Neurons in the Parietal Reach Region (PRR) are strongly

associated with the contralateral arm.

Steve W. Chang, Anthony R. Dickinson & Lawrence H. Snyder

Washington University School of Medicine 
St. Louis, MO

Neurons in posterior parietal cortex are active when movements are planned to visible targets. Previous experiments have identified the parietal reach region (PRR) as containing neurons more active prior to planned reaches than planned saccades. As a further test of the hypothesis that this region is specific for reaches, we asked whether neurons differentiated between reaches with the ipsilateral versus the contralateral limb. Such a differentiation would support a reach-specific role for this area.

Our experiments reveal three ways in which PRR neurons behave differentially for movements of the two arms. First, about half of PRR cells are activated prior to reaches with either arm (limb-independent), whereas about one third are activated exclusively or predominantly prior to reaches with just the contralateral arm (limb-dependent). Second, the activity of both groups of cells (limb-dependent and limb-independent) predict contralateral arm reach reaction times, while neither group predicts ipsilateral arm reaction times. Finally, preliminary data suggests that the targets of ipsilateral arm movements are represented in an eye-centered frame of reference, while targets of contralateral arm movements are represented in both eye and arm-centered frames of reference. These data are consistent with PRR supporting both eye- and arm-centered limb-dependent stages in the sensorimotor transformation for contralateral arm movements.

Support Contributed By: NEI; McDonnell & EJLB Foundations

Gordon Research Conference 2007

Bates College in Lewiston, ME