Background
State-of-the-art
Effects of electrical stimulation on neurons
Long-term potentiation (LTP), long-term depression (LTD) and plasticity
Spike timing-dependent plasticity (STDP)
Electrical stimulation methods
Transcranial magnetic stimulation
Transcranial direct current stimulation
Deep brain stimulation
Vagus nerve stimulation
Stimulation waveforms and protocols
Additional stimulation methods
Systematic literature review
Search terms: literature identification
(“transcranial magnetic stimulation” OR “transcranial direct current stimulation” OR “deep brain stimulation” OR “vagus nerve stimulation” OR "vagal nerve stimulation") AND (“traumatic brain injury” OR “tbi” OR “concussion”)
Inclusion criteria: literature screening
Eligibility: full-text assessment
Results
References | Main focus | Impairment | Animal model | Stimulation protocol | Stimulation time frame |
---|---|---|---|---|---|
Yoon YS et al. [138] | Effects of rTMS and EES on TBI | Motor function | 51 male Sprague–Dawley rats (21 died from TBI), Marmarou’s weight drop (450 g from 1 m, diffuse, mild TBI, medial impact), awake and immobilized during TMS | 90% of max. device output, 10 Hz, 3 s stim and 6 s pause, for 10 min | Twice per day, day 1–14 post-injury |
Yoon KJ et al. [152] | rTMS for behavioral recovery | Motor function, brain metabolism, cell death | 20 adult male Sprague–Dawley rats, lateral FPI (3.5–4 atm pressure, severe TBI), awake and immobilized during TMS | 80% of RMT, 10 Hz, 15 trains of 2 s, 1 s inter-train interval | 10 sessions over 2 weeks, beginning on 4th day post-injury |
Lu H et al. [153] | rTMS for pediatric TBI | Motor function | 26 juvenile Sprague–Dawley rats, CCI over left primary somatosensory cortex (severity unclear), TMS under 2% isoflurane | 25% of max. device output, 20 Hz, 9 trains of 100 pulses, 55 s inter-train interval, for 9 min | Twice per week, starting 9 post-injury, for 4 weeks |
Lu X et al. [156] | rTMS for neuromodulation and neurogenesis | Loss of brain parenchyma, reduced brain metabolism, neurological impairment | 38 adult Sprague–Dawley rats, Feeney’s weight drop (moderate TBI, right hemisphere), awake and immobilized during TMS | 60% of max. device output, 5 Hz, 36 trains of 25 pulses, 15 s inter-train interval, 900 pulses/day, figure-of-eight coil | From 2 days post-injury until 1 day before sacrificed (7/14/28 days after TBI) |
Verdugo-Diaz et al. [157] | Treatment with intermediate frequency rTMS | Mortality, general behavioral changes | 97 male Wistar rats, Marmarou’s weight drop (motor cortex, severe TBI), awake and immobilized during TMS (animals trained for immobilization) | 50% of max. device output (120% of RMT), 2 Hz, 15 min per day, figure-of-eight coil | Starting 1 day post-injury, for 7 consecutive days |
Shin et al. [154] | Therapy with rTMS and environmental enrichment | motor function | 97 male Sprague–Dawley rats, CCI (4 m/s, moderate TBI, right hemisphere), MEP assessment under isoflurane, electrophysiological recordings under urethane, fMRI under sedation, rTMS under 2% isoflurane | 10 Hz, 7 cycles of 4 s, 26 s between cycles, figure-of-eight coil, (stim. intensity unclear) | Starting 1 day post-injury, daily, for 6 days |
Sekar et al. [155] | Low-field magnetic stimulation (LFMS, rTMS variant) treatment after TBI | Cognitive and motor functions | 48 male C57BL/6 mice, weight drop (60 g from 1 m, closed head trauma, repetitive TBI, once daily for 3 consecutive days, severity unclear), awake and immobilized during TMS | 40 Hz, 6 ms pulses, 80 trains of 2 s, 8 s pause, magn. field changes between uniform and linear gradient every 2 min, for 20 min | Once per day, following recovery from rightening reflex after TBI, for 3 days and once on day 4 |
