Age-related changes in global motion coherence: conflicting haemodynamic and perceptual responses

Our aim was to use both behavioural and neuroimaging data to identify indicators of perceptual decline in motion processing. We employed a global motion coherence task and functional Near Infrared Spectroscopy (fNIRS). Healthy adults (n = 72, 18-85) were recruited into the following groups: young (n = 28, mean age = 28), middle-aged (n = 22, mean age = 50), and older adults (n = 23, mean age = 70). Participants were assessed on their motion coherence thresholds at 3 different speeds using a psychophysical design. As expected, we report age group differences in motion processing as demonstrated by higher motion coherence thresholds in older adults. Crucially, we add correlational data showing that global motion perception declines linearly as a function of age. The associated fNIRS recordings provide a clear physiological correlate of global motion perception. The crux of this study lies in the robust linear correlation between age and haemodynamic response for both measures of oxygenation. We hypothesise that there is an increase in neural recruitment, necessitating an increase in metabolic need and blood flow, which presents as a higher oxygenated haemoglobin response. We report age-related changes in motion perception with poorer behavioural performance (high motion coherence thresholds) associated with an increased haemodynamic response

Human central auditory plasticity: A review of functional nearâ infrared spectroscopy (fNIRS) to measure cochlear implant performance and tinnitus perception

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146915/1/lio2185_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146915/2/lio2185.pd

Validating an image-based fNIRS approach with fMRI and a working memory task

In the current study, we extend a previous methodological pipeline by adding a novel image reconstruction approach to move functional near-infrared (fNIRS) signals from channel-space on the surface of the head to voxel-space within the brain volume. We validate this methodology by comparing voxel-wise fNIRS results to functional magnetic resonance imaging (fMRI) results from a visual working memory (VWM) task using two approaches. In the first approach, significant voxel-wise correlations were observed between fNIRS and fMRI measures for all experimental conditions across brain regions in the fronto-parieto-temporal cortices. In the second approach, we conducted separate multi-factorial ANOVAs on fNIRS and fMRI measures and then examined the correspondence between main and interaction effects within common regions of interest. Both fMRI and fNIRS showed similar trends in activation within the VWM network when the number of items held in working memory increases. These results validate the image-based fNIRS approach

Using Functional Near Infrared Spectroscopy (fNIRS) to study dynamic stereoscopic depth perception

The parietal cortex has been widely implicated in the processing of depth perception by many neuroimaging studies, yet functional near infrared spectroscopy (fNIRS) has been an under-utilised tool to examine the relationship of oxy- ([HbO]) and de-oxyhaemoglobin ([HbR]) in perception. Here we examine the haemodynamic response (HDR) to the processing of induced depth stimulation using dynamic random-dot-stereograms (RDS). We used fNIRS to measure the HDR associated with depth perception in healthy young adults (n = 13, mean age 24). Using a blocked design, absolute values of [HbO] and [HbR] were recorded across parieto-occipital and occipital cortices, in response to dynamic RDS. Control and test images were identical except for the horizontal shift in pixels in the RDS that resulted in binocular disparity and induced the percept of a 3D sine wave that 'popped out' of the test stimulus. The control stimulus had zero disparity and induced a 'flat' percept. All participants had stereoacuity within normal clinical limits and successfully perceived the depth in the dynamic RDS. Results showed a significant effect of this complex visual stimulation in the right parieto-occipital cortex (p < 0.01, η(2) = 0.54). The test stimulus elicited a significant increase in [HbO] during depth perception compared to the control image (p < 0.001, 99.99 % CI [0.008-0.294]). The similarity between the two stimuli may have resulted in the HDR of the occipital cortex showing no significant increase or decrease of cerebral oxygenation levels during depth stimulation. Cerebral oxygenation measures of [HbO] confirmed the strong association of the right parieto-occipital cortex with processing depth perception. Our study demonstrates the validity of fNIRS to investigate [HbO] and [HbR] during high-level visual processing of complex stimuli

Brain Cortical Mapping by Simultaneous Recording of Functional Near Infrared Spectroscopy and Electroencephalograms from the Whole Brain During Right Median Nerve Stimulation

