In primates, the posterior parietal cortex (PPC) is implicated in planning and imagining motor tasks. Here, by recording from this region in a tetraplegic volunteer, the authors showed that the PPC has a similar role in humans. Imagining a movement regulated the activity of a single cell, and the patient could control cell firing by imagining different motor tasks. Cell activity was recorded and used to move a cursor on a screen. PPC neuronal activity coded both the goal and the trajectory of the intended movement when the patient was asked to imagine moving the cursor towards a target. The PPC may therefore be a promising target for neuroprosthetic development.