Responses of neurons in the auditory pathway of the barn owl to partially correlated binaural signals

1995 ◽  
Vol 74 (4) ◽  
pp. 1689-1700 ◽  
Author(s):  
Y. Albeck ◽  
M. Konishi
Keyword(s):  
Inferior Colliculus ◽  
Cross Correlation ◽  
Frequency Tuning ◽  
Neuronal Response ◽  
Interaural Time Difference ◽  
Central Nucleus ◽  
High Threshold ◽  
Correlation Model ◽  
Response Curves ◽  
The Cross

1. Extracellular single-unit recording in anesthetized barn owls was used to study neuronal response to dichotic stimuli of variable binaural correlation (BC). Recordings were made in the output fibers of nucleus laminaris (NL), the anterior division of the ventral lateral lemniscal nucleus (VLVa), the core of the central nucleus of the inferior colliculus (ICcC), the lateral shell of the central nucleus of the inferior colliculus (ICcLS), and the external nucleus of the inferior colliculus (ICx). 2. The response of all neurons sensitive to interaural time difference (ITD) varied with BC. The relationship between BC and impulse number fits a linear, a parabolic, or a ramp model. A linear or parabolic model fits most neurons in low-level nuclei. Higher order neurons in ICx did not respond to noise bursts with strong negative binaural correlation, creating a ramp-like response to BC. 3. A neuron's ability to detect ITD varied as a function of BC. Conversely, a neuron's response to BC changed with ITD. Neurons in NL, VLVa, and ICcC show almost periodic ITD response curves. In these neurons peaks and troughs of ITD response curves diminished as BC decreased, creating a flat ITD response when BC = 0. When BC was set to -1, the most favorable ITD became the least favorable one and vice versa. The ITD response curve of ICx neurons usually has a single dominant peak. The response of those neurons to a negatively correlated noise pair (BC = -1) showed two ITD peaks, flanking the position of the primary peak. 4. The parabolic BC response of NL neurons fits the prediction of the cross-correlation model, assuming half-wave rectification of the sound by the cochlea. Linear response is not predicted by the model. However, the parabolic and the linear neurons probably do not belong to two distinct groups as the difference between them is not statistically significant. Thus, the cross-correlation model provides a good description of the binaural response not only in NL but also in VLVa and ICcC. 5. Almost all ramp neurons occurred in either ICx or ICcLS where neurons are more broadly tuned to frequency than those in the lower nuclei. The synthesis of this response type requires, however, not only the convergence of different frequency channels but also inhibition between different ITD channels. We modeled the ramp response as a three-step process. First, different spectral channels converge to create broad frequency tuning. The response to variation in BC will be linear (or parabolic) because it is a sum of linear (parabolic) responses. Second, the activity in some adjacent ITD channels is subtracted by lateral inhibition. Finally, the result is rectified using a high threshold to avoid negative activity.

Central and peripheral contributions to coding of acoustic space by neurons in inferior colliculus of cat

1986 ◽  
Vol 55 (3) ◽  
pp. 587-603 ◽  
Author(s):  
M. B. Calford ◽  
D. R. Moore ◽  
M. E. Hutchings
Keyword(s):  
Inferior Colliculus ◽  
Single Unit ◽  
Arrival Time ◽  
Interaural Time Difference ◽  
Free Field ◽  
Low Frequency ◽  
Intensity Function ◽  
Central Nucleus ◽  
Stimulus Position ◽  
Acoustic Space

