Nov 27, 2006
This might mean such whales are more intelligent than they have been given credit for, and suggests the basis for complex brains either evolved more than once, or has gone unused by most species of animals, the researchers said.
The finding may help explain some of the behaviors seen in whales, such as intricate communication skills, the formation of alliances, cooperation, cultural transmission and tool usage, the researchers report in The Anatomical Record.
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 discovered a type of cell called a spindle neuron in the cortex, in areas comparable to where they are seen in humans and great apes.
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 researchers found spindle neurons in the same location (http://news.com.com/Blueprinting+the+human+brain/2100-11393_3-6071061.html) 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 organization in cetaceans and in hominids."