346 Self and the Phenomenon of Lifeb2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”brain structure. Historically, electrodes placed in freely moving rats led
to the discovery of pleasure centers in the brain.
Transcranial magnetic stimulation (TMS) — Application of a mag-
netic field to the brain through the intact skull has been used for treating
depression and anxiety. The procedure is non-invasive. The penetration
of the magnetic field is limited to the cortex of the brain and the effect is
not as focussed as electrode stimulation.
Transcranial Direct Current Stimulation (TDCS) — Delivery of
a small current through two electrodes attached to the scalp has been
used, attempting to improve cognitive function of patients.
In vitro stimulation coupled with recording of neurons in brain
slices can provide information on neuronal “memory” such as long-term
potentiation.Non-invasive imaging
Computerized axial tomography (CAT) — Also called CT scan.
Imaging of live brain in sections by computer synthesis of multiple X-ray
shots of the brain.
Magnetic resonance imaging (MRI) — Imaging of live brain in sec-
tions by computer synthesis of multiple nuclear magnetic resonance
(NMR) images of the brain. This uses a strong magnetic field in com-
bination with pulses of radio frequency waves, giving detailed images
of brain structures without harmful X-ray radiation. Particularly useful
for human subjects.
Functional MRI (fMRI) — Detects the level of oxygenated hemoglo-
bin (indirectly the oxygen level), which corresponds to the blood flow of
a given region of the brain. It is an indirect measure of metabolic activity
(reflecting the function) as opposed to plain MRI, which delineates only
the anatomic structures. By far the most useful technique for cognitive
neuroscience research.
Diffusion MRI (dMRI) — Detects direction of water diffusion, thus
delineating white matter tracts. An exquisite way to map out nerveb2726_Appendix-D.indd 346 6/12/2017 7:51:55 PM