We might make jokes about “losing a few brain cells” - but what happens when you
lose a LOT of brain cells all at the same time?
What happens when you lose an entire part of your brain?
A brain lesion occurs when damage from an injury or disease occurs in an area of the
brain. Brain lesions can be caused by many things, like traumatic head injuries, strokes,
or tumors, and can occur in almost any brain region and be almost any size.
Brain lesions are absolutely no fun, but sometimes they have the “silver lining” of helping
us learn something new about the human brain. Today, we’re going to talk about three of the most
famous brain lesions in history, and how these devastating lesions were able to teach
us some very important things about the structure and function of the human brain.
Lesion #1: Phineas Gage
In the 1840's, young Phineas Gage had a job setting explosive charges and blasting away
rock with blasting powder, sand, and a tamping iron. If you know anything about gunpowder,
you know that it doesn’t mix well with iron...maybe you can guess how this is going to end.
One afternoon, while packing down a charge with the tamping rod, Phineas set off an explosion
that sent the iron rod shooting through his cheek and out the top of his head. Miraculously,
Phineas did not die. A doctor cleaned up the wound and removed some brain that was still
protruding from the top of his head before binding him up (gross, right?). Within a month,
he was able to walk, talk, and live independently as he had before the accident. However, as
Phineas recovered, it became apparent that he was not the same.
Before the accident, Phineas was a very responsible and hard-working man. He was well liked by
his co-workers and employees. Following his accident, however, he lost his job, and those
that knew him described him as a completely different person. He became easily irritated
and used a great deal of foul language, described as capricious and impatient.
Phineas Gage’s injury had an enormous influence on discussions about the mind and brain - the
injury he suffered to his left frontal lobe sparked research and conversation about brain
damage and cerebral localization as it relates to personality.
The sensational nature of his injury and everything that followed have made Phineas Gage one of
the most famous brain lesion patients in the world.
Lesion #2: Tan
French epilepsy patient Leborgne was nicknamed “Tan”, because “Tan” was the only
word he was still able to say. The odd thing about Tan was that he did not appear to have
any type of cognitive deficit; he seemed to perfectly understand everything said to him
and was able to follow commands.
Dr. Paul Broca met Tan near the end of his life, and was immediately intrigued by him
and his condition. Following Tan’s death, Broca performed an autopsy and found a lesion
on the frontal lobe of his left cerebral hemisphere, just above his left eye. Broca called Tan’s
loss of language an “aphasia”, and today this area of the brain is known as “Broca’s
Area”. Damage to this particular region meant that a patient could still comprehend
and respond to speech normally, with no other cognitive deficits, but would be unable to
produce words or sentences in a meaningful way.
Patient Tan’s lesion proved to be extremely
important for catapulting our understanding of human language - a field where we are still
learning new things today.
Lesion #3: Henry Molaison, or H.M.
Henry Molaison was only a little boy when he had a bicycle accident that left him with
severe epilepsy. His seizures became worse as he grew older, and by the age of 26, they
were so frequent and so intense that he could not live anything resembling a normal life.
His doctors were able to pinpoint the origin of his seizures to Henry’s left and right
medial temporal lobes - the hippocampus, amygdala, and part of the entorhinal cortex - and decided
to remove the affected tissue. The surgery went smoothly and without any surprises - until
Henry woke up.
After his surgery, Henry could still remember his name and his childhood, but could not
remember any new events or facts. He couldn't form new memories.
By working with Henry, scientists learned important things about the role of the hippocampus
and amygdala in memory formation. Henry only had a deficit in his long-term memory; he
was still able to form habits, like finding his way to the hospital dining room, and perform
working memory tasks, like repeating a string of numbers. The study of Henry’s learning
abilities helped clarify the connections and differences between types of memory. It is
a strange irony that, because of his brain lesion, he never had any idea how famous he
was. He spent the rest of his life in a hospital, waking up each morning thinking he was still
26.
So there you have it: three lesions, three lives. Despite the unfortunate circumstances
that led to them, these individuals have helped inspire countless neuroscientists past, present,
and future. New technology means that we don't have to rely on these kinds of injuries to
uncover the secrets of the brain - but we shouldn't forget Phineas Gage, Patient Tan,
and Henry Molaison, and the things we learned about our own minds from their lesions.