Explain why a disorder of reactive movements is described as able to go in either direction, diminished or excessive.

A disturbance can go in either direction: reactive movements may be diminished or lost, giving a stiff, unresponsive impression, most classically in catatonia and parkinsonism, or they may become excessive and overly prompt, well beyond what the stimulus would warrant, as seen in severe anxiety. Because reactive movements normally give an overall impression of alertness and engagement with the surrounding world, a disturbance in either direction, too little or too much responsiveness, disrupts this normal impression in a way that is clinically informative, with the specific direction of the disturbance itself pointing toward a different underlying condition, diminished reactivity toward catatonia or parkinsonism, and excessive reactivity toward severe anxiety.