To investigate relationships between hemodynamic responses and neural activities in the somatosensory cortices, hemodynamic responses by near infrared spectroscopy (NIRS) and electroencephalograms (EEGs) were recorded simultaneously while subjects received electrical stimulation in the right median nerve. The statistical significance of the hemodynamic responses was evaluated by a general linear model (GLM) with the boxcar design matrix convoluted with Gaussian function. The resulting NIRS and EEGs data were stereotaxically superimposed on the reconstructed brain of each subject. The NIRS data indicated that changes in oxy-hemoglobin concentration increased at the contralateral primary somatosensory (SI) area; responses then spread to the more posterior and ipsilateral somatosensory areas. The EEG data indicated that positive somatosensory evoked potentials peaking at 22 ms latency (P22) were recorded from the contralateral SI area. Comparison of these two sets of data indicated that the distance between the dipoles of P22 and NIRS channels with maximum hemodynamic responses was less than 10 mm, and that the two topographical maps of hemodynamic responses and current source density of P22 were significantly correlated. Furthermore, when onset of the boxcar function was delayed 5–15 s (onset delay), hemodynamic responses in the bilateral parietal association cortices posterior to the SI were more strongly correlated to electrical stimulation. This suggests that GLM analysis with onset delay could reveal the temporal ordering of neural activation in the hierarchical somatosensory pathway, consistent with the neurophysiological data. The present results suggest that simultaneous NIRS and EEG recording is useful for correlating hemodynamic responses to neural activity

Multimodal Diffuse Optical Imaging Evidence of Age-Related Changes in Neural Substrates of Semantic Words Processing

RÉSUMÉ Le vieillissement rapide de la population au Canada changera les aspects démographiques à l’avenir par le fait que les personnes âgées de 65 ans et plus vont dépasser en volume les jeunes de moins de 20 ans. En sachant les coûts associés au traitement et au soutien des personnes âgées atteintes par une ou plusieurs démences cognitives, on admet l’importance des études gériatriques pour mieux comprendre les mécanismes neurophysiologiques du vieillissement. L’intérêt principal est de trouver un lien entre les effets neurologiques du vieillissement et ceux du déclin cognitif afin d’établir des stratégies qui encourageront un vieillissement en santé. Notre compréhension du cerveau a beaucoup évolué au cours des dernières décennies grâce à de nouvelles techniques en imagerie cérébrale. Pourtant, l’interprétation de ces données reste un défi. Dans le cas de l’imagerie fonctionnelle par résonance magnétique (IRM) ou par optique diffuse (IOD), la réponse neuronale est indirectement dérivée de l’hémodynamique. Cette dernière est sujette à de complexes interactions entre l’oxygénation du cerveau, le volume et le débit sanguin, ainsi que la structure hétérogène du cortex. Ces interactions rendent difficile une interprétation quantitative des données. Dans le cas des études en vieillissement cognitif, ces paramètres sont de plus modifiés par l’âge, ce qui mène à une importante variabilité interindividuelle dans l’interprétation des données. La caractérisation des effets neurophysiologiques du vieillissement sur les signaux d’imagerie cérébrale est donc essentielle pour permettre des études rigoureuses du déclin cognitif avec l’âge. Vu les limites en rapport avec les signaux intrinsèques de chacune des modalités d’imagerie non-invasive, l’intérêt pour les études multimodales s’accroît car elles permettent de calibrer avec plus de précision les données fonctionnelles. L’intégration des données complémentaires acquises via différentes modalités de neuroimagerie, dans cette étude, nous a permis de quantifier les activations neuronales et de surveiller leurs modifications reliées au vieillissement. Un montage de spectroscopie en temps résolu, fait au laboratoire, nous a fourni des données au repos sur la concentration en oxy- et déoxyhémoglobine, ainsi que sur le volume sanguin. En imagerie par résonance magnétique, une séquence anatomique nous a servi à 1) évaluer une potentielle corrélation entre l’épaisseur corticale (matières grise et blanche) et le niveau de la réponse hémodynamique et 2) Recaller la carte d’activité cérébrale de chaque participant sur son image anatomique. On rajoute ces dernières mesures comme régresseur à un modèle linéaire généralisé de la réponse hémodynamique. En faisant l’hypothèse que ces changements de bases sont liés à la physiologie,----------ABSTRACT The demographic features of the population of Canada will experience an unprecedented historical change in the near future by the number of individuals above 65 years surpassing the number of youngsters under 20 years. Considering the costly consequences of age-related cognitive decline, both for individuals and the society, studying the neurophysiological mechanisms of these unfavorable changes has become an utmost priority in health research. The main goal of this field is to link the effects of cerebral aging to those of cognitive aging in order to stablish strategies promoting healthy aging. Normal cerebral aging is accompanied by some neurophysiological and neuroanatomical alterations depending on epigenetics of individuals. Amongst neurophysiological deteriorations causing cognitive decline, one should account for the neural loss, cortical density reduction, neurovascular, metabolic, and neurotransmission dysfunctions. Taken together these alterations with age, we were interested to determine whether older adults are affected in their cognitive abilities by more than one simple factor. In another word, we aimed at exploring the potential relationship between the abovementioned age-related alterations with cognitive performance. However, the main challenge of such study appears when interpreting functional data regarding baseline measures of each individual. Thus, the increased inter and intra-individual variability in cognitive studies is mainly due to their large variations in structural and neurophysiological characteristics in the course of their lifespan. In this project, we defined a multi-modal neuroimaging protocol with the aim of calibrating the functional measures of task-related activity by measured individual baseline neurophysiological characteristics. To assess individuals` cerebral blood flow at rest, one of the constituent of hemodynamic response, we used an arterial-spin labeling sequence of magnetic resonance imaging. This technique based on tagging water in blood, gives the blood quantity emerging to brain. Carotids, the main arterial vessels that supply blood to brain, neck and face, are well known to be affected by age inter-individually and play as a non-functional moderator in hemodynamic response formation. As an estimate of total blood volume and baseline concentration of oxy- and deoxyhaemoglobin, we used a home-made 4-chanel time resolution optical device to acquire data from each participant’s prefrontal lobe. To refine the spatial resolution of non-invasive optical imaging, we also acquired anatomical MR images of each participant to 1) calculate cortical thickness with the objective of evaluating the correlatio

