Cerebellum and ocular system in the human

In vertebrates, the eyeballs are direct extensions of the brain; that is, they evolved after the brain, and are literally unimpeded access to the cerebellum and cerebrum. Because of this, many ocular tumors or injuries can be far more dangerous to the brain than growths or injuries on any other part of the skull.

Anatome ex omnium veterum recentiorumque observationibus. Thomas Bartholin, 1673.

The Curious Case of the Woman with No Cerebellum

Not sure how many of you have read about this by now, but it is such an amazing finding I decided to write about it (even though I retweeted this yesterday). 

This study is a clinical case report of a living patient with cerebellar   agenesis, an extremely rare condition characterized by the absence of the cerebellum. The cause is currently unknown, there are limited reported cases of complete cerebellar  agenesis, and most of what we know about the condition comes from autopsy reports instead of living patients. Moreover, the condition is difficult to study because most individuals with complete primary cerebellar agenesis are infants or children with severe mental impairment, epilepsy, hydrocephaly and other gross lesions of the CNS. The fact that this woman is alive and has a somewhat “normal” life is ground-breaking and presents a unique opportunity to study the condition.

The patient described in the study is 24 years old. She has mild mental impairment and moderate motor deficits. For example, she is unable to walk steadily and commonly experiences dizziness/nausea. She also has speech problems and cannot run or jump. However, she has no history of neurological disorders and even gave birth without any complications. 

Importantly, as shown above, CT  and MRI scans revealed no presence of recognizable cerebellar structures. Just look at that dark sport towards the back of the brain! In addition to these findings, magnetic resonance angiography also demonstrated vascular characteristics of this patient consistent with complete cerebellar agenesis- meaning that the arteries that normally supply this area were also absent bilaterally. How crazy is that? Futhermore, diffusion tensor imaging  indicated a complete lack of the efferent and afferent limbs of the cerebellum. 

Given that the cerebellum is responsible for both motor and non-motor functions, these results are pretty amazing. How can the brain compensate for such a heavy blow to its architecture and connectivity? According to the authors of the study: 

This surprising phenomenon supports the concept of extracerebellar motor system plasticity, especially cerebellum loss, occurring early in life. We conclude that the cerebellum is necessary for normal motor, language functional and mental development even in the presence of the functional compensation phenomenon.

Source:

Yu, F., Jiang, Q., Sun, X., and Zhang, R. (2014). A new case of complete primary cerebellar a genesis: clinical and imaging findings in a living patient. Brain. doi: 10.1093/brain/awu239

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Extraordinary Brain: Woman’s Missing Cerebellum Went Unnoticed for 24 Years

Doctors in China were surprised to find that a young woman who had lived a normal life for more than two decades was actually missing an important part of her brain, according to a new report of her case. The 24-year-old’s strange condition was discovered when she went to doctors because of a month long bout of nausea and vomiting. The patient told the doctors she had also experienced dizziness her entire life. She didn’t start walking until she was four and had never been able to walk steadily.

When the doctors scanned the woman’s brain, they found she had no cerebellum, a region of the brain thought to be crucial for walking and other movements. Instead, the scans showed a large hole filled with cerebrospinal fluid. 

"CT and MRI scans revealed no remnants of any cerebellar tissues, verifying complete absence of the cerebellum," the doctors wrote in the report, published Aug. 22 in the journal Brain.

The cerebellum, which means “little brain” in Latin, is responsible for coordination and fine movements, such as the movements of the mouth and tongue needed for producing speech. People with damage to this brain area typically experience debilitating motor difficulties. Yet contrary to the doctors’ expectations, the Chinese woman’s absence of the cerebellum resulted in only mild to moderate motor problems and slightly slurred pronunciation, according to the researchers. “This surprising phenomenon,” demonstrates the plasticity of the brain early in life, they wrote.

"It shows that the young brain tends to be much more flexible or adaptable to abnormalities," said Dr. Raj Narayan, chair of neurosurgery at North Shore University Hospital and Long Island Jewish Medical Center in New York, who wasn’t involved with the woman’s case. "When a person is either born with an abnormality or at a very young age loses a particular part of the brain, the rest of the brain tries to reconnect and to compensate for that loss or absence," Narayan said.

