More on Cortical Folding and Intelligence

The cerebral cortex is responsible for many important functions, including:

• thought
• memory
• language
• voluntary movement
• information processing
• reasoning
• perception
• consciousness

One distinction between the brains of mammals is that the brain surface is highly convoluted in some species and in others there is minimal degree of convolution (this is called lissencephalic). What is the significance of the amount of folding in the cortex? The thickness of the neocortex varies very little within or between mammals. Cortical folding seems to be the consequence of maintaining or increasing the ratio of neocortex volume to brain volume with increasing brain size (Macphail, 247).

Indices of cortical folding have been made by various scientists. Von Bonin (1941) devised an index of cortical folding using the ratio of the total cortical surface (as if it were laid out flat and unfolded) to the total exposed cortical surface. According to these indices, the ratio increases fairly regularly with overall brain volume. For example, man has an average ratio of 2.86; dolphin and whale ratios span from 4.0 to 8.55. Thus it would seem that man has less folding than these cetaceous species. In addition, it is interesting to note that although the brains of most of these animals were larger than the human brains, some dolphins have a brain volume considerably below that of the human average. What does this mean, in layman's terms? It would seem that cortical folding is, thus, mostly a matter of brain volume. Some mammals may show more or less folding than man, but there is no evidence that these convolutions indicate more or less behavioral complexity.

So, does this mean that since humans have more cortical folding that they're more intelligent? Well, it apparently seems to correlate with our ability to process information and use language, right? Does that therefore mean we're more intelligent than an animal without much cortical folding?

What does "intelligence" mean, anyway? Click here for a discussion of that.

Don't forget that there are multiple methods for studying the brain and its relationship to behavioral complexity. Let's take an indepth look at the other methods, which include:

• looking at the absolute magnitude of the brain
• measuring brain size versus body size
• measuring neocortex
• measuring volume of gray matter versus volume of nerve cells
• looking at specific brain structures