Neurology -- Correspondence for Hund-Georgiadis et al., 61 (9) 1276-1279

Correspondence published:

Impaired hemodynamics and neural activation?: A fMRI study of major cerebral artery stenosis: Iraj Derakhshan (4 December 2003)

Reply to Derakhshan: Margret Hund-Georgiadis, D. Yves von Cramon (4 December 2003)

Impaired hemodynamics and neural activation?: A fMRI study of major cerebral artery stenosis 4 December 2003

Iraj Derakhshan,
Private practice
415 Morris St., #401, Charleston, WV 25301
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Re: Impaired hemodynamics and neural activation?: A fMRI study of major cerebral artery stenosis

idneuro{at}hotmail.com Iraj Derakhshan

The data presented by Hund-Georgiadis et al [1] may be interpreted differently than suggested by the authors. The authors report the possible reorganization of the command structure of motor control as a “reserve strategy” revealed in two (behavioral) right-handed patients with stenosis of the middle cerebral arteries.
Patient 2 had severe stenosis of the distal trunk of the left MCA (Fig 1 of the article). According to the data depicted in the bar graph for different conditions in Fig.2, patient 2 showed no statistically significant difference between the activities of M1 cortices of the two sides when tapping with his right hand. This is opposite to the reaction in patient 1 who was also a behavioral right hander whose “motor cortices were structurally intact.”
The question that arises here relates to the anatomical underpinning of bilateral cortical activation or to cortical activation ipsilateral to the tapping hand when moving one or the other hand. This occurrence is indexed to laterality of motor control (in right- and left-handers) and has been interpreted as having “something to do with the use of the nondominant left hand”. [2] Its occurrence in the reverse in “converted” left handers has also been documented. [3] Hund-Georgiadis et al reported this very phenomenon (activation of motor cortex ipsilateral to the tapping hand) in a behavioral right- (and neural left-) hander. [4] Moving the nondominant effectors is a bi-hemispheric event with signals arising from the major hemisphere and then traversing the callosum for implementation by the minor hemisphere (evidenced in time-resolved studies). [5] Their patient 2 with bilateral cortical activation was not a real right-hander--but an ostensible one--and they should not have expected the same activation pattern as that observed in their patient 1 who was a real (i.e. neural) right-hander; regardless of the status of MCA in either case.
Similarly, the authors’ explanation that the activity patterns they depicted relate to a “redistribution of the motor network to the healthy hemisphere” is fraught with difficulty. For example, the nonexistence of ipsilateral control of volitional activity in humans; except those of the nondominant hand which will then involve the corpus callosum. [5] As for the results in the control subjects, statistically one of the six was a neural left hander [5]. This could have affected the normalized and averaged data presented.
References
1. Hund-Georgiadis M, Mildner T, Georgiadis D et al. Impaired hemodynamics and neural activation? A fMRI study of major cerebral artery stenosis. Neurology 2003; 61:1276-1279.
2. Beltramello A, Cerini R, Puppini G et al. Motor representation of the hand in the human cortex: an f-MRI study with a conventional 1.5 T clinical unit. Ital J Neurol Sci 1998; 19:277-284. (pp 282-283)
3. Siebner HR, Limmer C, Peinemann A et al. Long-term consequences of switching handedness: a positron emission tomography study on handwriting in "converted" left-handers. J Neurosci 2002; 22:2816-2825.
4. Derakhshan I, Hund-Georgiadis, Von Cramon DY. Crossed nonaphasia in a dextral with left hemispheric lesions: Handedness technically defined. Stroke 2002; 33:1749-1750. Erratum in Stroke 2002;33: 2524.
5. Derakhshan I, Franz EA, Rowse A. Handedness: Neural Versus Behavioral J Mot Behav 2003; 35:409-414.

Reply to Derakhshan 4 December 2003

Margret Hund-Georgiadis
MPI of Cognitive Neuroscience, Stephanstr. 1, D-04103 Leipzig,
D. Yves von Cramon
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Re: Reply to Derakhshan

hund{at}cns.mpg.de Margret Hund-Georgiadis, et al.

We thank Dr. Derakhshan for his comments regarding our article. He suggests a different interpretation of functional MRI activation data, at least for one of the reported patients of our previous study and implies that patient 2 of our study was actually a neural left-hander only masquerading behavioural right-handedness. Evidence for his assumption is derived from an equal involvement of both motor cortices associated with right-hand motor tapping.
We demonstrated that our patient was right-handed by every type of behavioural testing and therefore suggested a functional redistribution within the motor network, which occurs prior to structural damage.[1] Previous electrophysiological reseach confirms our findings.[6]
Although Dr. Derakhshan's interpretation cannot be ruled out, it appears improbable for several reasons: First, the concept of a neural or converted left-handedness is at best speculative. So far, no comprehensive study has shown how to determine this dominance type beyond an arbitrary definition.
Second, Dr. Derakhshan's theory does not take into account the influence of impaired hemodynamics on fMRI-signal changes. The BOLD signal in a hypoperfused hemisphere is very difficult to interpret. In any case, failure to see normal activation in the hypoperfused hemisphere cannot be interpreted as a lack of neuronal activity. Only additional activations in the ipsi- and contralateral hemisphere should allow some conclusions, in particular when contrasted with normal control data.
Third, to support the theory of converted left-handedness, Dr. Derakhshan refers to our previous paper on mirrored brain organization in a typical right-hander with left hemisphere lesions.[7] Dr. Derakhshan insists that this patient was a neural left-hander. We can only point out, as we did in a previous correspondence [4], that our patient was a right-handed man, who showed crossed non-aphasia following left-hemisphere stroke.
While we appreciate Dr. Derekhshan's interest in our work, and find his interpretations intriguing, we must state that they are not supported by current data.
References
6.) Bundo M, Inao S, Nakamura A, Kato T, Ito K, Tadokoro M, Kabeya R, Sugimoto T, Kajita Y, Yoshida J. Changes of neural activity correlate with the severity of cortical ischemia in patients with unilateral major cerebral artery occlusion.Stroke. 2002; 33:61-66.
7.) Hund-Georgiadis M, Zysset S, Weih K, Guthke T, von Cramon DY. Crossed nonaphasia in a dextral with left hemispheric lesions: a functional magnetic resonance imaging study of mirrored brain organization. Stroke 2001; 32:2703-2707.