Mirror neurons connect perception with action in a very direct way.
Observations of grasping and touching are connected with the motor
actions and (presumably) subjective experiences related to grasp-
ing and touching. Learning these associations between perception,
movement, and mental experience is what gives meaning to percep-
tions and actions. Neural networks involved in moving the tongue
and mouth, and the fingers and hands, allow us to learn associations
between vocalizations, hand movements, and perceptions—hence,
language.
In the 1960s and 1970s, elegant work by Roger Sperry (1913-1994)
and his students revealed a great deal of information about lateral-
ization of cerebral function for a variety of human behaviors. Sperry
worked with patients who suffered from severe epilepsy, in which
seizures propagated across the corpus callosum from one hemisphere
to the other and in so doing disabled large parts of the brain. Because
of the severity of their condition, a small number of these patients
underwent a surgical procedure in which their corpus callosum was
severed, disconnecting direct neural communication between the
two hemispheres of the cerebral cortex. This operation, called a cor-
pus callosotomy, substantially reduced the frequency and intensity
of seizures and may have been a life-saving surgery. A person who
has had this surgery is sometimes referred to as a split-brain patient,
because the brain has literally been split in two at the level of the cere-
bral cortex.
The corpus callosum is a large bundle of axons connecting the
right and left hemispheres of cerebral cortex in mammalian brains. In
humans, it spans several centimeters in the interior of the brain and
consists of approximately two hundred million axons. Experiments
with monkeys and dogs had shown that cutting the corpus callosum