Brain, Vol 121, Issue 1 77-89, Copyright © 1998 by Oxford University Press
G Robinson, J Blair and L Cipolotti
In this study we report a patient (A.N.G.) who, following a malignant left
frontal meningioma impinging upon Brodmann area 45, presented a 'pure'
dynamic aphasia. Her spontaneous speech was markedly reduced in the absence
of any syntactical impairment. Her naming, repetition and reading skills
were completely normal. Two experimental investigations were carried out.
The first investigation found that A.N.G. had a profound impairment in
phrase and sentence generation tasks given a verbal context. However, her
verbal generative skills were normal when she was asked to describe
pictorial scenes and complex actions. Moreover, it was found that A.N.G.
had no difficulty ordering the constituent words of a sentence. Thus, it
was concluded that her verbal planning skills were intact. The second
investigation tested a hypothesis that dynamic aphasia is due to an
inability to select a verbal response option whenever the stimulus
activates many competing verbal responses. Predictions based upon this
hypothesis were confirmed on three different verbal generation tasks. It
was found that our patient's grave verbal generative impairment was present
for tasks involving stimuli which activate many potential responses.
However, it was absent for tasks involving stimuli which activate few or
only a single 'prepotent' response. The findings are discussed with
reference to traditional interpretations of dynamic aphasia and more
general interpretations of prefrontal cortex functioning. On the basis of a
computational model of prefrontal cortex functioning, we propose that pure
dynamic aphasia may be caused by damage to a 'context' module containing
units responsible for selection of verbal response options. Moreover, it is
suggested that our findings support the view that Brodmann area 45 is
involved in verbal response generation to stimuli which activate many
potential response options.
ARTICLES
Dynamic aphasia: an inability to select between competing verbal responses?
Department of Clinical Neuropsychology, National Hospital for Neurology and Neurosurgery, London, UK.
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