|MadSci Network: Neuroscience|
The cerebrum has long been thought to be the neural center for intelligence, but no one part of the human brain determines a person's IQ. For example, there are functional individuals with measurable IQ who are devoid of a cerebrum. Nobody knows exactly how differences in intelligence develop.
The brain does not "control" or "limit" intelligence, nor does it control the speed of data transfer. Speed of propagation of neural impulses is controlled by several factors, all of which occur on the cellular level. These include the diameter of the neuron's axon (the long cord-like part of the neuron), the makeup of the neuron's plasma membrane (aka "neurilemma"), and whether or not the axon is myelinated.
Try the links in the MadSci Library for more information on Neuroscience.