Sparing of Verbs and Preserved, but Ineffectual Reading in a Patient with Impaired Word Production

Abstract

We report a patient who, following a left fronto-temporal lesion, showed a complete sparing of the semantic store and a deficit of word production characterized by two types of dissociations. First, oral and written output was severely disrupted in naming and partially impaired in repetition, writing to dictation and oral spelling, with the exception of verbs, which were normally produced in every modality and condition of stimulation. Second, reading was normal for all type of words as well as non-words.This pattern of deficits suggests two functional lesions, one affecting the connections between the semantic store and the phonological lexicon and the other damaging the sublexical route that converts sound to sound and sound to print. It also implies that words are independently organized in the phonological lexicon, based on their grammatical class and have discrete connections with the semantic store. However, CT scan evidence does not support the hypothesis that this functional dissociation finds its anatomical correlate in the specialization of the frontal premotor cortex for verbs and the antero-medial temporal cortex for nouns. In spite of his normal reading performance, both in terms of comprehension and of accuracy and speed in word production, the patient complained that he met with great difficulty in reading newspapers and books, to the point that he had to renounce to this previously favourite activity. It was found that it took him time and effort to grasp the meaning of complex sentences and passages and it was speculated that, contrary to single words and elementary sentences, comprehension of this type of material cannot be achieved by the mere access of ortographic stimuli to semantics, but requires the retrieval of wordforms. It would appear that a patient, whose lexical route is blocked, can only read passages, by first converting print to sound via the sublexical route and then re-entering the semantic store with oral input.