Diagnosis and treatment of neurogenic dysphagia - S1 guideline of the German Society of Neurology.

INTRODUCTION: Neurogenic dysphagia defines swallowing disorders caused by diseases of the central and peripheral nervous system, neuromuscular transmission, or muscles. Neurogenic dysphagia is one of the most common and at the same time most dangerous symptoms of many neurological diseases. Its most important sequelae include aspiration pneumonia, malnutrition and dehydration, and affected patients more often require long-term care and are exposed to an increased mortality. Based on a systematic pubmed research of related original papers, review articles, international guidelines and surveys about the diagnostics and treatment of neurogenic dysphagia, a consensus process was initiated, which included dysphagia experts from 27 medical societies. RECOMMENDATIONS: This guideline consists of 53 recommendations covering in its first part the whole diagnostic spectrum from the dysphagia specific medical history, initial dysphagia screening and clinical assessment, to more refined instrumental procedures, such as flexible endoscopic evaluation of swallowing, the videofluoroscopic swallowing study and high-resolution manometry. In addition, specific clinical scenarios are captured, among others the management of patients with nasogastric and tracheotomy tubes. The second part of this guideline is dedicated to the treatment of neurogenic dysphagia. Apart from dietary interventions and behavioral swallowing treatment, interventions to improve oral hygiene, pharmacological treatment options, different modalities of neurostimulation as well as minimally invasive and surgical therapies are dealt with. CONCLUSIONS: The diagnosis and treatment of neurogenic dysphagia is challenging and requires a joined effort of different medical professions. While the evidence supporting the implementation of dysphagia screening is rather convincing, further trials are needed to improve the quality of evidence for more refined methods of dysphagia diagnostics and, in particular, the different treatment options of neurogenic dysphagia. The present article is an abridged and translated version of the guideline recently published online ( https://www.awmf.org/uploads/tx_szleitlinien/030-111l_Neurogene-Dysphagie_2020-05.pdf ).

Modulation of attention functions by anodal tDCS on right PPC.

Attention is a complex construct that comprises at least three major subcomponents: alerting, spatial (re-)orienting, and executive functions, all of which have specific neural correlates along frontoparietal networks. Attention deficits are a common consequence of brain damage. Transcranial direct current stimulation (tDCS) has been shown to modulate spatial attention. We investigated whether tDCS of different stimulation targets differentially modulates alerting, spatial (re-)orienting, and executive functions. Twenty-four healthy participants were included in this randomized, double-blinded study, which employed a within-subject design. On four different days, the effects of 1.5 mA anodal tDCS (real and sham) on the left dorsolateral (EEG 10-20 point F3), left parietal (P3) and right parietal cortex (P4) were assessed using a modified attention network test. tDCS of the right parietal cortex enhanced spatial re-orienting, while tDCS of the other cortical targets did not modulate the assessed attention functions. With regard to visual field asymmetries in attentional processing, right parietal tDCS selectively enhanced mean network efficiency for targets presented in the contralateral left visual field. The observed visual field specific tDCS effects on reorienting suggest that systematic investigations into novel approaches for the treatment of patients suffering from spatial neglect patients are warranted.

Transcranial direct current stimulation (tDCS) of left parietal cortex facilitates gesture processing in healthy subjects.

Gesture processing deficits constitute a key symptom of apraxia, a disorder of motor cognition frequently observed after left-hemispheric stroke. The clinical relevance of apraxia stands in stark contrast to the paucity of therapeutic options available. Transcranial direct current stimulation (tDCS) is a promising tool for modulating disturbed network function after stroke. Here, we investigate the effect of parietal tDCS on gesture processing in healthy human subjects. Neuropsychological and imaging studies suggest that the imitation and matching of hand gestures involve the left inferior parietal lobe (IPL). Using neuronavigation based on cytoarchitectonically defined anatomical probability maps, tDCS was applied over left IPL-areas PF, PFm, or PG in healthy participants (n = 26). Before and after tDCS, subjects performed a gesture matching task and a person discrimination task for control. Changes in error rates and reaction times were analyzed for the effects of anodal and cathodal tDCS (compared with sham tDCS). Matching of hand gestures was specifically facilitated by anodal tDCS applied over the cytoarchitectonically defined IPL-area PFm, whereas tDCS over IPL-areas PF and PG did not elucidate significant effects. Taking into account tDCS electrode size and the central position of area PFm within IPL, it can be assumed that the observed effect is rather the result of a combined stimulation of the supramarginal and angular gyrus than an isolated PFm stimulation. Our data confirm the pivotal role of the left IPL in gesture processing. Furthermore, anatomically guided tDCS of the left IPL may constitute a promising approach to neurorehabilitation of apraxic patients with gesture processing deficits.

