a1 Department of Psychological Medicine, Institute of Psychiatry; Wellcome Department of Cognitive Neurology, c/o MRC Cyclotron Unit, Hammersmith Hospital; Department of Psychology, University College, London; Departments of Psychiatry and Neurology, Cornell Medical Centre, New York, USA
The neural correlates of inner speech and of auditory verbal imagery were examined in normal volunteers, using positron emission tomography (PET). Subjects were shown single words which they used to generate short, stereotyped sentences without speaking. In an inner speech task, sentences were silently articulated, while in an auditory verbal imagery condition, subjects imagined sentences being spoken to them in an another person's voice. Inner speech was associated with increased activity in the left inferior frontal gyrus. Auditory verbal imagery was associated with increases in the same region, and in the left premotor cortex, the supplementary motor area and the left temporal cortex. The data suggest that the silent articulation of sentences involves activity in an area concerned with speech generation, while imagining speech is associated with additional activity in regions associated with speech perception.
c1 Address for correspondence: Dr P. K. McGuire, Department of Psychological Medicine, Institute of Psychiatry, De Crespigny Park, London SE5 8AF.