Pure somaesthetic alexia: Somaesthetic-verbal disconnection for letters

Abstract

We studied a patient who manifested a bilateral reading disorder through the somaesthetic modality, without deficit of elementary tactile sensation or tactile object naming, due to a left parietal infarct. Detailed investigation established the following points. (i) The patient showed normal function on elementary somaesthetic examination, normal function on high level tactile perception, except for minimal impairment off the right hand on the two-point discrimination test, and normal latencies on the somatosensory evoked potential in both hands. (ii) The patient had difficulty in reading letters using any somaesthetic strategy (graphaesthesia, directional joint kinaesthesia and active touch) with either hand. (iii) On a same-different judgement task, the patient's performance with the right hand was slightly defective on graphaesthesia and active touch, but performance with the left hand was within the normal range for all of the strategies. The patient's disorder was highly category specific and modality specific, indicating that somaesthetic letter reading can be disrupted not only independent of other high level somaesthetic functions, like object recognition, but also independent of other modes of reading functions, such as visual reading. A lesion involving the intraparietal sulcus, the upper part of the inferior parietal lobule and the adjacent white matter in the left hemisphere may be capable of compromising the pathways for somaesthetic letter reading with both hands.