Brain activation during reading in deep dyslexia: An MEG study

Magnetoencephalographic (MEG) changes in cortical activity were studied in a chronic Finnish-speaking deep dyslexic patient during single-word and sen tence reading. It has been hypothesized that in deep dyslexia, written word recognition and its lexical-semantic analysis are subserved by the intact right hemisphere. However, in our patient, as well as in most nonimpaired r eaders, lexical-semantic processing as measured by sentence-final semantic- incongruency detection was related to the left superior-temporal cortex act ivation. Activations around this same cortical area could be identified in single-word reading as well. Another factor relevant to deep dyslexic readi ng, the morphological complexity of the presented words, was also studied. The effect of morphology was observed only during the preparation for oral output. By performing repeated recordings 1 year apart, ive were able to do cument significant variability in both the spontaneous activity and the evo ked responses in the lesioned left hemisphere even though at the behavioura l level, the patient's performance was stable. The observed variability emp hasizes the importance of estimating consistency of brain activity both wit hin and between measurements in brain-damaged individuals.