Transcranial Direct Current Stimulation Enhances Neuroplasticity and Accelerates Motor Recovery in a Stroke Mouse Model.

BACKGROUND: More effective strategies are needed to promote poststroke functional recovery. Here, we evaluated the impact of bihemispheric transcranial direct current stimulation (tDCS) on forelimb motor function recovery and the underlying mechanisms in mice subjected to focal ischemia of the motor cortex. METHODS: Photothrombotic stroke was induced in the forelimb brain motor area, and tDCS was applied once per day for 3 consecutive days, starting 72 hours after stroke. Grid-walking, single pellet reaching, and grip strength tests were conducted to assess motor function. Local field potentials were recorded to evaluate brain connectivity. Western immunoblotting, ELISA, quantitative real-time polymerase chain reaction, and Golgi-Cox staining were used to uncover tDCS-mediated stroke recovery mechanisms. RESULTS: Among our results, tDCS increased the rate of motor recovery, anticipating it at the early subacute stage. In this window, tDCS enhanced BDNF (brain-derived neurotrophic factor) expression and dendritic spine density in the peri-infarct motor cortex, along with increasing functional connectivity between motor and somatosensory cortices. Treatment with the BDNF TrkB (tropomyosin-related tyrosine kinase B) receptor inhibitor, ANA-12, prevented tDCS effects on motor recovery and connectivity as well as the increase of spine density, pERK (phosphorylated extracellular signal-regulated kinase), pCaMKII (phosphorylated calcium/calmodulin-dependent protein kinase II), pMEF (phosphorylated myocyte-enhancer factor), and PSD (postsynaptic density)-95. The tDCS-promoted rescue was paralleled by enhanced plasma BDNF level, suggesting its potential role as circulating prognostic biomarker. CONCLUSIONS: The rate of motor recovery is accelerated by tDCS applied in the subacute phase of stroke. Anticipation of motor recovery via vicariate pathways or neural reserve recruitment would potentially enhance the efficacy of standard treatments, such as physical therapy, which is often delayed to a later stage when plastic responses are progressively lower.

Sensitivity to temporal parameters of intraneural tactile sensory feedback.

BACKGROUND: Recent studies have shown that neural stimulation can be used to provide artificial sensory feedback to amputees eliciting sensations referred on the amputated hand. The temporal properties of the neural stimulation modulate aspects of evoked sensations that can be exploited in a bidirectional hand prosthesis. METHODS: We previously collected evidence that the derivative of the amplitude of the stimulation (intra-digit temporal dynamics) allows subjects to recognize object compliance and that the time delay among stimuli injected through electrodes implanted in different nerves (inter-digit temporal distance) allows to recognize object shapes. Nevertheless, a detailed characterization of the subjects' sensitivity to variations of intra-digit temporal dynamic and inter-digit temporal distance of the intraneural tactile feedback has not been executed. An exhaustive understanding of the overall potentials and limits of intraneural stimulation to deliver sensory feedback is of paramount importance to bring this approach closer and closer to the natural situation. To this aim, here we asked two trans-radial amputees to identify stimuli with different temporal characteristics delivered to the same active site (intra-digit temporal Dynamic Recognition (DR)) or between two active sites (inter-digit Temporal distance Recognition (TR)). Finally, we compared the results achieved for (simulated) TR with conceptually similar experiments with real objects with one subject. RESULTS: We found that the subjects were able to identify stimuli with temporal differences (perceptual thresholds) larger than 0.25 s for DR and larger than 0.125 s for TR, respectively. Moreover, we also found no statistically significant differences when the subjects were asked to identify three objects during simulated 'open-loop' TR experiments or real 'closed-loop' tests while controlling robotic hand. CONCLUSIONS: This study is a new step towards a more detailed analysis of the overall potentials and limits of intraneural sensory feedback. A full characterization is necessary to develop more advanced prostheses capable of restoring all lost functions and of being perceived more as a natural limb by users.

Biomimetic Intraneural Sensory Feedback Enhances Sensation Naturalness, Tactile Sensitivity, and Manual Dexterity in a Bidirectional Prosthesis.

