Have you ever wondered how scientists know what goes on inside the human brain? Of course, it’s a very complex organ and there is still so much to find out, but modern technology is allowing us to see inside working brains.
We’re all aware that different parts of our brain tend to govern different functions, eg sight, hearing, muscle movement, speech.
In the past, the main ways scientists could tell what part of the brain affected which functions, was either to conduct awful experiments on animals, or to study people who had brain injuries or brain-affecting illnesses such as strokes. They could observe the effect of the brain damage and, after the person died, they could see which areas of the brain had been affected.
There are a number of famous cases of this, notably Phineas Gage, a US railway foreman who was badly injured in an accident. He was tamping down some explosives into a hole with an iron rod, when the explosives ignited, blowing the rod through the front of his skull. Miraculously he survived, but his personality completely changed, leading early neuroscientists to the discovery that the frontal lobe of the brain is linked with personality.
In the early 50s, in an attempt to cure a Henry Molaison of debilitating epilepsy, a neurosurgeon removed areas of the patient’s brain, including hippocampi and amygdalae. The surgery worked to the extent that the epilepsy stopped, but Henry’s memory was severely impaired. Devastatingly, was totally unable to form new memories. He lived the rest of his life in an institution and was studied for the after-effects of the operation. Although he could not form new factual memories, it seems he was able to improve his skill in certain tasks. This tragic case contributed to scientists understand the link between brain function, learning and memory.
Another famous case demonstrated the brain’s amazing ability to rewire itself after being damaged. 65 year old poet and scholar, Pedro Bach-y-Rita, had a disabling stroke in the late 50s, which paralysed half his body and left him unable to speak. His son George took care of him after his initial rehabilitation in hospital. At first his father was pretty helpless, but George instinctively began to teach his father basic skills, as if he were a baby, first getting him to crawl, then playing childish games to improve co-ordination and dexterity. Eventually Pedro made a full recovery and a year later he returned to teaching full time. He died of a heart attack hiking on a mountain at an altitude of 9,000ft, seven years after his disabling stroke.
George’s brother Paul, a renowned neuroscientist, arranged for a post-mortem on his father. The findings were amazing, 97% of the nerves that join the cortex to the spine were destroyed, hence Pedro’s paralysis. The work that George had done rehabilitating his father had caused his brain to rewire itself to compensate for the devastating destruction. Incredible!
These days neuroscientists don’t have to wait for people to die to see which part of the brain does what. Scanning and imaging techniques have enabled them to observe a working brain in action.
Electroencephalography - EEG
The earliest scanner was an EEG which measures electrical brain activity, sometimes referred to as ‘brainwaves’, close to the surface of the brain. EEGs are often used to observe patterns of sleep and to diagnose epilepsy and other conditions.
Positron Emission Tomography (PET)
PET scans measure glucose (sugar) levels in the brain, showing the extent of nerve-cell activity in different regions. A special dye containing radioactive tracers is introduced into the blood stream. When different areas of the brain or body are active they use more fuel, oxygen and glucose, which can be detected by the scanners. A video image of the brain shows which areas are using more fuel. PET scans are useful in identifying general areas of activity and are sometimes used in detecting Alzheimer’s.
Computed Tomography (CT or CAT)
CT scans use special X-rays to take a series of images from different angles which are then combined to form a 3-dimensional image of the brain.
Magnetic Resonance Imaging (MRI)
MRI uses a strong magnetic field and radio waves to create detailed images of the brain. The magnets affect the nuclei of certain atoms in the brain (usually hydrogen atoms). They do this by disturbing the direction of rotation of the nuclei. As the rotation returns to its original position, a radio signal is emitted. The radio signals are used to produce detailed static images of the brain’s structure.
fMRI is a series of MRI images taken less than 1 second apart that are subsequently analysed. fMRIs show what happens in the brain when we perform certain tasks.
We are so fortunate to live in an age where it is possible to unlock the mysteries of the brain in action. fMRIs in particular have transformed our understanding and are used to determine what happens in the brain moment-by-moment when we perform certain tasks.