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Neuroanatomy of Motor Speech

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					Neuroanatomy of Motor Speech Speech apraxia without oral apraxia: Can normal brain function explain the physiopathology?
Leonardo Bonilha, Dana Moser, Chris Rorden, Gordon C. Baylis & Julius Fridriksson

Department of Communication Sciences & Disorders and Department of Psychology, University of South Carolina

Introduction • Apraxia of speech (AOS) is defined by the inability to plan the oral movements required for speech production. • Although AOS and oral motor apraxia can co-occur, AOS can occur in isolation. • Neuroanatomical substrates of motor speech planning are still controversial: o Classically, the left inferior frontal gyrus was thought to be responsible o More recently, studies have implicated the left insular cortex • Conflicting observations may be due to coexisting impairment in the insula and the inferior frontal gyrus in patients with disrupted brain structure. • Purpose: To investigate the neural basis of motor speech controls and non-speech oral movements in normal participants using functional neuroimaging.

Results (continued) • Speech motor movements (B): the left inferior frontal gyrus and bilateral middle frontal gyrus, thalami, and lateral temporal isocortex. • Non-speech movements (compared to speech) (C & E): mainly the primary motor cortex, but also insular cortex.

• Speech movements (compared to non-speech) (D & F): left inferior frontal gyrus, left middle and superior frontal gyrus, the caudate nuclei, and the thalamus.
Regions of Interests: • Pars triangularis—Mean activation was significantly higher than the activation of the insula during speech motor movements. • Insula—Mean activation was significantly higher than the activation of the pars triangularis during non-speech oral motor movements.

Method

Participants • 18 neurologically intact adults, right-handed, native English speakers, ages 18-25 years
Procedure • Two imitation tasks: 1) Non-speech oral movement pairs 2) Speech movements pairs • Participants viewed short video clips of a human mouth producing alternating movements while undergoing fMRI. For further description: • See (2006), NeuroReport, 17(10), 1027-1031 Discussion • Speech movements recruit the left inferior frontal gyrus, with no evidence of insular activation, which supports the findings from perfusion studies in AOS. • We provide evidence from normal brain function, minimizing potential confounding factors in the patient population. • We suggest that the left inferior frontal cortex, but not the insula, is crucial for orchestrating the oral movements associated with speech.

Figure 2. The differences between the distributions of activation of the left insula and the left pars triangularis, in association with speech and non-speech oral movements.

Results
Cortical Activity: • Non-speech oral motor movements (A): bilateral activation of the precentral cortex, thalamus, pyramidal tracts, and lateral temporal isocortex.

Figure 1. Statistical maps of significant activation recruited by producing movements. (A) Non-speech oral movements (B) Speech movements (C & E) Non-speech movements compared to speech movements (D & F) Speech movements compared to non-speech movements
Note: No significant activation of the insula during speech when compared to a control condition or when compared to non-speech movements


				
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