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Biomedical subjects

P H Jen

Publications and source records attributed to P H Jen.

72 records · Page 4Linked to original sources
PubMed1987

Auditory spatial response areas of single neurons and space representation in the cerebellum of echo locating bats.

Using free-field acoustic stimulation conditions, we studied the auditory spatial response areas of 242 cerebellar neurons of Eptesicus fuscus. A best frequency stimulus was delivered from a loudspeaker which was moved across the frontal auditory space in order to determine the response center of each cerebellar neuron. At the response center, the neuron had its lowest minimum threshold. The stimulus was then raised 5-15 dB above the lowest minimum threshold of each neuron and the spatial response area for each stimulus intensity was measured. The spatial response area of each neuron expanded asymmetrically with the stimulus intensity. The size of the spatial response area was not correlated with the minimum threshold, best frequency or recording depth of the neuron. The distribution of the best frequencies of single neurons was not correlated with their recording depths or minimum thresholds. The response centers of all cerebellar neurons were located within a small area of the central portion of the frontal auditory space suggesting that the cerebellum could play an effective role in orienting the bat toward the echo source within the frontal gaze during insect capture.

Acoustic Stimulation↗
PubMed1987

Pinna position affects the auditory space representation in the inferior colliculus of the FM bat, Eptesicus fuscus.

Using free-field acoustic stimulus conditions, we studied the auditory space representation in the inferior colliculus (IC) of the big brown bat, Eptesicus fuscus, under different pinna positions. Stimuli were delivered from a loudspeaker placed 14 cm in front of the bat to determine the best frequency (BF) of an isolated neuron. A BF stimulus was then delivered as the loudspeaker was moved across the frontal auditory space of the bat to locate the response center of the neuron. At the response center, the neuron has its lowest minimum threshold (MT). The stimulus was then raised 5-dB above the lowest MT to measure the spatial response area. Both response center and spatial response area of each neuron were measured under different pinna positions. Variations in the response center and MT of each neuron under different pinna positions was determined and a possible reason for this variation was discussed. The variation in auditory space representation in the IC due to variation in pinna position is presented. We suggest that during echolocation a bat could make changes in its pinna position to create additional binaural disparity for accurate target localization.

Animals↗
PubMed1984

Auditory space representation in the superior colliculus of the big brown bat, Eptesicus fuscus.

The auditory response areas of 123 superior collicular (SC) units of Eptesicus fuscus were studied under free-field acoustic stimulus conditions. A stimulus was delivered from a loudspeaker placed 14 cm in front of a bat. The best frequency of a unit was determined by changing the stimulus frequency until the minimum threshold was measured. A best frequency stimulus was then delivered as the loud-speaker was moved across the auditory space to determine the response center of the auditory response area of each unit. The response center was defined as the direction at which the unit had its lowest minimum threshold. The stimulus intensity was then raised 2-20 dB above the lowest minimum threshold of the unit and the response area for each stimulus intensity was determined. The response area of a unit expands with stimulus intensity, but the expansion is not even in all directions. The size of the response area of a unit does not correlate with its minimum threshold, best frequency, or recording depth. Response centers of 7 units were located directly in front of the animal, but most response centers were located in a limited portion of the contralateral auditory space. Although each unit has a response center which is the point of maximal sensitivity, the point-to-point representation of the auditory space is not systematically organized. We suggest that an animal with highly mobile external pinnae may not need an orderly auditory space map in its neural tissue for accurate sound localization.

Acoustic Stimulation↗
PubMed1984

Pinna orientation determines the maximal directional sensitivity of bat auditory neurons.

The auditory response areas of 192 inferior collicular neurons (IC) of Eptesicus fuscus were studied under free field acoustic stimulation. The boundary of the auditory response area of a neuron expands with stimulus intensity (Fig. 1). However, there is a response center within each neuron's response area at which the neuron has the maximal sensitivity. All response centers of the 192 neurons are located within a limited space of the bat's contralateral auditory space. The position of the response center of a neuron changes with different pinna orientations (Figs. 2 and 3) providing a bat with versatility in maximizing the sensitivity of its echolocation system.

Acoustic Stimulation↗
PubMed1984

Preference of a revolving target to a stationary one by the big brown bat, Eptesicus fuscus.

