1.4 The Instruments of Neuroscience

Question 1

Electroencephalography

Answer 1

Einthoven was able to make photographic recordings of the electrical activity of the cerebral cortex, using a galvanometer. He named this type of recording electroencephalography, this remained the sole technique for noninvasive brain study for a number of years.

Question 2

Measuring blood flow in the brain

Answer 2

Mosso recorded pulsations as blood flowed around and through the cortex in these patients and noticed that the pulsations of the brain increased locally during mental activities such as mathematical calculations. He inferred that blood flow followed function.

Question 3

Computerized axial tomography

Answer 3

Next to blood flow there was also interest in having good anatomical images that could pinpoint the location of tumors for other developments in instrumentation. Oldendorf wrote an article providing the first description of the basic concept that was later used for CT.

Question 4

Positron emission tomography and radioactive tracers

Answer 4

While the CT/CAT was great for revealing anatomical detail, it revealed little about function. CAT was used as a basis for developing positron emission tomography (PET), a noninvasive sectioning technique that could provide information about function. The development of PET goes hand in hand with the development of radioactive isotopes, or ‘tracers’, that it employs. These came from the hand of Curie and her husband. Radioactive forms of oxygen, nitrogen and carbon could be produced and injected into the blood circulation and would become incorporated into biologically active molecules. These molecules would concentrate in an organ, where the radioactivity would begin to decay. The concentration of the tracers would then be measured over time.

Question 5

Magnetic resonance Imaging

Answer 5

MRI is based on the principle of nuclear magnetic resonance, which was first described by Rabi. The protons in water molecules line up like little bar magnets. If the equilibrium of these protons is disturbed, then a measurable voltage is induced in a receiver coil. The voltage changes over time as a function of the proton’s environment. Analysis of the voltages can yield information about the examined tissue.

Question 6

Functional magnetic resonance imaging

Answer 6

An increase in oxygen delivery permitted more glucose to be metabolized, and thus more energy would be available for performing the task. Fox and Raichle found that although functional activity induced increases in blood flow, there was no corresponding increase in oxygen consumption. Functional MRI does not use ionizing radiation, it combines beautifully detailed images of the body with physiology related to brain function, and it is sensitive.