A primer of brain imaging technologies

CrossCurrents

Modern brain imaging techniques are revealing fascinating physical responses to changes in mood or cognition. Such responses were previously unmeasurable, except via subjective, anecdotal means, such as a client reporting that she was "feeling better." Toronto-based psychoan-alyst Dr. Norman Doidge says, "The key thing that most imaging techniques have in common is that they can show millions of neurons working together at a time. Since we know, roughly, the locations where many functions such as visual, verbal and emotional signals are processed, this gives us new kinds of crucial insights."

• Positron emission tomography (PET) illustrates which regions of the brain are active at a given time. A radioactive "tracer" is injected into the bloodstream and the brain is imaged when the person is engaged in particular activities, showing which regions of the brain are active.
   
• Single photon emission computed tomography (SPECT) is a cheaper version of PET technology, using longer-lasting tracers, so longer re-test periods are required. It is useful for drug-dependency research.
   
• Magnetic resonance imaging (MRI) uses magnetic fields and radio waves to produce high-quality images without use of a radioactive tracer.
   
• Functional magnetic resonance imaging (fMRI) relies on the magnetic qualities of blood to show sequential, movie-type images of blood flow in the brain as it is occurring. Unlike PET, fMRI can show whether brain activity occurs simultaneously or sequentially in various brain regions as the research subject engages in set activities.
   
• Electroencephalography (EEG) uses electrodes on the scalp to measure brainwaves (patterns of electrical activity emanating from the brain). Its greatest advantage is speed, and its drawback is its lack of special resolution. Often, EEG and MRI are used together to observe the location of activity in the brain.

Abigail Pugh

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