Neurologist

what happens around us is here

The outer limits of the human brain (3)

part3

Long-stayers

A STUDY published in August describes an autopsy of the brain of 115-year-old Hendrikje “Henny” van Andel-Schipper, a Dutch woman who was the world’s oldest woman at her death (Neurobiology of Aging, vol 29, p 1127). Remarkably, the autopsy revealed little vascular damage, almost no build-up of the proteins linked to degenerative diseases such as Alzheimer’s, and cell counts that seemed normal for an average 60 to 80 year old. The longevity of human cognition may extend far beyond most people’s natural lifespan, conclude Wilfred den Dunnen and his team from the University Medical Centre Groningen in the Netherlands.

The longevity of human cognition may extend far beyond a natural lifespan

Ageing inevitably brings changes to the human brain. There is some decline in the blood vessels servicing it, and in the quantity of myelin, the fatty material that insulates the nerve fibres. The brain reduces slightly in volume, the grooves all over its surface widen, and there’s a slight expansion of the cavities called ventricles. Age also brings a reduction in the speed at which nerve signals travel and there is a general decrease in coordination between different brain regions, which could explain why a person’s memory can seem ever more challenged. However, while memory may start to decline as early as our 20s or 30s, according to psychologists, experience and general knowledge compensate until at least our 50s or 60s. What’s more, functional imaging shows that often performance in cognitive tasks is maintained, at least to some extent, because the older brain compensates for any reduction in activity in specific regions by recruiting more areas to work on the problem.

Some researchers have suggested that dementia is almost inevitable in an aged brain. That view is being challenged as more and more sprightly centenarians have been found to have quite healthy minds and brains. There are no simple recipes for a long mental life – some risk factors for dementia run in families, others are spontaneous or build up over a lifetime – but high blood pressure, obesity and heart problems all increase the risk of stroke and dementia, while exercise and mental activity seem to reduce it. But clearly, old brains can show remarkable staying power.

Extraordinary talents

GLOBALLY there are around 100 “prodigious savants”, who show one remarkable skill in complete isolation to their other mental functions. Savants either have autism or have suffered brain damage at birth or later in life, and their general intelligence, excepting their remarkable skill, is poorer than average. Some have photographic memories of complex scenes and can draw or sculpt unbelievably accurate representations. Others can calculate numbers, squares, primes or calendar dates. Some can remember entire books and some can rattle off a piano concerto after a single hearing. Yet others can draw perfect circles. What leads to such islands of intelligence?

There are many theories. Savants always have amazing recall in some sphere or other, though the neuropsychological basis of this is not clear. Some researchers claim that practice, which is clearly obsessive and focused in some savants, could explain their skills. Others believe that developmental errors in the brain leave a few rare people with an incredible focus on detail, while losing the more general view. This might be because of damage, or perhaps an unusual pattern of connectivity in the left hemisphere, which sees the big picture, with overcompensation by the more detail-conscious right. Certainly, injury to the left hemisphere can lead to symptoms of autism, and MRI scans of people with autism suggest differences in white matter, with hyperconnectivity in some regions but fewer connections overall.

However, research by Allan Snyder from the Centre for the Mind in Sydney, Australia, has convinced him that savant-like skills lie within us all. He believes they result from a shutting down of some of the higher-order, “rule-based” cognition, which usually makes thinking more efficient and generalisable. These higher cortical functions normally turn large amounts of basic subconscious information into useful conscious concepts. Snyder has used transcranial magnetic stimulation – a blast of magnetic pulses that temporarily and harmlessly interrupts higher brain functions – to inactivate a small area of the cortex in volunteers, who he then asks to draw, proof-read or perform difficult calculations. He claims that this improves these skills in ordinary people. If Snyder is correct, the outer limits of some of our memory and information-processing capacities may only be revealed when parts of the brain are inactivated.

Savant-like skills may result from shutting down higher-order cognition

Athletic minds

THE bodies of athletes are clearly special – the result of good genes and lots of hard graft – but what about their brains? Is there any grey-matter advantage that helps the likes of Usain Bolt and Michael Phelps to outperform their rivals?

Many sports require specific patterns of stereotypical body movements, and these certainly leave their mark on the brain. In the somatosensory cortex, which monitors signals from different parts of the body, and the neighbouring motor cortex, which controls movements, areas corresponding to the most regularly used body parts expand with use.

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February 14, 2009 - Posted by | 1 |

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