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The patient's stepwise cognitive decline was characterized by unexpected exacerbation of"frontal"neurobehavior features following the occurrence of two posterior cortical lesions.At initial evaluation,the computed tomographic scan showed bilateral subcortical lacunae in basal ganglia and periventricular white matter,and symptoms included dysarthria and perseveration.The second evaluation,following a left posterior parietal lesion,revealed a range of new frontal features,including impulsivity, pull-to-stimulus,and difficulty shifting set.Following a subsequent right occipital infarct,further frontal lobe impairments emerged:forced grasp reflex and incontinence.We hypothesize that the cumulative effects of infarcts were synergistic.That is,the posterior cortical infarcts elicited frontal features that would not be expected from a simple sum of these lesions'effects. |
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