Delay lines and amplitude selectivity are created in subthalamic auditory nuclei: the brachium of the inferior colliculus of the mustached bat

1993 ◽  
Vol 69 (5) ◽  
pp. 1713-1724 ◽  
Author(s):  
N. Kuwabara ◽  
N. Suga
Keyword(s):  
Inferior Colliculus ◽  
Subthalamic Nucleus ◽  
Frequency Component ◽  
Nerve Fibers ◽  
Coincidence Detection ◽  
Delay Lines ◽  
Constant Frequency ◽  
Response Latencies ◽  
Mustached Bat ◽  
Species Specific

1. The biosonar pulse of the mustached bat, Pteronotus parnellii parnellii, consists of four harmonics of a constant-frequency component (CF1-4) followed by a frequency-modulated component (FM1-4). FM-FM combination-sensitive neurons in the auditory cortex and the medical geniculate body (MGB) show facilitative responses to certain combinations of FM components in a pulse-echo pair. They are tuned to particular delays of echo FMn (EFMn) (n = 2, 3, or 4) from pulse FM1 (PFM1). The neural mechanisms for creating their response properties involve delay lines, coincidence detection, and multiplication. Coincidence detection and multiplication take place in the MGB. It is not yet known where and how delay lines are created. The first aim of the present studies is to examine whether delay lines are created by subthalamic nuclei. FM-FM neurons are tuned to not only echo delays but also echo amplitudes. Therefore, the second aim of the present studies is to examine the extent to which amplitude selectivity is created by subthalamic nuclei. Responses of single nerve fibers to acoustic stimuli were recorded from the brachium of the inferior colliculus (BIC) using tungsten wire microelectrodes, and their response latencies and best amplitudes were measured. 2. All BIC fibers responded strongly to single tone bursts. No FM-FM combination-sensitive neurons were found in the BIC. The best frequencies of BIC fibers were predominantly within the frequency ranges of four harmonics of the species-specific biosonar pulse. 3. The response latencies of BIC fibers tuned to FM1 were more diverse (3.5-15.0 ms) than those of BIC fibers tuned to FMn (3.8-6.5 ms). This difference in latency distribution was independent of stimulus amplitude. These data are consistent with the theory that delay lines utilized by FM-FM neurons are created by neurons tuned to the "FM1 frequency," and indicate that the delay lines are mostly, if not all, created in a subthalamic nucleus or nuclei. 4. The best amplitudes of BIC fibers tuned to FM1 or CF1 were 63.2 +/- 4.5 (SE) dB SPL, and those of BIC fibers tuned to FMn or CFn were 48.2 +/- 10.7 dB SPL. The distribution of the best amplitudes of BIC fibers were very similar to those of FM-FM and CF/CF neurons in the MGB. These data indicate that the amplitude selectivity of thalamic FM-FM and CF/CF neurons is mainly a product of a subthalamic nucleus or nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Long delay lines for ranging are created by inhibition in the inferior colliculus of the mustached bat

1995 ◽  
Vol 74 (1) ◽  
pp. 1-11 ◽  
Author(s):  
I. Saitoh ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Receptor Antagonist ◽  
Inferior Colliculus ◽  
Coincidence Detection ◽  
Central Nucleus ◽  
Gamma Aminobutyric Acid ◽  
Delay Lines ◽  
Mustached Bat ◽  
Gabaa Receptor Antagonist ◽  
Medial Geniculate

1. The central auditory system of the mustached bat has arrays of delay-tuned (FM-FM combination-sensitive) neurons in the inferior colliculus, the medial geniculate body, and the auditory cortex. These neurons are tuned to particular echo delays, i.e., target distances. The neural mechanisms for creating the delay-tuned neurons involve delay lines, coincidence detection, and amplification. We have hypothesized that delay lines longer than 4 ms are created by inhibition occurring in the anterolateral division (ALD) of the central nucleus of the inferior colliculus. If this hypothesis is correct, suppression of inhibition occurring in the ALD must shorten the best delays of the collicular, thalamic, and cortical delay-tuned neurons. The aim of the present study is to test this hypothesis. Responses of single delay-tuned neurons in the FM-FM area of the auditory cortex were recorded with a tungsten-wire microelectrode, and the effects of iontophoretic microinjections of strychnine (STR) and/or bicuculline methiodide (BMI) into the ALD were examined on the responses of these neurons. 2. STR (glycine receptor antagonist) and/or BMI [gamma-aminobutyric acid-A (GABAA) receptor antagonist] injections into the ALD shortened the best delays of delay-tuned neurons in the FM-FM area with little change in their response patterns. The longer the best delay of a delay-tuned neuron, the larger the amount of shortening. 3. Inhibition mediated by glycine receptors plays a larger role in creating delay lines than that mediated by GABAA receptors, because STR and BMI, respectively, shortened the best delay of 91 and 74% of the neurons with best delays longer than 4.5 ms. 4. BMI has no effect on the best delays of delay-tuned neurons that were tuned to echo delays shorter than 4.5 ms. 5. The present data support the hypothesis that long delay lines utilized by delay-tuned neurons are created by inhibition occurring in the ALD of the inferior colliculus. However, the amount of shortening in delay lines by STR and/or BMI was generally smaller than that predicted by a neural network model. Therefore the present study partially answers the questions of where and how long delay lines were created.

