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There are several ways of determining hemisphere dominance in a living [[human]]. The [[Wada test]] involves introducing an [[anesthetic]] into one hemisphere of the brain through one of the two [[carotid artery | carotid arteries]]. Once one hemisphere is anesthetized, and a [[neuropsychology | neuropsychological]] exam is performed to determine dominance for such functions as language production and comprehension, verbal memory, and visual memory. More modern, less invasive, and in some cases costlier techniques, such as [[functional magnetic resonance imaging]] and [[transcranial magnetic stimulation]] can also be used to determine dominance, but their use is controversial and still considered experimental.
===Movement and sensation===▼
[[Image:Sensory and motor homunculi.jpg|thumb|Sensory and motor homunculi at the London Natural History Museum]]
▲===Movement and sensation===
In the [[1940s]], [[Canada | Canadian]] [[neurosurgery | neurosurgeon]] [[Wilder Penfield]] and his [[neurologist]] colleague [[Herbert Jasper]] developed a technique of brain mapping to help reduce [[Adverse effect (medicine) | side effect]]s caused by [[surgery]] to treat [[epilepsy]]. They stimulated [[motor cortex | motor]] and [[somatosensory cortex | somatosensory cortices]] of the brain with small electrical currents to activate discrete brain regions. They found that stimulation of one hemisphere's motor cortex could produce [[muscle]] contraction on the opposite side of the body. Furthermore, the functional map of the motor and [[Somatosensory system|sensory]] cortices is fairly consistent from person to person; Penfield and Jasper's famous pictures of the motor and sensory [[homunculus|homunculi]] were the result.
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