Effects of scanner acoustic noise on intrinsic brain activity during auditory stimulation.

INTRODUCTION: Although the effects of scanner background noise (SBN) during functional magnetic resonance imaging (fMRI) have been extensively investigated for the brain regions involved in auditory processing, its impact on other types of intrinsic brain activity has largely been neglected. The present study evaluated the influence of SBN on a number of intrinsic connectivity networks (ICNs) during auditory stimulation by comparing the results obtained using sparse temporal acquisition (STA) with those using continuous acquisition (CA). METHODS: Fourteen healthy subjects were presented with classical music pieces in a block paradigm during two sessions of STA and CA. A volume-matched CA dataset (CAm) was generated by subsampling the CA dataset to temporally match it with the STA data. Independent component analysis was performed on the concatenated STA-CAm datasets, and voxel data, time courses, power spectra, and functional connectivity were compared. RESULTS: The ICA revealed 19 ICNs; the auditory, default mode, salience, and frontoparietal networks showed greater activity in the STA. The spectral peaks in 17 networks corresponded to the stimulation cycles in the STA, while only five networks displayed this correspondence in the CA. The dorsal default mode and salience networks exhibited stronger correlations with the stimulus waveform in the STA. CONCLUSIONS: SBN appeared to influence not only the areas of auditory response but also the majority of other ICNs, including attention and sensory networks. Therefore, SBN should be regarded as a serious nuisance factor during fMRI studies investigating intrinsic brain activity under external stimulation or task loads.

Transcranial direct current stimulation of the left prefrontal cortex improves attention in patients with traumatic brain injury: a pilot study.

OBJECTIVE: To determine whether a single session of anodal transcranial direct current stimulation to the left dorsolateral prefrontal cortex improves attention in patients with traumatic brain injury. DESIGN: Double-blinded, cross-over design. PATIENTS: Nine patients with attention deficit after traumatic brain injury. METHODS: Patients underwent a computerized contrast reaction time task before and after the administration of real transcranial direct current stimulation (2 mA for 20 min) or sham transcranial direct current stimulation (2 mA for 1 min) to the left dorsolateral prefrontal cortex in a double-blind, crossover manner. RESULTS: Immediately post-stimulation, the transcranial direct current stimulation group showed a tendency of shortened reaction time relative to baseline (87.3 ± 7.8%), whereas the sham stimulation group (122.4 ± 715.5%) did not (p = 0.056). However, this difference was not significant 3 or 24 h after stimulation (p > 0.05). The numbers of correct responses were not changed at any time after stimulation. CONCLUSION: Anodal transcranial direct current stimulation applied to the left dorsolateral prefrontal cortex improves attention compared with sham stimulation in patients with traumatic brain injury, which suggests a potential role for this intervention in improving attention during cognitive training after traumatic brain injury. A further prospective randomized trial is required to confirm the benefits conferred by transcranial direct current stimulation in this patient population.

Effect of transcranial direct current stimulation on motor recovery in patients with subacute stroke.

OBJECTIVE: To test the hypothesis that 10 sessions of transcranial direct current stimulation combined with occupational therapy elicit more improvement in motor function of the paretic upper limb than sham stimulation in patients with subacute stroke. DESIGN: Eighteen patients with subacute stroke with hand motor impairment were randomly assigned to one of the three 10-day sessions of (a) anodal transcranial direct current stimulation over the affected motor cortex, (b) cathodal transcranial direct current stimulation over the unaffected motor cortex, or (c) sham stimulation. Blinded evaluators assessed upper limb motor impairment and global functional state with the Fugl-Meyer Assessment score and the Modified Barthel Index at baseline, 1 day after stimulation, and 6 mos after stimulation. RESULTS: Baseline scores for Fugl-Meyer Assessment and Modified Barthel Index were comparable in all groups (P > 0.05). At 6-mo follow-up, cathodal transcranial direct current stimulation led to a greater improvement in Fugl-Meyer Assessment than the sham procedure (P < 0.05). There was a significant inverse correlation between baseline Fugl-Meyer Assessment and Fugl-Meyer Assessment increase at 6 mos (r = -0.846; P < 0.01). CONCLUSIONS: Our results suggest a potentially beneficial effect of noninvasive cortical stimulation during rehabilitative motor training of patients who have suffered from subacute strokes.

Non-invasive cortical stimulation improves post-stroke attention decline.

PURPOSE: Attention decline after stroke is common and hampers the rehabilitation process, and non-invasive transcranial direct current stimulation (tDCS) has the potential to elicit behavioral changes by modulating cortical excitability. The authors tested the hypothesis that a single session of non-invasive cortical stimulation with excitatory anodal tDCS applied to the left dorsolateral prefrontal cortex (DLPFC) can improve attention in stroke patients. METHODS: Ten patients with post-stroke cognitive decline (MMSE 25) and 10 age-matched healthy controls participated in this double blind, sham-controlled, crossover study involving the administration of real (2 mA for 20 min) or sham stimulation (2 mA for 1 min) to the left DLPFC. Attention was measured using a computerized Go/No-Go test before and after intervention. Improvements in accuracy and speed after stimulation relative to baseline were compared for real and sham stimulations. RESULTS: In healthy controls, no significant improvement in Go/No-Go test was observed after either real or sham stimulation. However, in stroke patients, tDCS led to a significant improvement in response accuracy at 1 hour post-stimulation relative to baseline, and this improvement was maintained until 3 hours post-stimulation (P< 0.05), whereas sham stimulation did not lead to a significant improvement in response accuracy (P> 0.05). Changes in reaction times were comparable for the two stimulations (P> 0.05). CONCLUSION: Non invasive anodal tDCS applied to the left DLPFC was found to improve attention versus sham stimulation in stroke patients, which suggests that non-invasive cortical intervention could potentially be used during rehabilitative training to improve attention.