Qian et al. [158] | Investigation of cellular mechanisms caused by rTMS treatment | General overview | 45 male Sprague–Dawley rats, Feeney's weight drop (20 g × 30 cm impact force, moderate TBI), awake and immobilized during rTMS | 30% of motor threshold, 40 Hz, 40 trains of 1 s, in 15 s intervals | Starting 4 days post-injury, once daily, for 2 weeks, five times per week |
References | Stimulus location | Tests | Acquired parameters | Persistent effects | Main findings |
---|---|---|---|---|---|
Yoon YS et al. [138] | Center of the coil placed above injury site | Limb placement test, SPRT, RRT, immunohistochemistry | Limb placement changes, SPRT success rate, RRT performance time rate, c-Fos expression | Not investigated | TMS and EES resulted in significant improvement in SPRT and accelerated improvement in RRT, with particularly robust effects of EES |
Yoon KJ et al. [152] | Area with largest MEP amplitude at the weaker biceps femoris after suprathreshold stim., side not stated (probably ipsilateral) | Rotarod and beam balance tests, brain MRI, magnetic resonance spectroscopy, western blot, immunohistochemistry | Motor coordination, balance ability, intact and lesioned hemispheric volume, brain metabolism, apoptotic signaling | Not investigated | rTMS did not have beneficial effects on motor recovery, enhancement of anti-apoptotic response in perilesional area |
Lu H et al. [153] | Contralateral primary sensory region | Extracellular electrophysiological recordings, fMRI, open field test, forelimb and hindlimb reflex test, immunostaining | CaMKII expression (LTP), MUA responses, LFP magnitude, evoked fMRI cortical responses, behavioral tests (physiology and hyperactivity) | Long-lasting increase of excitability in non-injured cortex after 4 weeks of TMS therapy | Significant increases in evoked-fMRI cortical response, evoked synaptic activity, evoked neuronal firing and expression of neuroplasticity markers, decreased hyperactivity in behavioral tests |
Lu X et al. [156] | Whole brain influenced by magnetic field (max. stim. over the center of the brain) | Behavioral tests (mNSS evaluation), hematoxylin and eosin staining, immunohistochemistry, PET examination | Behavioral recovery, relative brain parenchyma loss, cell proliferation and neurogenesis, neuron protection, cell apoptosis, metabolic activity | Not investigated | High-frequency rTMS may decrease mortality, mature neuron loss, apoptosis, improve behavioral recovery, cell proliferation and neurogenesis in the SVZ, metabolic activity in the contralateral site was not affected |
Verdugo-Diaz et al. [157] | Injury site | Hunter’s 21-point behavioral-neurological scale, histology | Body weight, food intake, post-TBI bleeding and mortality, neurobehavioral score, cellular morphological changes, disruptions in hippocampal tissue architecture | Not investigated | Movement restriction prevents damage caused by TBI, intermediate-frequency rTMS slightly promotes behavioral and histologic recovery after TBI |
Shin et al. [154] | Midpoint between lambda and bregma, medial located | Beam walk and challenge ladder tests, electrophysiology, evoked LFP, MEP assessment, fMRI in the contralateral cortex | Beam traversal latency, mean speed and slips from ladder, MEP amplitude, LFP magnitude, fMRI activation maps | Combination of EE and TMS led to benefits in sensorimotor function lasting up to 6 weeks | Combined therapy with TMS and EE after TBI leads to functional improvements, possibly via cortical excitability and reorganization, long-term effects probably due to EE rather than TMS |
