A STUDY of the language skills of patients suffering from diseases that
impair memory has thrown up new clues about how the brain copes with language.
Neuroscientists in the US claim that two distinct parts of the brain鈥攅ach
associated with a different type of memory鈥攈andle the tasks of recalling
words and applying grammar rules. They also suggest that women keep more words
in memory than men.
Michael Ullman of Georgetown University in Washington DC and his colleagues
began their work by testing the language skills of a group of 24 patients with
Alzheimer鈥檚 disease. They found that their subjects had particular difficulty
with irregular verbs. A subject might, for instance, correctly give 鈥渃hopped鈥� as
the past tense of 鈥渃hop鈥� but then stumble when asked about 鈥渄ig鈥�.
That was not completely surprising, notes Ullman鈥攌nowing that 鈥渄ug鈥� is
the past tense of 鈥渄ig鈥� is a feat of memory, which is poor in Alzheimer鈥檚
patients. But the real surprise came when the researchers compared these
subjects with 45 people suffering from Parkinson鈥檚 or Huntington鈥檚 disease. They
had no trouble with 鈥渄ug鈥� or 鈥渟wam鈥�, but struggled when the past tense was
formed simply by adding 鈥渆d鈥�.
Advertisement
Ullman says that the language difficulties of the Parkinson鈥檚 and
Huntington鈥檚 patients were reminiscent of their physical disabilities.
Huntington鈥檚 patients, who suffer from uncontrollable movements, tended to use
runaway words鈥攕aying 鈥渓ookeded鈥� instead of 鈥渓ooked鈥�, for example.
Parkinson鈥檚 patients, who have difficulty using some muscles, were more likely
to leave off the 鈥渆d鈥� altogether and say 鈥渓ook鈥�.
The researchers claim in the latest issue of the Journal of Cognitive
Neuroscience (vol 9, p 289) that all this hints at how the human brain
handles language. They suggest that word memory relies on areas of the brain
that are responsible for 鈥渄eclarative memory鈥�, the memory of facts and events,
which is damaged by Alzheimer鈥檚. But the rules of grammar are processed by
sections of the brain that handle 鈥減rocedural memory鈥�. This type of memory is
used in physical activities such as lifting an arm鈥攁bilities sabotaged by
Huntington鈥檚 and Parkinson鈥檚.
鈥淭his has been a big argument in linguistics for years,鈥� says psychologist
Michael Gazzaniga at Dartmouth University in Hanover, New Hampshire. In the
debate over the importance of grammar rules versus rote memorisation, some
scientists have contended that language is mostly memory-driven. But Gazzaniga
says that the new findings 鈥渋ndicate strongly that both processes are at
飞辞谤办鈥�.
鈥淚t should really help us understand language,鈥� says Ullman. In a follow-up
study presented at a conference last week, he reported that men are more likely
than women to have difficulty with regular verbs after diseases that damage the
procedural memory. But both have problems forming the past tense of made-up
words such as 鈥渟puff鈥� (鈥渟puffed鈥�). This suggests, says Ullman, that women store
more words in memory than men, and fall back on the rules only when presented
with unfamiliar words.