Brain Activation During Reading in Deep Dyslexia: An MEG Study

Abstract

Magnetoencephalographic (MEG) changes in cortical activity were studied in a chronic Finnish-speaking deep dyslexic patient during single-word and sentence 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 readers, lexical-semantic processing as measured by sentence-final semantic-incongruency detection was related to the left superior-temporal cortex activation. Activations around this same cortical area could be identified in single-word reading as well. Another factor relevant to deep dyslexic reading, 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, we were able to document significant variability in both the spontaneous activity and the evoked responses in the lesioned left hemisphere even though at the behavioural level, the patient's performance was stable. The observed variability emphasizes the importance of estimating consistency of brain activity both within and between measurements in brain-damaged individuals.

References

1. Ahonen, A. L., Hämäläinen, M. S., Kajola, M. J., Knuutila, J. E. T., Laine, P. P., Lounasmaa, O. V., Parkkonen, L. T., Simola, J. T., & Tesche, C. D. (1993). 122-Channel SQUID instrument for investigating the magnetic signals from the human brain. Physica Scripta, T49, 198-205.
2. Coltheart, M. (1980). Deep dyslexia: A right-hemisphere hypothesis. In M. Coltheart, K. Patterson & J. C. Marshall (Eds.), Deep dyslexia (pp. 326-380). London: Routledge & Kegan Paul.
3. Ellis, A. W., & Young, A. W. (1988). Human cognitive neuropsychology . Hove, UK: Erlbaum.
4. Hämäläinen, M., Hari, R., Ilmoniemi, R. J., Knuutila, J., & Lounasmaa, O. V. (1993). Magnetoencephalography--theory, instrumentation, and applications to noninvasive studies of the working human brain. Reviews of Modern Physics, 65, 413-497.
5. Helenius, P., Salmelin, R., Service, E., & Connolly, J. F. (1998). Distinct time courses of word and context comprehension in the left temporal cortex. Brain, 121, 1133-1142.
6. Hyönä, J., Laine, M., & Niemi, J. (1995). Effects of a word's morphological complexity on readers' eye fixation patterns. In J. M. Findlay, R. W. Kentridge, & R. Walker (Eds.), Eye movement research: Mechanisms, processes and applications (pp. 445-452). Amsterdam: Elsevier.
7. Kutas, M., & Hillyard, S. A. (1980). Reading senseless sentences: Brain potentials reflect semantic incongruity. Science, 207, 203-205.
8. Laine, M., & Koivisto, M. (1998). Lexical access to inflected words as measured by lateralized visual lexical decision. Psychological Research, 61, 220-229.
9. Laine, M., & Niemi, J. (1997). Reading morphemes. Aphasiology, 11, 913-926.
10. Laine, M., Niemi, J., Koivuselkä-Sallinen, P., Ahlsén, E., & Hyönä J. (1994). A neurolinguistic analysis of morphological deficits in a Finnish-Swedish bilingual aphasic. Clinical Linguistics and Phonetics, 8, 177-200.
11. Laine, M., Niemi, J., Koivuselkä-Sallinen, P., & Hyönä, J. (1995). Morphological processing of polymorphemic nouns in a highly inflecting language. Cognitive Neuropsychology, 12, 457-502.
12. Laine, M., Niemi, J., & Marttila, R. (1990). Changing error patterns during reading recovery: A case study. Journal of Neurolinguistics, 5, 75-81.
13. Laine, M., Rinne, J. O., Krause, B. J., Teräs, M., & Sipilä, H. (1999a). Left hemisphere activation during processing of morphologically complex word forms in adults. Neuroscience Letters, 271, 85-88.
14. Laine, M., Vainio, S., & Hyönä, J. (1999b). Lexical access routes to nouns in a morphologically rich language. Journal of Memory and Language, 40, 109-135.
15. Laine, M., & Virtanen, P. (1996). Turun Sanomat computerized lexical data base (unpublished corpus and database program).
