Biomedical subjects

J S Kanwal

Publications and source records attributed to J S Kanwal.

14 recordsLinked to original sources

PubMed2000

A computer program for sequencing and presenting complex sounds for auditory neuroimaging studies.

This paper describes a computer program, named ASAP (audio sequencing and presentation), that runs on IBM PC compatible hardware with a Microsoft Windows operating system and has been specially designed for facilitating auditory neuroimaging studies. The program's main characteristics are: (1) the ability to generate sequences of complex sounds; (2) an easy-to-use, graphical user interface; (3) full compatibility with Microsoft Windows 95 or later and Windows NT version 4.0 or later software; (4) precise timing of selected sound sequences; (5) the capability of triggering other devices; (6) the capability of being triggered to deliver stimuli; (7) support for both monotic and dichotic sound sequences; and (8) rudimentary support for the simultaneous presentation of pictures/text and sound.

Acoustic Stimulation↗

PubMed2000

Auditory responses from the frontal cortex in the mustached bat, Pteronotus parnellii.

Response properties of neurons in an auditory field in the frontal cortex of the mustached bat, Pteronotus parnellii, have not been studied before. We recorded neural responses to constant frequency (CF) stimuli from the frontal auditory field in awake animals. The majority (75%) of neurons in this area responded well and often exhibited low thresholds to CF stimuli. Most CF-responsive neurons exhibited sharp tuning with values of > 180 for Q10db, a quality factor expressing the sharpness of tuning at 10dB above threshold. Neurons at 13 recording sites exhibited combination sensitivity in that their responses were facilitated by presenting combinations of either CF1/CF2 and/or CF1/CF3 components of the mustached bat's echolocation signal. Unlike the typical on-responses to a 30 ms tone, observed in the mustached bat's auditory cortex and at subcortical levels, many frontal auditory neurons exhibited loosely time locked firing patterns that lasted for > 100 ms.

Animals↗

PubMed1999

Anatomical and functional imaging of the auditory cortex in awake mustached bats using magnetic resonance technology.

The auditory cortex of mustached bats, Pteronotus parnellii, has been studied extensively using neuroanatomical tract-tracing and electrophysiological techniques to elucidate the functional organization and neural mechanisms important for auditory processing. While these techniques have identified several cortical maps involved in processing auditory information, there has been no direct observation of the dynamics of simultaneous activation of several discrete areas. We applied magnetic resonance (MR) imaging techniques for visualizing brain structures in awake bats using a 7-Tesla magnet system; we also investigated functional MR imaging by measuring changes in stimulus-correlated blood oxygenation levels to detect cortical areas exhibiting evoked neural activity. High resolution (100 microm) anatomical images were successfully acquired without any motion artifacts. It was possible to reconstruct the whole brain image and analyze brain surface structures with three dimensional (3D) MR imaging data. These data provide detailed morphometric measurements that will allow localization of stimulus specific neural activity patterns using modified functional magnetic-resonance-imaging (fMRI) protocols. Motion artifacts is the primary disadvantage of using awake bats; our study shows that fMRI of a bat's brain is feasible and may prove to be an important advancement for a further understanding of auditory processing in this species.Themes: Sensory systems, Neural basis of behavior.

Acoustic Stimulation↗

PubMed1999

Facilitatory and inhibitory frequency tuning of combination-sensitive neurons in the primary auditory cortex of mustached bats.