Are the initial frequency-modulated components of the mustached bat's biosonar pulses important for ranging?

1991 ◽  
Vol 66 (6) ◽  
pp. 1951-1964 ◽  
Author(s):  
D. C. Fitzpatrick ◽  
N. Suga ◽  
H. Misawa
Keyword(s):  
Maximum Amplitude ◽  
Signal Amplitude ◽  
Frequency Component ◽  
Target Range ◽  
Constant Frequency ◽  
Range Resolution ◽  
Mustached Bat ◽  
Pteronotus Parnellii ◽  
Target Ranging ◽  
The Mean

1. FM-FM neurons in the auditory cortex of the mustached bat, Pteronotus parnellii, are specialized to process target range. They respond when the terminal frequency-modulated component (TFM) of a biosonar pulse is paired with the TFM of the echo at a particular echo delay. Recently, it has been suggested that the initial FM components (IFMs) of biosonar signals may also be important for target ranging. To examine the possible role of IFMs in target ranging, we characterized the properties of IFMs and TFMs in biosonar pulses emitted by bats swung on a pendulum. We then studied responses of FM-FM neurons to synthesized biosonar signals containing IFMs and TFMs. 2. The mustached bat's biosonar signal consists of four harmonics, of which the second (H2) is the most intense. Each harmonic has an IFM in addition to a constant-frequency component (CF) and a TFM. Therefore each pulse potentially consists of 12 components, IFM1-4, CF1-4, and TFM1-4. The IFM sweeps up while the TFM sweeps down. 3. The IFM2 and TFM2 depths (i.e., bandwidths) were measured in 217 pulses from four animals. The mean IFM2 depth was much smaller than the mean TFM2 depth, 2.87 +/- 1.52 (SD) kHz compared with 16.27 +/- 1.08 kHz, respectively. The amplitude of the IFM2 continuously increased throughout its duration and was always less than the CF2 amplitude, whereas the TFM2 was relatively constant in amplitude over approximately three-quarters of its duration and was often the most intense part of the pulse. The maximum amplitude of the IFM2 was, on average, 11 dB smaller than that of the TFM2. Because range resolution increases with depth and the maximum detectable range increases with signal amplitude, the IFMs are poorly suited for ranging compared with the TFMs. 4. FM-FM neurons (n = 77) did not respond or responded very poorly to IFMs with depths and intensities similar to those emitted on the pendulum. The mean IFM2 depth at which a just-noticeable response appeared was 4.48 +/- 1.98 kHz. Only 14% of the pulses emitted on the pendulum had IFM2 depths that exceeded the mean IFM2 depth threshold of FM-FM neurons. 5. Most FM-FM neurons responded to IFMs that had depths comparable with those of TFMs. However, when all parameters were adjusted to optimize the response to TFMs and then readjusted to maximize the response to IFMs, 52% of 27 neurons tested responded significantly better to the optimal TFMs than to the optimal IFMs (P less than 0.05, t test).(ABSTRACT TRUNCATED AT 400 WORDS)

Duration tuning in the inferior colliculus of the mustached bat

2011 ◽  
Vol 106 (6) ◽  
pp. 3119-3128 ◽  
Author(s):  
Silvio Macías ◽  
Emanuel C. Mora ◽  
Julio C. Hechavarría ◽  
Manfred Kössl
Keyword(s):  
Inferior Colliculus ◽  
Sound Pressure ◽  
Frequency Range ◽  
Constant Frequency ◽  
Third Harmonic ◽  
Mustached Bat ◽  
Pteronotus Parnellii ◽  
Sound Levels ◽  
Response Profile ◽  
Band Pass

