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Motion artifacts are a significant source of noise in many functional near-infrared spectroscopy (fNIRS) experiments. Despite this, there is no well-established method for their removal. Instead, functional trials of fNIRS data containing a motion artifact are often rejected completely. However, in most experimental circumstances the number of trials is limited, and multiple motion artifacts are common, particularly in challenging populations. Many methods have been proposed recently to correct for motion artifacts, including principle component analysis, spline interpolation, Kalman filtering, wavelet filtering and correlation-based signal improvement. The performance of different techniques has been often compared in simulations, but only rarely has it been assessed on real functional data. Here, we compare the performance of these motion correction techniques on real functional data acquired during a cognitive task, which required the participant to speak aloud, leading to a low-frequency, low-amplitude motion artifact that is correlated with the hemodynamic response. To compare the efficacy of these methods, objective metrics related to the physiology of the hemodynamic response have been derived. Our results show that it is always better to correct for motion artifacts than reject trials, and that wavelet filtering is the most effective approach to correcting this type of artifact, reducing the area under the curve where the artifact is present in 93% of the cases. Our results therefore support previous studies that have shown wavelet filtering to be the most promising and powerful technique for the correction of motion artifacts in fNIRS data. The analyses performed here can serve as a guide for others to objectively test the impact of different motion correction algorithms and therefore select the most appropriate for the analysis of their own fNIRS experiment. •A comparison of motion artifact correction techniques on real data is performed.•Motion artifact correction is a crucial step in the fNIRS signal processing stream.•Wavelet filtering is a powerful tool for motion artifact correction.

Functional near infrared spectroscopy and electroencephalography are non-invasive techniques that rely on sensors placed over the scalp. The spatial localization of the measured brain activity requires the precise individuation of sensor positions and, when individual anatomical information is not available, the accurate registration of these sensor positions to a head atlas. Both these issues could be successfully addressed using a photogrammetry-based method. In this study we demonstrate that sensor positions can be accurately detected from a video recorded with a smartphone, with a median localization error of 0.7 mm, comparable if not lower, to that of conventional approaches. Furthermore, we demonstrate that the additional information of the shape of the participant’s head can be further exploited to improve the registration of the sensor’s positions to a head atlas, reducing the median sensor localization error of 31% compared to the standard registration approach.

Several studies have evaluated the effect of anodal transcranial direct current stimulation (tDCS) over the prefrontal cortex (PFC) for the enhancement of working memory (WM) performance in healthy older adults. However, the mixed results obtained so far suggest the need for concurrent brain imaging, in order to more directly examine tDCS effects. The present study adopted a continuous multimodal approach utilizing functional near-infrared spectroscopy (fNIRS) to examine the interactive effects of tDCS combined with manipulations of reward motivation. Twenty-one older adults (mean age = 69.7 years; SD = 5.05) performed an experimental visuo-spatial WM task before, during and after the delivery of 1.5 mA anodal tDCS/sham over the left prefrontal cortex (PFC). During stimulation, participants received performance-contingent reward for every fast and correct response during the WM task. In both sessions, hemodynamic activity of the bilateral frontal, motor and parietal areas was recorded across the entire duration of the WM task. Cognitive functions and reward sensitivity were also assessed with standard measures. Results demonstrated a significant impact of tDCS on both WM performance and hemodynamic activity. Specifically, faster responses in the WM task were observed both during and after anodal tDCS, while no differences were found under sham control conditions. However, these effects emerged only when taking into account individual visuo-spatial WM capacity. Additionally, during and after the anodal tDCS, increased hemodynamic activity relative to sham was observed in the bilateral PFC, while no effects of tDCS were detected in the motor and parietal areas. These results provide the first evidence of tDCS-dependent functional changes in PFC activity in healthy older adults during the execution of a WM task. Moreover, they highlight the utility of combining reward motivation with prefrontal anodal tDCS, as a potential strategy to improve WM efficiency in low performing healthy older adults. •fNIRS and tDCS were used in healthy older adults performing a working memory task.•Bilateral prefrontal hemodynamic activity increased with left prefrontal anodal tDCS.•Anodal tDCS combined with reward motivation improves working memory in older adults.

