Psycholinguistics Electrified II (1994-2005)

In 1994, there were only two dominant noninvasive techniques to offer insight about the functional organization of language from its brain bases: the behavior of brain-damaged patients (neuropsychology), and event-related brain potential (ERPs). Positron emission tomographic and magnetoencephalographic (MEG) measures begin to contribute in understanding neuropsychology. Over the ensuing decade plus, these have been joined by functional magnetic resonance imaging, transcranial magnetic stimulation, event related spectral changes in the electroencephalogram (EEG), and noninvasive optical imaging. These methods are closely related in their neural and physical bases: ERPs, event-related frequency changes in the EEG and MEG. The amplitude of the EEG is considerably smaller than invasively recorded field potentials because the skull is a strong electrical insulator. Like field potentials, the amplitude and polarity of the EEG depends on the number and amplitude of the contributing synaptic potentials, on whether current is flowing into or out of cells (i.e., movement of positive or negative ions, excitatory or inhibitory synaptic potentials), and on the geometric relationship between the synapses and electrode.