How a lateralized brain supports symmetrical bimanual tasks.

Full Abstract

A large repertoire of natural object manipulation tasks require precisely coupled symmetrical opposing forces by both hands on a single object. We asked how the lateralized brain handles this basic problem of spatial and temporal coordination. We show that the brain consistently appoints one of the hands as prime actor while the other assists, but the choice of acting hand is flexible. When study participants control a cursor by manipulating a tool held freely between the hands, the left hand becomes prime actor if the cursor moves directionally with the left-hand forces, whereas the right hand primarily acts if it moves with the opposing right-hand forces. In neurophysiological (electromyography, transcranial magnetic brain stimulation) and functional magnetic resonance brain imaging experiments we demonstrate that changes in hand assignment parallels a midline shift of lateralized activity in distal hand muscles, corticospinal pathways, and primary sensorimotor and cerebellar cortical areas. We conclude that the two hands can readily exchange roles as dominant actor in bimanual tasks. Spatial relationships between hand forces and goal motions determine hand assignments rather than habitual handedness. Finally, flexible role assignment of the hands is manifest at multiple levels of the motor system, from cortical regions all the way down to particular muscles.

Author information

Author/s: Johansson, Roland S (RS); Theorin, Anna (A); Westling, Göran (G); Andersson, Mikael (M); Ohki, Yukari (Y); Nyberg, Lars (L);

Affiliation: Department of Integrative Medical Biology, Physiology Section, Umeå University, Umeå, Sweden. roland.s.johansson(-atsign-)physiol.umu.se

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: PLoS biology (PLoS Biol), published in United States. (Language: eng)

Reference: 2006-Jun; vol 4 (issue 6) : pp e158

Dates: Created 2006/06/06; Completed 2006/08/11; Revised 2008/11/20;

PMID: 16669700, status: MEDLINE (last retrieval date: 2/18/2009, IMS Date: )

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