Investigating the structure and function of the nervous system and brain.
Neuroscience is defined as any of the sciences that deal with the structure or function of the nervous system and the brain. ('Neuro' comes from the Greek word 'neuron', meaning nerve.) The nervous system consists of two main parts - the central nervous system, composed of the brain and spinal cord and the peripheral nervous system, which includes the nerves that serve the neck and arms, trunk, legs, skeletal muscles and internal organs. The whole system is made up of a network of cells called neurons, which transmit information in the form of electrical signals.
Neuroscience is thus a diverse field, encompassing, among other things, the study of brain development, the senses, learning and memory, movement, sleep, stress, aging and neurological and psychiatric disorders, as well as the molecules, cells and genes which make the nervous system function.
Some of the earliest surgical procedures in human history were crude attempts to cure neurological problems. Skulls survive from the Neolithic period which show evidence of trepanning - that is, removing a piece of bone from the skull to provide entrance to the brain or relieve pressure on it. It was thought this would cure epilepsy, migraines and mental illness. Some skulls show evidence of healing after trepanning, indicating that individuals may have survived what was an immensely risky, and given the lack of anesthetic, painful, procedure. Over the centuries, trepanation continued to be used to treat a variety of symptoms and is still employed as a surgical procedure.
In the early days of neuroscience, the brain could only be explored in very limited ways through dissection after death. Modern non-invasive imaging techniques enable us to see the active brain inside a living person. We can see the inside of the brain using CAT (computerized axial tomography) and MRI (magnetic resonance imaging) scans. Electroencephalography (EEG) scans measure how active the brain is and fMRI (functional magnetic resonance imaging) and PET (positron emission tomography) scans illustrate which parts of the brain are active when carrying out particular tasks.
Such techniques are particularly useful to neuroscientists and doctors who are studying illnesses of the brain. Because the human brain is so complicated and has little capacity to regenerate, it is extremely vulnerable to damage - such as from trauma or stroke - and disease. Damage to, or loss of part of, the vast network of cells can have devastating results. Alzheimer's and Parkinson's diseases are examples of disorders of the nervous system in which brain cells gradually die. In disorders of the mind such as schizophrenia and depression, the symptoms are caused by more subtle changes in the brain. These are still poorly understood.
The study of psychology, which deals with mental processes and behaviour, has a complex relationship with neuroscience. Developing out of neuroscience in the late 19th century, when research into the brain was insufficient to answer the questions raised within the clinical experience, psychology carved out a separate path for itself. In recent years however, neurological and psychiatric research have begun to move closer together as advances in neuroscience shed light on the relationship between behaviour and the physical characteristics of the brain.
Sleep - which humans spend up to a third of their lives doing - is one area in which neuroscientists are shedding new light. Sleep is not a passive state, but a highly active period which helps consolidate memory and aids some types of learning. Increasingly links are being discovered between lack of sleep and obesity, heart disease, high blood pressure and strokes. Lack of sleep does not just affect health - it is believed to have been a contributory factor in disasters including Chernobyl and the Challenger shuttle explosion.
Research into the functioning of the human brain has greatly enhanced the understanding of learning, memory, intelligence and emotion and it has become possible to understand the complex processes occurring within a single neuron. However, there is still much to discover about how networks of neurons produce intellectual behavior, cognition, emotion, and physiological responses.