Practice – not miracles – makes perfect
Ainslie Johnstone, PhD student at the University of Oxford, studies the amazing ability of the brain to reorganise and adapt after injury. In her commended 2016 Max Perutz Science Writing Award article she describes how enhancing this process could help with brain injury recovery.
On 8 January 2011 Gabrielle Giffords, a US congresswoman, was shot in the head at point-blank range. The bullet struck Giffords’ forehead on the left-hand side and travelled straight through her brain, destroying everything in its path.
Though this assassination attempt ultimately failed, the congresswoman awoke from a medically induced coma, unable to speak, move, or breathe unassisted. Different regions of our brains are responsible for performing different functions, and the incident had damaged parts of Giffords’ brain controlling movement of the right side of her body, vision on the right, and areas responsible for speech and language.
Yet in August of the same year, less than eight months after the attack, Giffords walked back into Congress. She still had impaired vision on the right, and trouble moving her right arm and leg; but she could walk unassisted, understand language as normal, and was speaking in short sentences. The media reported the congresswoman’s miraculous recovery – but this was no miracle, just an example of neuroplasticity, which we study in my lab in Oxford. Neuroplasticity describes the way in which, even as adults, our brains can modify and adapt according to our needs.
Here in the UK there are around 1.1 million people who have survived some form of brain injury. These injuries can be caused by accidents, as in the case of Ms Giffords, or by a stroke, where blood supply to a group of neurons is cut off, causing them to die. Whatever the cause of brain injury, once fatal damage to neurons is done, it cannot be undone. The skills that these neurons were once responsible for will, at least temporarily, be lost.
This sudden loss of ability takes an emotional, as well as a physical toll: around two-thirds of people with brain injury go on to experience depression or anxiety. However, with rehabilitation and intensive practice of her lost skills, such as speaking and walking, our brains can reorganise their functions, as happened for Ms Giffords. Healthy brain cells, known as neurons, which were close to the damaged areas, had taken on the roles of their dead neighbours. This neuroplasticity is critical for allowing sufferers to regain full and independent lives, yet it is a process that is not very well understood.
My research focuses on how we can enhance neuroplasticity within areas of the brain that control our movements. This is particularly important for improving recovery after a stroke, where around 80 per cent of survivors are left with movement problems. I am trying to identify the best way for people to learn a new skill, and investigate how different methods of learning change the brain. As well as testing things like the effect of giving different instructions, I have also been experimenting with something a little more unusual. In an attempt to boost neuroplasticity I have been using tiny electric currents to stimulate the brain.
My technique of choice is called transcranial direct current stimulation, known as tDCS, which is not nearly as terrifying as it sounds. During my experiments, volunteers have two rubber electrodes attached to their head, one close to the movement control areas of the brain, and another on their forehead. tDCS works by sending a very low electric current through the brain, between the two electrodes – most people don’t feel anything. Participants in my experiments have either real or placebo tDCS while they practice a new skill. Those people who have real tDCS tend to learn skills faster, and remember them for longer, than people who have placebo.
While it’s pretty amazing that tDCS benefits skill learning, I am more interested in what it does to the brain. Using magnetic resonance brain imaging (MRI), and magnetic brain stimulation, I study how tDCS changes the amounts of certain natural chemicals within the brain. In my lab, we think that changing the amount of these neurochemicals is the first stage in allowing new connections to form between neurons. By creating these connections, areas of the brain are able to take on new roles as they are needed. This change in neurochemicals occurs when people intensively practice something, and when they receive tDCS. For this reason, we think that tDCS is boosting the natural neuroplasticity process.
Although most of my experiments are performed on healthy volunteers, the principles are just the same in an injured brain. In proof of this, researchers in my lab have recently demonstrated that tDCS improves arm movement training after a stroke. Stroke patients who received tDCS also maintained these improvements for longer after rehabilitation had ended.
While this finding is extremely exciting, understanding how tDCS causes these enhancements is crucial. By identifying the exact changes that must occur in the brain to allow neuroplasticity, we can develop the best rehabilitation techniques. We don’t need a miracle!