Cross-Frequency Coupling Between Brain and Body Biosignals: A Systemic Physiology Augmented Functional Near-Infrared Spectroscopy Hyperscanning Study.

BACKGROUND: Understanding the brain and body processes during interaction or cooperation between two or more subjects is an important topic in current neuroscientific research. In a previous study, we introduced a novel approach that enables investigation of the coupling of biosignals (brain and systemic physiology, SP) from two subjects: systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) hyperscanning. AIM: The aim was to extend our signal analysis approach by the cross-frequency time-dependent wavelet transform coherence (WTC) of the fNIRS and SP biosignals to gain new insights into the nature and cause of functional hyperconnectivity. SUBJECTS AND METHODS: 24 pairs of adults took part in a closed-eye versus prolonged eye-contact task of 10 min each. Brain and body activity was measured continuously by SPA-fNIRS hyperscanning. We calculated the time-dependent WTC of the biosignals for four different frequency bands: very low-frequency band (VLF, 0.002-0.08 Hz), low-frequency band 1 (LF1, 0.015-0.15 Hz), low-frequency band 2 (LF2, 0.08-0.15 Hz) and heart rate band (HR, 1-2 Hz). We then performed the cross-frequency correlated-coherence coupling analysis. RESULTS: A stronger cross-frequency coupling during the eye-contact condition (between 99 pairs of biosignals) was found than during the eye-closed condition (between 50 pairs of biosignals). Prolonged eye contact led to entrainment of the brain and body between different frequency bands and two subjects. The strongest hyperconnectivity was between the LF1-VLF frequency band. DISCUSSION AND CONCLUSION: With this exploratory study, we reveal further benefits of the SPA-fNIRS approach for future hyperscanning studies.

Machine Learning Distinguishes Familiar from Unfamiliar Pairs of Subjects Performing an Eye Contact Task: A Systemic Physiology Augmented Functional Near-Infrared Spectroscopy Hyperscanning Study.

BACKGROUND: Eye contact is an important aspect of human communication and social interactions. Changes in brain and systemic physiological activity associated with interactions between humans can be measured with systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) hyperscanning, enabling inter-brain and inter-body synchronisation to be determined. In a previous study, we found that pairs of subjects that are socially connected show higher brain and body synchrony. AIM: To enable a deeper understanding, our aim was to build and automatically detect the best set of features to distinguish between two different groups (familiar and unfamiliar pairs). MATERIAL AND METHODS: We defined several features based on the Spearman correlation and wavelet transform coherence (WTC) of biosignals measured on 23 pairs of subjects (13 familiar and 10 unfamiliar pairs) during eye contact for 10 min. Additional custom features that identify the maximum brain-to-body coupling instants between pairs were generated. RESULTS: After testing on combinations of different feature extraction methods, four subsets of features with the strongest discrimination power were taken into account to train a decision tree (DT) machine learning (ML) algorithm. We have obtained 95.65% classification accuracy using a leave-one-out cross-validation. The coupling features which represent the two maximum mean values resulting from the sum of 7 time-dependent WTC signals (oxyhaemoglobin concentration of the right prefrontal region, total haemoglobin concentration of the left and right prefrontal region, heart rate, electrodermal activity on the left and right wrist, and skin temperature on the right wrist) played an essential role in the classification accuracy. CONCLUSION: Training the DT-ML algorithm with combined brain and systemic physiology data provided higher accuracy than training it only with brain or systemic data alone. The results demonstrate the power of the SPA-fNIRS hyperscanning approach and the potential in applying ML to investigate the strength of social bonds in a wide range of social interaction contexts.

Parallel processing in human visual cortex revealed through the influence of their neural responses on the visual evoked potential.

