"My Words Come Out Wrong": When Thought and Language Are Disconnected from Speech
ABSTRACT
To communicate a thought through speech first requires selection of appropriate words and organization of them into a coherent message. This formulated message ultimately will activate 100 muscles between the lungs and lips to produce at least 14 distinct sounds per second that can be comprehended by a listener. This enormous brain-body achievement is reliant on one additional crucial neurologic act called “speech programming,” which occurs between message formulation and actual speech production. Speech programming organizes and packages the complex movement instructions that direct the activities of the muscles and structures that move to produce speech.
Spoken communication can break down in several ways. In “aphasia,” the ability to use the symbol system of language may be compromised. In what is called “dysarthria,” language functions adequately but the speech movements themselves are compromised by weakness, excessive tension, incoordination, or involuntary movements. When the speech programming stage is affected, the problem is called “apraxia of speech.” These problems may or may not be isolated and, unfortunately, any of one of them can have devastating consequences on the ability to communicate.
Although speech difficulty is well-recognized as a sign of stroke, it is often ignored as a sign of neurodegenerative disease. Nonetheless, we know that aphasia can be the only sign of neurodegenerative disease, in which case it is called “primary progressive aphasia” (PPA). Several subtypes of PPA have been described and their reliable identification has implications for localizing the disease in the brain, identifying the underlying pathology and, most important, patient care. Recent research has established that a subset of people who in the past have been classified as having PPA actually do not have aphasia at all but instead are unable to program speech movements, even though they can read, write, and comprehend speech normally. This condition is known as “primary progressive apraxia of speech” (PPAOS). PPAOSis localized in brain areas that differ from the localization of PPA subtypes, and its recognition predicts with high accuracy the underlying pathology – tauopathy, an abnormal accumulation in the brain of the protein tau. This presentation will address the clinical, neuroimaging, and pathological and biochemical features of PPAOS and the implications of its recognition for counseling and speech therapy management and medical therapy when disease modifying agents become available.
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