Recordings of response to free-field stimuli at best frequency were made from single units in the central nucleus of the inferior colliculus of anesthetized cats. Stimulus position was varied in azimuth, and the responses of units were compared with variation in the intensity and arrival time of the sound at each ear, derived from cochlear microphonic (CM) recordings. CM recordings were made at each frequency and at every point in space for which single-unit data were collected. Interaural time difference (delay) increased monotonically, but not linearly, as the stimulus was moved away from the midline. However, a given delay did not represent a single azimuth across frequency. Low-frequency interaural intensity differences (IIDs) were monotonic across azimuth and peaked at, or near, the poles. Higher-frequency IIDs were nonmonotonic and peaked relatively close to the midline, decreasing toward the poles. Units that showed little variation in discharge across azimuth formed 28% of the sample and were classified as omnidirectional. For other units, the spike-count intensity function and the variation of the CM with azimuth were combined to form a derived monaural azimuth function. For 29% of those units showing azimuthal sensitivity, the derived monaural azimuth function matched the actual azimuth function. This suggested that these units received input from only one ear. The largest group of azimuthally sensitive units (47%) was formed from those units inferred to be IID sensitive. At higher frequencies these units displayed a peaked azimuth function paralleling the nonmonotonic relation of IID to azimuth. The proportion of inferred IID-sensitive units was close to that found in dichotic studies.

scholarly journals Emergence of Multiplicative Auditory Responses in the Midbrain of the Barn Owl

2007 ◽  
Vol 98 (3) ◽  
pp. 1181-1193 ◽  
Author(s):  
Brian J. Fischer ◽  
José Luis Peña ◽  
Masakazu Konishi
Keyword(s):  
Inferior Colliculus ◽  
Interaural Time Difference ◽  
Extracellular Recording ◽  
Auditory Pathway ◽  
Barn Owl ◽  
Central Nucleus ◽  
Interaural Level Difference ◽  
Tyto Alba ◽  
Neural Responses ◽  
Auditory Responses

Space-specific neurons in the barn owl's auditory space map gain spatial selectivity through tuning to combinations of the interaural time difference (ITD) and interaural level difference (ILD). The combination of ITD and ILD in the subthreshold responses of space-specific neurons in the external nucleus of the inferior colliculus (ICx) is well described by a multiplication of ITD- and ILD-dependent components. It is unknown, however, how ITD and ILD are combined at the site of ITD and ILD convergence in the lateral shell of the central nucleus of the inferior colliculus (ICcl) and therefore whether ICx is the first site in the auditory pathway where multiplicative tuning to ITD- and ILD-dependent signals occurs. We used extracellular recording of single neurons to determine how ITD and ILD are combined in ICcl of the anesthetized barn owl ( Tyto alba). A comparison of additive, multiplicative, and linear-threshold models of neural responses shows that ITD and ILD are combined nonlinearly in ICcl, but the interaction of ITD and ILD is not uniformly multiplicative over the sample. A subset (61%) of the neural responses is well described by the multiplicative model, indicating that ICcl is the first site where multiplicative tuning to ITD- and ILD-dependent signals occurs. ICx, however, is the first site where multiplicative tuning is observed consistently. A network model shows that a linear combination of ICcl responses to ITD–ILD pairs is sufficient to produce the multiplicative subthreshold responses to ITD and ILD seen in ICx.

scholarly journals Preservation of Spectrotemporal Tuning Between the Nucleus Laminaris and the Inferior Colliculus of the Barn Owl

2007 ◽  
Vol 97 (5) ◽  
pp. 3544-3553 ◽  
Author(s):  
G. Björn Christianson ◽  
José Luis Peña
Keyword(s):  
Inferior Colliculus ◽  
Phase Locking ◽  
Interaural Time Difference ◽  
Barn Owl ◽  
Central Nucleus ◽  
Sound Recognition ◽  
Spectral Structure ◽  
Two Stages ◽  
The Brain ◽  
Ongoing Phase

Performing sound recognition is a task that requires an encoding of the time-varying spectral structure of the auditory stimulus. Similarly, computation of the interaural time difference (ITD) requires knowledge of the precise timing of the stimulus. Consistent with this, low-level nuclei of birds and mammals implicated in ITD processing encode the ongoing phase of a stimulus. However, the brain areas that follow the binaural convergence for the computation of ITD show a reduced capacity for phase locking. In addition, we have shown that in the barn owl there is a pooling of ITD-responsive neurons to improve the reliability of ITD coding. Here we demonstrate that despite two stages of convergence and an effective loss of phase information, the auditory system of the anesthetized barn owl displays a graceful transition to an envelope coding that preserves the spectrotemporal information throughout the ITD pathway to the neurons of the core of the central nucleus of the inferior colliculus.

Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. III. Evidence for cross-correlation

1987 ◽  
Vol 58 (3) ◽  
pp. 562-583 ◽  
Author(s):  
T. C. Yin ◽  
J. C. Chan ◽  
L. H. Carney
Keyword(s):  
Inferior Colliculus ◽  
Acoustic Signal ◽  
Cross Correlation ◽  
Low Frequency ◽  
Nerve Fibers ◽  
Broadband Noise ◽  
The Other ◽  
Central Nucleus ◽  
Interaural Phase ◽  
Phase Relationships

1. We tested the coincidence, or cross-correlation, model of Jeffress, which proposes a neuronal mechanism for sensitivity to interaural time differences (ITDs) in low-frequency cells in the central nucleus of the inferior colliculus (ICC) of the cat. Different tokens of Gaussian noise stimuli were delivered to the two ears. We studied the neural responses to changes in ITDs of these stimuli and examined the manner in which the binaural cells responded to them. All of our results support the idea that the central binaural neurons perform an operation very similar to cross-correlation on the inputs arriving from each side. These inputs are transformed from the actual acoustic signal by the peripheral auditory system, and these transformations are reflected in the properties of the cross-correlations. 2. The responses to ITDs of identical broadband noise stimuli to the two ears varies cyclically as a function of ITD at a frequency close to the best frequency of the neuron. This cyclic response is a consequence of the narrowband filtering of the wideband acoustic signal by the auditory nerve fibers. To examine the effects of using stimuli to the two ears that were correlated to each other to different degrees, we generated pairs of noises. Each pair consisted of one standard noise, which was delivered to one ear, and a linear sum of two standard uncorrelated noises, which was delivered to the other ear. The responses of 34 neurons in the ICC to ITDs of noises with variable interaural coherence were examined. When partially correlated noises were delivered, there was a positive and approximately linear relationship between the degree of modulation of the response as a function of ITD and interaural coherence. The degree of modulation was measured by the synchronization coefficient, or vector strength, over one period of the ITD curve. 3. We examined the effects of altering the interaural phase relationships of the input noise stimuli. The phase of the noise stimuli was changed by digitally filtering the standard noise so that only a phase delay was imposed. The responses to ITDs with differing interaural phase relationships were then studied by delivering a phase-shifted noise to one ear and the standard noise to the other. The ITD curves in response to phase-shifted noise were shifted by about the same amount as the shift of the stimulus; the shift of the response was measured with respect to the case with identical noises to the two ears.(ABSTRACT TRUNCATED AT 400 WORDS)

Response of auditory units in the barn owl's inferior colliculus to continuously varying interaural phase differences

1992 ◽  
Vol 67 (6) ◽  
pp. 1428-1436 ◽  
Author(s):  
A. Moiseff ◽  
T. Haresign
Keyword(s):  
Inferior Colliculus ◽  
Interaural Time Difference ◽  
Stimulus Onset ◽  
Central Nucleus ◽  
Intensity Difference ◽  
Phase Sensitivity ◽  
Tyto Alba ◽  
Interaural Phase ◽  
Stimulus Generation ◽  
Phase Differences

