Functional rather than effector-specific organization of human posterior parietal cortex.

Neurophysiological and neuroimaging studies have shown that the posterior parietal cortex (PPC) distinguishes between the planning of eye and hand movements. This distinction has usually been interpreted as evidence for a modular, effector-specific organization of this cerebral region. However, the eyes differ markedly from other body parts both in terms of their functional purpose and with regard to the spatial transformations required to plan goal-directed movements.

Behavioral and cortical mechanisms for spatial coding and action planning.

There is considerable evidence that the encoding of intended actions in visual space is represented in dynamic, gaze-centered maps, such that each eye movement requires an internal updating of these representations. Here, we review results from our own experiments on human subjects that test the additional geometric constraints to the dynamic updating of these spatial maps during whole-body motion. Subsequently, we summarize evidence and present new analyses of how these spatial signals may be integrated with motor effector signals in order to generate the appropriate commands for action.

Behavioral reference frames for planning human reaching movements.

At some stage in the process of a sensorimotor transformation for a reaching movement, information about the current position of the hand and information about the location of the target must be encoded in the same frame of reference to compute the hand-to-target difference vector. Two main hypotheses have been proposed regarding this reference frame: an eye-centered and a body-centered frame. Here we evaluated these hypotheses using the pointing errors that subjects made when planning and executing arm movements to memorized targets starting from various initial hand positions while keeping gaze fixed in various directions.