Biomedical subjects

Jagmeet S Kanwal

Publications and source records attributed to Jagmeet S Kanwal.

5 recordsLinked to original sources

PubMed2004

Oxytocin and vasopressin immunoreactivity within the forebrain and limbic-related areas in the mustached bat, Pteronotus parnellii.

The nonapeptides, oxytocin and arginine vasopressin, play an important role in mammalian social and reproductive behavior. Using immunocytochemical procedures, we identified oxytocin-immunoreactive neurons in the frontal and auditory cortices, limbic areas such as the medial septal nucleus, horizontal limb of the diagonal band and the amygdala. Only arginine vasopressin neurons were present in the bed nucleus of the stria terminalis. In limbic-related areas, the hypothalamic paraventricular and supraoptic nuclei and the nucleus centralis contained both oxytocin and arginine vasopressin neurons. The medial preoptic area showed a positive reaction for several arginine vasopressin fibers, but not oxytocin fibers, except in one female bat sacrificed during the breeding season. Arginine vasopressin fibers were observed in another limbic-related area, the periaqueductal gray. Furthermore, oxytocin was predominantly localized within sensory (e.g., auditory) and frontal cortex and limbic areas, whereas arginine vasopressin was restricted largely to known audiovocal regions of the periaqueductal gray. Classical neurosecretory nuclei in the hypothalamus contain both peptides. Oxytocin-immunoreactive neurons were also found in other structures such as the olfactory bulb, olfactory tubercle, primary and secondary motor cortex, fronto-parietal cortex, piriform cortex and the nucleus of the internal capsule. Both oxytocin and arginine vasopressin immunoreactivity was present in the suprachiasmatic nucleus, median eminence, neural lobe of the hypophysis and the pineal gland. Together with previous studies, the presence of these peptides within auditory areas of the cortex (sensory and frontal), and limbic as well as limbic-related regions provides anatomical evidence supporting their proposed role in social vocal behaviors and probably in auditory processing.

Animals↗

PubMed2004

Local field potentials and spiking activity in the primary auditory cortex in response to social calls.

The mustached bat, Pteronotus parnellii, uses complex communication sounds ("calls") for social interactions. We recorded both event-related local field potentials (LFPs) and single/few-unit (SU) spike activity from the same electrode in the posterior region of the primary auditory cortex (AIp) during presentation of simple syllabic calls to awake bats. Temporal properties of the LFPs, which reflect activity within local neuronal clusters, and spike discharges from SUs were studied at 138 recording sites in six bats using seven variants each of 14 simple syllables presented at intensity levels of 40-90 dB SPL. There was no clear spatial selectivity to different call types within the AIp area. Rather, as shown previously, single units responded to multiple call types with similar values of the peak response rate in the peri-stimulus time histogram (PSTH). The LFPs and SUs, however, showed a rich temporal structure that was unique for each call type. Multidimensional scaling (MDS) of the averaged waveforms of call-evoked LFPs and PSTHs revealed that calls were better segregated in the two-dimensional space based on the LFP compared with the PSTH data. A representation within the "LFP-space" revealed that one of the dimensions correlated with the predominant and fundamental frequency of a call. The other dimension showed a high correlation with "harmonic complexity" ("fine" spectral structure of a call). We suggest that the temporal pattern of LFP and spiking activity reflects call-specific dynamics at any locus within the AIp area. This dynamic contributes to a distributed (population-based) representation of calls. Alternatively stated, the fundamental frequency and harmonic structure of calls, and not the recording location within the AIp, determines the temporal structure of the call-evoked LFP.

Acoustic Stimulation↗

PubMed2003

Neurodynamics for auditory stream segregation: tracking sounds in the mustached bat's natural environment.

During navigation and the search phase of foraging, mustached bats emit approximately 25 ms long echolocation pulses (at 10-40 Hz) that contain multiple harmonics of a constant frequency (CF) component followed by a short (3 ms) downward frequency modulation. In the context of auditory stream segregation, therefore, bats may either perceive a coherent pulse-echo sequence (PEPE...), or segregated pulse and echo streams (P-P-P... and E-E-E...). To identify the neural mechanisms for stream segregation in bats, we developed a simple yet realistic neural network model with seven layers and 420 nodes. Our model required recurrent and lateral inhibition to enable output nodes in the network to 'latch-on' to a single tone (corresponding to a CF component in either the pulse or echo), i.e., exhibit differential suppression by the alternating two tones presented at a high rate (> 10 Hz). To test the applicability of our model to echolocation, we obtained neurophysiological data from the primary auditory cortex of awake mustached bats. Event-related potentials reliably reproduced the latching behaviour observed at output nodes in the network. Pulse as well as nontarget (clutter) echo CFs facilitated this latching. Individual single unit responses were erratic, but when summed over several recording sites, they also exhibited reliable latching behaviour even at 40 Hz. On the basis of these findings, we propose that a neural correlate of auditory stream segregation is present within localized synaptic activity in the mustached bat's auditory cortex and this mechanism may enhance the perception of echolocation sounds in the natural environment.

Acoustic Stimulation↗

PubMed2002

Oxytocin within auditory nuclei: a neuromodulatory function in sensory processing?

Oxytocin (OT) plays an important role in social bonding, ultrasonic vocalizations and other sexual behaviors in mammalian species. Although its presence within neuroendocrine regions in the forebrain is well established, its association with sensory nuclei remains unclear. We report here the presence of oxytocin immunoreactive neurons within several nuclei in the auditory brain stem of the mustached bat, Pteronotus parnellii. Immunocytochemical procedures revealed OT-immunoreactive perikarya and/or fiber terminals in restricted areas of the inferior colliculus (IC), superior olivary complex (SOC), including the medial and ventral nuclei of the trapezoid body, and in the cochlear nucleus. Perikarya were labeled predominantly in the IC and SOC and both perikarya and fiber terminals were labeled extensively in the cochlear nucleus.

Animals↗

PubMed2002

Modeling complex tone perception: grouping harmonics with combination-sensitive neurons.

Perception of complex communication sounds is a major function of the auditory system. To create a coherent precept of these sounds the auditory system may instantaneously group or bind multiple harmonics within complex sounds. This perception strategy simplifies further processing of complex sounds and facilitates their meaningful integration with other sensory inputs. Based on experimental data and a realistic model, we propose that associative learning of combinations of harmonic frequencies and nonlinear facilitation of responses to those combinations, also referred to as "combination-sensitivity," are important for spectral grouping. For our model, we simulated combination sensitivity using Hebbian and associative types of synaptic plasticity in auditory neurons. We also provided a parallel tonotopic input that converges and diverges within the network. Neurons in higher-order layers of the network exhibited an emergent property of multifrequency tuning that is consistent with experimental findings. Furthermore, this network had the capacity to "recognize" the pitch or fundamental frequency of a harmonic tone complex even when the fundamental frequency itself was missing.

Animals↗