Studying functional brain networks with concurrent transcranical alternating current stimulation and EEG

Recently transcranial electric stimulation (tES) has been widely used as a mean to modulate brain activity. The modulatory effects of tES have been studied with the excitability of primary motor cortex. However, tES effects are not limited to the site of stimulation but extended to other brain areas, suggesting a need for the study of functional brain networks. Transcranial alternating current stimulation (tACS) applies sinusoidal current at a specified frequency, presumably modulating brain activity in a frequency-specific manner. At a behavioural level, tACS has been confirmed to modulate behaviour, but its neurophysiological effects are still elusive. In addition, neural oscillations are considered to reflect rhythmic changes in transmission efficacy across brain networks, suggesting that tACS would provide a mean to modulate brain networks. To study neurophysiological effects of tACS, we have been developing a methodological framework by combining transcranial magnetic stimulation (TMS), EEG and tACS. We have developed the optimized concurrent tACS-EEG recording protocol and powerful artefact removal method that allow us to study neurophysiological effects of tACS. We also established the concurrent tACS-TMS-EEG recording to study brain network connectivity while introducing extrinsic oscillatory activity by tACS. We show that tACS modulate brain activity in a phase-dependent manner. Our methodological advancement will open an opportunity to study causal role of oscillatory brain activity in neural transmissions in cortical brain networks.

Theta burst stimulation improves overt visual search in spatial neglect independently of attentional load

Visual neglect is considerably exacerbated by increases in visual attentional load. These detrimental effects of attentional load are hypothesised to be dependent on an interplay between dysfunctional inter-hemispheric inhibitory dynamics and load-related modulation of activity in cortical areas such as the posterior parietal cortex (PPC). Continuous Theta Burst Stimulation (cTBS) over the contralesional PPC reduces neglect severity. It is unknown, however, whether such positive effects also operate in the presence of the detrimental effects of heightened attentional load. Here, we examined the effects of cTBS on neglect severity in overt visual search (i.e., with eye movements), as a function of high and low visual attentional load conditions. Performance was assessed on the basis of target detection rates and eye movements, in a computerised visual search task and in two paper-pencil tasks. cTBS significantly ameliorated target detection performance, independently of attentional load. These ameliorative effects were significantly larger in the high than the low load condition, thereby equating target detection across both conditions. Eye movement analyses revealed that the improvements were mediated by a redeployment of visual fixations to the contralesional visual field. These findings represent a substantive advance, because cTBS led to an unprecedented amelioration of overt search efficiency that was independent of visual attentional load.

How Transcranial Direct Current Stimulation Can Modulate Implicit Motor Sequence Learning and Consolidation: A Brief Review

The purpose of this review is to investigate how transcranial direct current stimulation(tDCS)can modulate implicit motor sequence learning and consolidation. So far, most of the studies have focused on the modulating effect of tDCS for explicit motor learning. Here, we focus explicitly on implicit motor sequence learning and consolidation in order to improve our understanding about the potential of tDCS to affect this kind of unconscious learning. Specifically, we concentrate on studies with the serial reaction time task (SRTT), the classical paradigm for measuring implicit motor sequence learning. The influence of tDCS has been investigated for the primary motor cortex, the premotor cortex, the prefrontal cortex, and the cerebellum. The results indicate that tDCS above the primary motor cortex gives raise to the most consistent modulating effects for both implicit motor sequence learning and consolidation.

Structural Organization of the Corpus Callosum Predicts Attentional Shifts after Continuous Theta Burst Stimulation