Sekar et al. [155] | Cortical and subcortical areas | RRT, open field test, novel location recognition test, immunohistochemistry, western blot | Time on rotarod, locomotor activity, cognitive function, PrPc level in plasma, GFAP, NeuN and PrPc protein levels, CLOCK and CRY2 levels | Not investigated | LFMS treatment improved motor and cognitive function in mice after repetitive TBI, restored PrPc level, decreased proteins associated with circadian rhythm, decreased GFAP levels, increased NeuN levels, and showed neuroprotective effects |
Qian et al. [158] | Coil placed above ipsilateral side, close to the scalp | mNSS assessment, TEM, immunohistochemistry, western blot, RT-PCR detection | Injury severity, synaptic ultrastructure, protein expression (BDNF, TrkB, NMDAR1, P-CREB, SYN), mRNA expression levels | Not investigated | rTMS may promote recovery of neurological functions in TBI rats through enhanced SYN protein levels to promote synaptic reconstruction and affecting the expression of proteins related to LTP occurrence |
References | Main focus | Impairment | Animal model | Stimulation protocol | Stimulation time frame |
---|---|---|---|---|---|
Yoon et al. [159] | Effects of anodal tDCS on behavioral and spatial memory in early stage TBI | Behavioral and spatial memory | 36 male Sprague–Dawley rats, lateral FPI (moderate TBI), anesthetized during tDCS | Anodal tDCS, 0.2 mA, (2.82 mA/cm2 current density), for 20 min | Once per day, for 5 days, starting 1 or 2 weeks post-injury |
Kim and Han [160] | Effects of anodal tDCS on neuroplasticity | Motor and sensory cortical excitability | 31 male Sprague–Dawley rats (postnatal day 42), weight drop (175 g from 30 cm, 3 consecutive times, repetitive mild TBI), anesthetized during all procedures and evaluations | Anodal tDCS, 0.2 mA (0.255 mA/cm2 current density), for 30 min | Once, directly after TBI |
Bragina et al. [161] | Perfusion and tissue oxygenation after anodal tDCS, motor and cognitive neurologic outcome | mCBF and tissue oxygenation, motor function | 40 mice, CCI (5 m/s, 2 mm from cortical surface, mild to moderate TBI), awake during tDCS | Repetitive anodal tDCS, 0.1 mA, for 15 min | Over 4 weeks, for 4 consecutive days at 3-day intervals, starting 1 or 3 weeks post-injury |
Yu et al. [162] | Effects of tDCS and ECS on motor and cognitive recovery, brain plasticity, spatial learning and memory | Motor and cognitive function | 30 male Sprague–Dawley rats, weight drop (moderate TBI), awake during tDCS | Anodal tDCS, 0.1 mA, 50 Hz, 200 µs pulses, for 30 min | Once per day from days 3 to 28 after electrode positioning |
Martens et al. [165] | Cathodal tDCS in the treatment of psychiatric-like symptoms after TBI | Impulsivity and attention | 20 male Long-Evans rats, bilateral, frontal CCI (severe TBI), anesthetized during tDCS | Cathodal tDCS, 800 µA (0.708 mA/cm2), 10 min | Once per day for 7 days (2 h before testing), starting 6 weeks post-injury |
Bragina et al. [164] | Effects of anodal tDCS on cerebrovascular reactivity and mCBF regulation | Cerebrovascular reactivity and mCBF | 20 mice, CCI (5 m/s, 2 mm from cortical surface, mild to moderate TBI), awake during tDCS | Anodal tDCS, 0.1 mA, for 15 min | Once, 3 weeks post-injury |
Park et al. [163] | Anodal tDCS to improve motor function after repetitive mild TBI | Motor function | 65 male Sprague–Dawley rats, weight drop (175 g from 30 cm, once daily for 3 days, repetitive mTBI), anesthetized during tDCS | Anodal tDCS, 0.2 mA (0.255 mA/cm2), for 30 min | Once, 24 h after last induction of mTBI |
References | Stimulus location | Tests | Acquired parameters | Persistent effects | Main findings |
---|---|---|---|---|---|