Modulation of top-down control of visual attention by cathodal tDCS over right IPS.

The right intraparietal sulcus (rIPS) is a key region for the endogenous control of selective visual attention in the human brain. Previous studies suggest that the rIPS is especially involved in top-down control and spatial distribution of attention across both visual hemifields. We further explored these attentional functions using transcranial direct current stimulation (tDCS) of the rIPS to modulate behavioral performance in a partial report task. Performance was analyzed according to the theory of visual attention (TVA) (Bundesen, 1990), which provides a computational framework to investigate different parameters of visuo-attentional processing such as top-down control, attentional weighting, capacity of visual short term memory, and processing speed. We investigated the effects of different tDCS current strengths (1 mA and 2 mA) in two experiments: 1 mA tDCS (anodal, cathodal, sham) did not affect any of the TVA parameters, but cathodal 2 mA stimulation significantly enhanced top-down control as evidenced by a reduction of the α parameter of TVA, regardless of hemifield. This differential impact on the top-down control component of attentional processing suggests that the horizontal rIPS is mainly involved in attentional selection as none of the spatial or resource variables of TVA were altered. Furthermore, the data add evidence to previous work highlighting (1) the importance of using appropriate current strength in stimulation protocols, and (2) that the often reported inhibitory effect of cathodal stimulation in e.g., motor tasks might not extend to cognitive paradigms.

Multi-session transcranial direct current stimulation (tDCS) elicits inflammatory and regenerative processes in the rat brain.

Transcranial direct current stimulation (tDCS) is increasingly being used in human studies as an adjuvant tool to promote recovery of function after stroke. However, its neurobiological effects are still largely unknown. Electric fields are known to influence the migration of various cell types in vitro, but effects in vivo remain to be shown. Hypothesizing that tDCS might elicit the recruitment of cells to the cortex, we here studied the effects of tDCS in the rat brain in vivo. Adult Wistar rats (n = 16) were randomized to either anodal or cathodal stimulation for either 5 or 10 consecutive days (500 µA, 15 min). Bromodeoxyuridine (BrdU) was given systemically to label dividing cells throughout the experiment. Immunohistochemical analyses ex vivo included stainings for activated microglia and endogenous neural stem cells (NSC). Multi-session tDCS with the chosen parameters did not cause a cortical lesion. An innate immune response with early upregulation of Iba1-positive activated microglia occurred after both cathodal and anodal tDCS. The involvement of adaptive immunity as assessed by ICAM1-immunoreactivity was less pronounced. Most interestingly, only cathodal tDCS increased the number of endogenous NSC in the stimulated cortex. After 10 days of cathodal stimulation, proliferating NSC increased by ∼60%, with a significant effect of both polarity and number of tDCS sessions on the recruitment of NSC. We demonstrate a pro-inflammatory effect of both cathodal and anodal tDCS, and a polarity-specific migratory effect on endogenous NSC in vivo. Our data suggest that tDCS in human stroke patients might also elicit NSC activation and modulate neuroinflammation.

Isometric contraction interferes with transcranial direct current stimulation (tDCS) induced plasticity: evidence of state-dependent neuromodulation in human motor cortex.

BACKGROUND AND PURPOSE: Neuroplastic alterations of cortical excitability and activity represent the likely neurophysiological foundation of learning and memory formation. Beyond their induction, alterations of these processes by subsequent modification of cortical activity, termed metaplasticity, came into the focus of interest recently. Animal slice experiments demonstrated that neuroplastic excitability enhancements, or diminutions, can be abolished by consecutive subthreshold stimulation. These processes, termed de-potentiation, and de-depression, have so far not been explored in humans. METHODS: We combined neuroplasticity induction by transcranial direct current stimulation (tDCS) applied to the hand area of primary motor cortex (M1), which can be used to induce long-lasting excitability enhancements or reductions, dependent on the polarity of stimulation, with short-lasting voluntary muscle contraction (VMC), which itself does not induce plastic cortical excitability changes. Corticospinal and intra-cortical M1 excitability were monitored by different transcranial magnetic stimulation (TMS) protocols. RESULTS: VMC reduced or tended to reverse the anodal tDCS-driven motor cortical excitability enhancement and the cathodal tDCS-induced excitability diminution. Our findings thus demonstrate de-potentiation- and de-depression-like phenomena at the system level in the human motor cortex. CONCLUSION: This neurophysiological study may contribute to a better understanding of the balance between induction and reversal of plasticity associated with motor learning and rehabilitation processes.

Processing of auditory motion in inferior parietal lobule: evidence from transcranial magnetic stimulation.

