Figure 1

Cortical circuits of speech motor control, schematic of the experimental setup and the behavioral response to pitch perturbation. (A) Anatomical locations of candidate cortical areas are depicted on a schematic brain diagram. The arrows indicate auditory feedback control pathways where feedback predictions (grey arrow) are compared with incoming feedback from primary auditory cortices (dashed arrow) in the posterior superior temporal/inferior parietal cortices to generate feedback corrections (black arrows). These key processing nodes (premotor cortex and posterior superior temporal/inferior parietal cortex) are modulated by prefrontal cortex (dotted lines). The experimental setup (B) illustrates the participant as they are lying supine in the MEG scanner. The subject speaks into an optical microphone and receives auditory feedback through a set of air-tube earphones. Their speech is passed through a digital signal processor, which generates the pitch-shifted audio feedback stimulus at a jittered delay after speech onset. The LCD panel directly in front of the subject gives a visual clue (a clearly identifiable colored circle), which prompts the participant to start speaking. (C) The magnitude of vocal response to perturbations of 100 cents for controls and patients with AD. Dark lines indicate the mean response, and the shaded areas indicate standard error, across the trials per each group. The time axis is time-locked to perturbation onset (0 ms). Grey shaded area indicates the duration of perturbation. Abbreviations: AD = Alzheimer’s disease. LCD = liquid crystal display; MEG = magnetoencephalography.