Transcranial Direct Current Stimulation Effects in Disorders of Consciousness

TDCS modulates cortical excitability in patients with disorders of consciousness

Transcranial direct current stimulation (tDCS)1 has been reported to be a promising technique for consciousness improvement for patients with disorders of consciousness (DOC).2 However, there has been no direct electrophysiological evidence to demonstrate the efficacy of tDCS on patients with DOC. Therefore, we aim to measure the cortical excitability changes induced by tDCS in patients with DOC, to find electrophysiological evidence supporting the therapeutic efficacy of tDCS on patients with DOC. In this study, we enrolled sixteen patients with DOC, including nine vegetative state (VS)3 and seven minimally conscious state (MCS)4 (six females and ten males). TMS-EEG was applied to assess cortical excitability changes after twenty minutes of anodal tDCS of the left dorsolateral prefrontal cortex. Global cerebral excitability were calculated to quantify cortical excitability in the temporal domain: four time intervals (0–100, 100–200, 200–300, 300-400 ms). Then local cerebral excitability in the significantly altered time windows were investigated (frontal, left/right hemispheres, central, and posterior). Compared to baseline and sham stimulation, we found that global cerebral excitability increased in early time windows (0–100 and 100-200 ms) for patients with MCS; for the patients with VS, global cerebral excitability increased in the 0-100 ms interval but decreased in the 300-400 ms interval. The local cerebral excitability was significantly different between MCS and VS. The results indicated that tDCS can effectively modulate the cortical excitability of patients with DOC; and the changes in excitability in temporal and spatial domains are different between patients with MCS and those with VS.

•

TDCS was used to alter cerebral excitability in patients of DOC.

•

TMS-EEG was used to evaluate cortical excitability changes in patients of DOC.

•

TDCS could induce significant cortical excitability changes in patients of DOC.

•

TDCS induced different temporal-spatial excitability changes between MCS and VS.

Functional Connectivity Substrates for tDCS Response in Minimally Conscious State Patients

Transcranial direct current stimulation (tDCS) is a non-invasive technique recently employed in disorders of consciousness, and determining a transitory recovery of signs of consciousness in almost half of minimally conscious state (MCS) patients. Although the rising evidences about its possible role in the treatment of many neurological and psychiatric conditions exist, no evidences exist about brain functional connectivity substrates underlying tDCS response. We retrospectively evaluated resting state functional Magnetic Resonance Imaging (fMRI) of 16 sub-acute and chronic MCS patients (6 tDCS responders) who successively received a single left dorsolateral prefrontal cortex (DLPFC) tDCS in a double-blind randomized cross-over trial. A seed-based approach for regions of left extrinsic control network (ECN) and default-mode network (DMN) was performed. tDCS responders showed an increased left intra-network connectivity for regions co-activated with left DLPFC, and significantly with left inferior frontal gyrus. Non-responders (NR) MCS patients showed an increased connectivity between left DLPFC and midline cortical structures, including anterior cingulate cortex and precuneus. Our findings suggest that a prior high connectivity with regions belonging to ECN can facilitate transitory recovery of consciousness in a subgroup of MCS patients that underwent tDCS treatment. Therefore, resting state-fMRI could be very valuable in detecting the neuronal conditions necessary for tDCS to improve behavior in MCS.

Evidence-based guidelines on the therapeutic use of transcranial direct current stimulation (tDCS)

