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Human speech requires a variety of coordinated motor control involving a network stretching across the brain. Alzheimer’s disease, which degrades the brain, can be detected in the lapses of reflexes involved in controlling pitch and control of the voice, according to a new study.

The Alzheimer’s patients demonstrate an inability to make themselves heard, because of the short-circuited networks in their brains, reports the University of California San Francisco team in the April issue of Neurobiology of Aging.

“The specific adjustments in vocal output require integration of brain regions involved in speech-motor control in order to detect the sensory feedback error and implement the motor correction,” they write.

In the speech of a healthy-brained person, small perturbations to their speech are accounted for, and then overcome with compensatory change in pitch. For instance, sudden loud sound will cause the person to start speaking louder to make themselves heard over the voice. If a high-pitched background noise interrupts someone mid-sentence, the speaker will naturally tend to lower their pitch to make themselves better heard.

The UCSF experiments recorded and scored two factors: peak compensation, and mean pitch-response-persistence.

The UCSF team found that 19 patients with Alzheimer’s could not control their voice, pitch modulation, and general speech patterns as well as a control group in a laboratory setting. The scores were based on delay, and failure to account for the voice changes typically recorded by a speaker.

Their conclusion: the patients had impaired prefrontal modulation of sensorimotor integration, as well as compromised plasticity-memory mechanisms.

“Cortical regions involved in the pitch reflex phenomenon are highly vulnerable targets of network disruption in Alzheimer’s disease,” they conclude.

The same UCSF team also delved into the overlooked seizures that go undiagnosed in Alzheimer’s patients, in a November publication. Writing in the journal Annals of Neurology, they found that subclinical epileptiform activity exists in a substantial proportion of patients – which may be boosting cognitive decline, unwittingly for patients, doctors, and surrounding family members. 

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