•An AO-PS (action observation - proprioceptive stimulation) protocol was proposed.•Oxyhemoglobin (HbO) concentration changes were evaluated with fNIRS.•TMS assessed primary motor cortex (M1) excitability changes before and after AO-PS.•AO-PS increased HbO concentration changes in sensorimotor and associative areas.•Superior parietal lobule activity correlated with long-term changes in M1 activity. The aim of this study was to investigate changes in cortical hemodynamic activity within a frontoparietal network during the administration of an innovative action observation (AO) and proprioceptive stimulation (PS) protocol, and to examine whether this activity could predict the efficacy of the protocol in evoking M1 plasticity, reflected in significant long-term changes in M1 excitability. AO-PS was composed of 50 bursts of combined stimuli. Each burst consisted of five couples of AO and PS during which participants observed a video showing thumb opposition movements and simultaneously received a mechanical vibration on the extensor pollicis brevis muscle (stimulation frequency 80 Hz). During AO-PS, the hemodynamic activity was measured by means of functional Near-Infrared Spectroscopy. Recruitment curves were assessed using transcranial magnetic stimulation before, immediately, 30 and 60 min after AO-PS, to evaluate changes in M1 excitability. During AO-PS, a significant increase in oxyhemoglobin (HbO) concentration changes was found in the following Brodmann Areas (BA): left and right BA6, BA44, and BA43, left BA3, BA4, BA40 and BA7. The highest increment was found in the left BA4. In left BA7 and BA40 the time-to-peak in HbO concentration changes were reached significantly later than in the other BAs. On average, no significant changes were observed after AO-PS administration in M1 excitability, but HbO concentration changes in the left BA7 correlated with plasticity index. These findings highlight the involvement of sensorimotor and associative fronto-parietal regions during AO-PS. Additionally, the activity of the left BA7 revealed the plasticity induced by AO-PS in M1.

•Nine-Hole peg test was compared with a new task involving the sensorimotor domain.•Sensorimotor and prefrontal activity during manual dexterity was assessed by fNIRS.•Right BA10 and BA11 are the substrate for cognitive planning in manual dexterity.•BA10 activity correlates with increased time to perform the nine-hole peg test.•Cognitive domain should be considered when manual dexterity is investigated. Manual dexterity is referred to as the skill to perform fine motor movements and it has been assumed to be associated to the cognitive domain, as well as the sensorimotor one. In this work, we investigated with functional near-infrared spectroscopy the cortical activations elicited by the execution of the 9-HPT, i.e., a standard test evaluating manual dexterity in which nine pegs were taken, placed into and then removed from nine holes on a board as quickly as possible. For comparison, we proposed a new active control task mainly involving the sensorimotor domain, in which the pegs must be placed and removed using the same single hole (1-HPT). Behaviorally, we found two distinct groups based on the difference between the execution time of the 9-HPT and the 1-HPT (ΔHPT). Cortical areas belonging to the network controlling reaching and grasping movements were active in both groups; however, participants showing a large ΔHPT presented significantly higher activation in prefrontal cortical areas (right BA10 and BA11) during 9-HPT and 1-HPT performance with respect to the participants with a small ΔHPT, who showed a deactivation in BA10. Unexpectedly, we observed a significant linear relationship between ΔHPT and right BA10 activity. This suggested that participants performing the 9-HPT more slowly than the 1-HPT recruited prefrontal areas implicitly exploiting the cognitive skills of planning, perhaps in search of a motor strategy to solve the test activating attentional and cognitive control processes, but this resulted not efficient and instead increased the time to accomplish a manual dexterity task.

The specialised regional functionality of the mature human cortex partly emerges through experience-dependent specialisation during early development. Our existing understanding of functional specialisation in the infant brain is based on evidence from unitary imaging modalities and has thus focused on isolated estimates of spatial or temporal selectivity of neural or haemodynamic activation, giving an incomplete picture. We speculate that functional specialisation will be underpinned by better coordinated haemodynamic and metabolic changes in a broadly orchestrated physiological response. To enable researchers to track this process through development, we develop new tools that allow the simultaneous measurement of coordinated neural activity (EEG), metabolic rate, and oxygenated blood supply (broadband near-infrared spectroscopy) in the awake infant. In 4- to 7-month-old infants, we use these new tools to show that social processing is accompanied by spatially and temporally specific increases in coupled activation in the temporal-parietal junction, a core hub region of the adult social brain. During non-social processing, coupled activation decreased in the same region, indicating specificity to social processing. Coupling was strongest with high-frequency brain activity (beta and gamma), consistent with the greater energetic requirements and more localised action of high-frequency brain activity. The development of simultaneous multimodal neural measures will enable future researchers to open new vistas in understanding functional specialisation of the brain.

