Topographical and structural characterization of the V1-V2 transition zone in the visual cortex of the long-finned pilot whale Globicephala melas (Traill, 1809).

The visual system of cetaceans is at best poorly understood. With a handful of electrophysiological studies and a limited number of histological preparations from well-preserved specimen, the investigation of the principles underlying the cortical organization in cetaceans remains a challenge. In the course of our current investigation, we identified the transition from V2 to V1 in the long-finned pilot whale Globicephala melas, only recognizable through immunocytochemistry, and a similar if not homologue transition in the sheep Ovis aries. Our results emphasize the importance of differential pattern recognition in which the application of different markers uncovers a diversity in a delphinid's cortex, formerly widely considered as uniform and archetypal. In fact, the evidence that we present suggests the existence of relatively unacknowledged areas beyond the well-known sensory territories in cetaceans.