The neural substrates of auditory motion processing are, at present, still a matter of debate. It has been hypothesized that motion information is, as in the visual system, processed separately from other aspects of auditory information, such as stationary location. Here we aimed to differentiate the location of auditory motion processing in human cortex using low-frequency repetitive transcranial magnetic stimulation (rTMS) in combination with a psychophysical task of motion discrimination. rTMS was applied offline to right posterior superior temporal gyrus, right inferior parietal lobule, right dorsal premotor cortex, or right primary somatosensory cortex (as reference site). A significant decrease in performance was obtained exclusively for sounds presented in left hemispace after rTMS over the right inferior parietal lobule (BA 40). This finding indicates that the inferior parietal lobule plays a crucial role in the analysis of moving sound, with an apparent contralaterality of cortical processing. Combined with previous studies which have demonstrated effects of rTMS on static sound localization for both inferior parietal and posterior temporal cortices, the results suggest a hierarchical processing of auditory spatial information, with higher-order functions of motion analysis, such as discrimination of motion direction, mainly taking place beyond the temporal lobe.

Functional localization in the human brain: Gradient-Echo, Spin-Echo, and arterial spin-labeling fMRI compared with neuronavigated TMS.

A spatial mismatch of up to 14 mm between optimal transcranial magnetic stimulation (TMS) site and functional magnetic resonance imaging (fMRI) signal has consistently been reported for the primary motor cortex. The underlying cause might be the effect of magnetic susceptibility around large draining veins in Gradient-Echo blood oxygenation level-dependent (GRE-BOLD) fMRI. We tested whether alternative fMRI sequences such as Spin-Echo (SE-BOLD) or Arterial Spin-Labeling (ASL) assessing cerebral blood flow (ASL-CBF) may localize neural activity closer to optimal TMS positions and primary motor cortex than GRE-BOLD. GRE-BOLD, SE-BOLD, and ASL-CBF signal changes during right thumb abductions were obtained from 15 healthy subjects at 3 Tesla. In 12 subjects, tissue at fMRI maxima was stimulated with neuronavigated TMS to compare motor-evoked potentials (MEPs). Euclidean distances between the fMRI center-of-gravity (CoG) and the TMS motor mapping CoG were calculated. Highest SE-BOLD and ASL-CBF signal changes were located in the anterior wall of the central sulcus [Brodmann Area 4 (BA4)], whereas highest GRE-BOLD signal changes were significantly closer to the gyral surface. TMS at GRE-BOLD maxima resulted in higher MEPs which might be attributed to significantly higher electric field strengths. TMS-CoGs were significantly anterior to fMRI-CoGs but distances were not statistically different across sequences. Our findings imply that spatial differences between fMRI and TMS are unlikely to be caused by spatial unspecificity of GRE-BOLD fMRI but might be attributed to other factors, e.g., interactions between TMS-induced electric field and neural tissue. Differences between techniques should be kept in mind when using fMRI coordinates as TMS (intervention) targets.

Inhibition of the anterior intraparietal area and the dorsal premotor cortex interfere with arbitrary visuo-motor mapping.

OBJECTIVE: The contribution of the human anterior intraparietal area and the dorsal premotor cortex to arbitrary visuo-motor mapping during grasping were tested. METHODS: Trained right-handed subjects reached for and pincer-grasped a cube with the right hand in the absence of visual feedback after the cube location had been displayed for 200ms. During the reaching movements, the colour of the cube changed and visual feedback about the change of colour was provided for 100ms at 500ms after movement onset (at the time of peak grasp aperture). Depending on colour, subjects were instructed to either pincer-grasp the cube in a horizontal or vertical grasp position with the latter necessitating wrist rotation (experiment 1) or to pincer-grasp and transport the cube to either a left or right target position (experiment 2). Within two consecutive 200ms time windows (TMS 1 and 2) starting 500ms and 700ms after movement onset, respectively, double pulses of supra-threshold transcranial magnetic stimulation (inter-stimulus interval: 100ms) were delivered over (i) the left primary motor cortex (90 degrees vertically angulated coil position, control stimulation), (ii) the left dorsal premotor cortex or (ii) the left anterior intraparietal area. RESULTS: Compared to control stimulation, stimulation of the anterior intraparietal area, but not of the dorsal premotor cortex, at TMS 1 delayed the times to wrist rotation (experiment 1) and hand transport (experiment 2). Compared to control stimulation, stimulation of the dorsal premotor cortex, but not of the anterior intraparietal area, at TMS 2 delayed both wrist rotation (experiment 1) and hand transport (experiment 2). CONCLUSIONS: We contend that the anterior intraparietal area and the dorsal premotor cortex are both involved albeit at different phases during the mapping of arbitrary visual cues with goal directed grasp and transport movements. SIGNIFICANCE: These data add to the current understanding of how human cortical areas work in concert during manual activities.