Patrick Hof and Estel Van der Gucht of the Department of Neuroscience at Mount Sinai School of Medicine in New York studied the brains of humpback whales and suggested that brain size might be a factor as the spindle neurons were found in the same location in toothed whales with the largest brains. As a rule, baleen whales such as humpbacks and others that filter water for food are considered less intelligent than toothed whales such as orcas.
The researchers reported that the information might clear up whale behaviors such as intricate communication, alliance forming, cooperation, cultural transmission and tool usage. The function of spindle neurons is not yet clear, but they may be involved in learning, recognizing the world around oneself, and other functions of cognition. However, that means they may also be vulnerable to brain disorders such as Alzheimer's disease, autism and schizophrenia.
Spindle neurons, the researchers said, probably first showed up in the common ancestor of hominids, humans and great apes roughly 15 million years ago, and are not found in lesser apes or monkeys. Cetaceans, on the other hand, would probably have evolved spindle neurons earlier, maybe as far back as 30 million years ago, the researchers said, adding that the neurons either only appeared in animals with the largest brains or evolved several times independently.
The researchers reported that the humpbacks' cerebral cortexes had island-like structures -- which have been found in other mammals -- that may have evolved as a way to promote fast, efficient communication between the neurons.
"In spite of the relative scarcity of information on many cetacean species, it is important to note in this context that sperm whales, killer whales, and certainly humpback whales, exhibit complex social patterns that included intricate communication skills, coalition-formation, cooperation, cultural transmission and tool usage," the researchers wrote. "It is thus likely that some of these abilities are related to comparable histologic complexity in brain organization in cetaceans and in hominids."