Yoon et al. [159] | Anode over perilesional area, cathode on chest | RRT, Barnes maze test, brain MRI, MRS, immunohistochemical analysis | Behavioral ability, spatial memory, lesion volume, brain edema, metabolites, BDNF expression | Beneficial effects visible 1 weeks after stimulation, no sustained effects after 3 weeks | tDCS increases recovery of spatial and memory functions when applied 2 weeks post injury, only improves spatial memory when applied 1 week post-injury |
Kim and Han [160] | Anode around left motor cortex, counter electrode on thorax | MEP and SEP test, brain MRI, immunohistochemical analysis | Recovery of righting reflex, MEP latency and amplitude, SEP latency and amplitude, brain volumetric changes, GFAP expression | Immunohistochemistry performed 12 days after stimulation, showed no significant improvements | Single anodal tDCS after rmTBI induces early recovery of consciousness, increases modulation of cortical excitability and promotes transient motor recovery |
Bragina et al. [161] | Anode near craniotomy, counter electrode on thorax | Custom-made LSCI, two-photon LSM, RRT, passive avoidance test, Y-maze test, Nissl staining | Regional and microvascular cerebral blood flow, motor deficits, learning, spatial and working memory | Preserved improvement in learning and motor abilities 1 week after stimulation was ended | Anodal tDCS increases brain microvascular blood flow and tissue oxygenation in TBI and sham mouse brain and could contribute to neurologic improvement |
Yu et al. [162] | Anode above lesion, cathode at trunk | Rehabilitation training (SPRT, RRT, Y-maze), neurological examination, histology, immunohistochemistry | Success rate of SPRT and Y-maze tests, average rates of RRT, lesion assessments, c-Fos expression | Not investigated | ES with rehabilitation training for TBI rats is effective for motor recovery and brain plasticity, ECS induces faster behavioral and cognitive improvements than tDCS |
Martens et al. [165] | Cathode near bregma, anode between scapulae | Five-choice serial reaction time task, analysis of brain slices to verify injury severity | Motor impulsivity, attention, relationship between magnitude of impairment and recovery | No lingering effects observed, disappeared after stimulation stopped | Relationship between magnitude of impulsive deficit and degree of tDCS-recovery, the most severely impaired subjects benefit the most from neuromodulation |
Bragina et al. [164] | Anode near craniotomy, cathode on thorax | Two-photon LSM (before and after stimulation), cerebrovascular reactivity test (hypercapnia) | mCBF (arteriolar diameter), brain tissue oxygen flow (NADH autofluorescence) | Not investigated | Anodal tDCS restores cerebrovascular reactivity of parenchymal arterioles and regulation of mCBF, could contribute to neurologic improvement |
Park et al. [163] | Anode over left M1 area, cathode on trunk | Brain MRI, histology, MEP evaluation (via TMS and needle electrodes), foot-fault test, rotarod test | Damage evaluation after repetitive mTBI, MEP amplitude and latency, motor coordination, sensorimotor function, balance alterations | Not investigated | Anodal tDCS at the M1 area after repetitive mTBI could improve MEP amplitude, balance control, postural orientation and motor endurance by activating the CST |
References | Main focus | Impairment | Animal model | Stimulation protocol | Stimulation time frame |
---|---|---|---|---|---|
Lee et al. [166] | Theta frequency DBS to improve spatial memory | Cognitive deficits | 56 adult male Sprague–Dawley rats, lateral FPI (moderate TBI), awake during DBS | 80 µA, 7.7 Hz, 1 ms pulses, for 1 min in exp. 1 and for 15 min in exp. 2 | From post-injury days 5 to 7, directly before Barnes maze experiment |