This remarkable ability of the brain is thought to decline with age. “As we get older, the ability of the brain to tolerate damage is much more limited,” Narayan said. “So, for example, in a 60-year-old person, if I took the cerebellum out, they would be severely impaired.”

This is not the first case of a person found to be missing the cerebellum. In fact, there have been eight other similar cases reported, the researchers said. However, most cases involved infants or children who also showed severe mental impairment, epilepsy and large structural abnormalities in their brains, and most did not survive the condition.

It is possible that more people are affected by this rare condition but they don’t get diagnosed or reported, Narayan said. “In the future, it may become more recognized because of brain imaging,” he added.

Single dose of antidepressant changes the brain

A single dose of antidepressant is enough to produce dramatic changes in the functional architecture of the human brain. Brain scans taken of people before and after an acute dose of a commonly prescribed SSRI (serotonin reuptake inhibitor) reveal changes in connectivity within three hours, say researchers who report their observations in the Cell Press journal Current Biology on September 18.

"We were not expecting the SSRI to have such a prominent effect on such a short timescale or for the resulting signal to encompass the entire brain," says Julia Sacher of the Max Planck Institute for Human Cognitive and Brain Sciences.

While SSRIs are among the most widely studied and prescribed form of antidepressants worldwide, it’s still not entirely clear how they work. The drugs are believed to change brain connectivity in important ways, but those effects had generally been thought to take place over a period of weeks, not hours.

The new findings show that changes begin to take place right away. Sacher says what they are seeing in medication-free individuals who had never taken antidepressants before may be an early marker of brain reorganization.

Study participants let their minds wander for about 15 minutes in a brain scanner that measures the oxygenation of blood flow in the brain. The researchers characterized three-dimensional images of each individual’s brain by measuring the number of connections between small blocks known as voxels (comparable to the pixels in an image) and the change in those connections with a single dose of escitalopram (trade name Lexapro).

Their whole-brain network analysis shows that one dose of the SSRI reduces the level of intrinsic connectivity in most parts of the brain. However, Sacher and her colleagues observed an increase in connectivity within two brain regions, specifically the cerebellum and thalamus.

The researchers say the new findings represent an essential first step toward clinical studies in patients suffering from depression. They also plan to compare the functional connectivity signature of brains in recovery and those of patients who fail to respond after weeks of SSRI treatment.

Understanding the differences between the brains of individuals who respond to SSRIs and those who don’t “could help to better predict who will benefit from this kind of antidepressant versus some other form of therapy,” Sacher says. “The hope that we have is that ultimately our work will help to guide better treatment decisions and tailor individualized therapy for patients suffering from depression.”

A woman living in China’s Shandong Province got a bit of a surprise recently when doctors at the Chinese PLA General Hospital told her that her brain was missing one of the most important centers for motor control: the cerebellum. She had initially checked herself into the hospital because of a bad case of dizziness and nausea.

Her diagnosis helped explain some of the challenges she had experienced through the course of her life, including slurred speech, delayed onset of walking until the age of seven and troubles with maintaining balance her entire life.

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Uvulas!

We all know about our uvula - or at least the palatine uvula - the one in our mouths. This hanging mass at the back of our mouth is formed from the soft palate, and is involved in the gag reflex and some languages (but not English). But did you know that we have more uvulas than just that?

Uvula means “little grape"in Latin, and a swollen uvula is called "ūvawhich is simply “grape”. Hanging grapes everywhere!

Everyone also has a cerebellar uvula, which is right next to the cerebellar tonsils (more tonsils!) and at the end of the cerebeallar vermis (“cerebellar worm”). This area of the brain is involved in posture and locomotion.

In addition to both of those, males also have a uvula of the urinary bladder. This is less of a “little grape”, and more of a slight elevation in the internal urethral orifice, caused by the prostate.

Anatomy: Descriptive and Surgical. Gray’s Anatomy, 1918.
[illustration source]

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How Can You Survive Without Part Of Your Brain? 

Ballet dancers’ brains adapt to stop them feeling dizzy

Scientists have discovered differences in the brain structure of ballet dancers that may help them avoid feeling dizzy when they perform pirouettes.