Hemodynamic correlates of spontaneous neural activity measured by human whole-head resting state EEG + fNIRS

The brains of awake, resting human subjects display spontaneously occurring neural activity patterns whose magnitude is typically many times greater than those triggered by cognitive or perceptual performance. Such resting state (RS) activity is thought to reflect the functional organization of the brain. In addition, both evoked and RS activation affect local cerebral hemodynamic properties through processes collectively referred to as neurovascular coupling. This is a major topic of interest due to its relationship with pathological conditions that include hypertension, stroke, subarachnoid hemorrhage, and traumatic brain injury. Its investigation calls for an ability to track both the neural and vascular aspects of brain function. We used scalp electroenc ephalography (EEG) which provided a measure of the electrical potentials generated by cortical postsynaptic currents. Simultaneously we utilized functional near-infrared spectroscopy (NIRS) to continuously monitor hemoglobin concentration changes in superficial cortical layers. The multi-modal signal from 18 healthy adult subjects allowed us to investigate the association of neural activity in a range of frequencies over the whole-head to local changes in hemoglobin concentrations. Our results verified the delayed alpha (8-16 Hz) modulation of hemodynamics in posterior areas known from the literature. They also indicated strong beta (16-32 Hz) modulation of hemodynamics. Analysis revealed, however, that beta modulation was likely generated by the alpha-beta coupling in EEG. Signals from the inferior electrode sites were dominated by scalp muscle related activity. Our study aimed to characterize the phenomena related to neurovascular coupling observable by practical, cost-effective, and non-invasive multi-modal techniques

NONINVASIVE NEAR-INFRARED DIFFUSE OPTICAL MONITORING OF CEREBRAL HEMODYNAMICS AND AUTOREGULATION

Many cerebral diseases are associated with abnormal cerebral hemodynamics and impaired cerebral autoregulation (CA). CA is a mechanism to maintain cerebral blood flow (CBF) stable when mean arterial pressure (MAP) fluctuates. Evaluating these abnormalities requires direct measurements of cerebral hemodynamics and MAP. Several near-infrared diffuse optical instruments have been developed in our laboratory for hemodynamic measurements including near-infrared spectroscopy (NIRS), diffuse correlation spectroscopy (DCS), hybrid NIRS/DCS, and dual-wavelength DCS flow-oximeter. We utilized these noninvasive technologies to quantify CBF and cerebral oxygenation in different populations under different physiological conditions/manipulations. A commercial finger plethysmograph was used to continuously monitor MAP. For investigating the impact of obstructive sleep apnea (OSA) on cerebral hemodynamics and CA, a portable DCS device was used to monitor relative changes of CBF (rCBF) during bilateral thigh cuff occlusion. Compared to healthy controls, smaller reductions in rCBF and MAP following cuff deflation were observed in patients with OSA, which might result from the impaired vasodilation. However, dynamic CAs quantified in time-domain (defined by rCBF drop/MAP drop) were not significantly different between the two groups. We also evaluated dynamic CA in frequency-domain, i.e., to quantify the phase shifts of low frequency oscillations (LFOs) at 0.1 Hz between cerebral hemodynamics and MAP under 3 different physiological conditions (i.e., supine resting, head-up tilt (HUT), paced breathing). To capture dynamic LFOs, a hybrid NIRS/DCS device was upgraded to achieve faster sampling rate and better signal-to-noise. We determined the best hemodynamic parameters (i.e., CBF, oxygenated and total hemoglobin concentrations) among the measured variables and optimal physiological condition (HUT) for detecting LFOs in healthy subjects. Finally, a novel dual-wavelength DCS flow-oximeter was developed to monitor cerebral hemodynamics during HUT-induced vasovagal presyncope (VVS) in healthy subjects. rCBF was found to have the best sensitivity for the assessment of VVS among the measured variables and was likely the final trigger of VVS. A threshold of ~50% rCBF decline was observed which can completely separate subjects with or without presyncope, suggesting its potential role for predicting VVS. With further development and applications, NIRS/DCS techniques are expected to have significant impacts on the evaluation of cerebral hemodynamics and autoregulation