Gonzalez et al. [167] | Behavioral and anatomical recovery after TBI | Cognitive deficits | 79 adult male Sprague–Dawley rats, FPI (moderate TBI), awake during DBS | 30 µA, 8 or 24 Hz, 1 ms pulses, 5 min alternated with 5 min break, over 12 daylight hours | Starting 4–6 h post-injury (or after 7 days in one group), for 8 weeks |
Tabansky et al. [175] | Temporally-patterned DBS after multiple TBI | Decreased arousal | 25 C57BL/6J mice (6–9 weeks old), weight drop (20 g from 25 cm, up to 5 times, moderate TBI), awake during DBS | 150 µA, 200 µs biphasic pulses, 125 Hz, for 10 min every 4 h over 1 day, diff. temporal patterns (varying interpulse intervals) | Starting 4–6 h post-injury, over the course of 1 day |
Lee et al. [168] | DBS to improve cognition after TBI | Cognitive deficits | 136 adult male Harlan Sprague–Dawley rats, lateral FPI (moderate TBI), awake during DBS | 20/80/200 µA, 7.7/100 Hz, 1 ms pulses exp. 1: for 15/30/60 s; exp. 2 and 3: starting 1 min before task, for 6 min | Exp. 1: 4 and 5 days post-injury, 2x/day; exp. 2 and 3: 5–7 days post-injury, 2x/day |
Chan et al. [171] | Motor recovery with DBS | Motor deficits | 32 male Long Evans Rats (7 were withdrawn), FPI in motor cortex contralateral to dominant forelimb (severity unclear), awake during DBS | 80% of individual motor threshold, 30 Hz, 400 µs pulses, 12 h per day | Starting 4 weeks post-injury, for 4 weeks |
Jen et al. [172] | DBS to modulate bladder function in TBI animals | Bladder dysfunction | 22 female Sprague–Dawley rats, weight drop (450 g from 2 m, severe TBI), anesthetized during DBS and cystometry | 1.5 V, 50 Hz, 182 µs pulses | One session, 1 week post-injury, during cystometry, triggered by EUS-EMG |
Praveen Rajneesh et al. [173] | DBS to treat bladder dysfunction after TBI | Bladder dysfunction | 49 male Sprague–Dawley rats, weight drop (450 g from 0.5, 1, 1.5, 2 and 2.25 m, severity unclear), anesthetized during DBS and cystometry | 1/1.5/2/2.5 V, 50 Hz, 182 µs biphasic pulses, for 10 s | One session, 1 week post-injury, during cystometry when bladder pressure exceeded threshold |
Praveen Rajneesh et al. [174] | DBS to improve bladder function after TBI | Bladder dysfunction | 28 male Sprague–Dawley rats, weight drop (450 g from 2 m, severe TBI), anesthetized during DBS and cystometry | 1/1.5/2/2.5 V (randomized sequence), 50 Hz, 182 µs pulses, for 10 s | One session, 1 week post-injury, during cystometry when bladder pressure exceeded threshold |
Dong et al. [176] | DBS to promote wakefulness after TBI | DoC | 55 Sprague–Dawley rats (28 male, 27 female), weight drop (400 g dropped from 40 to 44 cm, severity unclear), comatose but without anesthesia during DBS | 2–4 V, 200 Hz, 0.1 ms pulses, switch between left and right side of lateral hypothalamus every 5 min, for 1 h | Once, 2 h post-injury (1 h after electrode implantation) |
Aronson et al. [169] | Task-matched DBS to improve cognitive recovery after TBI | Cognitive deficits | 65 adult male C57BL/6 mice, CCI (5.2 m/s, 2.65 mm depth, moderate TBI), awake during DBS | 50 µA, 130 Hz, biphasic pulses, 80 µs per phase, 500 ms trains, 500 ms between trains | Starting 2 weeks post-injury, during Morris water maze, 5 s after success for 5 s, four times per day, for 5 days |
Chan et al. [170] | DBS to enhance cognitive recovery after TBI | Cognitive deficits | 33 male Long Evans rats, CCI (2.25 m/s, 2.5 mm depth, severity unclear), awake during DBS | 80% of motor threshold, 30 Hz, 400 µs pulses, charge-balanced | Starting 8 weeks post-injury, 12 h daily, for 4 weeks |
References | Stimulus location | Tests | Acquired parameters | Persistent effects | Main findings |
---|---|---|---|---|---|
