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What is a Sylvian Fissure?

By Maggie Worth
Updated Mar 03, 2024
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The Sylvian fissure is a deep, lateral indention that divides the lobes of the human brain. In essence, it divides the top of the brain from its bottom. It is the deepest and most easily discernible of the many fissures in the human brain. Other than serving as a major landmark of the brain's landscape, no purpose or specific function is known to be attributable to the Sylvian fissure.

In the front portion of the brain, the Sylvian fissure divides the frontal lobe — which controls decision-making, problem-solving, and emotion — from the temporal lobe — which regulates memory, language, and learning functions. In the rear portion of the brain, it divides the temporal lobe from the parietal lobe, which processes sensory input received from the body. The frontal and parietal lobes fall above the fissure, while the temporal lobe falls below it.

This fissure was referred to in early anatomical documents as the anfractuosa fissura. The Sylvian fissure is so-named because it is thought to have been discovered by Franciscus Sylvius, a professor of medicine at Leiden University. Modern science also calls this brain feature the lateral sulcus, the lateral fissure, or the fissure of Sylvius.

A Sylvian fissure begins at the roots of the eyes, passes across the temples, and ends near the roots of the brain stem. It does not completely encircle the brain. It occurs unilaterally, meaning that it appears across both hemispheres of the brain. It does not divide the brain into two roughly equal portions — as does the medial longitudinal fissure, which divides the brain into the left and right hemispheres. The portion of the brain above the Sylvian fissure is distinctly larger than the amount below it.

Injuries occurring near this feature may cause language impairment and result in difficulty learning new things or retaining and recalling information already learned. Such damage may also impair the brain's ability to process stimuli from the body, resulting in impairment in any of the five senses. Emotional instability or lack of emotional control may also characterize these injuries.

This particular fissure is one of the first fissures of the brain to develop in fetuses. It appears at about week 14 of the gestational period, at roughly the same time that the eyelids, fingernails, and reproductive organs develop. Most other brain fissures do not develop until week 20, and some develop as late as 33 weeks.

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Discussion Comments
By anon342759 — On Jul 23, 2013

I can't understand what causes the sylvian fissure. My granddaughter is going on five years old and I just want to know if anything is being done with patients who have this.

By anon331534 — On Apr 23, 2013

Well for those who are keen to have brains poked around when surgeons are in there, maybe they should be the ones to volunteer! I have recently had brain surgery and would be appalled to think that someone would want to poke around in such a delicate area when it's not their brain!

By browncoat — On Jun 18, 2012

@pleonasm - It's not as simple as doctors being able to poke around in the brain and not do any damage. The brain is extremely delicate, and even exposing it to the air carries risks. Spending surgical time experimenting on individual brains would be extremely immoral.

Not to mention, I actually don't think there is all that much we can learn from that kind of investigation that we don't already know.

And the reason we don't know the function of the Sylvian fissure is quite possibly because it doesn't have a function specifically, other than what the other fissures do, which is to provide more surface area for the brain. If the lobes of the brain had smooth surfaces, without folds, there would be much less grey matter, which is the part of the brain which processes information.

As to Sylvian fissure anatomy, likely it has no function beyond being one of those folds and just happens to be a particularly large fold.

By pleonasm — On Jun 17, 2012

It's amazing how little we seem to know about our own brains, even in this day and age. I wonder if we would know more if people were less moral about the way they test various theories on human subjects.

I'm most definitely not advocating a return to the days when scientists and doctors were able to do whatever they wanted, or worse, weren't allowed to do anything at all because of superstition (for example, they were all once expert grave robbers because that was the only way to get bodies for dissection).

But, I can't help but think that people who are going to go under brain surgery anyway ought to be able to grant permission for the doctors to, well, poke around in there a bit. There are ways to stimulate different areas without doing damage and they could learn things, like the Sylvian fissure function, for example.

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