Mustached bats, Pteronotus parnellii parnellii, emit echolocation pulses that consist of four harmonics with a fundamental consisting of a constant frequency (CF(1-4)) component followed by a short, frequency-modulated (FM(1-4)) component. During flight, the pulse fundamental frequency is systematically lowered by an amount proportional to the velocity of the bat relative to the background so that the Doppler-shifted echo CF(2) is maintained within a narrowband centered at approximately 61 kHz. In the primary auditory cortex, there is an expanded representation of 60.6- to 63. 0-kHz frequencies in the "Doppler-shifted CF processing" (DSCF) area where neurons show sharp, level-tolerant frequency tuning. More than 80% of DSCF neurons are facilitated by specific frequency combinations of approximately 25 kHz (BF(low)) and approximately 61 kHz (BF(high)). To examine the role of these neurons for fine frequency discrimination during echolocation, we measured the basic response parameters for facilitation to synthesized echolocation signals varied in frequency, intensity, and in their temporal structure. Excitatory response areas were determined by presenting single CF tones, facilitative curves were obtained by presenting paired CF tones. All neurons showing facilitation exhibit at least two facilitative response areas, one of broad spectral tuning to frequencies centered at BF(low) corresponding to a frequency in the lower half of the echolocation pulse FM(1) sweep and another of sharp tuning to frequencies centered at BF(high) corresponding to the CF(2) in the echo. Facilitative response areas for BF(high) are broadened by approximately 0.38 kHz at both the best amplitude and 50 dB above threshold response and show lower thresholds compared with the single-tone excitatory BF(high) response areas. An increase in the sensitivity of DSCF neurons would lead to target detection from farther away and/or for smaller targets than previously estimated on the basis of single-tone responses to BF(high). About 15% of DSCF neurons show oblique excitatory and facilitatory response areas at BF(high) so that the center frequency of the frequency-response function at any amplitude decreases with increasing stimulus amplitudes. DSCF neurons also have inhibitory response areas that either skirt or overlap both the excitatory and facilitatory response areas for BF(high) and sometimes for BF(low). Inhibition by a broad range of frequencies contributes to the observed sharpness of frequency tuning in these neurons. Recordings from orthogonal penetrations show that the best frequencies for facilitation as well as excitation do not change within a cortical column. There does not appear to be any systematic representation of facilitation ratios across the cortical surface of the DSCF area.

Animals↗

PubMed1997

Syntax processing by auditory cortical neurons in the FM-FM area of the mustached bat Pteronotus parnellii.

Syntax denotes a rule system that allows one to predict the sequencing of communication signals. Despite its significance for both human speech processing and animal acoustic communication, the representation of syntactic structure in the mammalian brain has not been studied electrophysiologically at the single-unit level. In the search for a neuronal correlate for syntax, we used playback of natural and temporally destructured complex species-specific communication calls-so-called composites-while recording extracellularly from neurons in a physiologically well defined area (the FM-FM area) of the mustached bat's auditory cortex. Even though this area is known to be involved in the processing of target distance information for echolocation, we found that units in the FM-FM area were highly responsive to composites. The finding that neuronal responses were strongly affected by manipulation in the time domain of the natural composite structure lends support to the hypothesis that syntax processing in mammals occurs at least at the level of the nonprimary auditory cortex.

Animal Communication↗

PubMed1997

Parallel medullary gustatospinal pathways in a catfish: possible neural substrates for taste-mediated food search.

Taste and tactile fibers in the facial nerve of catfish innervate extraoral taste buds and terminate somatotopically in the facial lobe (FL)-a medullary structure crucial for gustatory-mediated food search. The present study was performed to determine the neural linkages between the gustatory input and the spinal motor output. Spinal injections of horseradish peroxidase (HRP) label spinopetal cells in the octaval nuclei, the nucleus of the medial longitudinal fasciculus, and reticulospinal neurons (Rsps) in the brainstem medial reticular formation (RF), including the Mauthner cell. A somatotopically organized, direct faciospinal system originating from superficial cells scattered in the lateral lobule of the facial lobe (ll) is also labeled. The brainstem reticulospinal cells are segmentally organized into 14 clusters within eight segments of the reticular formation and includes one cluster (RS5) directly ventral to the FL. Injections of HRP or fluorescent tracers into the medial lobule of the FL label a facioreticular projection terminating around the Rsps of RS5. DiI injections into this area of the RF retrogradely label deeply situated bipolar neurons, especially in the medial and intermediate lobules of the FL. Electrophysiological recordings in and around RS5 show units with large receptive fields and with responses to chemical and tactile stimulation. The FL projects to the spinal cord via two pathways: (1) a topographically organized direct faciospinal pathway, and (2) an indirect facioreticulospinal pathway in which reticular neurons process and integrate gustatory information before influencing spinal circuitry for motor control during food search.

Animals↗

PubMed1996

Facilitative responses to species-specific calls in cortical FM-FM neurons of the mustached bat.

FM-FM neurons in the auditory cortex of the mustached bat are highly specialized for echolocation, responding facilitatively to the combination of frequency modulated (FM) components of biosonar pulse and its echo. Here we propose they are also specialized for processing bat communication calls. FM-FM neurons respond facilitatively to natural call syllable pairs, and exhibit inter-syllable interval tuning to the natural range of intervals. Our results support a role for 'combination-sensitive' neurons in communication, and suggest that cortical neurons can possess multiple distinct specialized modes of response.