1. We studied the response of single units in the central nucleus of the inferior colliculus (ICc) of the barn owl (Tyto alba) to continuously varying interaural phase differences (IPDs) and static IPDs. Interaural phase was varied in two ways: continuously, by delivering tones to each ear that varied by a few hertz (binaural beat, Fig. 1), and discretely, by delaying in fixed steps the phase of sound delivered to one ear relative to the other (static phase). Static presentations were repeated at several IPDs to characterize interaural phase sensitivity. 2. Units sensitive to IPDs responded to the binaural beat stimulus over a broad range of delta f(Fig. 4). We selected a 3-Hz delta f for most of our comparative measurements on the basis of constraints imposed by our stimulus generation system and because it allowed us to reduce the influence of responses to stimulus onset and offset (Fig. 3A). 3. Characteristic interaural time or phase sensitivity obtained by the use of the binaural beat stimulus were comparable with those obtained by the use of the static technique (Fig. 5; r2 = 0.93, Fig. 6). 4. The binaural beat stimulus facilitated the measurement of characteristic delay (CD) and characteristic phase (CP) of auditory units. We demonstrated that units in the owl's inferior colliculus (IC) include those that are maximally excited by specific IPDs (CP = 0 or 1.0) as well as those that are maximally suppressed by specific IPDs (CP = 0.5; Figs. 7 and 8). 5. The selectivity of units sensitive to IPD or interaural time difference (ITD) were weakly influenced by interaural intensity difference (IID).(ABSTRACT TRUNCATED AT 250 WORDS)

Corticofugal Shaping of Frequency Tuning Curves in the Central Nucleus of the Inferior Colliculus of Mice

2005 ◽  
Vol 93 (1) ◽  
pp. 71-83 ◽  
Author(s):  
Jun Yan ◽  
Yunfeng Zhang ◽  
Günter Ehret
Keyword(s):  
Auditory Cortex ◽  
Inferior Colliculus ◽  
Cortical Neurons ◽  
Frequency Tuning ◽  
Tuning Curve ◽  
Primary Auditory Cortex ◽  
Nerve Fibers ◽  
Cortical Activation ◽  
Central Nucleus ◽  
Tuning Curves

Plasticity of the auditory cortex can be induced by conditioning or focal cortical stimulation. The latter was used here to measure how stimulation in the tonotopy of the mouse primary auditory cortex influences frequency tuning in the midbrain central nucleus of the inferior colliculus (ICC). Shapes of collicular frequency tuning curves (FTCs) were quantified before and after cortical activation by measuring best frequencies, FTC bandwidths at various sound levels, level tolerance, Q-values, steepness of low- and high-frequency slopes, and asymmetries. We show here that all of these measures were significantly changed by focal cortical activation. The changes were dependent not only on the relationship of physiological properties between the stimulated cortical neurons and recorded collicular neurons but also on the tuning curve class of the collicular neuron. Cortical activation assimilated collicular FTC shapes; sharp and broad FTCs were changed to the shapes comparable to those of auditory nerve fibers. Plasticity in the ICC was organized in a center (excitatory)-surround (inhibitory) way with regard to the stimulated location (i.e., the frequency) of cortical tonotopy. This ensures, together with the spatial gradients of distribution of collicular FTC shapes, a sharp spectral filtering at the core of collicular frequency-band laminae and an increase in frequency selectivity at the periphery of the laminae. Mechanisms of FTC plasticity were suggested to comprise both corticofugal and local ICC components of excitatory and inhibitory modulation leading to a temporary change of the balance between excitation and inhibition in the ICC.

Role of GABA in shaping frequency tuning and creating FM sweep selectivity in the inferior colliculus

1996 ◽  
Vol 76 (2) ◽  
pp. 1059-1073 ◽  
Author(s):  
Z. M. Fuzessery ◽  
J. C. Hall
Keyword(s):  
Inferior Colliculus ◽  
Frequency Tuning ◽  
Response Magnitude ◽  
Central Nucleus ◽  
Gamma Aminobutyric Acid ◽  
Unit Recording ◽  
Tuning Curves ◽  
Sweep Direction ◽  
Species Specific

