Effects of motor preparation and spatial attention on corticospinal excitability in a delayed-response paradigm

The preparation of motor responses during the delay period of an instructed delay task is associated with sustained neural firing in the primate premotor cortex. It remains unclear how and when such preparation-related premotor activity influences the motor output system. In this study, we tested modulation of corticospinal excitability using single-pulse transcranial magnetic stimulation (TMS) during a delayed-response task. At the beginning of the delay interval participants were either provided with no information, spatial attentional information concerning location but not identity of an upcoming imperative stimulus, or information regarding the upcoming response. Behavioral data indicate that participants used all information available to them. Only when information concerning the upcoming response was provided did corticospinal excitability show differential modulation for the effector muscle compared to other task-unrelated muscles. We conclude that modulation of corticospinal excitability reflects specific response preparation, rather than non-specific event preparation

A Controlled Increase in Dietary Phosphate Elevates BP in Healthy Human Subjects.

Background Despite epidemiologic evidence for increased cardiovascular morbidity and mortality associated with both high dietary and serum phosphate in humans with normal renal function, no controlled phosphate intervention studies of systemic hemodynamics have been reported. Higher serum 25(OH) vitamin D levels are associated with better cardiovascular outcomes, but vitamin D increases intestinal phosphate absorption.Methods We conducted a prospective outpatient study with blinded assessment in 20 young adults with normal renal function randomized to high phosphate (regular diet plus 1 mmol/kg body wt per day of Na as neutral sodium phosphate) or low phosphate (regular diet plus lanthanum, 750 mg thrice/day, plus 0.7 mmol/kg body wt per day of Na as NaCl) for 11 weeks. After 6 weeks, all subjects received vitamin D3 (600,000 U) by intramuscular injection. Outcome parameters were 24-hour ambulatory systolic and diastolic BP (SBP and DBP), pulse rate (PR), biomarkers, and measures of endothelial and arterial function.Results Compared with the low-phosphate diet group, the high-phosphate diet group had a significant increase in mean±SEM fasting plasma phosphate concentration (0.23±0.11 mmol/L); 24-hour SBP and DBP (+4.1; 95% confidence interval [95% CI], 2.1 to 6.1; and +3.2; 95% CI, 1.2 to 5.2 mm Hg, respectively); mean 24-hour PR (+4.0; 95% CI, 2.0 to 6.0 beats/min); and urinary metanephrine and normetanephrine excretion (54; 95% CI, 50 to 70; and 122; 95% CI, 85 to 159 µg/24 hr, respectively). Vitamin D had no effect on any of these parameters. Neither high- nor low-phosphate diet nor vitamin D affected endothelial function or arterial elasticity.Conclusions Increased phosphate intake (controlled for sodium) significantly increases SBP, DBP, and PR in humans with normal renal function, in part, by increasing sympathoadrenergic activity

Image Artifacts in Concurrent Transcranial Magnetic Stimulation (TMS) and fMRI Caused by Leakage Currents: Modeling and Compensation

Purpose: To characterize and eliminate a new type of image artifact in concurrent transcranial magnetic stimulation and functional MRI (TMS-fMRI) caused by small leakage currents originating from the high-voltage capacitors in the TMS stimulator system.Materials and Methods: The artifacts in echo-planar images (EPI) caused by leakage currents were characterized and quantified in numerical simulations and phantom studies with different phantom-coil geometries. A relay-diode combination was devised and inserted in the TMS circuit that shorts the leakage current. Its effectiveness for artifact reduction was assessed in a phantom scan resembling a realistic TMS-fMRI experiment.Results: The leakage-current-induced signal changes exhibited a multipolar spatial pattern and the maxima exceeded 1% at realistic coil-cortex distances. The relay-diode combination effectively reduced the artifact to a negligible level.Conclusion: The leakage-current artifacts potentially obscure effects of interest or lead to false-positives. Since the artifact depends on the experimental setup and design (eg. amplitude of the leakage current, coil orientation, paradigm. EPI parameters), we recommend its assessment for each experiment. The relay-diode combination can eliminate the artifacts if necessary

Time-Dependent Changes in Human Corticospinal Excitability Reveal Value-Based Competition for Action during Decision Processing

