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Re: Crossed aphasia and crossed nonaphasia explained

Dear Editor,

I read with interest the recent report by Menon and colleagues in the Journal.[1] The explanations regarding the anatomy underpinning occurrences of crossed aphasia, i.e. transcallosal diaschisis (p. 342), does not hold since no such events occur in the vast majority of behavioral right-handers who sustained similar injuries to the temporoparietal lobe of the minor hemisphere as because there is no motor communication from the minor to the major hemisphere (see below for the newly discovered anatomical definitions of these terms).

The problem relates to the laterality of the command center which may or may not coincide with the behavioural handedness of the patient. Thus, it has been shown that behavioural handedness relates to neural handedness in a statistical manner, not biological.

Neural handedness is determined by the proximity of the dominant side of the body to the command centre (major hemisphere, the one with which we speak) by a callosum width, providing for a quick determination of the same with a reaction time test. The latter is longer on the entire nondominant side of the body by an interhemispheric transfer time (IHTT). This includes moving the eyes or the diaphragm in neural right handers.[2,3]

It would have been helpful to know if the patient had apraxia of the right hand side, a finding commonly reported in crossed aphasics, where the laterality of hemiparesis and apraxia simply switch sides, compared to what is the case when neural and behavioural handedness of the subject does match.[4-6]

More clinical information on the subjects of crossed aphasia and crossed nonaphasia may be obtained in my recent articles on the laterality of motor control in humans, the one-way callosal traffic scheme.[7-10]

References

1. Menon B, Vengamma B. A woman with language disturbance. Postgrad Med J. 2005; 81:341-342.

2. Derakhshan I. How do the eyes move together? New understandings help explain eye deviations in patients with stroke. CMAJ. 2005 Jan 18; 172:171-173.

3. Derakhshan I. In defense of the sinistrals: anatomy of handedness and the safety of prenatal ultrasound. Ultrasound Obstet Gynecol. 2003; 21:209-212.

4. Marien P, Engelborghs S, Vignolo LA, De Deyn PP. The many faces of crossed aphasia in dextrals: report of nine cases and review of the literature. Eur J Neurol. 2001; 8:643-658. (Table 2)

5. Derakhshan I. Handedness: neural versus behavioural. Eur J Neurol. 2002; 9:701-702.

6. Derakhshan I, Franz EA, Rowse A. An exchange on Franz, Rowse, and Ballantine (2002). Handedness, neural versus behavioral: is there a measureable callosal difference. J Mot Behav. 2003; 35:409-414.

7. Derakhshan I. Laterality of motor control revisited: directionality of callosal traffic and its rehabilitative implications. Top Stroke Rehabil. 2005; 12:76-82.

8. Derakhshan I. Handedness and macular vision: laterality of motor control underpins both. Neurol Res. 2004; 26:331-337.

9. Derakhshan I. Kernohan notch. J Neurosurg. 2004; 100:741-742.