[From Bruce Nevin (960411.17:20 EDT)]
From today's Boston Globe:
"Broker" is what scientists are calling a newly discovered brain function
that, most of the time, enables us to dip into our enormous store of words
and dredge up the correct one for a face or object.
Neuroscientists had long believed that retrieving known words was just a
two-step process: One part of your brain recognized the concept (it's an
eating utensil, or a musical instrument) and then triggered a separate
speech center that would in turn produce the specific word ("spoon" or
"clarinet").
But Dr. Hanna and Antonio Damasio, renowned neuroscientists at the
University of Iowa, say they've found there's a previously unsuspected
middleman.
"We find evidence that you don't go from concepts to words nonstop," said
Dr. Antonio Damasio in a telephone interview yesterday. "There's an
intermediary structure that helps you go from one to the other, like a
diplomatic broker that is talking to both sides at the same time."
Moreover, he said, there may be as many brokers as there are categories of
words. In experiments being reported today in the journal Nature, the
Damasios and their colleagues found at least three brokers: one that helps
retrieve names of familiar people, another for names of tools, and another
for animals.
Surprisingly, the areas of the brain that act as brokers, in effect as the
brain's dictionary or thesaurus, aren't part of structures long considered
the primary speech and language areas -- Broka's and Wernicke's areas.
Instead, they are scattered about the temporal lobe of the left hemisphere,
Damasio said.
The experiments that revealed the existence of the brokers were done in two
groups of people: 127 patients who had had strokes or other forms of brain
damage, and 7 normal volunteers.
The researchers asked the brain-damaged subjects to name objects in
pictures in a standard test and found that some of them made errors
indicating that a word-broker wasn't working.
Shown a skunk, for example, one said: "Oh, that animal makes a terrible
smell if you get close to it; it is black and white and gets squashed on
the road by cars sometimes."
His brain produced the right concept, but the brokering step failed, and he
couldn't recall the word. The researchers noted what part of the brain was
damaged in that patient and concluded that's where the "mental dictionary"
for animals was located.
The normal volunteers underwent PET scans, which revealed what parts of the
brain were especially active when they took various word-retrieval tests.
The "hot spots" turned out to be the same areas that were damaged and
inactive in the stroke patients who couldn't recall certain kinds of words.
The fact that there are many brokers may explain bizarre cases of people
with brain damage who can no longer name certain categories of words, like
tools or animals, but have no troubl naming others. Damasio said the
findings might someday help people who have difficulty thinking of certain
words.
In a commentary, neurophsychologist Alfonso Caramazza of Harvard University
praised the Damasios' work and called for studies to determine what other
brokers exist. "Are abstract concepts--justice, evidence and ambition, for
example--also represented categorically?" he asked.
It's not surprising that people's names are hard to dig up, Damasio added,
because "different brokers handle different levels of complexity, and the
names of specific people involve the highest levels of complexity. When
you're distracted or tired, those may be hard to retrieve, while you'd have
less trouble coming up with the name of a tool or an animal."
The Damasios' co-authors are Thomas J. Grabowski, Daniel Tranel and Richard
D. Hichwa.
(Byline: Richard Saltus, Globe Staff)
Bruce