摘要:

Both tympanic and nontympanic pathways of sound reception are utilized by anuran amphibians. The relationship between body size and the acoustic responsiveness of various body surfaces that may serve as pathways for sound reception in anurans was analyzed. The motion of the different surfaces (tympanum, lateral body wall, lateral head surface, and dorsal shoulder surface) produced by sound was measured with a laser vibrometer in anuran species. The frequency response and amplitude levels of motion of these body surfaces clearly were linked with size. In all animals, nontympanic surfaces were most responsive to low frequencies, and the tympanum was most responsive to high frequencies. However, the responsiveness of nontympanic surfaces was greater, and extended to higher frequencies, in small anurans. In the smallest animals studied, nontympanic surfaces were often more responsive than the tympanum up to frequencies as high as 2500 Hz. In larger anurans, nontympanic responsiveness tended to decrease, and tympanic responsiveness tended to increase. In the largest animals studied, the tympanum was the most responsive surface at all except very low frequencies below about 200–300 Hz. These results suggest that small anurans can utilize nontympanic pathways for effective sound reception over a broad frequency range, whereas large anurans are more restricted to using a standard tympanic middle ear for hearing. This effect of body size on the utility of nontympanic sound reception may explain evolutionary patterns of tympanic ear reduction and loss observed in several small species of anuran

ISSN:0006-8977    

DOI:10.1159/000114111

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The forebrain of hedgehogs is considered by many investigators as one of the simplest and most primitive among extant placental mammals. In a recent study we have shown that the auditory cortex of the long-eared hedgehog (Hemiechinus auritus) comprises two distinct auditory fields, which are tonotopically organized. In this study, we describe tuning properties of single cells in these two fields. Application of the Q10dB and Square Root measures for determining sharpness of tuning revealed that, although most of the cells in the more anterior field, which is considered primary, are sharply tuned, on the average they are more broadly tuned than cells in the primary auditory cortex of other mammals. In the posterior field, the distribution of narrowly and broadly tuned cells is equal. Narrowly tuned cells in both fields are equally narrow, as are the broadly tuned cells. Latencies of single cells in both fields are frequency and intensity dependent and are somewhat longer than these found in other mammals. The distribution of BFs vs. threshold intensity matches fairly well the behavioral audiogram previously described. Our findings suggest that, in spite of the view that the isocortex of hedgehogs represents a ''primitive'' condition, some basic tuning properties of their auditory cortex cells are comparable to those of other mammals.

ISSN:0006-8977    

DOI:10.1159/000114112

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The contribution of forebrain structures to the control of visually guided eating behaviors was studied using a technique for reversible ''visual decerebration''. The procedure is based upon the fact that structures in the thalamus and telencephalon receive their visual inputs primarily from the contralateral eye. When the eye contralateral to the ablated hemisphere is occluded, the remaining eye has unilateral access to these structures. When the eye ipsilateral to the ablated hemisphere is occluded, the bird is functionally decerebrate; i.e., visual processing by the remaining eye is restricted to structures caudal to the forebrain. The performance of normal and hemispherectomized subjects under binocular and monocular (unilateral, decerebrate) viewing conditions was compared on tests of ingestive efficiency, identification, conditioned peck localization, and grasping. In normal subjects, differences between right and left eye were not significant on any of these tasks. In hemispherectomized subjects, monocular performance on the first three tasks depended critically upon which eye was occluded. In the decerebrate condition (i.e., when the eye opposite the ablated hemisphere was used) performance on the identification, ingestive efficiency and peck localization tasks was significantly degraded, but grasping was unimpaired. We conclude that the brain structures critical for the visuomotor control of grasping lie caudal to the forebrain.

ISSN:0006-8977    

DOI:10.1159/000114113

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The retinofugal projections in the bowfin, a non-teleost actinopterygian, were studied by autoradiographic and horseradish peroxidase methods, and the cytoarchitecture of retinorecipient regions of the diencephalon was analyzed with serially sectioned, Bodian stained material. Nuclei were identified in the thalamus, the periventricular portion of the posterior tuberculum, synencephalon, and pretectum which are homologous to like-named nuclei in teleosts and other non-teleost actinopterygian fishes. Of particular note, a posterior pretectal nucleus and, possibly, a homologue of nucleus corticalis were found to be present in the pretectum. These nuclei have previously been identified only jn teleosts. The posterior pretectal nucleus is relatively small in the bowfin, and the distribution of a small, versus a large, posterior pretectal nucleus in Teleostei and Halecomorphi suggests that this nucleus was small plesiomorphically. The pattern of retinofugal projections in the bowfin is similar to that in other non-teleost actinopterygian fishes and in teleosts in most regards. Contralaterally, the retina projects to nuclei in the dorsal and ventral thalamus, superficial and central pretectum, dorsal and ventral accessory optic nuclei, and to the optic tectum. Additionally, there are sparse projections to the suprachiasmatic nucleus in the preoptic area, the periventricular nucleus of the posterior tuberculum, and the dorsal and ventral periventricular pretectal nuclei. Ipsilateral projections are sparse and are derived from fibers which do not decussate in the optic chiasm. Undecussated ipsilateral retinal projections, as present in the bowfin, are a widely distributed character in vertebrates and appear to be plesiomorphic for vertebrates.

ISSN:0006-8977    

DOI:10.1159/000114114

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000114115

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0006-8977    

DOI:10.1159/000114116

出版商:S. Karger AG    

年代:1992

数据来源: Karger