“…3,7 Apart from a few studies focused on the diurnal and partially social species (e.g., A. aculeatus and O. cyanea), 35,37,39,53 our current knowledge around octopus behavior and cognitive ability is mainly based on those predominantly nocturnal and asocial species with the 5-gyrus VL (e.g., O. vulgaris and O. bimaculoides). 10,21,25,55,[106][107][108][109] The 5-gyrus VL could contain approximately 13% of CNS nervous cells to form what has been called ''the fan-out fan-in neural network'' in charge of visual and tactile learning and memory along with other cognitive activities. 10,11,21,25,28,41,44,45,49,56 Recently, Shigeno and Ragsdale 15 demonstrated heterogeneities of neurochemical distribution patterns in the 5-gyrus VL where the transmitter 5-HT was found mainly in neurons of the two lateral gyri.…”