Effects of transcranial direct current stimulation over the human motor cortex on corticospinal and transcallosal excitability.
ABSTRACT Weak transcranial direct current stimulation (tDCS) can induce long lasting changes in cortical excitability. In the present study we asked whether tDCS applied to the left primary motor cortex (M1) also produces aftereffects distant from the site of the stimulating electrodes. We therefore tested corticospinal excitability in the left and the right M1 and transcallosal excitability between the two cortices using transcranial magnetic stimulation (TMS) before and after applying tDCS. Eight healthy subjects received 10 min of anodal or cathodal tDCS (1 mA) to the left M1. We examined the amplitude of contralateral motor evoked potentials (MEPs) and the onset latency and duration of transcallosal inhibition with single pulse TMS. MEPs evoked from the tDCS stimulated (left) M1 were increased by 32% after anodal and decreased by 27% after cathodal tDCS, while transcallosal inhibition evoked from the left M1 remained unchanged. The effect on MEPs evoked from the left M1 lasted longer for cathodal than for anodal tDCS. MEPs evoked from the right M1 were unchanged whilst the duration of transcallosal inhibition evoked from the right M1 was shortened after cathodal tDCS and prolonged after anodal tDCS. The duration of transcallosal inhibition returned to control values before the effect on the MEPs from the left M1 had recovered. These findings are compatible with the idea that tDCS-induced aftereffects in the cortical motor system are limited to the stimulated hemisphere, and that tDCS not only affects corticospinal circuits involved in producing MEPs but also inhibitory interneurons mediating transcallosal inhibition from the contralateral hemisphere.
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ABSTRACT: Noninvasive brain stimulation, including repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), have gained popularity in the stroke rehabilitation literature. Little is known about the time course and duration of effects of noninvasive brain stimulation on corticospinal excitability in individuals with stroke. We examined the aftereffects of a single session of high-frequency rTMS (5 Hz) and anodal tDCS on corticospinal excitability in the same sample of participants with chronic stroke. Ten individuals with chronic stroke participated in this randomized cross-over study. Participants received 1 session of rTMS and 1 session of tDCS, with 1 week between sessions. During the rTMS session, 5-Hz rTMS (total of 1200 stimuli) was administered to the ipsilesional primary motor cortex (M1). For anodal tDCS, 1 mA of direct current was delivered to the ipsilesional M1 for 20 minutes. Motor evoked potentials were measured before and after (immediately, 15 minutes, 30 minutes, and 60 minutes) each stimulation session. Both 5-Hz rTMS and anodal tDCS significantly increased corticospinal excitability for 30 to 60 minutes after stimulation. There was no statistically significant difference between the 2 stimulation techniques in their effects on motor evoked potentials. No changes in measures of motor or cognitive performance were observed. Both 5-Hz rTMS and anodal tDCS induced effects on corticospinal excitability in persons with chronic stroke lasting at least 1 hour after stimulation. In the absence of concurrent motor practice, neither form of stimulation applied in a single session was associated the changes in motor performance. These approaches to increased cortical excitability may be of value as adjuncts to training.Video Abstract Available: See Video (Supplemental Digital Content 1, http://links.lww.com/JNPT/A83) for more insights from the authors.Journal of neurologic physical therapy: JNPT 11/2014; 39(1). DOI:10.1097/NPT.0000000000000064 · 2.89 Impact Factor
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ABSTRACT: Background: Little is known about the linguistic, structural and functional recovery on which the production of aphasic recurring utterances (RUs) is based. Methods & Procedures: Retrospective database analysis was performed to study the prevalence of RUs among aphasia patients. Language features and recovery were examined in patients with RUs, who were matched with aphasic controls with similar demographic and clinical characteristics. Outcomes & Results: Of the 147 aphasia patients admitted to a rehabilitation unit, between 2008 and 2012, 12.92% exhibited some form of RU. When we examined the prevalence among those with global aphasia, it increased to 24.6%. Each patient displayed the stereotypy, with some meaningful modulation or intonation with communicative intent. Although there was some recovery (particularly in comprehension), language of all patients remained severely impaired. Patients with RU scored considerably less than the control group in aphasia quotient (U = 209.00; p =.000), in naming task (U = 174.0; p =.002) and in word repetition (U = 196.0; p =.000). But there were no significant differences between the two groups on a comprehension task (t = -.75 (1,28); p =.261) and Token test scores (U = 321.1; p =.130). Conclusions: Our data support the notion that RUs do not represent an absence of language abilities. Language characteristics and recovery pattern were discussed in terms of cognitive processes and neuroplasticity. The social impact of RUs is also highlighted.Aphasiology 06/2014; 28(11):1350-1363. DOI:10.1080/02687038.2014.921884 · 1.73 Impact Factor
Brain Stimulation 01/2015; DOI:10.1016/j.brs.2015.01.402 · 5.43 Impact Factor