Children often memorise things ‘by heart’, especially when learning their lines for a school play, learning a song and even their times tables. This saying dates back over 5000 years, to the ancient Egyptians, who believed that the heart was the organ responsible for thoughts. During this time the brain was considered of little significance, and as such no direct link was ever made between cognition and the brain until the 6th century BC when the Pythagorean natural philosopher Alcmaeon of Croton first proposed that the ‘seat of sensations’ was the brain, and suggested that all senses were in some way connected to it. During the 4th century BC Hippocrates built upon this concept proposing that the brain was the organ responsible for thought and a century later the Greek anatomist and physician Erasistratus of Ceos established the differences between sensory nerve cells and motor neurons. He mapped out the arteries and veins in the circulatory system, showed clearly that the function of the heart was to pump blood around the body and introduced the concept that the ‘spirit’ (pneuma) drove muscles from the brain by ‘flowing’ along the nerves.
It took another 500 years before the next significant step in understanding the brain and the nervous system was made. The Greek anatomist Galen studied and dissected the brains of various mammals concluding that the cerebellum was responsible for controlling the muscles, and that certain parts of the spinal cord were linked to specific muscles and parts of a body.
The second millennium saw contributions from Islamic scholars. The influential Iberian physician and surgeon Al-Zahrawi studied the effects of head injuries making significant advances in the understanding of mental health. His contemporary, the Persian polymath Ibn Sina, studied the anatomy of the skull and the effects of skull fractures. He discovered the cerebellar vermis and the caudate nucleus which are responsible for body posture and movement, explaining numerous head-related conditions such as epilepsy, stroke and dementia, as well as conditions related to schizophrenia.
By the end of the Middle Ages, progress in understanding the brain and the nervous system was gaining momentum with the Italian physicians Guido da Vigevano and Modino de Lucci producing textbooks of anatomy which contained detailed accounts of the physiognomy of the brain.
Work on human cadavers became commonplace during the 16th century. The Flemish anatomist Andreas Vesalius described the putamen and corpus callosum, proposing that the brain comprised of seven nerve centres. The well-known French natural philosopher Rene Descartes focused on the relationship between the brain and the mind suggesting that the pineal gland and the cerebrospinal fluid formed the interface between the physiological and the psychological. The mid-1600s saw the Dutch biologist Jan Swammerdam carry out experiments which demonstrated that nerves did not require spirit from the brain to make muscles react, refuting the millennia-old theory describing their behaviour.
Up to this time much was based on observation but there was little true understanding of brain and nerve functionality. It took the discovery of electricity for the Italian husband and wife team Luigi and Lucia Galvani to identify its role in the function of nerves. The use of case studies to progress our understanding of the functions of different parts of the brain resulted in significant progress being made during the 19th century, assisted by the advent of powerful microscopes which allowed workers to study nerves and brain tissue at the cellular level.
During the 1890s, Camillo Golgi at the University of Pavia in Italy used silver chromate to highlight the complex structures of individual neurons, a technique that was used to great effect by his Spanish contemporary Santiago Ramon y Cajal who received the 1906 Nobel Prize in Physiology or Medicine for his experiments on brain tissue, its neural nature and hence its electrical dependency. This led to the understanding that the nervous system consisted of individual cells known as neurons and the work of the English physiologist John Langley and his fellow compatriot Gotch at the turn of the 20th century. This established the reliance of nerves on chemical ‘messengers' and the function of chemical receptors which transfer nervous impulses between neurons, such that impulses can only travel in a single direction along their length.
The Russian neurologist Vladimir Bekhterev determined the importance of the hippocampus in memory retention whilst the English neurophysiologist Charles Sherrington contributed to our understanding of motor neurons which drive muscles, and the selective behaviour of synapses between neurons. Studies at the electrochemical level began to understand how neurons fired, with workers like Edgar Adrian observing nerve fibres in action. By the mid-1940s Kenneth Cole of Columbia University was making significant advances in modelling the electrochemical properties of nerves and brain tissue culminating in the FitzHugh-Nagumo model of neurotransmission which enabled the German Bernard Katz to successfully describe in detail the behaviour of synapses.
Today thousands of researchers are involved in making advances in our understanding of the brain and the nervous system making neuroscience an important branch of medicine. Their involvement in tackling diseases such as Parkinson’s and conditions such as dementia, paralysis, as well as mental health issues is invaluable to our personal and social wellbeing.
Pharmacological techniques relying on brain chemistry, as well as medical tools such as magnetic resonance imaging (MRI), which use the electrical impulse in our brains have enabled this to be done ever more effectively with measurable levels of success. More recently, the well-known neurosurgeon Alim-Louis Benabid at the University of Grenoble brought together much of our understanding of the brain and the nervous system to successfully enable a completely paralysed individual to use an exoskeleton to re-establish movement in his limbs. This he did by directly connecting his brain to sensors via electronic circuits. It seems that the idea of a Cyborg is no longer contained within the realms of Dr Who fiction.
Little Einstein’s Corner - Nerves and Senses
We sense and feel the world around us through our nervous system. We use our eyes, our ears, smell and touch to do so, and often our bodies respond. Here are a couple of experiments which demonstrate how what we sense changes the state of our body, as our brains respond to this.
For the first experiment you will need a hand-held mirror. Draw the curtains in a room and shut the door so that it can be darkened when the light is switched off. With the light on look at the size of the pupils in your eyes, switch the light off for a minute, and switch it on again. Look at the size of your pupils as soon as the light has been switched on and compare them to before. They should be much larger now, as your pupils have opened up in the dark to let more light in.
The 2nd experiment needs a friend and a chair. Sit on the chair cross-legged and ask your friend to lightly hit you below the knee with the edge of their hand. If hit at the correct place, your knee should kick your leg forward and you have no control of it.
The first experiment shows how your brain controls your eyes when it gets dark, and the second is a reflex which is your nervous system reacting on its own.