The patient, a 22-year-old, agreed to participate in a series of language experiments while the electrodes were still implanted.
Scientists asked him to name and categorize a variety of pictures and words. During some of these tests, scientists used the grid to monitor brain activity; in others, they applied a mild electrical current through two electrodes.
"The current temporarily and safely depolarizes the nerve cells in the vicinity of the electrodes," says Hart. "We've shown previously that this will temporarily disable the area of the brain where it's applied, but the effect doesn't spread to other nearby areas and is safely reversible."
That makes the current a good test of whether a brain area is critical for a task, Hart notes.
"We were able to show that an area known as the left occipitotemporal gyrus, located on the base of the brain, is linked in our patient to many of the word recognition activities we tested," says Hart. "Applying current here as we presented the patient with a new test could cause problems in understanding what objects are; misinterpretations of verbs, colors, or shapes; and word-finding difficulties in spontaneous speech."
Hart says the finding suggests that there may a stage in language processing where different kinds of language activities, all performed in various parts of the brain, come to the same brain area to complete a common step.
To time brain activity, researchers applied the current at various times
while the subject was recognizing a picture, noting when the current disabled
his ability to name a picture and when it didn't, a technique Hart calls
"timeslici
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Contact: Michael Purdy
mpurdy@welchlink.welch.jhu.edu
(410)955-8725
Johns Hopkins Medical Institutions
26-May-1998