Understanding How Alzheimer’s Disease Affects Speaking

How precisely our speech matches our intended vocal pitch is a newly discovered symptom of Alzheimer’s disease (AD). Neurodegenerative diseases like AD can disrupt the intricate neural networks responsible for speech production, and understanding this disruption may enable advancements in therapeutic interventions to help individuals with speech impairments regain their ability to communicate effectively.

When we speak, we easily manage to produce smooth, intelligible sounds through delicate interplay of neural and muscular systems. As we talk, our vocal cords vibrate at a specific frequency, producing a sound with a particular pitch. However, our vocal cords aren't always perfectly precise. They sometimes produce sounds that deviate from the intended pitch. Our brains detect these naturally occurring deviations and send corrective signals to our vocal muscles. These signals fine-tune the tension and vibration of the vocal cords, bringing the pitch back on track, a newly described phenomenon called pitch centering. This continuous adjustment or centering ensures that our speech output remains as intended, smooth and intelligible.

In a recent paper published in Frontiers in Human Neuroscience, Anantajit Subrahmanya, Drs. Kamalini Ranasinshe, Hardik Kothare, Inez Raharjo, Kwang Kim, and senior authors Drs. John Houde and Srikantan Nagarajan, investigated how patients with AD exhibit pitch centering. This study showed that healthy controls and individuals with AD exhibit a unique pattern of pitch centering. While healthy individuals can effectively correct pitch errors both above and below the target pitch, AD patients seem to struggle more with correcting errors above the target pitch. This asymmetry suggests that AD may impair the brain’s ability to accurately perceive and respond to pitch deviations.

"We are very excited about characterizing this novel phenomenon of pitch centering in healthy adults and discovering that it is affected in individuals with Alzheimer’s disease. At the Speech Neuroscience and Biomagnetic Imaging Laboratories at UCSF we are currently conducting imaging studies to better understand the neurological basis of these and other speech motor control abnormalities in AD and other dementias" says Srikantan Nagarajan, PhD, the senior author of the study.

Understanding the neural mechanisms of pitch centering in particular and speech motor control in general has significant implications for the development of interventions to improve speech and communication in individuals with neurodegenerative diseases. By targeting specific neural pathways involved in pitch control, researchers may be able to develop therapies that help individuals with AD and other speech disorders maintain intelligible speech.