A group of European experts was commissioned by the European Chapter of the International Federation of Clinical Neurophysiology to gather knowledge about the state of the art of the therapeutic use of transcranial direct current stimulation (tDCS) from studies published up until September 2016, regarding pain, Parkinson's disease, other movement disorders, motor stroke, poststroke aphasia, multiple sclerosis, epilepsy, consciousness disorders, Alzheimer's disease, tinnitus, depression, schizophrenia, and craving/addiction. The evidence-based analysis included only studies based on repeated tDCS sessions with sham tDCS control procedure; 25 patients or more having received active treatment was required for Class I, while a lower number of 10-24 patients was accepted for Class II studies. Current evidence does not allow making any recommendation of Level A (definite efficacy) for any indication. Level B recommendation (probable efficacy) is proposed for: (i) anodal tDCS of the left primary motor cortex (M1) (with right orbitofrontal cathode) in fibromyalgia; (ii) anodal tDCS of the left dorsolateral prefrontal cortex (DLPFC) (with right orbitofrontal cathode) in major depressive episode without drug resistance; (iii) anodal tDCS of the right DLPFC (with left DLPFC cathode) in addiction/craving. Level C recommendation (possible efficacy) is proposed for anodal tDCS of the left M1 (or contralateral to pain side, with right orbitofrontal cathode) in chronic lower limb neuropathic pain secondary to spinal cord lesion. Conversely, Level B recommendation (probable inefficacy) is conferred on the absence of clinical effects of: (i) anodal tDCS of the left temporal cortex (with right orbitofrontal cathode) in tinnitus; (ii) anodal tDCS of the left DLPFC (with right orbitofrontal cathode) in drug-resistant major depressive episode. It remains to be clarified whether the probable or possible therapeutic effects of tDCS are clinically meaningful and how to optimally perform tDCS in a therapeutic setting. In addition, the easy management and low cost of tDCS devices allow at home use by the patient, but this might raise ethical and legal concerns with regard to potential misuse or overuse. We must be careful to avoid inappropriate applications of this technique by ensuring rigorous training of the professionals and education of the patients.

Assistive technology to help persons in a minimally conscious state develop responding and stimulation control: Performance assessment and social rating

BACKGROUND

Post-coma persons in a minimally conscious state (MCS) and with extensive motor impairment and lack of speech tend to be passive and isolated.

OBJECTIVE

This study aimed to (a) further assess a technology-aided approach for fostering MCS participants' responding and stimulation control and (b) carry out a social validation check about the approach.

METHODS

Eight MCS participants were exposed to the aforementioned approach according to an ABAB design. The technology included optic, pressure or touch microswitches to monitor eyelid, hand or finger responses and a computer system that allowed those responses to produce brief periods of positive stimulation during the B (intervention) phases of the study. Eighty-four university psychology students and 42 care and health professionals were involved in the social validation check.

RESULTS

The MCS participants showed clear increases in their response frequencies, thus producing increases in their levels of environmental stimulation input, during the B phases of the study. The students and care and health professionals involved in the social validation check rated the technology-aided approach more positively than a control condition in which stimulation was automatically presented to the participants.

CONCLUSIONS

A technology-aided approach to foster responding and stimulation control in MCS persons may be effective and socially desirable.

A Narrative Review of Pharmacologic and Non-pharmacologic Interventions for Disorders of Consciousness Following Brain Injury in the Pediatric Population

Traumatic brain injury (TBI) is the most common cause of long-term disability in the United States. A significant proportion of children who experience a TBI will have moderate or severe injuries, which includes a period of decreased responsiveness. Both pharmacological and non-pharmacological modalities are used for treating disorders of consciousness after TBI in children. However, the evidence supporting the use of potential therapies is relatively scant, even in adults, and overall, there is a paucity of study in pediatrics. The goal of this review is to describe the state of the science for use of pharmacologic and non-pharmacologic interventions for disorders of consciousness in the pediatric population.

The Role of Neuroimaging Techniques in Establishing Diagnosis, Prognosis and Therapy in Disorders of Consciousness

Non-communicative brain damaged patients raise important clinical and scientific issues. Here, we review three major pathological disorders of consciousness: coma, the unresponsive wakefulness syndrome and the minimally conscious state. A number of clinical studies highlight the difficulty in making a correct diagnosis in patients with disorders of consciousness based only on behavioral examinations. The increasing use of neuroimaging techniques allows improving clinical characterization of these patients. Recent neuroimaging studies using positron emission tomography, functional magnetic resonance imaging, electroencephalography and transcranial magnetic stimulation can help assess diagnosis, prognosis, and therapeutic treatment. These techniques, using resting state, passive and active paradigms, also highlight possible dissociations between consciousness and responsiveness, and are facilitating a more accurate understanding of brain function in this challenging population.

Transcranial Alternating Current Stimulation in Patients with Chronic Disorder of Consciousness: A Possible Way to Cut the Diagnostic Gordian Knot?