1. We examined the role of gamma-aminobutyric acid (GABA)-mediated inhibition in shaping excitatory tuning curves and creating selectivity for frequency-modulated (FM) sweeps in 29 neurons in the central nucleus of the inferior colliculus (ICC) of the pallid bat, with the use of single-unit recording coupled with the iontophoretic application of bicuculline methiodide (BIC), an antagonist of GABAA receptors. 2. BIC increased response magnitude 2 to 6 times over pretreatment levels in > 80% of neurons tested, and converted > 50% of nonmonotonic intensity-rate functions to monotonic or plateaued functions, demonstrating that GABAergic input normally limited response magnitude and inhibited responses at higher intensities. BIC typically had little effect on response thresholds, except in more specialized neurons that normally responded poorly to tones. In these cases, BIC disinhibited the neurons' responses to tones and lowered excitatory thresholds as much as 25 dB. 3. We examined the effects of BIC application on both excitatory and inhibitory tuning curves (measured with simultaneous 2-tone inhibition) to determine whether inhibitory curves were GABA mediated and whether removal of this inhibition was accompanied by an expansion of the excitatory curve. BIC had variable effects on the width of excitatory curves. In most cases, excitatory curves were at least slightly broadened, and expanded into regions previously occupied by inhibitory curves. In most cases, excitatory curves were at least slightly broadened, and expanded into regions previously occupied by inhibitory curves. However, in a few cases, inhibitory curves could be eliminated without an expansion of the excitatory curve. The greatest effect was seen in neurons with closed excitatory tuning curves; blocking GABAergic input caused the curves to open, allowing the neurons to respond at higher intensities. 4. Approximately 50% of the neurons in the ICC tuned to the spectrum of the bat's downward FM sweeping biosonar pulse respond preferentially to downward FM sweeps and not to upward sweeps, tones, or noise. In all neurons tested, BIC at least partially destroyed selectivity for sweep direction. This destruction could occur, however, without a loss of response exclusivity; in some cases, the neurons still did not respond to tones or noise. These results suggest that response selectivity for a species-specific signal is created by GABAergic input to ICC neurons. These results are used to suggest a mechanism that creates selectivity for FM sweep direction.

Serotonin Effects on Frequency Tuning of Inferior Colliculus Neurons

2001 ◽  
Vol 85 (2) ◽  
pp. 828-842 ◽  
Author(s):  
Laura M. Hurley ◽  
George D. Pollak
Keyword(s):  
Inferior Colliculus ◽  
Frequency Tuning ◽  
Gain Control ◽  
Central Nucleus ◽  
Complex Signals ◽  
Constant Intensity ◽  
Fm Signals ◽  
Spectral Components ◽  
Induced Changes ◽  
Response Area

We investigated the modulatory effects of serotonin on the tuning of 114 neurons in the central nucleus of the inferior colliculus (ICc) of Mexican free-tailed bats and how serotonin-induced changes in tuning influenced responses to complex signals. We obtained a “response area” for each neuron, defined as the frequency range that evoked discharges and the spike counts evoked by those frequencies at a constant intensity. We then iontophoretically applied serotonin and compared response areas obtained before and during the application of serotonin. In 58 cells, we also assessed how serotonin-induced changes in response areas correlated with changes in the responses to brief frequency-modulated (FM) sweeps whose structure simulated natural echolocation calls. Serotonin profoundly changed tone-evoked spike counts in 60% of the neurons (68/114). In most neurons, serotonin exerted a gain control, facilitating or depressing the responses to all frequencies in their response areas. In many cells, serotonergic effects on tones were reflected in the responses to FM signals. The most interesting effects were in those cells in which serotonin selectively changed the responsiveness to only some frequencies in the neuron's response area and had little or no effect on other frequencies. This caused predictable changes in responses to the more complex FM sweeps whose spectral components passed through the neurons' response areas. Our results suggest that serotonin, whose release varies with behavioral state, functionally reconfigures the circuitry of the IC and may modulate the perception of acoustic signals under different behavioral states.

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