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Re: Laterality of motor control in deep brain stimulation

Dear Editor,

The article by Putzke and colleagues [1] on bilateral deep brain stimulation (DBS) for ameliorating essential tremor contains several laterality indexed aspects of clinical interest (not mentioned by the authors):

They stimulated the ventral intermediate nucleus of thalamus (Vim) on the left side in 20 of 22 patients with essential tremor, assumed to have been right handers at the rate of ~ ninety percent. It might also be safely assumed that their choice of the left hemisphere as the first target was based either on the severity of the tremor (on the right) or the fact that their patients were mostly right handed. At any case, they did not find " an additional incremental effect following placement of the second lead [stimulating the right Vim]," as seen in their Fig. 1. There was, however, a significant improvement in ipsilateral upper extremity tremor when stimulating the left Vim (table 3). Similarly, "none of the three individuals with trunk tremor at baseline had observable tremor with stimulation during both the unilateral [left]and bilateral [left and right stimulation] period."

This bilaterality of the effect of one hemisphere (and its thalamus, see reference 7) in motor control is the hallmark of the executive hemisphere, as revealed in my clinical and time resolved studies and analyses of the literature [2-5]. Separately, Hellwig et al have shown significant callosally mediated coherence of the EEG and EMG oscillations in patients with essential tremor [6], while laterality indexed asymmetry in occurrence of aphasia and neglect has been reported in thalamic lesions (similar to that of the cortex) [7].

Given the above considerations, the data submitted by Putzke et al supports the notion that the essential consideration in DBS for tremor is securing the laterality of the major (executive) hemisphere in individual subjects since stimulating the thalamus in the major hemisphere will have bilateral effect, obviating the need for additional surgery at a later date.

The above referenced studies have shown that behavioral handedness is only a rough guide as to the neural handedness of the subject; i.e. the directionality of callosal traffic between two hemispheres. The latter may be secured noninvasively and inexpensively by measuring the reaction time of two muscles symmetrically located. The side with the shorter reaction time is opposite to the major hemisphere. The difference between the two sides is equal to the interhemispheric transfer time (IHTT) [2-5].

References

1. Putzke JD, Uitti RJ, Obwegeser AA, Wszolek ZK, Wharen RE. Bilateral thalamic deep brain stimulation: midline tremor control.J Neurol Neurosurg Psychiatry. 2005;76:684-690.

2. Derakhshan I. Crossed-uncrossed difference (CUD) in a new light: anatomy of the negative CUD in Poffenberger's paradigm. Acta Neurol Scand. 2006;113:203-208.

3. Derakhshan I. Laterality of motor control revisited: directionality of callosal traffic and its rehabilitative implications. Top Stroke Rehabil. 2005;12:76-82. 4:

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

5. 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.

6. Hellwig B, Schelter B, Guschlbauer B, Timmer J, Lucking CH. Dynamic synchronisation of central oscillators in essential tremor. Clin Neurophysiol. 2003;114:1462-1467.