Peripheral intraneural stimulation can provide tactile information to amputees. However, efforts are still necessary to identify encoding strategy eliciting percepts that are felt as both natural and effective for prosthesis control. Here we compared the naturalness and efficacy of different encoding strategies to deliver neural stimulation to trans-radial amputees implanted with intraneural electrodes. Biomimetic frequency modulation was perceived as more natural, while amplitude modulation enabled better performance in tasks requiring fine identification of the applied force. Notably, the optimal combination of naturalness and sensitivity of the tactile feedback can be achieved with "hybrid" encoding strategies based on simultaneous biomimetic frequency and amplitude neuromodulation. These strategies improved the gross manual dexterity of the subjects during functional task while maintaining high levels of manual accuracy. They also improved prosthesis embodiment, reducing abnormal phantom limb perceptions ("telescoping effect"). Hybrid strategies are able to provide highly sensitive and natural percepts and should be preferred. VIDEO ABSTRACT.

Development of a neurotechnological system for relieving phantom limb pain using transverse intrafascicular electrodes (TIME).

Phantom limb pain (PLP) is a chronic condition that develops in the majority of amputees. The underlying mechanisms are not completely understood, and thus, no treatment is fully effective. Based on recent studies, we hypothesize that electrical stimulation of afferent nerves might alleviate PLP by giving sensory input to the patient if nerve fibers can be activated selectively. The critical component in this scheme is the implantable electrode structure. We present a review of a novel electrode concept to distribute highly selective electrode contacts over the complete cross section of a peripheral nerve to create a distributed activation of small nerve fiber ensembles at the fascicular level, the transverse intrafascicular multichannel nerve electrode (TIME). The acute and chronic implantations in a small animal model exhibited a good surface and structural biocompatibility as well as excellent selectivity. Implantation studies on large animal models that are closer to human nerve size and anatomical complexity have also been conducted. They proved implant stability and the ability to selectively activate nerve fascicles in a limited proximity to the implant. These encouraging results have opened the way forward for human clinical trials in amputees to investigate the effect of selective electrical stimulation on PLP.

Hand somatosensory subcortical and cortical sources assessed by functional source separation: an EEG study.

We propose a novel electroencephalographic application of a recently developed cerebral source extraction method (Functional Source Separation, FSS), which starts from extracranial signals and adds a functional constraint to the cost function of a basic independent component analysis model without requiring solutions to be independent. Five ad-hoc functional constraints were used to extract the activity reflecting the temporal sequence of sensory information processing along the somatosensory pathway in response to the separate left and right median nerve galvanic stimulation. Constraints required only the maximization of the responsiveness at specific latencies following sensory stimulation, without taking into account that any frequency or spatial information. After source extraction, the reliability of identified FS was assessed based on the position of single dipoles fitted on its retroprojected signals and on a discrepancy measure. The FS positions were consistent with previously reported data (two early subcortical sources localized in the brain stem and thalamus, the three later sources in cortical areas), leaving negligible residual activity at the corresponding latencies. The high-frequency component of the oscillatory activity (HFO) of the extracted component was analyzed. The integrity of the low amplitude HFOs was preserved for each FS. On the basis of our data, we suggest that FSS can be an effective tool to investigate the HFO behavior of the different neuronal pools, recruited at successive times after median nerve galvanic stimulation. As FSs are reconstructed along the entire experimental session, directional and dynamic HFO synchronization phenomena can be studied.

Functional cortico-muscular coupling during upright standing in athletes and nonathletes: a coherence electroencephalographic-electromyographic study.

We tested the hypothesis that functional cortico-muscular coupling of brain rhythms is implied in the control of lower limb muscles for upright standing. Electroencephalographic (EEG; Be-plus Eb-Neuro) and electromyographic (EMG) data were recorded in 18 fencing and 19 karate elite athletes, 14 karate amateurs, and 9 non-athletes, during quiet upright standing with open and closed eyes conditions. Cortico-muscular coupling was evaluated by computing EEG-EMG spectral coherence and directed transfer function (DTF). Body sway area did not differ among the groups. In non-athletes, the EEG-EMG coherence (gastrocnemius lateralis) at centro-parietal and parasylvian alpha rhythms (about 8-12 Hz) was higher during the open than closed eyes condition. This was not true in the elite athletes. At the same alpha rhythms, the sport amateurs presented values halfway between the non-athletes and elite athletes. Finally, the DTF was higher for cortico-muscular than muscular-cortical direction. These results suggest that visual information affects cortico-muscular coherence at 8-12 Hz in non-athletes and amateur athletes but not in elite athletes. In elite athletes, this might be due to a long training for the control of equilibrium based on proprioceptive and tactile inputs.

High-gamma band activity of primary hand cortical areas: a sensorimotor feedback efficiency index.