The research suggests that years of training can enable dancers to suppress signals from the balance organs in the inner ear.

The findings, published in the journal Cerebral Cortex, could help to improve treatment for patients with chronic dizziness. Around one in four people experience this condition at some time in their lives.

Normally, the feeling of dizziness stems from the vestibular organs in the inner ear. These fluid-filled chambers sense rotation of the head through tiny hairs that sense the fluid moving. After turning around rapidly, the fluid continues to move, which can make you feel like you’re still spinning.

Ballet dancers can perform multiple pirouettes with little or no feeling of dizziness. The findings show that this feat isn’t just down to spotting, a technique dancers use that involves rapidly moving the head to fix their gaze on the same spot as much as possible.

Researchers at Imperial College London recruited 29 female ballet dancers and, as a comparison group, 20 female rowers whose age and fitness levels matched the dancers’.

The volunteers were spun around in a chair in a dark room. They were asked to turn a handle in time with how quickly they felt like they were still spinning after they had stopped. The researchers also measured eye reflexes triggered by input from the vestibular organs. Later, they examined the participants’ brain structure with MRI scans.

In dancers, both the eye reflexes and their perception of spinning lasted a shorter time than in the rowers.

Dr Barry Seemungal, from the Department of Medicine at Imperial, said: “Dizziness, which is the feeling that we are moving when in fact we are still, is a common problem. I see a lot of patients who have suffered from dizziness for a long time. Ballet dancers seem to be able to train themselves not to get dizzy, so we wondered whether we could use the same principles to help our patients.”

The brain scans revealed differences between the groups in two parts of the brain: an area in the cerebellum where sensory input from the vestibular organs is processed and in the cerebral cortex, which is responsible for the perception of dizziness.

The area in the cerebellum was smaller in dancers. Dr Seemungal thinks this is because dancers would be better off not using their vestibular systems, relying instead on highly co-ordinated pre-programmed movements.

“It’s not useful for a ballet dancer to feel dizzy or off balance. Their brains adapt over years of training to suppress that input. Consequently, the signal going to the brain areas responsible for perception of dizziness in the cerebral cortex is reduced, making dancers resistant to feeling dizzy.

“If we can target that same brain area or monitor it in patients with chronic dizziness, we can begin to understand how to treat them better.”

Another finding in the study may be important for how chronic dizzy patients are tested in the clinic. In the control group, the perception of spinning closely matched the eye reflexes triggered by vestibular signals, but in dancers, the two were uncoupled.

“This shows that the sensation of spinning is separate from the reflexes that make your eyes move back and forth,” Dr Seemungal said. “In many clinics, it’s common to only measure the reflexes, meaning that when these tests come back normal the patient is told that there is nothing wrong. But that’s only half the story. You need to look at tests that assess both reflex and sensation.”

Woman of 24 found to have no cerebellum in her brain
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DON’T mind the gap. A woman has reached the age of 24 without anyone realising she was missing a large part of her brain. The case highlights just how adaptable the organ is. The discovery was made when the woman was admitted to the Chinese PLA General Hospital of Jinan Military Area Command in Shandong Province complaining of dizziness and nausea. She told doctors she’d had problems walking steadily for most of her life, and her mother reported that she hadn’t walked until she was 7 and that her speech only became intelligible at the age of 6. Doctors did a CAT scan and immediately identified the source of the problem – her entire cerebellum was missing (see scan, below left). The space where it should be was empty of tissue. Instead it was filled with cerebrospinal fluid, which cushions the brain and provides defence against disease. The cerebellum – sometimes known as the “little brain” – is located underneath the two hemispheres. It looks different from the rest of the brain because it consists of much smaller and more compact folds of tissue. It represents about 10 per cent of the brain’s total volume but contains 50 per cent of its neurons. Although it is not unheard of to have part of your brain missing, either congenitally or from surgery, the woman joins an elite club of just nine people who are known to have lived without their entire cerebellum. A detailed description of how the disorder affects a living adult is almost non-existent, say doctors from the Chinese hospital, because most people with the condition die at a young age and the problem is only discovered on autopsy (Brain, doi.org/vh7). (via Woman of 24 found to have no cerebellum in her brain - health - 10 September 2014 - New Scientist)

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