Speech‐induced changes in corticospinal excitability

Abstract

The aim of the experiments was to investigate the effects of speech on the excitability of corticospinal pathways to human hand muscles. Single transcranial magnetic stimuli were given randomly over the hand area of either the left or right motor cortex of 10 right-handed and 3 left-handed normal volunteers. Electromyographic responses were recorded in the relaxed first dorsal interosseous muscle while the subjects (a) read aloud a piece of text, (b) read silently, (c) spoke spontaneously, or (d) made sounds without speaking. The only consistent effect across subjects occurred during task a, which significantly increased the size of responses evoked in the dominant hand of all subjects, but had either no effect (8 subjects) or a smaller effect in the nondominant hand. Tasks b and d had no reliable effect, whereas task c tended to increase response size in both hands. Control measurements suggest that the effects in task a were caused by changes in cortical rather than spinal excitability. This is the first demonstration of lateralized speech effects on the excitability of cortical arm areas. The results provide a useful adjunct to other tests of cerebral dominance, using only single- rather than repetitive-pulse cortical stimulation.

Dissociated Representations of Deceptive Intentions and Kinematic Adaptations in the Observer's Motor System

“…We counterbalanced the up-or down-position of the verbal descriptors in order to avoid participants to plan their response in advance. A verbal, rather than a motor, response was required at the end of each video clip to avoid MEPs contamination (Tokimura et al 1996;Meister et al 2003;Gentilucci et al 2006). Twenty-four repetitions for each of the 3 possible actions with the light or the heavy object were presented, thus leading to a total of 144 trials.…”

Are There Excitability Changes in the Hand Motor Cortex During Speech in Left-Handed Subjects?

“…4,7,17) However, rTMS appears to be less reliable than the Wada test. 6) Lateralized speech effects on the excitability of the cortical hand motor area were first demonstrated in 1996, 28) and has been replicated and confirmed in several studies. 15,16,25) The effect is restricted to the hand area because MEPs from the leg area are unchanged by the task.…”

“…Because the Wada test is invasive, other methods have been proposed, such as positron emission tomography, 20) fMR imaging, 3) functional Doppler sonography, 14) assessment of event-related brain potentials, 9) and TMS. 19,28) TMS is a noninvasive method to investigate the awake human nervous system. 2) Speech suppression and speech activation studies have been reported in human subjects.…”

“…We previously observed that motor evoked potentials (MEPs) of the dominant-hand muscles elicited by transcranial magnetic stimulation (TMS) to the contralateral motor cortex were enhanced when subjects read aloud, and proposed a technique to identify the dominant hemisphere. 28) Repetitive TMS (rTMS), 11,17,19) low frequency rTMS, 26) and functional magnetic resonance (fMR) imaging 3,12) are non-invasive methods to determine speech dominancy, which have established left hemispheric speech dominancy in right-handers. However, the dominant hemisphere in left-handers remains to be established.…”

Noninvasive Determination of Speech Dominance by Single Magnetic Stimulation of the Bilateral Hand Motor Cortex

“…12) We previously showed that single magnetic stimuli delivered at intensities safe for use with normal subjects could be used to detect lateralized effects on brain function. 23) Electromyographic (EMG) responses in the relaxed hand muscles evoked by transcranial stimulation of the motor cortex of the dominant hemisphere were enhanced if stimuli were delivered while subjects read aloud. This effect clearly depended on lateral dominance in normal subjects.…”