Sensory feedback in motor control is widely recognized to be the key link between the activity of the primary motor cortex to the motor behavior. Through an ad-hoc developed procedure for source extraction (functional source separation), the primary sensory and motor cortex activities (FS(S1) and FS(M1)) were obtained from magnetoencephalographic recordings during a sensorimotor task sequence, and sensorimotor interaction was assessed. Source activity spectral powers were evaluated in the alpha (8-13 Hz), beta (14-32 Hz), gamma1 (33-60 Hz) and gamma2 (61-90 Hz) frequency bands. FS(S1) and FS(M1)had different spectral properties, with FS(S1) prevailing in alpha and FS(M1) in gamma band. Both FS(S1) and FS(M1) were reactive in the different sensorimotor tasks with respect to rest in all frequency bands, except for gamma2. During an isometric contraction, we searched for an index dependent on the performance level and with low variability in the healthy population. We found these properties satisfied within a relationship between FS(S1) and FS(M1) in the gamma2 band. This sensorimotor feedback efficiency index quantitatively estimates the continuous functional balance between primary sensory and motor areas devoted to hand control and seems promising for future developments, as it is easily assessable in patients.

Functional coupling between anterior prefrontal cortex (BA10) and hand muscle contraction during intentional and imitative motor acts.

The present study tested the hypothesis that functional cortico-muscular coupling is a putative physiological mechanism by which Brodmann area 10 (BA10) of anterior prefrontal cortex controls subjects' behavior. Intracerebral stereo electroencephalographic (SEEG) data were recorded from BA10 of epilepsy subjects in the course of pre-surgical monitoring. During the SEEG recordings, these subjects were engaged in three conditions: the execution of intentional hand muscle contractions as triggered by auditory stimuli ("EXE"); the execution of the same muscle contractions as an imitation of a person seated in front of the subject ("IMI"); and the mere observation of the hand muscle contractions performed by that person ("OBS"). SEEG frequency bands of interest were theta (4-7 Hz), alpha (8-12 Hz), beta 1 (13-21 Hz), beta 2 (22-30 Hz), and gamma (31-45 Hz). Results showed that functional cortico-muscular coupling at gamma band was higher in amplitude during the intentional muscle contraction ("EXE") than the other conditions ("IMI" and "OBS"). Instead, cortico-muscular coupling at theta band was higher in amplitude during the imitative muscle contraction ("IMI") than the other conditions ("EXE" and "OBS"). In parallel, there was an increase of SEEG gamma band power during the intentional muscle contraction and an increase of SEEG theta band power during its imitation. The present results suggest that anterior prefrontal cortex (BA10) might control subjects' behavior by means of functional cortico-muscular coupling at selective frequency bands (theta and wide gamma rhythms).

Expression of ectonucleotidase CD39 by Foxp3+ Treg cells: hydrolysis of extracellular ATP and immune suppression.

In the immune system, extracellular ATP functions as a "natural adjuvant" that exhibits multiple proinflammatory effects. It is released by damaged cells as an indicator of trauma and cell death but can be inactivated by CD39 (nucleoside triphosphate diphosphohydrolase-1 [NTPDase 1]), an ectoenzyme that degrades ATP to AMP. Here, we show that CD39 is expressed primarily by immune-suppressive Foxp3(+) regulatory T (Treg) cells. In mice, the enzyme is present on virtually all CD4(+)CD25(+) cells. CD39 expression is driven by the Treg-specific transcription factor Foxp3 and its catalytic activity is strongly enhanced by T-cell receptor (TCR) ligation. Activated Treg cells are therefore able to abrogate ATP-related effects such as P2 receptor-mediated cell toxicity and ATP-driven maturation of dendritic cells. Also, human Treg cells express CD39. In contrast to mice, CD39 expression in man is restricted to a subset of Foxp3(+) regulatory effector/memory-like T (T(REM)) cells. Notably, patients with the remitting/relapsing form of multiple sclerosis (MS) have strikingly reduced numbers of CD39(+) Treg cells in the blood. Thus, in humans CD39 is a marker of a Treg subset likely involved in the control of the inflammatory autoimmune disease.

Fetal auditory responses to external sounds and mother's heart beat: detection improved by Independent Component Analysis.