Lee et al. [166] | Medial septal nucleus | Video-EEG, Barnes maze | Exp 1.: electrode placement, spatial working memory, search strategy; exp. 2: hippocampal theta power (during stim. and after 15 min) | No persisting effects observed | FPI attenuates hippocampal theta, MSN theta frequency stimulation immediately before trials improves spatial working memory |
Gonzalez et al. [167] | Midbrain median raphe and dorsal raphe | Morris water maze, neuroanatomical analysis, cylinder test | Reference memory, working memory, forelimb reaching asymmetry, forebrain volumes, cAMP levels | Not investigated | 8 Hz early MR stimulation can restore forelimb reaching, reference memory, working memory and parietal-occipital cortex volume |
Tabansky et al. [175] | Central thalamus (bilaterally) | NSS test (circular open maze, hindlimb reflex, beam walk), parental care, elevated plus maze, light–dark transition, pheromenal spatial learning, T-maze, partition test, social discrimination | Injury severity (NSS) and effects of DBS: motor activity deficits, recovery without intervention, nocturnal behavior pattern, behavioral changes | Not investigated | Multiple TBI results in acute deficits for 11–14 days, chaotic simulation increases motor activity more than fixed or random stimulation |
Lee et al. [168] | Medial septal nucleus | EEG, object exploration task, Barnes maze, histology | EEG (theta frequency time, phase coherence, peak frequency), behavioral changes (object exploration, search strategy) | No persisting effects observed | FPI diminishes hippocampal theta, no change in phase coherence, shift in peak frequency, MSN stimulation increased hippocampal theta |
Chan et al. [171] | Contralateral LCN | Pasta matrix test, cylinder and horizontal ladder tests, histology, RNA microarray assay, immunohistochemistry, western blot | Forepaw dexterity, spontaneous forepaw use, motor coordination, electrode location, lesion volume, various genetic and cellular parameters | Not investigated | LCN DBS can enhance motor recovery after TBI by elevating neuronal excitability and mediating anti-apoptotic and anti-inflammatory effects |
Jen et al. [172] | Rostral pontine reticular nucleus (PnO) | EUS-EMG, continuous-infusion cystometry, MRI, assessment of closed-loop control DBS prototype to improve voiding function | Cystometric parameters (volume threshold, contraction amplitude and duration, residual and voided volume, voiding efficiency), electrode position, tissue damage | Not investigated | Designed DBS closed-loop control system prototype for TBI rats and proved its feasibility (detected bladder voiding cycles, significantly improved voiding efficiency) |
Praveen Rajneesh et al. [173] | Rostral pontine reticular nucleus (PnO) | Impact height, cystometric measurements, MRI | Effect of impact height on mortality rate, cystometric parameters (volume threshold, contraction amplitude and duration), TBI impact, electrode position | Not investigated | Established weight drop TBI model for significant voiding dysfunction, show therapeutic effects of PnO-DBS on voiding dysfunction and bladder control in rats after TBI |
Praveen Rajneesh et al. [174] | Pedunculopontine tegmental nucleus (PPTg) | Cystometric measurements (CMG), external urethral sphincter electromyography (EUS-EMG), MRI | Cystometric parameters, EUS-EMG parameters (burst period, active period and silent period), DBS electrode tip localization | Not investigated | DBS was capable of inducing potential neural regulation that could control bladder functions, PPTg is a promising target of new therapies for lower urinary tract dysfunction |
