Distribution of combination-sensitive neurons in the ventral fringe area of the auditory cortex of the mustached bat

1989 ◽  
Vol 61 (1) ◽  
pp. 202-207 ◽  
Author(s):  
H. Edamatsu ◽  
M. Kawasaki ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Functional Organization ◽  
Target Range ◽  
Sound Pulse ◽  
Constant Frequency ◽  
Mustached Bat ◽  
Essential Components ◽  
Tritiated Amino Acids ◽  
Pulse Echo ◽  
Echo Delay

1. The orientation sound (pulse) of the mustached bat, Pteronotus parnellii parnellii, consists of long constant-frequency components (CF1-4) and short frequency-modulated components (FM1-4). The auditory cortex of this bat contains several combination-sensitive areas: FM-FM, DF, VA, VF, and CF/CF. The FM-FM area consists of neurons tuned to a combination of the pulse FM1 and the echo FMn (n = 2, 3, or 4) and has an echo-delay (target-range) axis. Our preliminary anatomical studies with tritiated amino acids suggest that the FM-FM area projects to the dorsal fringe (DF) area, which in turn projects to the ventral fringe (VF) area. The aim of our study was to characterize the response properties of VF neurons and to explore the functional organization of the VF area. Acoustic stimuli delivered to the bats were CF tones, FM sounds, and their combinations mimicking the pulse emitted by the mustached bat and the echo. 2. Like the FM-FM and DF areas, the VF area is composed of three types of FM-FM combination-sensitive neurons: FM1-FM2, FM1-FM3, and FM1-FM4. These neurons show little or no response to a pulse alone, echo alone, single CF tone or single FM sound. They do, however, show a strong facilitative response to a pulse-echo pair with a particular echo delay. The essential components in the pulse-echo pair for facilitation are the FM1 of the pulse and the FMn of the echo.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in response properties of neurons between two delay-tuned areas in the auditory cortex of the mustached bat

1993 ◽  
Vol 69 (5) ◽  
pp. 1700-1712 ◽  
Author(s):  
H. Edamatsu ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Poor Response ◽  
Target Range ◽  
Terminal Phase ◽  
Sound Pulse ◽  
Response Properties ◽  
Tuning Curves ◽  
Mustached Bat ◽  
Echo Delay ◽  
Delay Tuning

1. The orientation sound (pulse) of the mustached bat, Pteronotus parnellii parnellii, consists of four harmonics (H1-4), each containing a long constant-frequency component (CF1-4) followed by a short frequency-modulated component (FM1-4). The auditory cortex of this species contains several "combination-sensitive" areas: FM-FM, dorsal fringe (DF), ventral fringe (VF), CF/CF, and H1-H2. The FM-FM, DF, and VF areas each consist of neurons tuned to particular delays of echo FMn (n = 2, 3, or 4) from pulse FM1, and have an echo-delay (target-range) axis. This delay axis is from 0.4 to approximately 18 ms in the FM-FM area, to approximately 9 ms in the DF area, and to approximately 5 ms in the VF area. Therefore we hypothesized that the VF area was more specialized for the processing of range information in the terminal phase of echolocation than was the FM-FM area. The aim of our present studies was to find differences in response properties between neurons with best delays shorter than 6 ms in the VF and FM-FM areas and thus to test our hypothesis. 2. In the terminal phase of target-directed flight, the rate of pulse emission becomes higher, pulse duration (in particular, CF duration) becomes shorter, echo delay becomes shorter, and echoes (both the CF and FM components) are less Doppler shifted. Therefore, a "temporal-pattern-simulating (TPS)" stimulus was designed to mimic the train of pulse-echo pairs that would be heard by the bat during the terminal phase, and responses of single neurons to the TPS stimulus and other types of stimuli were recorded from the VF and FM-FM areas of the auditory cortex of unanesthetized bats with a tungsten-wire microelectrode. 3. Best delays of the neurons studied range between 0.9 and 5.5 ms (2.64 +/- 0.72 ms, N = 181) for the VF area, and between 0.6 and 6.0 ms (3.64 +/- 1.14, N = 144) for the FM-FM area. More neurons in the VF area than those in the FM-FM area showed no response or a poor response to the TPS stimulus. Therefore VF neurons are less suited than neurons in the FM-FM area for processing target ranges in the terminal phase of target-directed flight. Facilitative delay-tuning curves were commonly sandwiched between inhibitory delay-tuning curves. The lack of response or poor response to the TPS stimulus can be explained by this inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition and level-tolerant frequency tuning in the auditory cortex of the mustached bat