Unresponsive wakefulness syndrome (UWS) is a chronic disorder of consciousness (DOC) characterized by a lack of awareness and purposeful motor behaviors, owing to an extensive brain connectivity impairment. Nevertheless, some UWS patients may retain residual brain connectivity patterns, which may sustain a covert awareness, namely functional locked-in syndrome (fLIS). We evaluated the possibility of bringing to light such residual neural networks using a non-invasive neurostimulation protocol. To this end, we enrolled 15 healthy individuals and 26 DOC patients (minimally conscious state-MCS- and UWS), who underwent a γ-band transcranial alternating current stimulation (tACS) over the right dorsolateral prefrontal cortex. We measured the effects of tACS on power and partial-directed coherence within local and long-range cortical networks, before and after the protocol application. tACS was able to specifically modulate large-scale cortical effective connectivity and excitability in all the MCS participants and some UWS patients, who could be, therefore, considered as suffering from fLIS. Hence, tACS could be a useful approach in supporting a DOC differential diagnosis, depending on the level of preservation of the cortical large-scale effective connectivity.

Noninvasive brain stimulation for persistent postconcussion symptoms in mild traumatic brain injury

Mild traumatic brain injury (mTBI) is typically followed by various postconcussive symptoms (PCS), including headache, depression, and cognitive deficits. In 15-25% of cases, PCS persists beyond the usual 3-month recovery period, interfering with activities of daily living and responding poorly to pharmacotherapy. We tested the safety, tolerability, and efficacy of repetitive transcranial magnetic stimulation (rTMS) over the left dorsolateral prefrontal cortex (DLPFC) for alleviating PCS. Fifteen eligible patients with mTBI and PCS > 3 months postinjury consented to 20 sessions of rTMS (20 × 5-sec trains; 10 Hz at 110% threshold), with clinical and functional magnetic resonance imaging (fMRI) assessments before and after intervention and clinical assessment at 3-month follow-up. Primary outcomes were tolerability, safety, and efficacy, as measured with the PCS Scale. Secondary outcomes included the Cognitive Symptoms Questionnaire, neuropsychological test performance, and working memory task-associated activity as assessed with fMRI. Twelve patients completed all sessions. Three withdrew because of worsening symptoms or for an unrelated event. Stimulation intensity was increased gradually across sessions, and all subjects tolerated the protocol by the sixth session. Commonly reported side effects among completers were increased headache (n = 3) and greater sleep disturbance (n = 3). Participants also reported positive outcomes such as less sleep disturbance (n = 3), and better mental focus (n = 3). On average, PCS scores declined by 14.6 points (p = 0.009) and fMRI task-related activation peaks in the DLPFC increased after rTMS. rTMS is safe, tolerated by most patients with mTBI, and associated with both a reduction in severity of PCS and an increase in task-related activations in DLPFC. Assessment of this intervention in a randomized, control trial is warranted.

Sites of electrical stimulation used in neurology

Rehabilitation aims to decrease neurological impairments, in guiding plasticity. Electrical stimulation has been used for many years in rehabilitation treatment of neurological disabilities as a tool for neuromodulation inducing plasticity, although the mechanisms of its action are not well known. The applications vary, encompassing therapeutic and rehabilitative aims. The type and site of stimulation vary depending on the objectives. Some techniques are widely used in clinical practice; others are still in the research stage. They may be invasive, epidural or in direct contact with neurons; they may be noninvasive, applied transcutaneously or indirectly by current vectors. The indications vary: mobility, functionality, pain as well as pharyngeal, respiratory, and perineal function. This paper aims to summarize current data on electrical neuromodulation techniques used in neurorehabilitation, their effects and their mechanisms of action.

Clinical utility of brain stimulation modalities following traumatic brain injury: current evidence

Traumatic brain injury (TBI) remains the main cause of disability and a major public health problem worldwide. This review focuses on the neurophysiology of TBI, and the rationale and current state of evidence of clinical application of brain stimulation to promote TBI recovery, particularly on consciousness, cognitive function, motor impairments, and psychiatric conditions. We discuss the mechanisms of different brain stimulation techniques including major noninvasive and invasive stimulations. Thus far, most noninvasive brain stimulation interventions have been nontargeted and focused on the chronic phase of recovery after TBI. In the acute stages, there is limited available evidence of the efficacy and safety of brain stimulation to improve functional outcomes. Comparing the studies across different techniques, transcranial direct current stimulation is the intervention that currently has the higher number of properly designed clinical trials, though total number is still small. We recognize the need for larger studies with target neuroplasticity modulation to fully explore the benefits of brain stimulation to effect TBI recovery during different stages of recovery.

