Automatic-voluntary dissociation: an unusual facial paresis in a patient with probable multiple sclerosis

A patient with multiple sclerosis is described who presented with a unilateral loss of voluntary function of his lower face muscles. However, in an emotional situation, there was strong involuntary innervation of these muscles: automatic-voluntary dissociation. The subcortical afferents to the facial motor nucleus are discussed. It is hypothesized that cortical disinhibition of midbrain nuclei underlies the accentuated involuntary innervation.