Repetitive transcranial magnetic stimulation (rTMS) applied over the right posterior parietal cortex (PPC) in healthy participants has been shown to trigger a significant rightward shift in the spatial allocation of visual attention, temporarily mimicking spatial deficits observed in neglect. In contrast, rTMS applied over the left PPC triggers a weaker or null attentional shift. However, large interindividual differences in responses to rTMS have been reported. Studies measuring changes in brain activation suggest that the effects of rTMS may depend on both interhemispheric and intrahemispheric interactions between cortical loci controlling visual attention. Here, we investigated whether variability in the structural organization of human white matter pathways subserving visual attention, as assessed by diffusion magnetic resonance imaging and tractography, could explain interindividual differences in the effects of rTMS. Most participants showed a rightward shift in the allocation of spatial attention after rTMS over the right intraparietal sulcus (IPS), but the size of this effect varied largely across participants. Conversely, rTMS over the left IPS resulted in strikingly opposed individual responses, with some participants responding with rightward and some with leftward attentional shifts. We demonstrate that microstructural and macrostructural variability within the corpus callosum, consistent with differential effects on cross-hemispheric interactions, predicts both the extent and the direction of the response to rTMS. Together, our findings suggest that the corpus callosum may have a dual inhibitory and excitatory function in maintaining the interhemispheric dynamics that underlie the allocation of spatial attention. SIGNIFICANCE STATEMENT: The posterior parietal cortex (PPC) controls allocation of attention across left versus right visual fields. Damage to this area results in neglect, characterized by a lack of spatial awareness of the side of space contralateral to the brain injury. Transcranial magnetic stimulation over the PPC is used to study cognitive mechanisms of spatial attention and to examine the potential of this technique to treat neglect. However, large individual differences in behavioral responses to stimulation have been reported. We demonstrate that the variability in the structural organization of the corpus callosum accounts for these differences. Our findings suggest novel dual mechanism of the corpus callosum function in spatial attention and have broader implications for the use of stimulation in neglect rehabilitation.

Tibial Nerve Stimulation for Treating Neurogenic Lower Urinary Tract Dysfunction: A Systematic Review

CONTEXT Tibial nerve stimulation (TNS) is a promising therapy for non-neurogenic lower urinary tract dysfunction and might also be a valuable option for patients with an underlying neurological disorder. OBJECTIVE We systematically reviewed all available evidence on the efficacy and safety of TNS for treating neurogenic lower urinary tract dysfunction (NLUTD). EVIDENCE ACQUISITION The review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement. EVIDENCE SYNTHESIS After screening 1943 articles, 16 studies (4 randomized controlled trials [RCTs], 9 prospective cohort studies, 2 retrospective case series, and 1 case report) enrolling 469 patients (283 women and 186 men) were included. Five studies reported on acute TNS and 11 on chronic TNS. In acute and chronic TNS, the mean increase of maximum cystometric capacity ranged from 56 to 132mL and from 49 to 150mL, and the mean increase of bladder volume at first detrusor overactivity ranged from 44 to 92mL and from 93 to 121mL, respectively. In acute and chronic TNS, the mean decrease of maximum detrusor pressure during the storage phase ranged from 5 to 15cm H2O and from 4 to 21cm H2O, respectively. In chronic TNS, the mean decrease in number of voids per 24h, in number of leakages per 24h, and in postvoid residual ranged from 3 to 7, from 1 to 4, and from 15 to 55mL, respectively. No TNS-related adverse events have been reported. Risk of bias and confounding was high in most studies. CONCLUSIONS Although preliminary data of RCTs and non-RCTs suggest TNS might be effective and safe for treating NLUTD, the evidence base is poor, derived from small, mostly noncomparative studies with a high risk of bias and confounding. More reliable data from well-designed RCTs are needed to reach definitive conclusions. PATIENT SUMMARY Early data suggest tibial nerve stimulation might be effective and safe for treating neurogenic lower urinary tract dysfunction, but more reliable evidence is required.

Transcutaneous Electrical Nerve Stimulation for Treating Neurogenic Lower Urinary Tract Dysfunction: A Systematic Review