Our choices often require appropriate actions to obtain a preferred outcome, but the neural underpinnings that link decision making and action selection remain largely undetermined. Recent theories propose that action selection occurs simultaneously, i.e., parallel in time, with the decision process. Specifically, it is thought that action selection in motor regions originates from a competitive process that is gradually biased by evidence signals originating in other regions, such as those specialized in value computations. Biases reflecting the evaluation of choice options should thus emerge in the motor system before the decision process is complete. Using transcranial magnetic stimulation, we sought direct physiological evidence for this prediction by measuring changes in corticospinal excitability in human motor cortex during value-based decisions. We found that excitability for chosen versus unchosen actions distinguishes the forthcoming choice before completion of the decision process. Both excitability and reaction times varied as a function of the subjective value-difference between chosen and unchosen actions, consistent with this effect being value-driven. This relationship was not observed in the absence of a decision. Our data provide novel evidence in humans that internally generated value-based decisions influence the competition between action representations in motor cortex before the decision process is complete. This is incompatible with models of serial processing of stimulus, decision, and action

Distinct causal influences of parietal versus frontal areas on human visual cortex: evidence from concurrent TMS-fMRI

It has often been proposed that regions of the human parietal and/or frontal lobe may modulate activity in visual cortex, for example, during selective attention or saccade preparation. However, direct evidence for such causal claims is largely missing in human studies, and it remains unclear to what degree the putative roles of parietal and frontal regions in modulating visual cortex may differ. Here we used transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) concurrently, to show that stimulating right human intraparietal sulcus (IPS, at a site previously implicated in attention) elicits a pattern of activity changes in visual cortex that strongly depends on current visual context. Increased intensity of IPS TMS affected the blood oxygen level–dependent (BOLD) signal in V5/MT+ only when moving stimuli were present to drive this visual region, whereas TMS-elicited BOLD signal changes were observed in areas V1–V4 only during the absence of visual input. These influences of IPS TMS upon remote visual cortex differed significantly from corresponding effects of frontal (eye field) TMS, in terms of how they related to current visual input and their spatial topography for retinotopic areas V1–V4. Our results show directly that parietal and frontal regions can indeed have distinct patterns of causal influence upon functional activity in human visual cortex. Key words: attention, frontal cortex, functional magnetic resonance imaging, parietal cortex, top--down, transcranial magnetic stimulatio

On the synchronization of transcranial magnetic stimulation and functional echo-planar imaging

Purpose: To minimize artifacts in echo-planar imaging (EPI) of human brain function introduced by simultaneous transcranial magnetic stimulation (TMS). Materials and Methods: Distortions due to TMS pulses (0.25 msec, 2.0 T) were studied at 2.0 T before and during EPI. Results: Best results were obtained if both the EPI section orientation and the frequency-encoding gradient were parallel to the plane of the TMS coil. Under these conditions, a TMS pulse caused image distortions when preceding the EPI sequence by less than 100 msec. Recordings with a magnetic field gradient pick-up coil revealed transient magnetic fields after TMS, which are generated by eddy currents in the TMS coil. TMS during image acquisition completely spoiled all transverse magnetizations and induced disturbances ranging from image corruption to mild image blurring, depending on the affected low and high spatial frequencies. Simultaneous TMS and radio-frequency (RF) excitation gave rise to T1- dependent signal changes that lasted for several seconds and yielded pronounced false-positive activations during functional brain mapping. Conclusion: To ensure reliable and robust combinations, TMS should be applied at least 100 msec before EPI while completely avoiding any pulses during imaging

Using Proactive Maintenance Strategy for Sustainable Electric Power Production in Nigeria

An unpleasant turn of events would compel and prevail upon power plants owners and operators looking for alternative for keeping maintenance activities up and awake. Thus, causing a break away from outdated traditional system originally practiced in maintenance organizations, which affects operations in terms of costs and energy required for sustainable activity in the power production industry; via Generation, Transmission and Distribution. However, the only inevitably obtainable option as per organizational success in the power industry is through a substituent for a failure based system with success based strategy that is concerned with optimization of complex processes, systems or organization by developing, improving and implementing integrated systems of people, money, knowledge, information and equipment, central to manufacturing and production operations. A platform intended to deliver on plant (a) availability (b) reliability and (c) sustainability, which lead to reduced maintenance costs and increased profitability. Keywords: maintenance management; strategy implementation, power sector, performance optimization DOI: 10.7176/IEL/11-3-03 Publication date:October 31st 202

A Future of Current Flow Modelling for Transcranial Electrical Stimulation?

