Each hemisphere receives information primarily from the opposite side of the body.
That is, information from the right hand goes to the left hemisphere and vice versa.
This is called contralateral innervation.
The two hemispheres are interconnected by sets of bands.
The largest is called the corpus callosum.
For medical reasons, the corpus callosum has been cut in some people. We call them “split-brain” patients.
Tests with these patients have revealed that the two hemispheres of the brain have unique abilities.
The left hemisphere is better at language.
If a right-handed split brain patient holds an object in their left hand, the information goes to the right hemisphere and
usually, the split-brain patient will not know what the object is.
If the object is placed in the right hand, the information goes to the left hemisphere
and the patient has no problem naming the object.
The right hemisphere is very good at spatial tasks.
If the split-brain patient has to solve a simple puzzle with their right hand
the information goes to the left hemisphere and they will usually fail.
If the split-brain patient is allowed to use their left hand
the information goes directly to the right hemisphere and they will succeed.
People with an intact corpus callosum do not have these problems because information
can be transferred from one hemisphere to the other via the corpus callosum.
These differences in abilities of the two hemispheres is called hemispheric specialization.