fMRI reveals two distinct cerebral networks subserving speech motor control.
BACKGROUND
There are few data on the cerebral organization of motor aspects of speech production and the pathomechanisms of dysarthric deficits subsequent to brain lesions and diseases. The authors used fMRI to further examine the neural basis of speech motor control.


RESULTS
In eight healthy volunteers, fMRI was performed during syllable repetitions synchronized to click trains (2 to 6 Hz; vs a passive listening task). Bilateral hemodynamic responses emerged at the level of the mesiofrontal and sensorimotor cortex, putamen/pallidum, thalamus, and cerebellum (two distinct activation spots at either side). In contrast, dorsolateral premotor cortex and anterior insula showed left-sided activation. Calculation of rate/response functions revealed a negative linear relationship between repetition frequency and blood oxygen level-dependent (BOLD) signal change within the striatum, whereas both cerebellar hemispheres exhibited a step-wise increase of activation at approximately 3 Hz. Analysis of the temporal dynamics of the BOLD effect found the various cortical and subcortical brain regions engaged in speech motor control to be organized into two separate networks (medial and dorsolateral premotor cortex, anterior insula, and superior cerebellum vs sensorimotor cortex, basal ganglia, and inferior cerebellum).


CONCLUSIONS
These data provide evidence for two levels of speech motor control bound, most presumably, to motor preparation and execution processes. They also help to explain clinical observations such as an unimpaired or even accelerated speaking rate in Parkinson disease and slowed speech tempo, which does not fall below a rate of 3 Hz, in cerebellar disorders.
Riecker
A
A
Department of General Neurology, Hertie Institute for Clinical Brain Research, University of Tuebingen, Tuebingen, Germany. axel.riecker@web.de
Mathiak
K
K
Wildgruber
D
D
Erb
M
M
Hertrich
I
I
Grodd
W
W
Ackermann
H
H
D000293:Adolescent; D000328:Adult; D016477:Artifacts; D001931:Brain Mapping; D002531:Cerebellum / Q000098:blood supply / Q000502:physiology; D002540:Cerebral Cortex / Q000098:blood supply / Q000502:physiology; D004292:Dominance, Cerebral; D005260:Female; D005625:Frontal Lobe / Q000098:blood supply / Q000502:physiology; D005917:Globus Pallidus / Q000098:blood supply / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000098:blood supply / Q000502:physiology; D010699:Phonation / Q000502:physiology*; D017397:Prefrontal Cortex / Q000098:blood supply / Q000502:physiology; D011699:Putamen / Q000098:blood supply / Q000502:physiology; D012016:Reference Values; D013003:Somatosensory Cortex / Q000098:blood supply / Q000502:physiology; D013060:Speech / Q000502:physiology*; D013382:Subtraction Technique; D013788:Thalamus / Q000098:blood supply / Q000502:physiology