ways of investigating the brain

• PET Scans use radioactive isotopes with a long half-life. As the isotope decays, these particles interact and are combined with glucose or water molecules, forming radiotracers. An increased number of radiotracers will gather in areas of the brain with high levels of activity, due to such areas have a larger requirement for oxygenated blood. Therefore, such highly active areas will appear brightly coloured on the PET scans, as the emitted positron collides with an electron, resulting in the emission of gamma rays which are detected by the scan.
• PET scans are very expensive and so are not extensively used in public healthcare systems only for diagnosis purposes. Some people may object to the use of radioactive tracers in their blood, due to exposure to ionising radiation which may lead to cancer. Therefore, only one or two PET scans can be carried out on an annual basis.
• Very useful for the diagnosis and monitoring of progressive, neurodegenerative diseases, such as Alzheimer’s (characterised by a reduction in glucose metabolism rates in the brain).
• fMRI scans rely on the haemodynamic response. Areas of the brain with high levels of activity have a larger requirement for oxygenated blood, leading to a higher rate of blood deoxygenation. As measured through the bold response, the deoxyhaemoglobin in the blood in these highly active areas absorbs the signal produced by the scan, so such areas appear brightly coloured on the scan.
• High temporal resolution as up to 4 images can be produced per second. Can be used whilst a patient is carrying out a task, and so data from fMRI scans can help us to make inferences about brain function and localisation. Does not use ionising radiation, unlike PET scans, and so is safer.
• however poor temporal resolution because there is approximately a 5 second difference between neuronal activity and the produced image
• EEG scans use electrodes attached to the scalp, EEG scans measures and amplifies the electric activity across the whole brain i.e. action potentials being transmitted across the axons of neurons.
• Particularly useful in investigating the characteristics of the different stages of sleep. Much higher temporal resolution than fMRI scans, and so more appropriate for the monitoring of ongoing cerebral states and activity.
• Lower temporal resolution compared to fMRI scans, with particular difficulty in differentiating activity between areas.
• Useful in the diagnosis of epilepsy, which is characterised by random bursts of activity.
• Post-mortem examinations = These involve a comparison of the patient’s brain with that of a healthy, neurotypical brain. Any differences (abnormally large ) are assumed to have caused the neurological problem the patient faced in their lifetime.
• Ethical issues arise because informed consent cannot always be obtained before the patient dies or from the family. The patient may be unable to give informed consent e.g. HM suffered from deficits in his short-term memory, and so would not remember having signed the document.
• Particularly useful for advancing medical knowledge, e.g. Broca used a post-mortem examination on his patient Tan, which led to the identification of Broca’s area and was the foundation of further research into the theory of the localisation of brain function.