CONTEXT Transcutaneous electrical nerve stimulation (TENS) is a promising therapy for non-neurogenic lower urinary tract dysfunction and might also be a valuable option in patients with an underlying neurological disorder. OBJECTIVE We systematically reviewed all available evidence on the efficacy and safety of TENS for treating neurogenic lower urinary tract dysfunction. EVIDENCE ACQUISITION The review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement. EVIDENCE SYNTHESIS After screening 1943 articles, 22 studies (two randomised controlled trials, 14 prospective cohort studies, five retrospective case series, and one case report) enrolling 450 patients were included. Eleven studies reported on acute TENS and 11 on chronic TENS. In acute TENS and chronic TENS, the mean increase of maximum cystometric capacity ranged from 69ml to 163ml and from 4ml to 156ml, the mean change of bladder volume at first detrusor overactivity from a decrease of 13ml to an increase of 175ml and from an increase of 10ml to 120ml, a mean decrease of maximum detrusor pressure at first detrusor overactivity from 18 cmH20 to 72 cmH20 and 8 cmH20, and a mean decrease of maximum storage detrusor pressure from 20 cmH20 to 58 cmH2O and from 3 cmH20 to 8 cmH2O, respectively. In chronic TENS, a mean decrease in the number of voids and leakages per 24h ranged from 1 to 3 and from 0 to 4, a mean increase of maximum flow rate from 2ml/s to 7ml/s, and a mean change of postvoid residual from an increase of 26ml to a decrease of 85ml. No TENS-related serious adverse events have been reported. Risk of bias and confounding was high in most studies. CONCLUSIONS Although preliminary data suggest TENS might be effective and safe for treating neurogenic lower urinary tract dysfunction, the evidence base is poor and more reliable data from well-designed randomised controlled trials are needed to make definitive conclusions. PATIENT SUMMARY Early data suggest that transcutaneous electrical nerve stimulation might be effective and safe for treating neurogenic lower urinary tract dysfunction, but more reliable evidence is required.

Bilateral deep brain stimulation: the placement of the second electrode is not necessarily less accurate than that of the first one.

BACKGROUND Deep brain stimulation (DBS) is recognized as an effective treatment for movement disorders. We recently changed our technique, limiting the number of brain penetrations to three per side. OBJECTIVES The first aim was to evaluate the electrode precision on both sides of surgery since we implemented this surgical technique. The second aim was to analyse whether or not the electrode placement was improved with microrecording and macrostimulation. METHODS We retrospectively reviewed operation protocols and MRIs of 30 patients who underwent bilateral DBS. For microrecording and macrostimulation, we used three parallel channels of the 'Ben Gun' centred on the MRI-planned target. Pre- and post-operative MRIs were merged. The distance between the planned target and the centre of the implanted electrode artefact was measured. RESULTS There was no significant difference in targeting precision on both sides of surgery. There was more intra-operative adjustment of the second electrode positioning based on microrecording and macrostimulation, which allowed to significantly approach the MRI-planned target on the medial-lateral axis. CONCLUSION There was more electrode adjustment needed on the second side, possibly in relation with brain shift. We thus suggest performing a single central track with electrophysiological and clinical assessment, with multidirectional exploration on demand for suboptimal clinical responses.

Effects of subthalamic nucleus stimulation on cognition and mood in Parkinson’s disease (PD)

Objective: To assess the neuropsychological outcome as a safety measure and quality control in patients with subthalamic nucleus (STN) stimulation for PD. Background: Deep brain stimulation (DBS) is considered a relatively safe treatment used in patients with movement disorders. However, neuropsychological alterations have been reported in patients with STN DBS for PD. Cognition and mood are important determinants of quality of life in PD patients and must be assessed for safety control. Methods: Seventeen consecutive patients (8 women) who underwent STN DBS for PD have been assessed before and 4 months after surgery. Besides motor symptoms (UPDRS-III), mood (Beck Depression Inventory, Hamilton Depression Rating Scale) and neuropsychological aspects, mainly executive functions, have been assessed (mini mental state examination, semantic and phonematic verbal fluency, go-no go test, stroop test, trail making test, tests of alertness and attention, digit span, wordlist learning, praxia, Boston naming test, figure drawing, visual perception). Paired t-tests were used for comparisons before and after surgery. Results: Patients were 61.6±7.8 years old at baseline assessment. All surgeries were performed without major adverse events. Motor symptoms ‘‘on’’ medication remained stable whereas they improved in the ‘‘off’’ condition (p<0.001). Mood was not depressed before surgery and remained unchanged at follow-up. All neuropsychological assessment outcome measures remained stable at follow-up with the exception of semantic verbal fluency and wordlist learning. Semantic verbal fluency decreased by 21±16% (p<0.001) and there was a trend to worse phonematic verbal fluency after surgery (p=0.06). Recall of a list of 10 words was worse after surgery only for the third attempt of recall (13%, p<0.005). Conclusions: Verbal fluency decreased in our patients after STN DBS, as previously reported. The procedure was otherwise safe and did not lead to deterioration of mood.