1985 ◽  
Vol 53 (4) ◽  
pp. 1109-1145 ◽  
Author(s):  
N. Suga ◽  
K. Tsuzuki
Keyword(s):  
Auditory Cortex ◽  
Frequency Analysis ◽  
Frequency Tuning ◽  
Neural Basis ◽  
Single Tone ◽  
Tuning Curves ◽  
Mustached Bat ◽  
Essential Components ◽  
High Stimulus ◽  
Pulse Echo

For echolocation the mustached bat, Pteronotus parnellii, emits complex orientation sounds (pulses), each consisting of four harmonics with long constant-frequency components (CF1-4) followed by short frequency-modulated components (FM1-4). The CF signals are best suited for target detection and measurement of target velocity. The CF/CF area of the auditory cortex of this species contains neurons sensitive to pulse-echo pairs. These CF/CF combination-sensitive neurons extract velocity information from Doppler-shifted echoes. In this study we electrophysiologically investigated the frequency tuning of CF/CF neurons for excitation, facilitation, and inhibition. CF1/CF2 and CF1/CF3 combination-sensitive neurons responded poorly to individual signal elements in pulse-echo pairs but showed strong facilitation of responses to pulse-echo pairs. The essential components in the pairs were CF1 of the pulse and CF2 or CF3 of the echo. In 68% of CF/CF neurons, the frequency-tuning curves for facilitation were extremely sharp for CF2 or CF3 and were "level-tolerant" so that the bandwidths of the tuning curves were less than 5.0% of best frequencies even at high stimulus levels. Facilitative tuning curves for CF1 were level tolerant only in 6% of the neurons studied. CF/CF neurons were specialized for fine analysis of the frequency relationship between two CF sounds regardless of sound pressure levels. Some CF/CF neurons responded to single-tone stimuli. Frequency-tuning curves for excitation (responses to single-tone stimuli) were extremely sharp and level tolerant for CF2 or CF3 in 59% of CF1/CF2 neurons and 70% of CF1/CF3 neurons. Tuning to CF1 was level tolerant in only 9% of these neurons. Sharp level-tolerant tuning may be the neural basis for small difference limens in frequency at high stimulus levels. Sharp level-tolerant tuning curves were sandwiched between broad inhibitory areas. Best frequencies for inhibition were slightly higher or lower than the best frequencies for facilitation and excitation. We thus conclude that sharp level-tolerant tuning curves are produced by inhibition. The extent to which neural sharpening occurred differed among groups of neurons tuned to different frequencies. The more important the frequency analysis of a particular component in biosonar signals, the more pronounced the neural sharpening. This was in addition to the peripheral specialization for fine frequency analysis of that component. The difference in bandwidth or quality factor between the excitatory tuning curves of peripheral neurons and the facilitative and excitatory tuning curves of CF/CF neurons was larger at higher stimulus levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Multiple time axes for representation of echo delays in the auditory cortex of the mustached bat

1986 ◽  
Vol 55 (4) ◽  
pp. 776-805 ◽  
Author(s):  
N. Suga ◽  
J. Horikawa
Keyword(s):  
Auditory Cortex ◽  
Tuning Curve ◽  
Electrophysiological Study ◽  
Great Majority ◽  
Major Axis ◽  
Essential Elements ◽  
Multiple Time ◽  
Sound Pulse ◽  
Constant Frequency ◽  
Mustached Bat