Utilizing a three-ramp platform, we studied the detection of a revolving and a stationary target in the presence of background clutter by trained Eptesicus fuscus. During the test, the mean amplitude of echo from either target was always larger than that of the background echoes at the bat-to-target distance of 30, 70 and 100 cm. The amplitude of the echo reflected back from a revolving target was modulated between a maximum and a minimum value. An electric motor was used to revolve a target. The frequency contents of the motor noise were mostly below 1 kHz. While the total percent response of approaching either target is always more than 90% at every bat-to-target distance tested, the bats approach a revolving target more frequently than a stationary one. Echolocation pulses emitted by the bats during the test were recorded and analyzed. The bats shortened their pulse durations and interpulse intervals and lowered the frequency contents as they entered into the crawling phase from the searching phase. Potential interference of background echoes and ambient noise with the performance of the bats is discussed. The preference of a revolving target to a stationary one by the bats is perhaps due to the fact that a revolving target has a higher releasing value than a stationary one does.

Animals↗
PubMed1983

Mapping of the auditory area in the cerebellar vermis and hemispheres of the mustache bat, Pteronotus parnellii parnellii.

Microelectrode mapping of the auditory areas in the cerebellar vermis and hemispheres of mustache bats, Pteronotus parnellii parnellii, reveals that a large area of the bat's cerebellum contains units responding to acoustic signals. A study of frequency tuning of isolated units shows that there are two large groups of auditory units. The units of one group are sharply tuned to a very narrow band of frequency with BFs between 60 and 64 kHz. The units of the other group are broadly tuned, with BFs between 47 and 59 kHz. These two groups of units are probably involved in processing the predominant CF and FM portions of the bat's orientation sounds during echolocation.

Acoustic Stimulation↗
PubMed1982

Responses of cerebellar neurons of the CF-FM bat, Pteronotus parnellii to acoustic stimuli.

Single units (125) which faithfully discharged action potentials to acoustic stimuli (35 ms in duration with 0.5 ms rise and decay times) were recorded in the cerebellar vermis and hemispheres of the CF-FM bat, Pteronotus parnellii. These units had response latencies between 1.5 and 27 ms and minimum thresholds between 2 and 83.5 dB SPL. Best frequencies (BFs) of these units ranged from 30.32 to 79.28 kHz, but more than half (64 units, 51.2%) were between 59.73 and 63.32 kHz. While most tuning curves of these units were either broad or irregular, those curves with BFs tuned at around 61 kHz which is the frequency of the predominant CF component of the bat's echolocation signals were extremely narrow with Q10-dB values as high as 153. Those units (29) with BFs tuned near the 61 kHz also showed off-responses. These data indicate that auditory specialization for processing of species-specific orientation signals also exists in the cerebellum of this bat.

Animals↗
PubMed1981

Mapping of the auditory area in the cerebellar vermis and hemispheres of the little brown bats, Myotis lucifugus.

Mapping of auditory area in the cerebellar vermis and hemispheres of little brown bats, Myotis lucifugus, shows that a large area of the bat's cerebellum contains units responding to acoustic stimuli. These units had latencies between 4 and 34 msec and best frequencies between 33.0 and 92.5 kHZ. The Q10-dB values of their tuning curves ranged from 2.0 to 19.7. Most of the units studied fired only a few impulses during a stimulus with minimum thresholds between 22 and 90 dB SPL. Units in the cerebellar vermis tend to have higher best frequencies and shorter latencies than those in the cerebellar hemispheres. However, there is no evidence of clear tonotopic organization therein.

Animals↗
PubMed1980

Neurons in the cerebellum of echolocating bats respond to acoustic signals.

Single neurons responding to auditory stimuli (40 msec duration, 0.5 msec rise-decay time) could be isolated from rather large areas of the cerebellar vermis and hemispheres of an echolocating bat, Eptesicus fuscus. These neurons had latencies between 4 and 13 msec and best frequencies between 22 and 77 kHz. The Q10-dB values of their tuning curves were between 1.4 and 16.6. When acoustic stimuli were delivered though the earphones, tuning curves measured from each ear alone were nearly identical in shape and best frequency. The minimum thresholds of these neurons were between 12 and 65 dB SPL. Apparently, these are suitable for reception of the bat's echolocating signals.

Acoustic Stimulation↗
PubMed1980

Coding of directional information by single neurones in the S-segment of the FM bat, Myotis lucifugus.

1. Response parameters of S-segment neurones of the FM bat Myotis lucifugus were measured as a sound was delivered from different azimuthal angles around the animal's head. 2. The response parameters investigated were the amplitude and threshold of the evoked potential (N3) of the S-segment, together with the threshold, latency and number of impulses (per stimulus pulse) of single units. 3. All the neurones studied had their lowest thresholds either at 20-40 degrees contralateral, or 20-40 degrees ipsilateral or at the front (0 degrees). 4. The amplitude of the sound affected the relationship between stimulus direction and the amplitude of a non-monotonic N3, and the relationship between stimulus direction and the number of impulses of a non-monotonic single unit. It had so such effects with a monotonic N3 and a monotonic single unit. 5. From a study of N3 amplitudes and numbers of impulses of single neurones, it appeared that an azimuthal difference as small as 3 degrees could be easily coded at a 95% correct level with stimuli presented at around 20 degrees ipsilateral, 20 degrees contralateral, and at the front. 6. The inter-aural pressure difference (IPD), which is considered an essential cue for echolocation in Myotis (Shimozawa et al. 1974), changed linearly with angle from 0 to 40 degrees lateral at a rate of 0.4 dB/degree for sounds between 33.5 and 49.0 kHz. 7. Assuming the just-detectable IPD to be 0.5 dB (as in man), the minimum detectable azimuthal difference of Myotis around the median plane would be 1.25 degrees.

