Seite - 54 - in Cyborg Mind - What Brain–Computer and Mind–Cyberspace Interfaces Mean for Cyberneuroethics

54 • Cyborg Mind Magnetic Resonance Imaging (MRI) It was in 1980 that, for the first time, a UK team used a Magnetic Resonance Imaging (MRI) machine to obtain a clinically useful image of a patient’s internal tissues. This identified a primary tumour in the patient’s chest, an abnormal liver and secondary cancer in his bones.31 An MRI scanner consists of a large cylinder containing an extremely pow- erful magnet. When a patient lies inside the scanner, a magnetic field is then created, causing changes in the magnetic properties of atoms in the body, which are subsequently analysed through a computer in order to produce images. These include pictures of organs, soft tissues, bone and virtually all other internal body structures. One of the advantages of MRI is that the dif- ferent elements of a brain structure can be given different contrasts, enabling a detailed anatomical structure to be visualised. Detailed magnetic resonance images are now the most sensitive imaging test of the head and brain in routine clinical practice. They can indicate if there are any changes in shape caused by a tumour, stroke or injury and can also be employed to investigate neurological disorders such as Alzheimer’s disease and epilepsy.32 However, MRI cannot show anything about the cell- level functioning of any of the brain areas. Functional MRI (fMRI) The most widely used extension of MRI to detect aspects of neuronal activity in the brain is called functional Magnetic Resonance Imaging (fMRI), which uses Blood Oxygenation Level Dependent (BOLD) imaging. This measures changes in the oxygenation level of the blood and indicates which areas of the brain are most active at any given time. These variations arise because neurons consume oxygen when they are active, which leads to compensatory changes in local blood flow to the active area. Usually, fMRI is used while a participant performs certain tasks, enabling researchers to associate brain activity with sensory, motor or cognitive pro- cesses. But it is important to emphasise that BOLD measures neuronal activ- ity indirectly through measuring changes in blood oxygenation levels. Since blood flow takes place several seconds after neuronal firing, this limits the temporal resolution of fMRI, meaning that although the image is detailed, it is impossible to observe rapid changes in activity. Typically, fMRI is combined with a rapid production of brain data, giving a continuous series of images of the brain  – one every few seconds over a period of about 40 minutes  – while the participant performs particular tasks. This enables an examination of the nature of brain processes with respect to brain activity.33 It should be noted that fMRI has now largely supplanted PET for provid- ing dynamic images of brain activation because it is an entirely noninvasive This open access edition has been made available under a CC-BY-NC-ND 4.0 license thanks to the support of Knowledge Unlatched. Not for resale.