Non-Invasive Brain Stimulation for the Treatment of Symptoms Following Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) is a common cause of physical, psychological, and cognitive impairment, but many current treatments for TBI are ineffective or produce adverse side effects. Non-invasive methods of brain stimulation could help ameliorate some common trauma-induced symptoms.

OBJECTIVE

This review summarizes instances in which repetitive Transcranial Magnetic Stimulation (rTMS) and transcranial Direct Current Stimulation (tDCS) have been used to treat symptoms following a TBI. A subsequent discussion attempts to determine the value of these methods in light of their potential risks.

METHODS

The research databases of PubMed/MEDLINE and PsycINFO were electronically searched using terms relevant to the use of rTMS and tDCS as a tool to decrease symptoms in the context of rehabilitation post-TBI.

RESULTS

Eight case-studies and four multi-subject reports using rTMS and six multi--subject studies using tDCS were found. Two instances of seizure are discussed.

CONCLUSION

There is evidence that rTMS can be an effective treatment option for some post-TBI symptoms, such as depression, tinnitus, and neglect. Although the safety of this method remains uncertain, the use of rTMS in cases of mild TBI without obvious structural damage may be justified. Evidence on the effectiveness of tDCS is mixed, highlighting the need for additional investigations.

A Single Session of Repetitive Transcranial Magnetic Stimulation Over the Dorsolateral Prefrontal Cortex in Patients With Unresponsive Wakefulness Syndrome

Background. The level of consciousness is regulated by the activation of the frontal parietal network since a disruption within this interregional cortical connectivity is associated with a consciousness breakdown. Objective. The primary aim of the present study was to examine the feasibility and the safety of a single session of repetitive transcranial magnetic stimulation (rTMS), delivered over the dorsolateral prefrontal cortex (DLPFC), in patients with unresponsive wakefulness syndrome (UWS). As a secondary aim, we investigated the efficacy of rTMS over DLPFC on cortico-cortical connectivity as tested with paired-pulse and dual-coil TMS techniques. Methods. We enrolled 10 healthy and 10 postanoxic UWS subjects. After clinical assessment, subjects underwent a single/paired pulse TMS paradigm evaluating the inhibitory and facilitatory intracortical circuits. In addition, several interregional interactions between primary motor, dorsal and ventral premotor, supplementary motor, and posterior parietal cortex areas were investigated by means of dual-coil TMS technique. These parameters were evaluated at baseline, immediately after, and 60 minutes after a protocol of 10-Hz rTMS delivered at the level of the DLPFC. Results. rTMS over DLPFC did not cause any adverse events. We showed that rTMS over DLPFC did not induce, at group level, any clinical improvement or intra-/intercortical connectivity changes. Interestingly, in 3 patients rTMS induced a significant, although transient, clinical improvement associated with a short-lasting reshaping of brain connectivity. Conclusions. We demonstrated that a single session of 10-Hz rTMS over the right DLPFC may transiently improve consciousness and partially restore the connectivity within several cortical areas in some patients with UWS.

Technology-based intervention programs to promote stimulation control and communication in post-coma persons with different levels of disability

Post-coma persons in a minimally conscious state and with extensive motor impairment or emerging/emerged from such a state, but affected by lack of speech and motor impairment, tend to be passive and isolated. A way to help them develop functional responding to control environmental events and communication involves the use of intervention programs relying on assistive technology. This paper provides an overview of technology-based intervention programs for enabling the participants to (a) access brief periods of stimulation through one or two microswitches, (b) pursue stimulation and social contact through the combination of a microswitch and a sensor connected to a speech generating device (SGD) or through two SGD-related sensors, (c) control stimulation options through computer or radio systems and a microswitch, (d) communicate through modified messaging or telephone systems operated via microswitch, and (e) control combinations of leisure and communication options through computer systems operated via microswitch. Twenty-six studies, involving a total of 52 participants, were included in this paper. The intervention programs were carried out using single-subject methodology, and their outcomes were generally considered positive from the standpoint of the participants and their context. Practical implications of the programs are discussed.