We studied duration tuning in neurons of the inferior colliculus (IC) of the mustached bat. Duration-tuned neurons in the IC of the mustached bat fall into three main types: short (16 of 136), band (34 of 136), and long (29 of 136) pass. The remaining 51 neurons showed no selectivity for the duration of sounds. The distribution of best durations was double peaked with maxima around 3 and 17 ms, which correlate with the duration of the short frequency-modulated (FM) and the long constant-frequency (CF) signals emitted by Pteronotus parnellii. Since there are no individual neurons with a double-peaked duration response profile, both types of temporal processing seem to be well segregated in the IC. Most short- and band-pass units with best frequency in the CF2 range responded to best durations > 9 ms (66%, 18 of 27 units). However, there is no evidence for a bias toward longer durations as there is for neurons tuned to the frequency range of the FM component of the third harmonic, where 83% (10 of 12 neurons) showed best durations longer than 9 ms. In most duration-tuned neurons, response areas as a function of stimulus duration and intensity showed either V or U shape, with duration tuning retained across the range of sound levels tested. Duration tuning was affected by changes in sound pressure level in only six neurons. In all duration-tuned neurons, latencies measured at the best duration were longer than best durations, suggesting that behavioral decisions based on analysis of the duration of the pulses would not be expected to be complete until well after the stimulus has occurred.

Frequency and amplitude representations in anterior primary auditory cortex of the mustached bat

1983 ◽  
Vol 50 (5) ◽  
pp. 1182-1196 ◽  
Author(s):  
A. Asanuma ◽  
D. Wong ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Second Harmonic ◽  
Free Field ◽  
Primary Auditory Cortex ◽  
Frequency Component ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Pteronotus Parnellii ◽  
Frequency Representation ◽  
Pure Tones

The orientation sound emitted by the Panamanian mustached bat, Pteronotus parnellii rubiginosus, consists of four harmonics. The third harmonic is 6-12 dB weaker than the predominant second harmonic and consists of a long constant-frequency component (CF3) at about 92 kHz and a short frequency-modulated component (FM3) sweeping from about 92 to 74 kHz. Our primary aim is to examine how CF3 and FM3 are represented in a region of the primary auditory cortex anterior to the Doppler-shifted constant-frequency (DSCF) area. Extracellular recordings of neuronal responses from the unanesthetized animal were obtained during free-field stimulation of the ears with pure tones. FM sounds, and signals simulating their orientation sounds and echoes. Response properties of neurons and tonotopic and amplitopic representations were examined in the primary and the anteroventral nonprimary auditory cortex. In the anterior primary auditory cortex, neurons responded strongly to single pure tones but showed no facilitative responses to paired stimuli. Neurons with best frequencies from 110 to 90 kHz were tonotopically organized rostrocaudally, with higher frequencies located more rostrally. Neurons tuned to 92-94 kHz were overpresented, whereas neurons tuned to sound between 64 and 91 kHz were rarely found. Consequently a striking discontinuity in frequency representation from 91 to 64 kHz was found across the anterior DSCF border. Most neurons exhibited monotonic impulse-count functions and responded maximally to sound pressure level (SPL). There were also neurons that responded best to weak sounds but unlike the DSCF area, amplitopic representation was not found. Thus, the DSCF area is quite unique not only in its extensive representation of frequencies in the second harmonic CF component but also in its amplitopic representation. The anteroventral nonprimary auditory cortex consisted of neurons broadly tuned to pure tones between 88 and 99 kHz. Neither tonotopic nor amplitopic representation was observed. Caudal to this area and near the anteroventral border of the DSCF area, a small cluster of FM-FM neurons sensitive to particular echo delays was identified. The responses of these neurons fluctuated significantly during repetitive stimulation.

Doppler-shift compensation by the mustached bat: quantitative data.

