Central Organization of Wave Localization in the Clawed Frog, <i>Xenopus laevis</i>

Abstract

The organization of water wave localization within the midbrain of the clawed frog Xenopus was investigated by performing behavioral tests on frogs that had partial midbrain ablations. The criterion of localization was the orientation of turns toward the origin of impinging waves. All lesion effects became apparent as localization failure within an angular sector of wave direction. The sectors were contralateral to the lesion and of various sizes, some comprising the complete hemifield. Localization outside of the sectors was not affected. Thus, wave localization is topologically organized with respect to wave direction. Two topological projections were found. Lesions of the first projection resulted in unoriented responses to the affected wave directions. After lesions of the other projection, the frog responded to waves from the affected directions by lunges without turns. It is suggested that the two types of localization failures are due to impairment of the sensory wave direction detection and of the sensorimotor transfer, respectively. The essential midbrain areas are presumably the magnocellular nucleus of the torus magnocellularis and the ventrolateral tectum, but a considerable part of the localization might be done in the medulla.

Central Organization of Wave Localization in the Clawed Frog, <i>Xenopus laevis</i>

“…If not indicated otherwise, each of the described lesion types was tested at least three times, and the results were uniform for each type. The conclusions are further corroborated by the results of a considerable number of smaller lesions, which are described in the companion paper [Elepfandt, 1988].…”

“…The present paper demonstrates that the midbrain is nec essary for wave localization and that the localization is organized in the form of a functional chiasm. In the companion paper, I describe a dual topological organization for wave localization in the midbrain [Elepfandt, 1988]. Preliminary reports have appeared elsewhere [Elepfandt, 1984b[Elepfandt, , 1986a.…”

Neural responses to water surface waves in the midbrain of the aquatic predator Xenopus laevis laevis

“…1985b; Will, 1989; Edwards & Kelley, 2001). Among these nuclei, the TM possibly exhibits divisions concerned with wave source localization and frequency resolution, respectively (Elepfandt, 1988b; Reisbeck, 1994). Notably, substantial projections of the torus semicircularis reach the optic tectum (OT), where lateral line units of remarkable spatial selectivity were observed (Zittlau et al.…”

“…Potentially at least, some of those units could match by their spatial tuning the behavioural localization accuracy of the animal (5°; Elepfandt, 1982). Behavioural tests after midbrain lesions had suggested that it is mainly the anterior extension of the TM which is involved in stimulus localization and that here wave source directions are represented in a systematic order (Elepfandt, 1988b). In this regard, the prevalence of BF classes ≤ 25 Hz in the rostral midbrain invites us to consider these frequencies to be vital for wave source localization.…”