Animal Communication↗

PubMed1994

Analysis of acoustic elements and syntax in communication sounds emitted by mustached bats.

Mustached bats, Pteronotus parnellii parnellii spend most of their lives in the dark and use their auditory system for acoustic communication as well as echolocation. The sound spectrograms of their communication sounds or "calls" revealed that this species produces a rich variety of calls. These calls consist of one or more of the 33 different types of discrete sounds or "syllables" that are emitted singly and/or in combination. These syllables can be further classified as 19 simple syllables, 14 composites, and three subsyllables. Simple syllables consist of characteristic geometric patterns of CF (constant frequency), FM (frequency modulation), and NB (noise burst) sounds that are defined quantitatively using statistical criteria. Composites consist of simple syllables or subsyllables conjoined without any silent interval. Most syllable types exhibit a large intrinsic variation in their physical structure compared to the stereotypic echolocation pulses. Syllable domains are defined on the basis of multiple parameters, although these can be collapsed onto three dimensions that capture 99% of the measured variation among different types of syllables. Temporal analysis of multisyllabic constructs reveals several syntactical rules for syllable transitions.

Acoustics↗

PubMed1993

Combination-sensitive neurons in the primary auditory cortex of the mustached bat.

In the mustached bat, Pteronotus parnellii, neurons in the primary auditory cortex (AI) have been thought to respond primarily to single frequencies, as in other mammals. However, neurons in the Doppler-shifted constant-frequency (DSCF) area, a part of the mustached bat's AI that contains an overrepresentation of the prominent CF2 component of the biosonar signal, were found to show facilitative responses to combinations of different frequencies in the pulse and echo. The essential components for facilitation were the pulse FM1 and the echo CF2. The FM1-CF2 facilitation was sensitive to echo delays, indicating that DSCF neurons respond better to targets within particular ranges. On average, the longest discriminable echo delay, based on increased impulse counts due to facilitation, corresponded to a target range of 4.3 m, and the most discriminable delay corresponded to a target 3.6 m distant. Since mustached bats first show a behavioral response to a target at a distance of 3-4 m, DSCF neurons are suited to signal the presence of an insect within this behaviorally important range. DSCF neurons were broadly tuned to echo delay, with the average minimum discriminable echo delay corresponding to a target range of 1.9 m, and the delay tuning of the neurons followed (tracked) changes in pulse duration, indicating that facilitation occurs during much of the approach phase of insect pursuit when target characterization is presumably occurring. These results show that AI neurons in the mustached bat are specialized to respond to complex, behaviorally relevant stimuli during the search and approach phases of insect pursuit.

Acoustic Stimulation↗

PubMed1992

Ascending general visceral pathways within the brainstems of two teleost fishes: Ictalurus punctatus and Carassius auratus.

The primary general visceral nucleus in goldfish (Carassius auratus) and catfish (Ictalurus punctatus) is located at the ventroposterior boundary of the vagal gustatory lobe and receives coelomic visceral, but not gustatory inputs. The neuronal tracer horseradish peroxidase (HRP) was employed to visualize sources of input to and ascending projections from the primary general visceral nucleus in these species. In addition, immunocytochemical techniques were utilized to define the cytological divisions within the pontine gustatory-visceral complex. The pontine secondary visceral nuclei in both catfish and goldfish contains numerous somata and fibers immunoreactive for calcitonin gene-related peptide (CGRP). In contrast, the secondary gustatory nuclei are devoid of fibers and cells immunoreactive for CGRP. In both the goldfish and the channel catfish, the primary general visceral nucleus receives input from the vagal gustatory lobe, as well as the medullary reticular formation. In the channel catfish, the primary general visceral nucleus projects bilaterally to the secondary visceral nucleus, which lies rostrolateral to the secondary gustatory nucleus in the dorsal pons. Fibers cross the midline via the rostral part of the isthmic commissure. Injection of HRP into the primary general visceral nucleus of a goldfish labels ascending fibers that project to a secondary visceral nucleus situated ventral, lateral, and rostral to the secondary gustatory complex. In general, the results indicate that general visceral systems ascend in parallel to gustatory systems within the brainstem, and that general visceral but not gustatory nuclei are immunoreactive for the peptide CGRP.

