**7. General discussion**

It is generally accepted that, in both *left- and right-handed* subjects, the preferred hand is controlled mainly by the hemisphere *contralateral* to that hand, whereas the *non-preferred* hand is controlled by *both hemispheres*. In relation to *left-to-right switches* in handedness, the switched individuals have been found to share features of both left-handers and right-handers regarding their motor control architectures. ([1], see Introduction).

encoding for that hand. There was no difficulty or delay, however, to successfully use thus acquired memory for guiding drawing with the right hand. It should be noted that, in the drawing phase, the hand under training receives multifaceted, Cognitive-Kinesthetic feedback, which affects the initial haptic memory, corrects and sharpens it, thus adding another layer of

Brain Reorganization in Late Adulthood: Rapid Left-to-Right Switch of Handedness…

http://dx.doi.org/10.5772/intechopen.76317

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An important practical implication of these findings is that the effects of the Cognitive-Kinesthetic Training can generalize over the full "perception-cognition-action loop" involved throughout the process, which suggests its usefulness not only in the domains of spatial cog-

This study is the first to show results that contradict the models of the nondominant hand always being controlled by both hemispheres, as had been previously thought. It is particularly remarkable that this brief memory-guided drawing training was able to switch lifelong handedness, overturning almost six decades of dominance of the right hemisphere by inducing profound suppression in the previously dominant hemisphere. In terms of handedness research as a whole, the study suggests a critical role for functional mechanisms, such as inter-hemispheric competition, as opposed to an inherent structural predetermination in hand dominance. The results are consequently of high relevance to the long-standing debate about the sources of hemispheric asymmetry. The unprecedented effect on handedness of the rapid Cognitive-Kinesthetic Drawing Training also implies the powerful potential of this training for further rehabilitation domains, such as the rehabilitation of stroke or trauma

This research was supported by the National Eye Institute at the National Institute of Health (RO1EY024056) and National Science Foundation (NSF/SL-CN: 1640914) awarded to Lora Likova. The author would like to thank Christopher W. Tyler for helpful discussions on the manuscript, Kristyo Mineff for assisting with the drawing training, Spero Nicholas for helping with the functional Magnetic Resonance Imaging (fMRI) data collection, and preprocessing.

nition and memory rehabilitation but also in motor control rehabilitation as well.

enhancement and embodiment to the overall encoding.

**8. Conclusions**

affecting hand control.

**Acknowledgements**

**Author details**

Address all correspondence to: lora@ski.org

Smith-Kettlewell Eye Research Institute, San Francisco, CA, USA

Lora T. Likova

Before training, the results for both the *preferred/*left and the *non-preferred/*right hand conformed to these preexisting models: the *preferred*/left hand produced predominantly *contralateral* activation, whereas the *non-preferred*/right hand produced a more balanced *bilateral* activation, indicating control by both hemispheres.

*After* training, however, the bilateral pattern expected in switchers was not observed any more. Instead, the non-preferred/right hand underwent a strong training-based reorganization of its motor control architecture, so as its bilateral activation pattern radically changed post-training into a contralateral one. Remarkably, this *contralaterality* (left hemisphere > right hemisphere) was caused not by increased contralateral (left) activation but by a massive suppression in the ipsilateral (right) hemisphere; it is particularly surprising that this happened despite the fact that the right hemisphere has been the dominant one since birth.

These findings show for the first time that the dominance of the preferred hemisphere can be rapidly overturned, and that this can happen even in late adulthood after decades of established dominance. Note that, until now, despite long-standing efforts across many disciplines to achieve a fully-fledged hand switching in left-handers, the best that has been achieved has been to engage the contralateral left hemisphere without being able to overturn the ipsilateral right hemisphere control [1, 12]. The fact that the Cognitive-Kinesthetic Drawing Training was able to transform the bilateral into a definitive contralateral pattern, and to do so effectively and efficiently, implies a serious deficiency in the current knowledge on motor control plasticity, and the need for enhanced investigation into this process. Moreover, the power of this memory-driven motor training to rapidly drive motor-control plasticity, in addition to the previously shown effects on memory and spatial cognition, for example [2–5, 39–41], suggests strong involvement of cognitive mechanisms in this process, as codified earlier by the introduction of the "perception-cognition-action loop" concept.

The resulting neural reorganization in this congenitally left-handed individual was correlated with similarly remarkable enhancement in the memory-drawing performance of the non-preferred hand, which post-training resembled the original much better than pre-training, and moreover, significantly better than the experienced preferred hand. This was particularly unexpected because the left hand had several additional advantages. First, the *haptic exploration* of the originals was *always* done with the *left* hand, thus providing a direct perception and encoding of this hand's movements along the lines of that image. In contrast, the non-preferred right hand *never* received any direct encoding of the trajectory but for planning and execution of the drawing trajectory it had to use the memory image developed through the other hand. Second, the nature of the left-hand exploration phase represents a strong form of *dual* memory encoding for that hand. There was no difficulty or delay, however, to successfully use thus acquired memory for guiding drawing with the right hand. It should be noted that, in the drawing phase, the hand under training receives multifaceted, Cognitive-Kinesthetic feedback, which affects the initial haptic memory, corrects and sharpens it, thus adding another layer of enhancement and embodiment to the overall encoding.

An important practical implication of these findings is that the effects of the Cognitive-Kinesthetic Training can generalize over the full "perception-cognition-action loop" involved throughout the process, which suggests its usefulness not only in the domains of spatial cognition and memory rehabilitation but also in motor control rehabilitation as well.
