M. Vergari

Improved naming after transcranial direct current stimulation in aphasia

Transcranial direct current stimulation (tDCS) has been proposed as an adjuvant technique to improve functional recovery after ischaemic stroke. This study evaluated the effect of tDCS over the left frontotemporal areas in eight chronic non-fluent post-stroke aphasic patients. The protocol consisted of the assessment of picture naming (accuracy and response time) before and immediately after anodal or cathodal tDCS (2 mA, 10 minutes) and sham stimulation. Whereas anodal tDCS and sham tDCS failed to induce any changes, cathodal tDCS significantly improved the accuracy of the picture naming task by a mean of 33.6% (SEM 13.8%).

Transcranial direct current stimulation improves recognition memory in Alzheimer disease

Objective: To evaluate the cognitive effect of transcranial direct current stimulation (tDCS) over the temporoparietal areas in patients with Alzheimer disease (AD). Methods: In 10 patients with probable AD, we delivered anodal tDCS (AtDCS), cathodal tDCS (CtDCS), and sham tDCS (StDCS) over the temporoparietal areas in three sessions. In each session recognition memory and visual attention were tested at baseline (prestimulation) and 30 minutes after tDCS ended (poststimulation). Results: After AtDCS, accuracy of the word recognition memory task increased (prestimulation: 15.5 ± 0.9, poststimulation: 17.9 ± 0.8, p = 0.0068) whereas after CtDCS it decreased (15.8 ± 0.6 vs 13.2 ± 0.9, p = 0.011) and after StDCS it remained unchanged (16.3 ± 0.7 vs 16.0 ± 1.0, p = 0.75). tDCS left the visual attention-reaction times unchanged. Conclusion: Transcranial direct current stimulation (tDCS) delivered over the temporoparietal areas can specifically affect a recognition memory performance in patients with Alzheimer disease (AD). Because tDCS is simple, safe and inexpensive, our finding prompts studies using repeated tDCS, in conjunction with other therapeutic interventions for treating patients with AD.

Cerebellar transcranial direct current stimulation impairs the practice-dependent proficiency increase in working memory

How the cerebellum is involved in the practice and proficiency of non-motor functions is still unclear. We tested whether transcranial direct current stimulation (tDCS) over the cerebellum (cerebellar tDCS) induces after-effects on the practice-dependent increase in the proficiency of a working memory (WM) task (Sternberg test) in 13 healthy subjects. We also assessed the effects of cerebellar tDCS on visual evoked potentials (VEPs) in four subjects and compared the effects of cerebellar tDCS on the Sternberg test with those elicited by tDCS delivered over the prefrontal cortex in five subjects. Our experiments showed that anodal or cathodal tDCS over the cerebellum impaired the practice-dependent improvement in the reaction times in a WM task. Because tDCS delivered over the prefrontal cortex induced an immediate change in the WM task but left the practice-dependent proficiency unchanged, the effects of cerebellar tDCS are structure-specific. Cerebellar tDCS left VEPs unaffected, its effect on the Sternberg task therefore seems unlikely to arise from visual system involvement. In conclusion, tDCS over the cerebellum specifically impairs the practice-dependent proficiency increase in verbal WM.

Prolonged visual memory enhancement after direct current stimulation in Alzheimer's disease

BACKGROUND Immediately after patients with Alzheimers disease (AD) receive a single anodal transcranial direct current stimulation (tDCS) session their memory performance improves. Whether multiple tDCS sessions improve memory performance in the longer term remains unclear. OBJECTIVE In this study we aimed to assess memory changes after five consecutive sessions of anodal tDCS applied over the temporal cortex in patients with AD. METHODS A total of 15 patients were enrolled in two centers. Cognitive functions were evaluated before and after therapeutic tDCS. tDCS was delivered bilaterally through two scalp anodal electrodes placed over the temporal regions and a reference electrode over the right deltoid muscle. The stimulating current was set at 2 mA intensity and was delivered for 30 minutes per day for 5 consecutive days. RESULTS After patients received tDCS, their performance in a visual recognition memory test significantly improved. We found a main effect of tDCS on memory performance, i.e., anodal stimulation improved it by 8.99% from baseline, whereas sham stimulation decreased it by 2.62%. tDCS failed to influence differentially general cognitive performance measures or a visual attention measure. CONCLUSIONS Our findings show that after patients with AD receive anodal tDCS over the temporal cerebral cortex in five consecutive daily sessions their visual recognition memory improves and the improvement persists for at least 4 weeks after therapy. These encouraging results provide additional support for continuing to investigate anodal tDCS as an adjuvant treatment for patients with AD.