16. Mäkelä, J. P., Ahonen, A., Hämäläinen, M., Hari, R., Ilmoniemi, R., Kajola, M., Knuutila, J., Lounasmaa, O. V., McEvoy, L., Salmelin, R., Salonen, O., Sams, M., Simola, J., Tesche, C., & Vasama, J.-P. (1993). Functional differences between auditory cortices of the two hemispheres revealed by whole-head neuromagnetic recording. Human Brain Mapping, 1, 48-56.
17. Mäkelä, J. P., Salmelin, R., Kotila, M., Salonen, O., Laaksonen, R., Hokkanen, L., & Hari, R. (1998). Modification of neuromagnetic cortical signals by thalamic infarctions. Electroencephalography and Clinical Neurophysiology, 106, 433-443.
18. Michel, F., Henaff, M. F., & Intriligator, J. (1996). Two different readers in the same brain after a posterior callosal lesion. NeuroReport, 7, 786-788.
19. Niemi, J., Laine, M., & Tuominen, J. (1994). Cognitive morphology in Finnish: Foundations of a new model. Language and Cognitive Processes, 9, 423-446.
20. Price, C. J. (1998). The functional anatomy of word comprehension and production. Trends in Cognitive Sciences, 2, 281-288.
21. Price, C. J., Howard, D., Patterson, K., Warburton, E. A., Friston, K. J., & Frackowiak, R. S. J. (1998). A functional neuroimaging description of two deep dyslexic patients. Journal of Cognitive Neuroscience, 10, 303-315.
22. Roeltgen, D. P. (1987). Loss of deep dyslexic reading ability from a second left-hemispheric lesion. Archives of Neurology, 44, 346-348.
23. Saffran, E. M., Bogyo, L. C., Schwartz, M. F., & Marin, O. S. M. (1980). Does deep dyslexia reflect right-hemisphere reading? In M. Coltheart, K. Patterson, & J. C. Marshall (Eds.), Deep dyslexia (pp. 381-406). London: Routledge & Kegan Paul.
24. Salmelin, R., Forss, N., Knuutila, J., & Hari, R. (1995). Bilateral activation of the human somatomotor cortex by distal hand movements. Electroencephalography and Clinical Neurophysiology, 95, 444-452.
25. Salmelin, R., & Hari, R. (1994). Characterization of spontaneous MEG rhythms in healthy adults. Electroencephalography and Clinical Neurophysiology, 91, 237-248.
26. Salmelin, R., Hari, R., Lounasmaa, O. V., & Sams, M. (1994). Dynamics of brain activation during picture naming. Nature, 368, 463-465.
27. Salmelin, R., Schnitzler, A., Schmitz, F., Jäincke, L., Witte, O. W., & Freund, H.-J. (1998). Functional organization of the auditory cortex is different in stutterers and fluent speakers. NeuroReport, 9, 2225-2229.
28. Salmelin, R., Service, E., Kiesilä, P., Uutela, K., & Salonen, O. (1996). Impaired visual word processing in dyslexia revealed with magnetoencephalography. Annals of Neurology, 40, 157-162.
29. Saukkonen, P., Haipus, M., Niemikorpi, A., & Sulkala, H. (1979). Suomen kielen taajuussanasto {Frequency dictionary of Finnish language}. Porvoo, Finland: WSOY.
30. Tranel, D., Damasio, H., & Damasio, A. R. (1997). On the neurology of naming. In H. Goodglass & A. Wingfield (Eds.), Anomia. Neuroanatomical and cognitive correlates (pp. 65-90). San Diego, CA: Academic Press.
31. Ullman, M. T., Corkin, S., Coppola, M., Hickok, G., Growdon, J. H., Koroshetz, W. J., & Pinker, S. (1997). A neural dissociation within language: Evidence that the mental dictionary is part of declarative memory, and that grammatical rules are processed by the procedural system. Journal of Cognitive Neuroscience, 9, 266-276.
32. Uusitalo, M. A., & Ilmoniemi, R. J. (1997). Signal-space projection method for separating MEG or EEG into components. Medical and Biological Engineering and Computing, 35, 135-140.
33. Vandenberghe, R., Price, C., Wise, R., Josephs, O., & Frackowiak, R. S. J. (1996). Functional anatomy of a common semantic system for words and pictures. Nature, 383, 254-256.
34. Vanier, M., & Caplan, D. (1990). CT-scan correlates of agrammatism. In L. Menn & L. K. Obler (Eds.), Agrammatic aphasia. A cross-language narrative sourcebook (pp. 37- 114). Amsterdam: John Benjamins.
35. Weekes, B., Coltheart, M., & Gordon, E. (1997). Deep dyslexia and right hemisphere reading--a regional cerebral blood flow study. Aphasiology, 11, 1139-1158.