Background: Directing attention to relevant visual objects while ignoring distracting stimuli is crucial for effective perception and goal-directed behavior. Event-related potential (ERP) studies using the additional-singleton paradigm have provided valuable insights into how the human brain processes competing salient stimuli by monitoring N2pc and PD, two event-related components thought to reflect target selection and distractor suppression, respectively. However, whether these components reflect the activity of a single or distinct neural mechanism remains controversial. Herein, we investigated the neural substrate of N2pc and PD by manipulating the vertical elevation of target and distractor relative to the visual horizontal meridian using two variants of the additional-singleton paradigm. Methods: In Experiment 1, participants searched for a shape singleton and identified the orientation of an embedded tilted bar while ignoring a color singleton. In Experiment 2, the tilted bars were removed and participants performed a shape search while ignoring a color singleton. Electroencephalogram (EEG) recordings at posterior sites (PO7/8) measured N2pc and PD components. Reaction times and ERP amplitudes were analyzed across conditions. Results: The results of both Experiments 1 and 2 showed that N2pc and PD responded in opposite ways to the manipulation of vertical elevation. N2pc was robust for targets in the lower visual hemifield and reversed in polarity (i.e., post-N2pc positivity ) for targets in the upper visual hemifield. Conversely, PD was more pronounced for distractors in the upper visual hemifield and nil for those in the lower visual hemifield. Critically, vertical elevation did not influence psychophysical estimates of search efficiency in either experiment, suggesting that the relationship between these components and their functional significance is less straightforward than previously thought. Conclusions: These results provide empirical support for the idea that N2pc and PD are influenced by the retinotopic organization of the visual cortex in a manner consistent with the neural and functional dissociation of target selection and distractor suppression in visual search.

Time-of-day is rarely considered during experimental protocols investigating motor behavior and neural activity. The goal of this work was to investigate differences in functional cortical connectivity at rest linked to the time of the day using functional Near-Infrared Spectroscopy (fNIRS). Since resting-state brain is shown to be a succession of cognitive, emotional, perceptual, and motor processes that can be both conscious and nonconscious, we studied self-generated thought with the goal to help in understanding brain dynamics. We used the New-York Cognition Questionnaire (NYC-Q) for retrospective introspection to explore a possible relationship between the ongoing experience and the brain at resting-state to gather information about the overall ongoing experience of subjects. We found differences in resting-state functional connectivity in the inter-hemispheric parietal cortices, which was significantly greater in the morning than in the afternoon, whilst the intra-hemispheric fronto-parietal functional connectivity was significantly greater in the afternoon than in the morning. When we administered the NYC-Q we found that the score of the question 27 (“during RS acquisition my thoughts were like a television program or film”) was significantly greater in the afternoon with respect to the morning. High scores in question 27 point to a form of thought based on imagery. It is conceivable to think that the unique relationship found between NYC-Q question 27 and the fronto-parietal functional connectivity might be related to a mental imagery process during resting-state in the afternoon.

Functional near-infrared spectroscopy (fNIRS) uses near-infrared light to measure cortical concentration changes in oxygenated (HbO) and deoxygenated hemoglobin (HbR) held to be correlated with cognitive activity. Providing a parametric depiction of such changes in the classic form of stimulus-evoked hemodynamic responses (HRs) can be attained with this technique only by solving two problems. One problem concerns the separation of informative optical signal from structurally analogous noise generated by a variety of spurious sources, such as heart beat, respiration, and vasomotor waves. Another problem pertains to the inherent variability of HRs, which is notoriously contingent on the type of experiment, brain region monitored, and human phenotype. A novel method was devised in the present context to solve both problems based on a two-step algorithm combining the treatment of noise-only data extrapolated from a reference-channel and a Bayesian filter applied on a per-trial basis. The present method was compared to two current methods based on conventional averaging, namely, a typical averaging method and an averaging method implementing the use of a reference-channel. The result of the comparison, carried out both on artificial and real data, revealed a sensitive accuracy improvement in HR estimation using the present method relative to each of the other methods. ► Estimation of stimulus-evoked hemodynamic activity in the human cortex using fNIRS ► A novel approach to increase signal-to-noise ratio of the hemodynamic response ► Sizable accuracy improvements demonstrated using both artificial and human data ► No need for a-priori information on hemodynamic response's profile ► Applicable to a large class of fNIRS experiments, including event-related designs