Animals↗
PubMed1976

Disproportionate tonotopic representation for processing CF-FM sonar signals in the mustache bat auditory cortex.

The extent of cortical representation of the peripheral sensory field depends on its importance for species behavior. The orientation sound of the mustache bat (Pteronotus parnellii rubiginosus) invariably consists of long constant-frequency and short frequency-modulated components and is indispensable for its survival. A disproportionately large part of the auditory cortex of this bat is occupied by neurons processing the predominant components in the orientation signal and Doppler-shifted echoes. This disproportionate cortical representation related to features of biologically significant signals is comparable to that in the somatosensory and visual systems in many mammals, but it has not previously been observed in the auditory system.

Action Potentials↗
PubMed1976

Coordinated activities of middle-ear and laryngeal muscles in echolocating bats.

The middle-ear muscles and laryngeal muscles of the little brown bat (Myotis lucifugus) are highly developed. When the bat emits orientation sounds, action potentials of middle-ear muscles appear approximately 3 milliseconds after those of the laryngeal muscles; this activity of middle-ear muscles attenuates the vocal self-stimulation and improves the performance of the echolocation system. When an acoustic stimulus is delivered, both types of muscles contract; action potentials of the laryngeal muscles appear approximately 3 milliseconds after those of the middle-ear muscles. These two groups of muscles are apparently activated in a coordinated manner not only by the nerve impulses from the vocalization center, but also by those from the auditory system.

Action Potentials↗
PubMed1975

Peripheral control of acoustic signals in the auditory system of echolocating bats.

Many species of echolocating bats emit intense orientation sounds. If such intense sounds directly stimulated their ears, detection of faint echoes would be impaired. Therefore, possible mechanisms for the attenuation of self-stimulation were studied with Myotis lucifugus. The acoustic middle-ear-muscle reflex could perfectly and transiently regulate the amplitude of an incoming signal only at its beginning. However, its shortest latency in terms of electromyograms and of the attenuation of the cochlear microphonic was 3-4 and 4-8 msec, respectively, so that these muscles failed to attenuate orientation signals by the reflex. The muscles, however, received a message from the vocalization system when the bat vocalized, and contracted synchronously with vocalization. The duration of the contraction-relaxation was so short that the self-stimulation was attenuated, but the echoes were not. The tetanus-fusion frequency of tha stapedium muscle ranged between 260 and 320/sec. Unlike the efferent fibres in the lateral-line and vestibular systems, the olivo-cochlear bundle showed no sign of attenuation of self-stimulation.

Acoustic Stimulation↗
PubMed1975

Peripheral specialization for fine analysis of doppler-shifted echoes in the auditory system of the "CF-FM" bat Pteronotus parnellii.

Pteronotus parnellii uses the second harmonic (61-62 kHz) of the CF component in its orientation sounds for Doppler-shift compensation. The bat's inner ear is mechanically specialized for fine analysis of sounds at about 61-62 kHz. Because of this specialization, cochlear microphonics (CM) evoked by 61-62 kHz tone bursts exhibit prominent transients, slow increase and decrease in amplitude at the onset and cessation of these stimuli. CM-responses to 60-61 kHz tone bursts show a prominent input-output non-linearity and transients. Accordingly, a summated response of primary auditory neurones (N1) appears not only at the onset of the stimuli, but also at the cessation. N1-off is sharply tuned at 60-61 kHz, while N1-on is tuned at 63-64 kHz, which is 2 kHz higher than the best frequency of the auditory system because of the envelope-distortion originating from sharp mechanical tuning. Single peripheral neurones sensitive to 61-62 kHz sounds have an unusually sharp tuning curve and show phase-locked responses to beats of up to 3 kHz. Information about the frequencies of Doppler-shifted echoes is thus coded by a set of sharply tuned neurones and also discharges phase-locked to beats. Neurones with a best frequency between 55 and 64 kHz show not only tonic on-responses but also off-responses which are apparently related to the mechanical off-transient occuring in the inner ear and not to a rebound from neural inhibition.

Action Potentials↗