The properties of the orientation sound (pulse) of the Jamaican mustached bat, Pteronotus parnellii parnellii is the same as the Panamanian mustached bat, P.p. rubiginosus. It consists of four harmonics, each containing a long constant-frequency (CF) component followed by a short frequency-modulated (FM) component. Thus, there are eight components in total: CF1-4 and FM1-4. The combination-sensitive area of the auditory cortex in P.p. parnellii consists of two major divisions (FM-FM and CF/CF areas) as in P.p. rubiginosus. The FM-FM area projects to the dorsal fringe (DF) and other areas. Response latencies of neurons in the DF area are longer than those in the FM-FM area. The distribution of latencies is unimodal for the FM-FM area, but bimodal for the DF area. In this electrophysiological study of the response properties of neurons in the DF and FM-FM areas, our aim was to find out how signal processing might be different between the two areas. Both the FM-FM and DF areas consist of three types of FM-FM combination-sensitive neurons: FM1-FM2, FM1-FM3, and FM1-FM4. They do not respond or respond poorly to pulse alone, echo alone, single CF tones or single FM sounds. But they show strong facilitation of response to the echo when it is delivered with particular delays from the pulse. The essential elements in the pulse-echo pair for facilitation are the FM1 of the pulse and FM2 or FM3 or FM4 of the echo. In both the FM-FM and DF areas, the great majority of neurons show short-lasting facilitation, and other neurons show long-lasting facilitation. FM-FM neurons are tuned to particular echo delays, i.e., target ranges. In both the FM-FM and DF areas, the width of a delay-tuning curve is linearly related to the value of a best delay. There is no sign that processing of range information is more specialized in the DF area than the FM-FM area. In both the FM-FM and DF areas, three types of FM-FM neurons form independent clusters. Along the major axis of each cluster, best delays for facilitative responses of neurons systematically change according to the loci of the neurons. The more posterior the location, the longer the best delay is. Therefore, there are six time (i.e., range) axes in total. The time axis in the DF area is shorter than that in the FM-FM area.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Echo-acoustic flow shapes object representation in spatially complex acoustic scenes

2017 ◽  
Vol 117 (6) ◽  
pp. 2113-2124 ◽  
Author(s):  
Wolfgang Greiter ◽  
Uwe Firzlaff
Keyword(s):  
Auditory Cortex ◽  
Object Representation ◽  
Flight Path ◽  
Target Range ◽  
Complex Signal ◽  
Acoustic Space ◽  
Acoustic Pattern ◽  
Phyllostomus Discolor ◽  
Pulse Echo ◽  
Echo Delay

Echolocating bats use echoes of their sonar emissions to determine the position and distance of objects or prey. Target distance is represented as a map of echo delay in the auditory cortex (AC) of bats. During a bat’s flight through a natural complex environment, echo streams are reflected from multiple objects along its flight path. Separating such complex streams of echoes or other sounds is a challenge for the auditory system of bats as well as other animals. We investigated the representation of multiple echo streams in the AC of anesthetized bats ( Phyllostomus discolor) and tested the hypothesis that neurons can lock on echoes from specific objects in a complex echo-acoustic pattern while the representation of surrounding objects is suppressed. We combined naturalistic pulse/echo sequences simulating a bat’s flight through a virtual acoustic space with extracellular recordings. Neurons could selectively lock on echoes from one object in complex echo streams originating from two different objects along a virtual flight path. The objects were processed sequentially in the order in which they were approached. Object selection depended on sequential changes of echo delay and amplitude, but not on absolute values. Furthermore, the detailed representation of the object echo delays in the cortical target range map was not fixed but could be dynamically adapted depending on the temporal pattern of sonar emission during target approach within a simulated flight sequence. NEW & NOTEWORTHY Complex signal analysis is a challenging task in sensory processing for all animals, particularly for bats because they use echolocation for navigation in darkness. Recent studies proposed that the bat’s perceptional system might organize complex echo-acoustic information into auditory streams, allowing it to track specific auditory objects during flight. We show that in the auditory cortex of bats, neurons can selectively respond to echo streams from specific objects.

