During decision making, activity in several brain areas is increased, but their role in decision making is not known. Katz et al. recorded from neurons in the lateral intraparietal area (LIP) and middle temporal area (MT) of awake behaving rhesus macaques while they performed a motion-direction discrimination task. Neurons in the LIP exhibited changes in firing pattern that correlated strongly with the animals' choice in the task; by contrast, changes in the firing of MT neurons were weakly correlated with choice. However, pharmacologically silencing LIP neurons had no effect on task performance, whereas silencing MT neurons strongly disrupted it, indicating a dissociation between correlation and causation in decision making.