Transcranial magnetic stimulation (TMS) inhibits cortical dendrites

One of the leading approaches to non-invasively treat a variety of brain disorders is transcranial magnetic stimulation (TMS). However, despite its clinical prevalence, very little is known about the action of TMS at the cellular level let alone what effect it might have at the subcellular level (e.g. dendrites). Here, we examine the effect of single-pulse TMS on dendritic activity in layer 5 pyramidal neurons of the somatosensory cortex using an optical fiber imaging approach. We find that TMS causes GABAB-mediated inhibition of sensory-evoked dendritic Ca(2+) activity. We conclude that TMS directly activates fibers within the upper cortical layers that leads to the activation of dendrite-targeting inhibitory neurons which in turn suppress dendritic Ca(2+) activity. This result implies a specificity of TMS at the dendritic level that could in principle be exploited for investigating these structures non-invasively.

AN ASCENDING SEROTONERGIC PAIN MODULATION SYSTEM

This dissertation describes an ascending serotonergic pain modulation system projecting from the dorsal raphe (DR) nucleus of the midbrain to the parafascicularis (PF) nucleus of the thalamus. Previous studies by other investigators have led to the hypothesis that the DR would modulate responses to noxious stimuli in the PF by using 5HT. These other studies have shown that the DR contains serotonergic (5HT) cell bodies which project to many areas of the forebrain including the PF, that the PF is involved in pain perception, that electrical stimulation of the DR causes analgesia, and 5HT is necessary for this type of analgesia. One theory of the mechanisms of an endogenous pain modulation system is that brainstem nuclei have a decsending projection to the spinal cord to inhibit responses to noxious input at this level. The present study tests the hypothesis that there is also an ascending pain modulation pathway from the brainstem to the thalamus.^ To test this hypothesis, several types of experiments were performed on anesthetised rats. The major results of the experiments are as follows: (1) Three types of spontaneously active PF neurons were found: slow units firing at 1-10 spikes/sec, bursting units firing 2-5 times in 10-20 msec, pattern repeating every 1-2 sec, and fast units firing at 15-40 spikes/sec. The first two groups showed similar results to the treatments and were analysed together. The fast firing units did not respond to any of the treatments. (2) Noxious stimuli primarily increased neuronal firing rates in the PF, where as DR stimulation primarily decreased neuronal activity. DR stimulation applied simultaneously with noxious stimuli decreased the responses to the noxious stimuli as recorded in the PF units. (3) Microiontophoretically applied 5HT in the PF decreased spontaneous activity in the PF in a dose dependent manner and decreases responses to noxious stimuli in the PF. (4) Reduction of brain 5HT by 5,7 dihydroxytryptamine, a potent 5HT neurotoxin, caused PF units to be hypersensitive to both noxious and non noxious stimuli, reversed the effects of DR stimulation so that DR stimulation increased single units activity in the PF, and prolonged and intensified the depressant action of microiontophoretically applied 5HT. The results of this study are consistent with the hypothesis that the DR uses 5HT in a direct ascending pathway to the PF to modulate pain in the thalamus. ^

STIMULATION THROUGH TLR4 INCREASES FVIII INHIBITOR FORMATION IN A MOUSE MODEL OF HEMOPHILIA A

Hemophilia A is a clotting disorder caused by functional factor VIII (FVIII) deficiency. About 25% of patients treated with therapeutic recombinant FVIII develop antibodies (inhibitors) that render subsequent FVIII treatments ineffective. The immune mechanisms of inhibitor formation are not entirely understood, but circumstantial evidence indicates a role for increased inflammatory response, possibly via stimulation of Toll-like receptors (TLRs), at the time of FVIII immunization. I hypothesized that stimulation through TLR4 in conjunction with FVIII treatments would increase the formation of FVIII inhibitors. To test this hypothesis, FVIII K.O. mice were injected with recombinant human FVIII with or without concomitant doses of TLR4 agonist (lipopoysaccharide; LPS). The addition of LPS combined with FVIII significantly increased the rate and the production of anti-FVIII IgG antibodies and neutralizing FVIII inhibitors. In the spleen, repeated in vivo TLR4 stimulation with LPS increased the relative percentage of macrophages and dendritic cells (DCs) over the course of 4 injections. However, repeated in vivo FVIII stimulation significantly increased the density of TLR4 expressed on the surface of all spleen antigen presenting cells (APCs). Culture of splenocytes isolated from mice revealed that the combined stimulation of LPS and FVIII also synergistically increased early secretion of the inflammatory cytokines IL-6, TNF-α, and IL-10, which was not maintained throughout the course of the repeated injections. While cytokine secretion was relatively unchanged in response to FVIII re-stimulation in culture, LPS re-stimulation in culture induced increased and prolonged inflammatory cytokine secretion. Re-stimulation with both LPS and FVIII induced cytokine secretion similar to LPS stimulation alone. Interestingly, long term treatment of mice with LPS alone resulted in splenocytes that showed reduced response to FVIII in culture. Together these results indicated that creating a pro-inflammatory environment through the combined stimulation of chronic, low-dose LPS and FVIII changed not only the populations but also the repertoire of APCs in the spleen, triggering the increased production of FVIII inhibitors. These results suggested an anti-inflammatory regimen should be instituted for all hemophilia A patients to reduce or delay the formation of FVIII inhibitors during replacement therapy.