Dong et al. [176] | Lateral hypothalamic area, left and right side | Assessment of consciousness, OX1R antagonist injection, EEG, western blot analysis, immunohistochemistry | Degree of consciousness (I–VI), delta activity, protein expression (OX1R, α1-AR and GABABR) | Not investigated | LHA-DBS-induced wake promotion results in upregulation of α1-AR expression and downregulation of GABABR expression mediated by the orexins/OX1R pathway, LHA-DBS can be used to promote wakefulness |
Aronson et al. [169] | Unilateral, cathode in the nucleus accumbens, anode just below the dura | Morris water maze, real-time place preference assay, immunohistochemistry, gene expression analysis | Spatial memory performance, search pattern efficiency, hedonic response, synaptic density and neuronal growth (synapsin-1 and GAP43), neurogenesis | Persistent effects observed 10 days after stimulation cessation | Task-matched DBS of the nucleus accumbens improves recovery of spatial memory in a TBI mouse model, stimulation led to cellular adaptation and upregulation of genes associated with neural differentiation, migration, cell signaling and proliferation |
Chan et al. [170] | LCN, unilateral | Barnes maze, baited Y-maze, novel object recognition task, immunohistochemistry, Western blot, Nissl staining | Long-term spatial memory, memory retention, recognition memory, electrode placement, protein expression (CaMKIIα, BDNF, p75NTR), pre- (synapsin I) and post-synaptic (PSD-95) markers | Not investigated | Unilateral LCN DBS is an effective treatment for cognitive deficits in a TBI rat model by enhancing functional connectivity across perilesional cortical and thalamic brain regions |
References | Main focus | Impairment | Animal model | Stimulation protocol | Stimulation time frame |
---|---|---|---|---|---|
Smith et al. [177] | VNS to increase cognitive and motor recovery after TBI | Motor and cognitive function | 57 male Long-Evans hooded rats, lateral FPI (left hemisphere, moderate TBI), awake during VNS | 0.5 mA, 20 Hz, 30 s trains of 0.5 ms biphasic pulses, 30 min intervals | Starting 2 h post-injury, for 14 days |
Smith et al. [178] | VNS for functional recovery after TBI | Motor and cognitive deficits | 48 Long Evans hooded rats, FPI (moderate TBI), awake during VNS | 0.5 mA, 20 Hz, 30 s trains of 0.5 ms biphasic pulses, 30 min intervals | Starting 24 h post-injury, for 14 days |
Neese et al. [184] | VNS to protect GABAergic neurons after TBI | Reduction of GABAergic neurons | 24 male Long Evans hooded rats, unilateral FPI (severity unclear), awake during VNS | 0.5 mA, 20 Hz, 30 s trains of 0.5 ms biphasic pulses, 30 min intervals | Starting 24 h post-injury, for 14 days |
Clough et al. [182] | Effects of VNS on development of cerebral edema | Cerebral edema | 19 male Long Evans hooded rats, unilateral FPI (moderate TBI), awake during VNS | 0.5 mA, 20 Hz, 30 s trains of 0.5 ms biphasic pulses, 30 min intervals | Starting 2 h post-injury, for 48 h |
Zhou et al. [183] | Neuroprotective effects of VNS | Brain edema | 28 adult male New Zealand rabbits, brain explosive injury (firecracker with charge quantity of 50 ± 5 mg black powder, severity unclear), conscious during injury (unclear for VNS) | 10 V, 5 Hz, 5 ms pulses, for 20 min | Starting 1 h post-injury, for 20 min |
Pruitt et al. [179] | VNS with physical rehabilitation to enhance recovery | Motor function | 28 adult female Sprague–Dawley rats, CCI to cortex (3 m/s impact, severity unclear), awake during VNS | 0.8 mA, 30 Hz, 500 ms trains of 15 biphasic pulses, 100 µs phase duration | Starting on day 9 post-injury, within 45 ms of successful trials, alongside rehabilitation |
Dong and Feng [180] | VNS to promote wakefulness after TBI | DoC | 120 Sprague–Dawley rats (half male, half female), weight drop (400 g dropped from 40 to 44 cm, severity unclear), anesthetized during VNS | 1 mA, 30 Hz, 0.5 ms pulses, for 15 min | Once, directly after TBI |
