Lecture

Socrates and other Greek philosophers correctly surmised that mental operations are supported by the brain. But how 1.4 kg of biological tissue can provide the substrate for lifetimes of intense personal experience, the achievements of culture and science, and our refined skills from snooker to musicianship and neurosurgery continues to be mysterious. Understanding brain processes, not only brain structures, is self-evidently vital in this endeavour. These processes operate at several timescales: milliseconds, seconds, minutes, hours, days and years. Our quintessentially non-invasive technique for seeing our brains, MRI, may never be able to track changes at the first of these timescales. MRI has been used mainly to study brain responses over seconds. But there would be little point in having a brain if it could not adapt to experience, and fortunately these longer timescales are also available to MRI. Adaptive changes are driven by training, education, and by probabilistic learning in culturally-maintained social contexts. It appears that an important function of sleep is to integrate and consolidate such changes.

Over time scales of minutes, changes in patterns of brain activity can easily be observed using BOLD fMRI. Longer term changes in activation can also be monitored, using carefully controlled experimental fMRI designs. Over weeks and months, neural plasticity results in physical changes of grey matter density and cortical thickness, which can be measured using high quality structural MRI scanning. At high field strength, images can be obtained at 0.5 mm resolution in a few minutes of scanning time. Quantitative measurements of brain changes over time require isotropic resolution.

The concept of a static human brain, similar to the hardware of a computer, is thus becoming obsolete, and is being replaced by that of a complex self-adapting system, in which the wiring and computational elements are themselves products of previous experience. MRI at high field has the potential to track quantitatively some of these systematic changes over relatively short periods of time. This may have important implications for educational and other social policies.