1994 ◽  
Vol 188 (1) ◽  
pp. 115-129 ◽  
Author(s):  
A W Keating ◽  
O W Henson ◽  
M M Henson ◽  
W C Lancaster ◽  
D H Xie
Keyword(s):  
Doppler Shift ◽  
Quantitative Data ◽  
Second Harmonic ◽  
Frequency Component ◽  
Reference Frequency ◽  
Constant Frequency ◽  
Doppler Shifts ◽  
Mustached Bat ◽  
Pteronotus Parnellii ◽  
Significant Difference

Quantitative data for Doppler-shift compensation by Pteronotus parnellii parnellii were obtained with a device which propelled the bats at constant velocities over a distance of 12 m. The bats compensated for Doppler shifts at all velocities tested (0.1-5.0 ms-1). The main findings were (1) that compensation was usually accomplished by a progressive lowering of the approximately 61 kHz second harmonic constant-frequency component of emitted sounds in small frequency steps (93 +/- 72 Hz); (2) that the time needed to reach a steady compensation level averaged 514 +/- 230 ms and the number of pulses required to reach full compensation averaged 10.78 +/- 5.16; (3) that the animals compensated to hold the echo (reference) frequency at a value that was slightly higher than the resting frequency and slightly lower than the cochlear resonance frequency; (4) that reference frequency varied as a function of velocity, the higher the velocity of the animal, the higher was the reference frequency (slope 55 Hz m-1s-2); and (5) that the mean reference frequency was always an undercompensation. The average amount of undercompensation was 15.8%. There was a significant difference (P < or = 0.005) in Doppler-shift compensation data collected at velocities that differed by 0.1 ms-1. A velocity difference of 0.1 ms-1 corresponds to a Doppler-shift difference of about 35 Hz in the approximately 61 kHz signals reaching the ear.

scholarly journals Sex-dependent hemispheric asymmetries for processing frequency-modulated sounds in the primary auditory cortex of the mustached bat

2012 ◽  
Vol 108 (6) ◽  
pp. 1548-1566 ◽  
Author(s):  
Stuart D. Washington ◽  
Jagmeet S. Kanwal
Keyword(s):  
Auditory Cortex ◽  
Primary Auditory Cortex ◽  
Tone Burst ◽  
Hemispheric Differences ◽  
Constant Frequency ◽  
Response Latencies ◽  
Peak Response ◽  
Response Characteristics ◽  
Species Specific ◽  
The Right

Species-specific vocalizations of mammals, including humans, contain slow and fast frequency modulations (FMs) as well as tone and noise bursts. In this study, we established sex-specific hemispheric differences in the tonal and FM response characteristics of neurons in the Doppler-shifted constant-frequency processing area in the mustached bat's primary auditory cortex (A1). We recorded single-unit cortical activity from the right and left A1 in awake bats in response to the presentation of tone bursts and linear FM sweeps that are contained within their echolocation and/or communication sounds. Peak response latencies to neurons' preferred or best FMs were significantly longer on the right compared with the left in both sexes, and in males this right-left difference was also present for the most excitatory tone burst. Based on peak response magnitudes, right hemispheric A1 neurons in males preferred low-rate, narrowband FMs, whereas those on the left were less selective, responding to FMs with a variety of rates and bandwidths. The distributions of parameters for best FMs in females were similar on the two sides. Together, our data provide the first strong physiological support of a sex-specific, spectrotemporal hemispheric asymmetry for the representation of tones and FMs in a nonhuman mammal. Specifically, our results demonstrate a left hemispheric bias in males for the representation of a diverse array of FMs differing in rate and bandwidth. We propose that these asymmetries underlie lateralized processing of communication sounds and are common to species as divergent as bats and humans.

The personalized auditory cortex of the mustached bat: adaptation for echolocation

1987 ◽  
Vol 58 (4) ◽  
pp. 643-654 ◽  
Author(s):  
N. Suga ◽  
H. Niwa ◽  
I. Taniguchi ◽  
D. Margoliash
Keyword(s):  
Auditory Cortex ◽  
Second Harmonic ◽  
Frequency Component ◽  
Masking Effect ◽  
Reference Frequency ◽  
Sexually Dimorphic ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Pteronotus Parnellii ◽  
Almost All