Afferent Pathways↗

PubMed1988

Forebrain connections of the gustatory system in ictalurid catfishes.

Horseradish peroxidase tracing and extracellular electrophysiological recording techniques were employed to delineate prosencephalic connections of the gustatory system in ictalurid catfishes. The isthmic secondary gustatory nucleus projects rostrally to several areas of the ventral diencephalon including the nucleus lobobulbaris and the nucleus lateralis thalami. Injections of HRP in the vicinity of the nucleus lobobulbaris reveal an ascending projection to the telencephalon terminating in the area dorsalis pars medialis (Dm) and the medial region of area dorsalis pars centralis (Dc). Conversely, injections of HRP into the gustatory region of area dorsalis pars medialis label small neurons in the nucleus lobobulbaris. Gustatory neurons in the telencephalon send descending projections via the medial and lateral forebrain bundles to several nuclei in the anterior and ventroposterior diencephalon. The nucleus lateralis thalami, a diencephalic nucleus, receives ascending gustatory projections from the secondary gustatory nucleus but does not project to the telencephalon. Neurons in both the nucleus lateralis thalami and the telencephalic gustatory target exhibit multiple extraoral and oral receptive fields and complex responses to chemical (taste) and tactile stimulation.

Afferent Pathways↗

PubMed1988

Overlapping taste and tactile maps of the oropharynx in the vagal lobe of the channel catfish, Ictalurus punctatus.

Microelectrode mapping experiments indicate an ipsilateral representation of the oropharynx and a well-defined, bilateral input from the proximal portion of the maxillary barbels and snout region within the vagal lobe of channel catfish. The map of the oropharyngeal epithelium is distorted so that the gill arches are rotated through an angle of 90 degrees along the transverse plane, and the dorsally mapped region of the gill rakers is tilted posteriorly in the sagittal plane of the vagal lobe. Multiunit recording studies fail to provide definitive boundaries of adjacently mapped domains of oropharyngeal structures. Gustatory receptive fields of neurons in the vagal lobe correspond to their location on the topological map obtained by tactile stimulation of the oropharyngeal epithelium. A few single unit recordings indicate restricted receptive fields and different response patterns of taste, tactile, and proprioceptive neurons in the vagal lobe of catfish.

Animals↗

PubMed1987

Central projections of the glossopharyngeal and vagal nerves in the channel catfish, Ictalurus punctatus: clues to differential processing of visceral inputs.

Transganglionic transport of horseradish peroxidase was used to trace the pattern of medullary terminations of the glossopharyngeal and vagal nerve complex in the channel catfish, Ictalurus punctatus. The glossopharyngeal root terminates centrally in the anterior end of the vagal lobe except for two fascicles that terminate in separate regions of the nucleus intermedius of the facial lobe. Vagal nerve branches innervating regions of the oropharynx terminate in an overlapping, segmental fashion throughout the ipsilateral vagal lobe and the nucleus intermedius of the vagal lobe. The descending branch of the vagus, innervating the abdominal viscera, terminates in the general visceral nucleus and in the nucleus intermedius of the vagal lobe. In addition, abdominal visceral fibers decussate through the commissural nucleus of Cajal and terminate in the general visceral nucleus of the contralateral side. Efferents included in the oropharyngeal and abdominal branches of the vagus also originate from two morphologically separable populations of motor neurons.

Afferent Pathways↗

PubMed1987

Taste responses to amino acids from facial nerve branches innervating oral and extra-oral taste buds in the channel catfish, Ictalurus punctatus.

Electrophysiological recordings were obtained from two branches of the facial nerve innervating oral and extra-oral taste receptive fields, respectively, in the channel catfish, Ictalurus punctatus. The results indicate that taste buds innervated by the ramus ophthalmicus superficialis (ros), innervating taste buds on the nasal barbel, and the ramus palatinus (rp), innervating taste buds on the anterior palate, have similar chemical specificities for amino acids. Among the amino acids tested, the most stimulatory compounds for both the ros and rp were L-alanine and L-arginine, having estimated electrophysiological thresholds of approximately 10(-9) M. Dose-response functions for amino acid stimuli recorded from both the ros and rp were power functions extending over 5 log units of stimulus concentrations. The general similarity in the nature of the taste input from spatially distinct gustatory areas supports a chemotactic role of the facial taste system in the channel catfish.

Adaptation, Physiological↗