Although the function of spindle neurons is not well understood, they may be involved in cognition - learning, remembering and recognizing the world around oneself. Spindle cells may be affected by Alzheimer's disease and other debilitating brain disorders such as autism and schizophrenia.

The researches found spindle neurons in the same location in toothed whales with the largest brains, which the researchers said suggests that they may be related to brain size. Toothed whales such as orcas are generally considered more intelligent than baleen whales such as humpbacks and blue whales, which filter water for their food.

The humpbacks also had structures that resembled "islands" in the cerebral cortex, also seen in some other mammals.

These islands may have evolved in order to promote fast and efficient communication between neurons, the researchers said.

Spindle neurons probably first appeared in the common ancestor of hominids, humans and great apes about 15 million years ago, the researchers said - they are not seen in lesser apes or monkeys.

In cetaceans they would have evolved earlier, possibly as early as 30 million years ago, the researchers said.

Either the spindle neurons were only kept in the animals with the largest brains or they evolved several times independently, the researchers said.

"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 organisation in cetaceans and in hominids."

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