1. In the mustached bat, Pteronotus parnellii, the "resting" frequency of the constant-frequency component of the second harmonic (CF2) of the orientation sound (biosonar signal) is different among individuals within a range from 59.69 to 63.33 kHz. The standard deviation of CF2 resting frequency is 0.091 kHz on the average for individual bats. The male's CF2 resting frequency (61.250 +/- 0.534 kHz, n = 58) is 1.040 kHz lower than the female's (62.290 +/- 0.539 kHz, n = 58) on the average. Females' resting frequencies measured in December are not different from those measured in April when almost all of them are pregnant. Therefore, the orientation sound is sexually dimorphic. 2. In the DSCF (Doppler-shifted CF processing) area of the auditory cortex, tonotopic representation differs among individual bats. The higher the CF2 resting frequency of the bat's own sound, the higher the frequencies represented in the DSCF area of that bat. There is a unique match between the tonotopic representation and the CF2 resting frequency. This match indicates that the auditory cortex is "personalized" for echolocation and that the CF2 resting frequency is like a signature of the orientation sound. 3. If a bat's resting frequency is normalized to 61.00 kHz, the DSCF area overrepresents 60.6-62.3 kHz. The central region of this overrepresented band is 61.1-61.2 kHz. This focal band matches the "reference" frequency to which the CF2 frequency of a Doppler-shifted echo is stabilized by Doppler-shift compensation. 4. Since DSCF neurons are extraordinarily sharply tuned in frequency, the personalization of the auditory cortex or system is not only suited for the detection of wing beats of insects, but also for the reduction of the masking effect on echolocation of consepecific's biosonar signals. 5. Because the orientation sound is sexually dimorphic and the auditory cortex is personalized, the tonotopic representation of the auditory cortex is also sexually dimorphic.

Postnatal Development of Cochlear Function in the Mustached Bat, Pteronotus parnellii

2003 ◽  
Vol 90 (4) ◽  
pp. 2261-2273 ◽  
Author(s):  
M. Kössl ◽  
E. Foeller ◽  
M. Drexl ◽  
M. Vater ◽  
E. Mora ◽  
...  
Keyword(s):  
Postnatal Development ◽  
Second Harmonic ◽  
Frequency Component ◽  
Cochlear Microphonic ◽  
Cochlear Function ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Pteronotus Parnellii ◽  
Compound Action Potentials ◽  
Stimulus Offset

Postnatal development of the mustached bat's cochlea was studied by measuring cochlear microphonic and compound action potentials. In adults, a cochlear resonance is involved in enhanced tuning to the second harmonic constant frequency component (CF2) of their echolocation calls at ∼61 kHz This resonance is present immediately after birth in bats that do not yet echolocate. Its frequency is lower (46 kHz) and the corresponding threshold minimum of cochlear microphonic potentials is broader than in adults. Long-lasting ringing of the cochlear microphonic potential after tone stimulus offset that characterizes the adult auditory response close to CF2 is absent in newborns. In the course of the first 5 postnatal weeks, there is a concomitant upward shift of CF2 and the frequency of cochlear threshold minima. Up to the end of the third postnatal week, sensitivity of auditory threshold minima and the Q value of the cochlear resonance increase at a fast rate. Between 2 and 4 wk of age, two cochlear microphonic threshold minima are found consistently in the CF2 range that differ in their level-dependent dynamic growth behavior and are 1.5–5.7 kHz apart from each other. In older animals, there is a single minimum that approaches adult tuning in its sharpness. The data provide evidence to show that during maturation of the cochlea, the frequency and the sensitivity of the threshold minimum associated with CF2 increases and that these increases are associated with the fusion of two resonances that are partly dissociated in developing animals.

Combination-sensitive neurons in the medial geniculate body of the mustached bat: encoding of target range information

1991 ◽  
Vol 65 (6) ◽  
pp. 1275-1296 ◽  
Author(s):  
J. F. Olsen ◽  
N. Suga
Keyword(s):  
Stimulus Frequency ◽  
Medial Geniculate Body ◽  
Neural Mechanism ◽  
Coincidence Detection ◽  
Target Range ◽  
Time Interval ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Medial Geniculate ◽  
Pulse Echo

