The parietal reach region, in the posterior parietal cortex, has been characterized as coding targets for reaching in an eye-centered frame of reference. We now show that in fact, a substantial minority of PRR neurons are arm-centered, and other PRR neurons are intermdiate between
eye- and arm-centered. We also find that these cells are gain-field modulated by the distance between starting arm and starting gaze position.
This gain field modulation could directly contribute to a reference frame transformation.
In the second half of the talk, we will show that both single unit recording in monkey PRR, as well as BOLD activations in human posterior parietal cortex, show that the parietal cortex represents reach targets for both limbs, with a bias for the contralateral limb. Three additional lines of evidence strongly suggest, however, that the posterior parietal cortex controls only the contralateral limb. We will discuss the significance of these findings, both in terms of parietal control of reaching and in understanding the limitations of single unit and BOLD data.