An associated movement (AM) is an unintentional, involuntary, spontaneous, automatic movement that accompanies some other voluntary (or involuntary) movement. The associated, or synkinetic, movement is often one that serves to fix a part of the body as another part is voluntarily activated. Associated movements often occur because of activation of the synergistic and fixation muscles involved in a particular motion, or spread of the activation to nearby motor neuron pools. This activity is normally suppressed by the descending motor pathways, but in the face of disease becomes clinically apparent. The corticospinal pathways are concerned primarily with fine, fractionated, discrete movements of the distal extremities. Disease in the corticospinal pathways may eliminate discrete distal movement but not affect mass movements of the proximal muscles. The mass movements usually play a secondary, supportive role, particularly in fixation of the part to be moved. However, when the distal movements are paralyzed, the primary movement left may be the associated mass movement. Associated movements are, to a certain extent, postural or righting reflexes that have a peculiarly widespread distribution. They may be clinical homologues of movements seen in decerebrate animals. Associated movements are more complex manifestations of motor function than the simple reflexes, but are more primitive than voluntary movements. They are probably initiated and largely controlled by the extrapyramidal system and its connections, although the corticospinal system also plays a role.