FoundationalConceptsNeuroscience

spin because the spin of a subatomic particle produces effects analo-
gous to the behavior of a spinning toy top or a gyroscope (Fig. 17.1).
Atomic nuclei possess a nuclear spin that arises from the combination
of the spins of the constituent protons and neutrons. (Similarly, the
spin of each proton and neutron arises from the spins of their con-
stituent particles, the quarks.)
One property of nuclear spin is that it interacts with magnetic
fields. In fact, a subatomic particle will align its spin with an imposed
magnetic field, analogous to a compass needle aligning in Earth’s
magnetic field. In addition, the alignment of nuclear spin in a mag-
netic field may be perturbed in specific ways if the atomic nucleus is
exposed to just the right energy of electromagnetic radiation—the
exact energy required depends on the strength of the imposed mag-
netic field and the nature of the chemical surroundings of the atomic
nucleus being measured. The chemical surroundings play such a role
because many of the nearby atoms will have magnetic properties that
contribute to the local magnetic field.
Experimental technologies were developed in the 1940s to measure
these effects. The process was called nuclear magnetic resonance, or
NMR. An NMR spectrometer consists of a large magnet to produce a
very strong magnetic field, and a device to generate electromagnetic
radiation of appropriate energy to perturb the alignment of nuclear
spins. For magnets that are typically one to several teslas in strength,
the corresponding energies of perturbing frequency are typically in
the radio-frequency region of the electromagnetic spectrum (rela-
tively low energy compared with visible light).
A tesla is a unit of magnetic field strength, named after the inven-
tor, engineer, and wizard of electricity Nikola Tesla (1856-1943). One
tesla is equivalent to 10,000 gauss—a gauss is another unit of mag-
netic field strength named after the mathematician and physicist Carl