In this paper, we present a magnetoencephalographic study of the fetal auditory response to external stimuli and to the sound of the mother's heartbeat. We describe how an ad hoc functional selection procedure allowed us to isolate the sources in the fetal brain responding to sounds only, after the application to the recorded data of a standard Independent Component Analysis algorithm. In our experiment, acoustic stimuli were delivered to twelve healthy women with uncomplicated pregnancies at a time between 36 and 40 weeks gestational age, with their fetuses in breech presentation. Ultrasound images allowed determination of the region over the women's abdomen nearest to the fetal head, over which both the acoustic stimulator and the MEG sensors were subsequently placed. In 8 out of the 12 cases, our analysis provided consistent evidence of a fetal response both to the mother's heartbeat and to the external auditory stimulation; both were characterized by a clear prominent component at around 200 ms latency, which is widely accepted as the marker of the fetal response to auditory stimuli.

Neural connectivity in hand sensorimotor brain areas: an evaluation by evoked field morphology.

The connectivity pattern of the neural network devoted to sensory processing depends on the timing of relay recruitment from receptors to cortical areas. The aim of the present work was to uncover and quantify the way the cortical relay recruitment is reflected in the shape of the brain-evoked responses. We recorded the magnetic somatosensory evoked fields (SEF) generated in 36 volunteers by separate bilateral electrical stimulation of median nerve, thumb, and little fingers. After defining an index that quantifies the shape similarity of two SEF traces, we studied the morphologic characteristics of the recorded SEFs within the 20-ms time window that followed the impulse arrival at the primary sensory cortex. Based on our similarity criterion, the shape of the SEFs obtained stimulating the median nerve was observed to be more similar to the one obtained from the thumb (same median nerve innervation) than to the one obtained from the little finger (ulnar nerve innervation). In addition, SEF shapes associated with different brain regions were more similar within an individual than between subjects. Because the SEF morphologic characteristics turned out to be quite diverse among subjects, we defined similarity levels that allowed us to identify three main classes of SEF shapes in normalcy. We show evidence that the morphology of the evoked response describes the anatomo-functional connectivity pattern in the primary sensory areas. Our findings suggest the possible existence of a thalamo-cortico-thalamic responsiveness loop related to the different classes.

Inhibition of auditory cortical responses to ipsilateral stimuli during dichotic listening: evidence from magnetoencephalography.

The present magnetoencephalography (MEG) study on auditory evoked magnetic fields (AEFs) was aimed at verifying whether during dichotic listening the contralateral auditory pathway inhibits the ipsilateral one, as suggested by behavioural and patient studies. Ten healthy subjects were given a randomized series of three complex tones (261, 293 and 391 Hz, 500 ms duration), which were delivered monotically and dichotically with different intensities [60, 70 or 80 dBA (audio decibels)]. MEG data were recorded from the right auditory cortex. Results showed that the M100 amplitude over the right auditory cortex increased progressively when tones of increasing intensity were provided at the ipsilateral (right) ear. This effect on M100 was abolished when a concurrent tone of constant intensity was delivered dichotically at the contralateral (left) ear, suggesting that the contralateral pathway inhibited the ipsilateral one. The ipsilateral inhibition was present only when the contralateral tone fundamental frequency was similar to the ipsilateral tone. It was proposed that the occlusion mechanism would be exerted in cortical auditory areas as the dichotic effects were observed at M100 but not M50 component. This is the first evidence showing a neurophysiological inhibition driven by the contralateral auditory pathway over the ipsilateral one during dichotic listening.

Auditory sensory processing in autism: a magnetoencephalographic study.

BACKGROUND: Patients with autism show clinical features suggestive of abnormal processing of auditory and other sensory information. We hypothesized that low-functioning autistic subjects present abnormalities in discriminating simple auditory stimuli at sensory system preconscious stages of cortical processing. METHODS: To verify our hypothesis, we used magnetoencephalographic measurements of mismatch field (MMF), which reflects the detection of a change in the physical characteristics of a repetitive sound. Fourteen patients (aged 8-32 years) who met DSM-IV diagnostic criteria for autistic disorder participated in an auditory oddball experiment. Ten healthy participants matched for age and gender acted as control subjects. RESULTS: Significant differences in cerebral responses between patients and control subjects were recorded. Whereas control subjects showed a clearly identifiable MMF, with distinct generators in the M100 brain wave with regard to latency, position, and strength, no identifiable MMF was present in the autistic group. CONCLUSIONS: Our findings suggest that low-functioning autistic subjects present a dysfunction at preconscious stages of cortical auditory discrimination, playing a role in the abnormal processing of auditory sensory afferences. The attention independence of the MMF allows for exclusion of an effect related to impaired attention or task-related responses.