1. Delay-tuned combination-sensitive neurons (FM-FM neurons) have been discovered in the dorsal and medial divisions of the medial geniculate body (MGB) of the mustached bat (Pteronotus parnellii). In this paper we present evidence for a thalamic origin for FM-FM neurons. Our examination of the response properties of FM-FM neurons indicates that the neural mechanism of delay-tuning depends on coincidence detection and involves an interaction between neural inhibition and excitation. 2. The biosonar pulse (P) and its echo (E) produced and heard by the mustached bat consist of four harmonics; each harmonic contains a constant frequency (CF) component and a frequency modulated (FM) component. Thus the pulse-echo pair contains eight CF components (PCF1-4, ECF1-4) and eight FM components (PFM1-4, EFM1-4). The stimuli used in this study consisted of CF, FM, and CF-FM sounds: paired CF-FM sounds were used to simulate any two harmonics of pulse-echo pairs. The responses of FM-FM neurons in the MGB were recorded extracellularly. We found that FM-FM neurons respond poorly or not at all to single sounds, respond strongly to paired sounds, and are tuned to the frequency and amplitude of each sound of the pair and to the time interval separating them (simulated echo delay). 3. All FM-FM neurons are facilitated by paired FM sounds and most are facilitated by paired CF sounds. Best facilitative frequencies measured with paired CF sounds fall outside the frequency ranges of the CF components of biosonar signals, whereas best facilitative frequencies measured with paired FM sounds fall within the frequency ranges of the FM components of biosonar signals. Thus FM-FM neurons are expected to respond selectively to combinations of FM components in biosonar signals. The FM components of pulse-echo pairs essential to facilitate FM-FM neurons are the FM component of the fundamental of the pulse (PFM1) in combination with the FM component of the second, third, or fourth harmonic of an echo (EFM2, EFM3, EFM4; collectively, EFMn). 4. The frequency combinations to which FM-FM neurons are tuned reflect small deviations from the harmonic relationship such as occurs in combinations of FM components from pulses and Doppler-shifted echoes. Compared with CF/CF neurons, however, FM-FM neurons are broadly tuned to stimulus frequency. Thus FM-FM neurons are Doppler-shift tolerant and relatively unspecialized for processing velocity information in the frequency domain.(ABSTRACT TRUNCATED AT 400 WORDS)

Inactivation of the DSCF area of the auditory cortex with muscimol disrupts frequency discrimination in the mustached bat

1992 ◽  
Vol 68 (5) ◽  
pp. 1613-1623 ◽  
Author(s):  
H. Riquimaroux ◽  
S. J. Gaioni ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Doppler Shift ◽  
Broad Band ◽  
Primary Auditory Cortex ◽  
Tone Burst ◽  
Signal Pulse ◽  
Gamma Aminobutyric Acid ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Leg Flexion

1. The Jamaican mustached bat uses a biosonar signal (pulse) with eight major components: four harmonics each consisting of a long constant frequency (CF1-4) component followed by a short frequency-modulated (FM1-4) component. While flying, the bat adjusts the frequency of its pulse so as to maintain the CF2 of the Doppler-shifted echo at a frequency to which its cochlea is very sharply tuned. This Doppler shift (DS) compensation likely is mediated or influenced by the Doppler-shifted CF (DSCF) processing area of the primary auditory cortex, which only represents frequencies in the range of echo CF2s (60.6 to 62.3 kHz when the "resting" frequency of the CF2 is 61.0 kHz). 2. We trained four bats to discriminate between different trains of paired tone bursts that mimicked a bat's pulse CF2 and the accompanying echo CF2. The frequency of these CF2s ranged between 61.0 and 64.0 kHz. A discriminated shock avoidance procedure response was employed using a leg flexion. For one stimulus, the S+, the pulse and echo CF2s were the same frequency (delta f = 0, i.e., no Doppler shift). A leg flexion during the S+ turned off both the S+ and the scheduled shock. For a second stimulus, the S-, the echo CF2 was 0.05, 0.1, 0.3, 0.5, or 2.0 kHz higher than the pulse CF2. A delta f of 0.05 kHz was a frequency difference of 0.08%. No shock followed the S-, and leg flexions had no consequences. Correct responses consisted of a leg flexion during the S+ and no flexion during the S-; these responses were added together to compute the percentage of correct responses. When a bat correctly responded at better than 75% for all the delta f s, muscimol, a potent agonist of gamma-aminobutyric acid, was bilaterally applied to inactivate the DSCF area. Performance on each delta f discrimination was then measured. 3. Initial attempts to condition the bats to flex their legs to the CF tones mimicking part of the natural pulses and echoes failed. When broad-band noise bursts were substituted, however, the conditioned response was rapidly established. The noise band-width was gradually reduced and then replaced with the CF tones. Discrimination training with the tone burst trains then commenced. Throughout this procedure, the bats maintained their responding to the stimuli. The bats typically required approximately 20-30 sessions to perform consistently (> or = 75% correct responses) a discrimination involving a 2 kHz delta f.(ABSTRACT TRUNCATED AT 400 WORDS)

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