Dolphin Brain

Comparison between Humans' and Dolphins' brains

Comparison of Cetacean and Primate Cerebral Cortexes

General Characteristics of the Cerebral Cortex
The cerebral cortex is the outer layer of advanced brains that evolved latest in all animals. It is the seat of all higher mental functions. All mammals and most other animals have one to some degree, but in the primates and cetaceans it is extremely well-developed.
In cetaceans, the cerebral cortex is very large, especially in relation to the rest of the brain. Since the cerebral cortex covers the more primitive areas of the brain in a thin layer, the amount of surface area available for it is important. The brain manages to obtain more cerebral cortex through encephalization, or convolutions on the surface of the brain. The amount of encephalization is considered an important factor in intelligence, since it can greatly increase the amount of area for the cerebral cortex (Morgane 1974).
Only in primates and cetaceans does the brain possess any significant amount of encephalization. As a matter of fact, cetacean brains have much more encephalization than human brains. For example a dolphin brain (one of the smaller of the cetaceans) has 40% more cerebral cortex than a human (Morgane 1974). The human cerebral cortex is divided into rather distinct layers, and it is believed that this indicates a higher level of complexity and development over those which lack the layering. Early studies showed that cetaceans have very little lamination; that most of the cerebral cortex was muddied together. Later studies proved this wrong (Bunnel 1974). The cetacean cerebral cortex is as layered as our own. The individual layers are similar or even identical between the two.
Another facet is the amount of regional differentiation in the cerebral cortex (Morgane 1974). A greater amount of separation in areas would seem to point towards a greater specialization of these areas. At least for humans it would seem to indicate that. Our brains have highly specialized sections, but as to whether or not this is necessary to possess high intelligence remains to be seen. Cetacean brains seem to possess comparable differentiation, but there has not been enough research done to be sure.
Specific Regions
Cetacean brains have many of the same features as other primate brains. The frontal lobe is the general region in which abstract thought is believed to occur. In cetaceans it is as developed, if not moreso in many species, as it is in humans. The parietal lobe, which is related to association of senses and generally making sense of the senses is quite large in cetaceans. In dolphins, it is as large as the human parietal and frontal lobes put together (Lilly 1975).
The temporal lobe in cetaceans is also very well developed and extremely large in comparison to the rest of their brain. In fact, there are portions which are equivalent to Broca's and Wernicke's areas in the cetacean brain (Bunnel 1974, Jacobs 1974, Lilly 1975). This area represents all of the senses together, whereas primate brains represent the senses separately and they are only connected by long bundles of neurons.
Lastly, the relative size of the motor and sensory centers are reversed in cetaceans in comparison to primates. Primates favor the motor cortex, whereas the cetaceans greatly favor the sensory region (and are not very balanced at all between the two).
Neural Density and Relations
The cetacean neural density is comparable to that of humans and some of the higher primates. However, the density is slightly less in some regions of the cetacean brain (Bunnel 1974). A high ratio is necessary for such things as emotional control, objectivity, reality orientation, humor, logically consistent abstract thought, and higher creativity. There seems to be a clear correspondence between the ratio and these abilities. Cetaceans have a ratio that surpasses even the healthiest of humans. This is supported by behavior studies of captured dolphins who show a high amount of playfulness and enjoyment even when in captivity. Humans under such circumstances would not fare quite so well.
Excerpt taken from "The Neurological and Environmental Basis for Differing Intelligences: A Comparison of Primate and Cetacean Mentality" by Kenneth Marable