Author: vaughanbell

Science News has an article on one of the most important future topics in neuroscience – epigenetics, the science of how information coded in the genes is used when the brain does its work.

Almost every cell in the body has a copy of the DNA, and therefore has the capability to express any protein.

But you wouldn’t want proteins that are used for digesting food produced in the brain, so the body has various ways of regulating which proteins get expressed at any one time. This is epigenetics.

If DNA is like a blueprint, epigenetics is the committee of civil engineers that coordinate the construction site.

We’ve known from twin studies and molecular genetic research that genes and the environment both influence cognition and behaviour, but these studies only give statistical associations. What they don’t tell us is how this happens.

In a sense, epigenetics is the scientific glue that allows us to understand how genes influence learning and behaviour, but also how learning and behaviour influences the expression of genes.

In other words, its goal is to explain how the environment combines with genetic information in the brain.

Needless to say, much epigenetic research is focusing on mental illness, the classic example of how genetic risk, experience and environment combine with sometimes disastrous consequences.

One of the most interesting aspects is that there is growing evidence that epigenetic information can be inherited. So your experiences may actually cause changes to gene regulation that are then passed on to offspring.

Link to Science New article on epigenetics.
Link to abstract of good review article on epigenetics and cognition.

Neurophilosophy has a fascinating article on the recent archaeological discovery of numerous ancient Incan skulls of which over 1 in 6 showed signs of trepanation – an ancient form of brain surgery where a hole was drilled in the skull.

What’s surprising is just how common it was. 66 skulls from Incan burial sites had a total of 109 trepanation holes. Some, like the one pictured, obviously needed a significant amount of skill and practice to complete.

And with this many examples, the archaeologists could make some fascinating inferences about the purpose and success of these operations:

Andrushko and Verano argue that the Incas performed trepanation primarily to treat head injuries incurred during battle, because the holes are most often found at the front of the skull to the left, consistent with injuries caused by a right-handed opponent during face-to-face combat, and because adult males are overrepresented in the sample. The procedure was evidently used to treat mastoiditis (an infection of the region of the temporal bone behind the ear) as well.

The authors also show that the success rate of the procedure improved with time, as the Inca empire progressed and made advances in medicine. The earliest specimens, dated to around 1,000 A.D., showed no signs of bone growth around the perforations, suggesting that the procedure was often fatal. But specimens dating to around 400 years later suggest a survival rate of around 90%.

Link to Neurophilosophy article on prehistoric Inca neurosurgery.

Phantom limbs are a well-known phenomenon where sensations and feelings are still experienced from a missing limb. In rare cases after brain injury, an additional phantom limb can appear – causing the sensation of a phantom third hand, arm or leg.

The drawings on the left are from two case studies of people with these ‘supernumerary phantom limbs’ recently published in the journal Neurology. They show an artist’s impression of the body sensations of two patients who suffered brain stem strokes.

Both patients had the experience of having a third arm and a third leg, although the male patients had the leg ‘appear’ along the midline of the body, while the female patient seemed to experience it ‘superimposed’ upon an existing leg.

One distressing element for the female patient was that although the patient could ‘move’ the phantom arm voluntarily, “she described occasional loss of control and feeling strangulated by the phantom arm around the neck”.

Two earlier case studies from neuropsychologist Peter Halligan and colleagues reported similarly disembodied extra limbs, but this time after damage to the right hemisphere of the brain.

As is more common after right hemisphere damage, these tended to have a delusional quality, so they weren’t just sensations – the patients genuinely believe their additional limbs existed.

One gentleman believed that he had a third arm in the middle of his body, and another believed that he had a third hand.

In this last case, the patient reported actually ‘seeing’ the additional limb, similar to this case study of a gentleman who believed he had a third leg protruding from his left knee after suffering a stroke that affected the thalamus:

He consistently maintained that the phantom leg was attached to his knee with a “bone plate” that “had no flesh on it”. However, he reported that the phantom limb itself looked normal and had a shinbone and a foot. It usually “appeared” in the morning when he was helped to put on his trousers. The patient stated that the phantom limb prevented him from turning over in bed, but did not adversely affect him otherwise.

When asked about how he knew about this leg he said that he could see it (despite his severe visual impairment) and feel it with his hand. He believed that the phantom limb belonged to him, although he readily accepted that it was not “normal” to have three legs. Initially he reported that the “leg” was growing from his own knee, but then reasoned that (given its size) he would have noticed it before the stroke.

At other times he believed the leg was attached to him by the nursing staff, but could not explain why. The patient was aware of phantom limb phenomena as his wife was an amputee. He was also aware that a stroke may affect perception and cognition. He did not believe either issue applied in his case.

The experience of a ‘supernumerary phantom limb’ is usually the result of a brain injury and typically resolves over time.

Phantom limbs are thought to arise because the somatosensory cortex, the part of the brain that represents the body’s sensations and feelings, reorganises so that the area previously used to represent the limb is partially ‘re-used’ for other functions, meaning the sensations sometimes get activated when these other functions are active.

Nevertheless, supernumerary phantom limbs are still mysterious, largely due to the small number of cases and diverse brain areas involved.

There is some suspicion that they might be caused because of disrupted communication between parietal lobes, which are known to represent body image, and the sensory feedback from the nerves in the body.

Link to abstract of Neurology case studies.
Link to full text of 1993 case study.
Link to full text of 1995 study.

I’m thoroughly digging the brain section of the Radiology Picture of the Day website. As you might expect, it’s a wonderfully geeky place where radiologists post an image every day, often brain CTs or MRIs, with a little gem of wisdom with each one.

One of the most interesting is the pictured CT scan with a ‘ring artefact’. I’ve contrast enhanced the image so you can see the circle or ring near the centre a little more clearly.

It’s a known imaging problem caused by poor calibration of the scanner.

However, the Radiology Picture of the Day entry notes that these were given special significance by the quacktastic German physician Ryke Geerd Hamer who claimed that his ‘New Medicine’ could cure 98% of all cancers.

He gave these rings the rather immodest name ‘Hamer Foci’ and if they appeared in the brain, apparently this meant cancer was elsewhere in the body.

For Hamer, cancer was simply the body’s reaction to a psychological conflict, and presumably this was what he thought the CT scanner was picking up.

This is despite the fact that CT scans only picture large scale structure on which psychological changes make no recognisable impact.

A curious case of neuroimaging apophenia.

Link to ‘Ring Artefact with Pseudomedical Interpretation’.

To coincide with stroke awareness month, a new report from the US Government’s Center for Disease and Control and Prevention has highlighted that less than half of people surveyed could identify the potentially life-saving early warning signs of stroke.

A stroke, known medically as a cerebrovascular accident, is where the blood supply to the brain is interrupted because of blockage or damage to an essential blood vessel.

It can be fatal, and more often leads to significant brain damage, but this can be limited or a life potentially saved if it is detected and treated as soon as possible.

The following are warning signs of stroke. If someone you know experiences any of these, call an ambulance or get them medical care as soon as possible.

Sudden numbness or weakness of the face, arm or leg, especially on one side of the body

Sudden confusion, trouble speaking or understanding

Sudden trouble seeing in one or both eyes

Sudden trouble walking, dizziness, loss of balance or coordination

Sudden, severe headache with no known cause

To reduce your chances of having a stroke, you need to look after your cardiovascular health.

Essentially, healthy body, healthy brain – so alcohol, smoking, excess fatty food, little exercise and head injury will increase the chances of blood supply problems in the brain.

Link to CDC report on stroke awareness.
Link to write-up from Yahoo! News.