Central representation of spatial and temporal surface wave parameters in the African clawed frog
Xenopus laevis employs mechano-sensory lateral lines to, for instance, capture arthropods on the surface of turbid waters with poor visibility based on incoming wave signals. To characterise central representations of surface waves emitted from different locations, responses to several wave parameters were extracellularly recorded across brainstem, midbrain and thalamic areas. Overall, 339 of 411 statistically analysed responses showed significantly altered spike rates during the presentation of surface waves. Of these units, 45.1 % were obtained in the torus semicircularis including its laminar subnucleus (23.3 %) that is known to process auditory cues. Wave parameters contributing to central object representations were indicated by response rates that systematically varied with amplitude (76.3 % of 160 tested units), frequency (74.4 % of 270 tested units), source angle (93.7 % of 79 tested units), or source distance (63.8 % of 218 tested units). Map-like parameter representations were rather diffuse, yet an increased fraction of units tuned to frontal source angles was observed at deeper tissue layers (>180 μm), and an increased fraction of best neuronal responses to low wave frequencies (≤25 Hz) at rostral midbrain sections. Responses to wave frequencies remained largely robust across tested unit samples independent of source angles, and distances (N = 62). In comparison, spatial response characteristics seemed fragile across different wave frequencies in 68.3 % of 41 recordings.