Chronotopically Organized Target-Distance Map in the Auditory Cortex of the Short-Tailed Fruit Bat

2010 ◽  
Vol 103 (1) ◽  
pp. 322-333 ◽  
Author(s):  
Cornelia Hagemann ◽  
Karl-Heinz Esser ◽  
Manfred Kössl
Keyword(s):  
Auditory Cortex ◽  
Neural Representation ◽  
Spatial Distance ◽  
Target Range ◽  
Constant Frequency ◽  
Distance Map ◽  
Fruit Bat ◽  
Object Distance ◽  
Auditory Cortices ◽  
Echo Delay

Topographic cortical representation of echo delay, the cue for target range, is an organizational feature implemented in the auditory cortices of certain bats dedicated to catch flying insects. Such cortical echo-delay maps provide a calibrated neural representation of object spatial distance. To assess general requirements for echo-delay computations, cortical delay sensitivity was examined in the short-tailed fruit bat Carollia perspicillata that uses frequency-modulated (FM) echolocation signals. Delay-tuned neurons with temporal specificity comparable to those of insectivorous bats are located within the high-frequency (HF) field of the auditory cortex. All recorded neurons in the HF field respond well to single pure-tone and FM-FM stimulus pairs. The neurons respond to identical FM harmonic components in echolocation pulse and delayed echo (e.g., FM2-FM2). Their characteristic delays (CDs) for low echo amplitudes range between 1 and 24 ms, which is comparable to other bat species. Maps of the topography of FM-FM neurons show that they are distributed across the entire HF area and organized along a rostrocaudal echo-delay axis representing object distance. Rostrally located neurons tuned to delays of 2–8 ms are overrepresented (66% of CDs). Neurons with longer delays (≥10 ms) are located throughout the caudal half of the HF field. The delay-sensitive chronotopic area covers ∼3.3 mm in rostrocaudal and ∼3.7 mm in dorsoventral direction, which is comparable or slightly larger than the size of cortical delay-tuned areas in insectivorous constant frequency bats, the only other bat species for which cortical chronotopy has been demonstrated. This indicates that chronotopic cortical organization is not only used exclusively for precise insect localization in constant frequency bats but could also be of advantage for general orientation tasks.

Combination-sensitive neurons in the ventroanterior area of the auditory cortex of the mustached bat

1988 ◽  
Vol 60 (6) ◽  
pp. 1908-1923 ◽  
Author(s):  
K. Tsuzuki ◽  
N. Suga
Keyword(s):  
Auditory Cortex ◽  
Functional Organization ◽  
Primary Auditory Cortex ◽  
Great Majority ◽  
Signal Pulse ◽  
Constant Frequency ◽  
Response Properties ◽  
Tuning Curves ◽  
Mustached Bat ◽  
Anterior Division