Transcranial direct current stimulation (tDCS) in unipolar vs. bipolar depressive disorder

Transcranial direct current stimulation (tDCS) is a non-invasive method for brain stimulation. Although pilot trials have shown that tDCS yields promising results for major depressive disorder (MDD), its efficacy for bipolar depressive disorder (BDD), a condition with high prevalence and poor treatment outcomes, is unknown. In a previous study we explored the effectiveness of tDCS for MDD. Here, we expanded our research, recruiting patients with MDD and BDD. We enrolled 31 hospitalized patients (24 women) aged 30-70 years 17 with MDD and 14 with BDD (n = 14). All patients received stable drug regimens for at least two weeks before enrollment and drug dosages remained unchanged throughout the study. We applied tDCS over the dorsolateral prefrontal cortex (anodal electrode on the left and cathodal on the right) using a 2 mA-current for 20 min, twice-daily, for 5 consecutive days. Depression was measured at baseline, after 5 tDCS sessions, one week later, and one month after treatment onset. We used the scales of Beck (BDI) and Hamilton-21 items (HDRS). All patients tolerated treatment well without adverse effects. After the fifth tDCS session, depressive symptoms in both study groups diminished, and the beneficial effect persisted at one week and one month. In conclusion, our preliminary study suggests that tDCS is a promising treatment for patients with MDD and BDD.2.

Effect of spinal transcutaneous direct current stimulation on somatosensory evoked potentials in humans

OBJECTIVE Invasive stimulation of the spinal cord is used to treat a number of pathological conditions. Aiming to modulate human spinal cord function non-invasively, we evaluated whether transcutaneous direct current (DC) stimulation induces long-lasting changes in conduction along the sensory spinal pathways. METHODS Somatosensory evoked potentials (SEPs) by posterior tibial nerve and by median nerve stimulation were recorded, before, at current offset and at 20 min after transcutaneous anodal or cathodal DC stimulation over the thoracic spinal cord (2.5 mA, 15 min) in a group of 12 healthy subjects. RESULTS Whereas both polarities left the spinal (N22) and the cortical potentials (P39) unchanged, anodal transcutaneous spinal DC stimulation decreased significantly by about 25% the amplitude of the cervico-medullary component of posterior tibial nerve SEPs (P30) for at least 20 min. Thoracic transcutaneous spinal cord stimulation left median nerve SEPs unchanged. CONCLUSIONS Transcutaneous DC stimulation over the thoracic spinal cord induces changes in conduction along human lemniscal pathway that persist after stimulation ends. SIGNIFICANCE Our results support the use of transcutaneous DC stimulation as a novel tool for non-invasive spinal neuromodulation. Because the method is non-expensive and simple, it can be tested in patients with disorders presently treated with invasive procedures.

Brain Switches Utilitarian Behavior: Does Gender Make the Difference?

Decision often implies a utilitarian choice based on personal gain, even at the expense of damaging others. Despite the social implications of utilitarian behavior, its neurophysiological bases remain largely unknown. To assess how the human brain controls utilitarian behavior, we delivered transcranial direct current stimulation (tDCS) over the ventral prefrontal cortex (VPC) and over the occipital cortex (OC) in 78 healthy subjects. Utilitarian judgment was assessed with the moral judgment task before and after tDCS. At baseline, females provided fewer utilitarian answers than males for personal moral dilemmas (p = .007). In males, VPC-tDCS failed to induce changes and in both genders OC-tDCS left utilitarian judgments unchanged. In females, cathodal VPC-tDCS tended to decrease whereas anodal VPC-tDCS significantly increased utilitarian responses (p = .005). In males and females, reaction times for utilitarian responses significantly decreased after cathodal (p<.001) but not after anodal (p = .735) VPC-tDCS. We conclude that ventral prefrontal tDCS interferes with utilitarian decisions, influencing the evaluation of the advantages and disadvantages of each option in both sexes, but does so more strongly in females. Whereas cathodal tDCS alters the time for utilitarian reasoning in both sexes, anodal stimulation interferes more incisively in women, modifying utilitarian reasoning and the possible consequent actions. The gender-related tDCS-induced changes suggest that the VPC differentially controls utilitarian reasoning in females and in males. The gender-specific functional organization of the brain areas involved in utilitarian behavior could be a correlate of the moral and social behavioral differences between the two sexes.