Purpose of Review: Transcranialelectrical stimulation (tES) is used to non-invasively modulate brain activityin health and disease. Current flow modeling (CFM) provides estimates of whereand how much electrical current is delivered to in the brain during tES. Ittherefore holds promise as a method to reduce commonplace variability in tESdelivery and, in turn, the outcomes of stimulation. However, the adoption ofCFM has not yet been widespread and its impact on tES outcome variability isunclear. Here, we discuss the potential barriers to effective, practicalCFM-informed tES use. Recent Findings: CFMhas progressed from models based on concentric spheres to gyri-precise headmodels derived from individual MRI scans. Users can now estimate the intensityof electrical fields (E-fields), their spatial extent, and the direction ofcurrent flow in a target brain region during tES. Here. we consider the multi-dimensionalchallenge of implementing CFM to optimise stimulation dose: this requiresinformed decisions to prioritise E-field characteristics most likely to resultin desired stimulation outcomes, though the physiological consequences of themodelled current flow are often unknown. Second, we address the issue of adisconnect between predictions of E-field characteristics provided by CFMs andpredictions of the physiological consequences of stimulation which CFMs are notdesigned to address. Third, we discuss how ongoing development of CFM inconjunction with other modelling approaches could overcome these challengeswhile maintaining accessibility for widespread use. Summary: Theincreasing complexity and sophistication of CFM is a mandatory step towards dosecontrol and precise, individualised delivery of tES. However, it also riskscounteracting the appeal of tES as a straightforward, cost-effective tool forneuromodulation, particularly in clinical settings

Active Inference, Attention, and Motor Preparation

Perception is the foundation of cognition and is fundamental to our beliefs and consequent action planning. The Editorial (this issue) asks: “what mechanisms, if any, mediate between perceptual and cognitive processes?” It has recently been argued that attention might furnish such a mechanism. In this paper, we pursue the idea that action planning (motor preparation) is an attentional phenomenon directed toward kinesthetic signals. This rests on a view of motor control as active inference, where predictions of proprioceptive signals are fulfilled by peripheral motor reflexes. If valid, active inference suggests that attention should not be limited to the optimal biasing of perceptual signals in the exteroceptive (e.g., visual) domain but should also bias proprioceptive signals during movement. Here, we investigate this idea using a classical attention (Posner) paradigm cast in a motor setting. Specially, we looked for decreases in reaction times when movements were preceded by valid relative to invalid cues. Furthermore, we addressed the hierarchical level at which putative attentional effects were expressed by independently cueing the nature of the movement and the hand used to execute it. We found a significant interaction between the validity of movement and effector cues on reaction times. This suggests that attentional bias might be mediated at a low level in the motor hierarchy, in an intrinsic frame of reference. This finding is consistent with attentional enabling of top-down predictions of proprioceptive input and may rely upon the same synaptic mechanisms that mediate directed spatial attention in the visual system

Response repetition biases in human perceptual decisions are explained by activity decay in competitive attractor models

Animals and humans have a tendency to repeat recent choices, a phenomenon known as choice hysteresis. The mechanism for this choice bias remains unclear. Using an established, biophysically informed model of a competitive attractor network for decision making, we found that decaying tail activity from the previous trial caused choice hysteresis, especially during difficult trials, and accurately predicted human perceptual choices. In the model, choice variability could be directionally altered through amplification or dampening of post-trial activity decay through simulated depolarizing or hyperpolarizing network stimulation. An analogous intervention using transcranial direct current stimulation (tDCS) over left dorsolateral prefrontal cortex (dlPFC) yielded a close match between model predictions and experimental results: net soma depolarizing currents increased choice hysteresis, while hyperpolarizing currents suppressed it. Residual activity in competitive attractor networks within dlPFC may thus give rise to biases in perceptual choices, which can be directionally controlled through non-invasive brain stimulation