1. Because the ventroanterior (VA) area is one of the target areas of the FM-FM area in the auditory cortex of the mustached bat, Pteronotus parnellii parnellii, response properties of combination-sensitive neurons in this area were studied with constant-frequency (CF) tones, frequency-modulated (FM) sounds, and sounds similar to the bat's biosonar signal (pulse), which consisted of long CF components (CF1-4) and short FM components (FM1-4). CF1-4 and FM1-4 are the components in the four harmonics (H1-4) of the pulse. 2. Combination-sensitive neurons are clustered in a small area immediately anteroventral to the Doppler-shifted CF processing (DSCF) area and posteroventral to the anterior division of the primary auditory cortex. Because this cluster in the VA area is small, it was difficult to record a sufficient number of combination-sensitive neurons to explore the functional organization of the cluster, but it was found that the response properties of these VA neurons were unique. 3. Combination-sensitive neurons in the VA area are tuned to particular combinations of signal elements similar to the first and second harmonics of the pulse and/or echo. Unlike neurons in the FM-FM, dorsal fringe (DF), and CF/CF areas, no neurons in the VA area are tuned to the signal elements in the first and third or fourth harmonics. 4. The great majority of combination-sensitive neurons in the VA area can not be easily classified into either FM-FM or CF/CF neurons, because they show facilitative responses to combinations of CF1/CF2, FM1-FM2, and FM1-CF2. Therefore, they are called H1-H2 neurons. In the FM-FM and CF/CF areas, all the neurons could be easily classified as FM-FM or CF/CF. This uniqueness of H1-H2 neurons is related to the fact that their best frequencies for facilitation are predominantly between 61.0 and 62.0 kHz, i.e., within the frequency range of stabilized Doppler-shifted echo CF2. 5. In addition to 27 H1-H2 neurons, 7 FM1-FM2 neurons were also recorded in the VA area. The best delays of these H1-H2 and FM1-FM2 neurons measured with FM1-FM2 pairs are between 1 and 10 ms. Unlike neurons in the FM-FM and DF areas, their delay-tuning curves are very broad, even if their best delays are short, and extend beyond zero delay to several millisecond "negative" delays of the FM2 from the FM1, i.e., several millisecond delays of the FM1 from the FM2.(ABSTRACT TRUNCATED AT 400 WORDS)

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)

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)

Tonotopic and functional organization in the auditory cortex of the big brown bat, Eptesicus fuscus

1993 ◽  
Vol 70 (5) ◽  
pp. 1988-2009 ◽  
Author(s):  
S. P. Dear ◽  
J. Fritz ◽  
T. Haresign ◽  
M. Ferragamo ◽  
J. A. Simmons
Keyword(s):  
Auditory Cortex ◽  
Surface Area ◽  
Cortical Neurons ◽  
Functional Organization ◽  
Primary Auditory Cortex ◽  
Target Range ◽  
Cortical Surface ◽  
Behavioral Experiments ◽  
Cortical Surface Area ◽  
Harmonic Ratio

1. In Eptesicus the auditory cortex, as defined by electrical activity recorded from microelectrodes in response to tone bursts, FM sweeps, and combinations of FM sweeps, encompasses an average cortical surface area of 5.7 mm2. This area is large with respect to the total cortical surface area and reflects the importance of auditory processing to this species of bat. 2. The predominant pattern of organization in response to tone bursts observed in each cortex is tonotopic, with three discernible divisions revealed by our data. However, although cortical best-frequency (BF) maps from most of the individual bats are similar, no two maps are identical. The largest division contains an average of 84% of the auditory cortical surface area, with BF tonotopically mapped from high to low along the anteroposterior axis and is part of the primary auditory cortex. The medium division encompasses an average of 13% of the auditory cortical surface area, with highly variable BF organization across bats. The third region is the smallest, with an average of only 3% of auditory cortical surface area and is located at the anterolateral edge of the cortex. This region is marked by a reversal of the tonotopic axis and a restriction in the range of BFs as compared with the larger, tonotopically organized division. 3. A population of cortical neurons was found (n = 39) in which each neuron exhibited two BF threshold minima (BF1 and BF2) in response to tone bursts. These neurons thus have multipeaked frequency threshold tuning curves. In Eptesicus the majority of multipeaked frequency-tuned neurons (n = 27) have threshold minima at frequencies that correspond to a harmonic ratio of three-to-one. In contrast, the majority of multipeaked neurons in cats have threshold minima at frequencies in a ratio of three-to-two. A three-to-one harmonic ratio corresponds to the "spectral notches" produced by interference between overlapping echoes from multiple reflective surfaces in complex sonar targets. Behavioral experiments have demonstrated the ability of Eptesicus to use spectral interference notches for perceiving target shape, and this subpopulation of multipeaked frequency-tuned neurons may be involved in coding of spectral notches. 4. The auditory cortex contains delay-tuned neurons that encode target range (n = 99). Most delay-tuned neurons respond poorly to tones or individual FM sweeps and require combinations of FM sweeps. They are combination sensitive and delay tuned.(ABSTRACT TRUNCATED AT 400 WORDS)

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