea pig MGB. The corticofugal modulation of the firing pattern of the thalamic neurons might enable single neurons to encode more auditory information using not only the firing rate but also the firing pattern.

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