Transcutaneous spinal cord direct current stimulation inhibits the lower limb nociceptive flexion reflex in human beings

&NA; Aiming at developing a new, noninvasive approach to spinal cord neuromodulation, we evaluated whether transcutaneous direct current (DC) stimulation induces long‐lasting changes in the central pain pathways in human beings. A double‐blind crossover design was used to investigate the effects of anodal direct current (2 mA, 15 min) applied on the skin overlying the thoracic spinal cord on the lower‐limb flexion reflex in a group of 11 healthy volunteers. To investigate whether transcutaneous spinal cord DC stimulation (tsDCS) acts indirectly on the nociceptive reflex by modulating excitability in mono‐oligosynaptic segmental reflex pathways, we also evaluated the H‐reflex size from soleus muscle after tibial nerve stimulation. In our healthy subjects, anodal thoracic tsDCS reduced the total lower‐limb flexion reflex area by 40.25% immediately after stimulation (T0) and by 46.9% 30 min after stimulation offset (T30). When we analyzed the 2 lower‐limb flexion reflex components (RII tactile and RIII nociceptive) separately, we found that anodal tsDCS induced a significant reduction in RIII area with a slight but not significant effect on RII area. After anodal tsDCS, the RIII area decreased by 27% at T0 and by 28% at T30. Both sham and active tsDCS left all the tested H‐reflex variables unchanged. None of our subjects reported adverse effects after active stimulation. These results suggest that tsDCS holds promise as a tool that is complementary or alternative to drugs and invasive spinal cord electrical stimulation for managing pain. Thoracic transcutaneous direct current stimulation induces depression of nociceptive lower limb flexion reflex in human beings that persists after stimulation offset; this form of stimulation holds promise as a tool that is complementary or alternative to drugs and invasive spinal cord electrical stimulation for managing pain.

Transcranial cerebellar direct current stimulation and transcutaneous spinal cord direct current stimulation as innovative tools for neuroscientists

Two neuromodulatory techniques based on applying direct current (DC) non‐invasively through the skin, transcranial cerebellar direct current stimulation (tDCS) and transcutaneous spinal DCS, can induce prolonged functional changes consistent with a direct influence on the human cerebellum and spinal cord. In this article we review the major experimental works on cerebellar tDCS and on spinal tDCS, and their preliminary clinical applications. Cerebellar tDCS modulates cerebellar motor cortical inhibition, gait adaptation, motor behaviour, and cognition (learning, language, memory, attention). Spinal tDCS influences the ascending and descending spinal pathways, and spinal reflex excitability. In the anaesthetised mouse, DC stimulation applied under the skin along the entire spinal cord may affect GABAergic and glutamatergic systems. Preliminary clinical studies in patients with cerebellar disorders, and in animals and patients with spinal cord injuries, have reported beneficial effects. Overall the available data show that cerebellar tDCS and spinal tDCS are two novel approaches for inducing prolonged functional changes and neuroplasticity in the human cerebellum and spinal cord, and both are new tools for experimental and clinical neuroscientists.

Dorsolateral prefrontal cortex specifically processes general - but not personal - knowledge deception: Multiple brain networks for lying.

Despite intensive research into ways of detecting deception in legal, moral and clinical contexts, few experimental data are available on the neural substrate for the different types of lies. We used transcranial direct current stimulation (tDCS) to modulate dorsolateral prefrontal cortex (DLPFC) function and to assess its influence on various types of lies. Twenty healthy volunteers were tested before and after tDCS (anodal and sham). In each session the Guilty Knowledge Task and Visual Attention Task were administered at baseline and immediately after tDCS ended. A computer-controlled task was used to evaluate truthful responses and lie responses to questions referring to personal information and general knowledge. Dependent variables collected were reaction times (RTs) and accuracy. At baseline the RTs were significantly longer for lies than for truthful responses. After sham stimulation, lie responses remained unchanged (p = 0.24) but after anodal tDCS, RTs decreased significantly only for lies involving general knowledge (p = 0.02). tDCS left the Visual Attention Task unaffected. These findings show that manipulating DLPFC function with tDCS specifically modulates deceptive responses for general information leaving those on personal information unaffected. Multiple cortical networks intervene in deception involving general and personal knowledge. Deception referring to general and personal knowledge probably involves multiple cortical networks.