Dong et al. [181] | VNS for wake-promotion after TBI | DoC | 120 male Sprague–Dawley rats, weight drop (400 g dropped from 40 to 44 cm, severity unclear), anesthetized during VNS | 1 mA, 30 Hz, 0.5 ms pulse width, for 15 min | Once, directly after TBI |
References | Stimulus location | Tests | Acquired parameters | Persistent effects | Main findings |
---|---|---|---|---|---|
Smith et al. [177] | Left vagus nerve, cervical part | Skilled forelimb reaching, beam walk, inclined plane, forelimb flexion, locomotor placing, Morris water maze, histology | Behavioral recovery, cognitive recovery, histologic changes (lesion cavity size, neurodegeneration, hippocampal pyramidal neuron death, reactive astrocytosis) | Not investigated | VNS improves the rate of recovery and performance of rats in a FPI model as shown in multiple behavioral and cognitive tests |
Smith et al. [178] | Left vagus nerve | Injury severity, skilled forelimb reaching, beam walk, forelimb flexion, locomotor placing, Morris water maze, histology | Duration of apnea and unconsciousness, behavioral and cognitive recovery, lesion analysis (tissue loss near injury), neurodegeneration (FluoroJade) | Not investigated | VNS facilitates rate of recovery and final level of motor and cognitive performance following FPI, can be applied starting 2–24 h post-injury |
Neese et al. [184] | Left vagus nerve, cervical part | Histology | Number of GAD positive cells in cerebral cortices and hippocampal hilus | Not investigated | FPI induces a significant loss of GAD-like immunoreactive cells, VNS has an overall protective effect on GABAergic neurons |
Clough et al. [182] | Left vagus nerve, cervical part | Beam walk, locomotor placing | Vestibulomotor function, motor coordination, coordination of limb placing, regional brain water content | Not investigated | Chronic, intermittent VNS in rats attenuates development of cerebral edema |
Zhou et al. [183] | Right vagus nerve | CT imaging, blood analysis, histology | Cranial CT images, TNF-α, IL-1β and IL-10 serum concentrations, histological parameters (pathological manifestations, brain water content) | Not investigated | VNS reduced levels of TNF-α and IL-1β, increased levels of IL-10, and reduced degree of cerebral edema, VNS may exert neuroprotective effects against explosive injury |
Pruitt et al. [179] | Left vagus nerve, cervical part | Two 30 min behavioral training sessions (pull task) per day (5 days per week, starting 7 days after VNS implantation, for 6 weeks), histology | Pull task performance, mean maximal pull force, motor recovery, lesion size | Not investigated | VNS paired with physical rehabilitation enhances recovery of forelimb function and pull strength after TBI |
Dong and Feng [180] | Left vagus nerve, cervical part | OX1R antagonist injection, assessment of consciousness, ELISA, western blot analysis, immunohistochemistry | Behavior and consciousness levels 1 h after TBI, orexin-A and OX1R expression in prefrontal cortex at 6, 12 and 24 h after TBI | Not investigated | VNS might promote wakefulness in comatose TBI rats through upregulation of orexin-A and OX1R expression in prefrontal cortex, VNS is a promising method to wake patients from TBI-induced coma |
Dong et al. [181] | Left vagus nerve, cervical part | OX1R antagonist injection, assessment of consciousness, western blot analysis, immunohistochemistry | Degree of consciousness (I–VI), protein concentration in brain tissue (excitatory and inhibitory neurotransmitter receptors), brain section visualization | Not investigated | VNS could promote arousal and improve consciousness after TBI, potential treatment for comatose individuals affected by TBI |