Mechanism of molecular regulation of nuclear -encoded mitochondrial gene expression by electrical stimulation in the cultured neonatal rat cardiac myocytes

To answer the question whether increased energy demand resulting from myocyte hypertrophy and enhanced $\beta$-myosin heavy chain mRNA, contractile protein synthesis and assembly leads to mitochondrial proliferation and differentiation, we set up an electrical stimulation model of cultured neonatal rat cardiac myocytes. We describe, as a result of increased contractile activity, increased mitochondrial profiles, cytochrome oxidase mRNA, and activity, as well as a switch in mitochondrial carnitine palmitoyltransferase-I (CPT-I) from the liver to muscle isoform. We investigate physiological pathways that lead to accumulation of gene transcripts for nuclear encoded mitochondrial proteins in the heart. Cardiomyocytes were stimulated for varying times up to 72 hr in serum-free culture. The mRNA contents for genes associated with transcriptional activation (c-fos, c-jun, junB, nuclear respiratory factor 1 (Nrf-1)), mitochondrial proliferation (cytochrome c (Cyt c), cytochrome oxidase), and mitochondrial differentiation (carnitine palmitonyltransferase I (CPT-I) isoforms) were measured. The results establish a temporal pattern of mRNA induction beginning with c-fos (0.25-3 hr) and followed by c-jun (0.5-3 hr), junB (0.5-6 hr), NRF-1 (1-12 hr), Cyt c (12-72 hr), cytochrome c oxidase (12-72 hr). Induction of the latter was accompanied by a marked decrease in the liver-specific CPT-I mRNA. Electrical stimulation increased c-fos, $\beta$-myosin heavy chain, and Cyt c promoter activities. These increases coincided with a rise in their respective endogenous gene transcripts. NRF-1, cAMP response element (CRE), and Sp-1 site mutations within the Cyt c promoter reduced luciferase expression in both stimulated and nonstimulated myocytes. Mutations in the Nrf-1 and CRE sites inhibited the induction by electrical stimulation or by transfection of c-jun into non-paced cardiac myocytes whereas mutation of the Sp-1 site maintained or increased the fold induction. This is consistent with the appearance of NRF-1 and fos/jun mRNAs prior to that of Cyt c. Overexpression of c-jun by transfection also activates the Nrf-1 and Cyt c mRNA sequentially. Electrical stimulation of cardiac myocytes activates the c-Jun-N-terminal kinase so that the fold-activation of the cyt c promoter is increased by pacing when either c-jun or c-fos/c-jun are cotransfected. We have identified physical association of Nrf-1 protein with the Nrf-1 enhancer element and of c-Jun with the CRE binding sites on the Cyt c promoter. This is the first demonstration that induction of Nrf-1 and c-Jun by pacing of cardiac myocytes directly mediates Cyt c gene expression and mitochondrial proliferation in response to hypertrophic stimuli in the heart.^ Subsequent to gene activation pathways that lead to mitochondrial proliferation, we observed an isoform switch in CPT-I from the liver to muscle mRNA. We have found that the half-life for the muscle CPT-I is not affected by electrical stimulation, but electrical decrease the T1/2 in the liver CPT-I by greater than 50%. This suggests that the liver CPT-I switch to muscle isoform is due to (1) a decrease in T1/2 of liver CPT-I and (2) activation of muscle CPT-Itranscripts by electrical stimulation. (Abstract shortened by UMI.) ^