Ways of studying the brain: scanning techniques including functional magnetic resonance imaging (fMRI), electroencephalogram (EEGs) and event-related potentials (ERPs), and post-mortem examinations.

What this dot point is asking

AQA wants you to describe the four ways of studying the brain (fMRI, EEG, ERPs and post-mortems) and evaluate them. The exam skill is to explain how each method works and to compare them on spatial and temporal resolution, the trade-off that runs through the whole topic.

The four methods

The four methods differ in what they measure and how directly. fMRI measures the haemodynamic response: when a region is active it uses more oxygen, so blood flow increases, and fMRI detects this to produce a dynamic, three-dimensional map of which regions are active during a task. The EEG measures the brain's electrical activity directly using electrodes on the scalp, producing wave patterns that reflect overall activity and are used to study sleep stages and diagnose epilepsy. ERPs are derived from EEG data: a stimulus is presented many times and the recordings are averaged so that random background activity cancels out, leaving the small, specific electrical response to that stimulus, which lets researchers study the timing of cognitive processes. Post-mortem examination studies brain tissue after death, often correlating structural abnormalities with the behaviour shown in life, and historically this was how Broca and Wernicke located their language areas.

Strengths and limitations

The central evaluative idea is the trade-off between spatial resolution (how precisely a method locates activity) and temporal resolution (how precisely it captures timing). fMRI has good spatial resolution, locating activity to within a few millimetres, but poor temporal resolution because of the roughly five-second lag in the blood-flow response, and it does not require radiation, making it non-invasive. EEGs and ERPs have outstanding temporal resolution (milliseconds), capturing activity almost in real time, but poor spatial resolution, since scalp electrodes cannot pinpoint deep or precise sources. Post-mortems allow detailed examination of deep brain structures that scans struggle to reach, but they cannot show the living brain in action, the damage observed may not be what caused the behaviour (a causation problem), and obtaining informed consent before death raises ethical issues. A further point that applies to fMRI and EEG is that they show only that activity correlates with a task, not that the region causes the behaviour.