The neural response in the human visual system is composed of magno-, parvo- and koniocellular input from the retina. Signal differences from functional imaging between health and individuals with a cognitive weakness are attributed to a dysfunction of a specific retinal input. Yet, anatomical interconnections within the human visual system obscure individual contribution to the neural response in V1. Deflections in the visual evoked potential (VEP) arise from an interaction between electric dipoles, their strength determined by the size of the neural population active during temporal - and spatial luminance contrast processing. To investigate interaction between these neural responses, we recorded the VEP over visual cortex of 14 healthy adults viewing four series of windmill patterns. Within a series, the relative area white in a pattern varied systematically. Between series, the number of sectors across which this area was distributed doubled. These patterns were viewed as pattern alternating and on-/off stimuli. P100/P1 amplitude increased linearly with the relative area white in the pattern, while N135/N1 and P240/P2 amplitude increased with the number of sectors of which the area white was distributed. The decreases P100 amplitude with increasing number of sectors is attributed to an interaction between electric dipoles located in granular and supragranular layers of V1. Differences between the VEP components obtained during a pattern reversing display and following pattern onset are accounted for by the transient and sustained nature of neural responses processing temporal - and spatial luminance contrast and ability of these responses to manifest in the VEP.

Prediction of future falls in a community dwelling older adult population using instrumented balance and gait analysis.

BACKGROUND: The role of instrumented balance and gait assessment when screening for prospective fallers is currently a topic of controversial discussion. OBJECTIVES: This study analyzed the association between variables derived from static posturography, instrumented gait analysis and clinical assessments with the occurrence of prospective falls in a sample of community dwelling older people. METHODS: In this study 84 older people were analyzed. Based on a prospective occurrence of falls, participants were categorized into fallers and non-fallers. Variables derived from clinical assessments, static posturography and instrumented gait analysis were evaluated with respect to the association with the occurrence of prospective falls using a forward stepwise, binary, logistic regression procedure. RESULTS: Fallers displayed a significantly shorter single support time during walking while counting backwards, increased mediolateral to anteroposterior sway amplitude ratio, increased fast mediolateral oscillations and a larger coefficient (Coeff) of sway direction during various static posturography tests. Previous falls were insignificantly associated with the occurrence of prospective falls. CONCLUSION: Variables derived from posturography and instrumented gait analysis showed significant associations with the occurrence of prospective falls in a sample of community dwelling older adults.

How depth of anesthesia influences the blood oxygenation level-dependent signal from the visual cortex of children.

BACKGROUND AND PURPOSE: Functional MR imaging (fMRI) is playing an important role in investigations of cortical development and maturation. Functional MR imaging in young children or infants frequently involves measuring a clinical population under sedation or anesthesia. We examined the effect of depth of anesthesia on the extent and amplitude of the blood oxygen level-dependent (BOLD) response. METHOD: We performed BOLD-based fMRI on a visual stimulus flickering at 8 Hz at sevoflurane concentrations of 0.5 minimum alveolar concentration (MAC), 0.75 MAC, and 1.0 MAC, on 16 children at least 5 years of age. We determined the extent of activation by counting the number of activated voxels and assessed the change in the local deoxyhemoglobin concentration by comparing DeltaR2*. RESULTS: The number of activated voxels of the positive BOLD response was higher at 0.75 MAC than at 0.5 MAC or 1.0 MAC. The magnitude of their mean DeltaR2* steadily declined as the level of sevoflurane was increased from 0.5 MAC to 1.0 MAC. The extent of activation of the negative BOLD response declined progressively from 0.5 MAC to 1.0 MAC. The magnitude of their mean amplitude of the DeltaR2* did not change with sevoflurane concentrations. The change in the extent of activation and the magnitude of DeltaR2* when the concentration of sevoflurane increased from 0.5 MAC to 0.75 MAC was due to its vasodilative property. The change in the extent of activation and the amplitude of DeltaR2* following the increase in the concentration of sevoflurane from 0.75 MAC and 1.0 MAC was due to its anesthetic property. This was the case for both the positive and negative BOLD response. CONCLUSIONS: Careful adjustment of anesthetic depth can be used advantageously when performing BOLD-based fMRI measurements in children.

Inaudible functional MRI using a truly mute gradient echo sequence.

We performed functional MRI experiments using a mute version of a gradient echo sequence on adult volunteers using either a simple visual stimulus (flicker goggles: 4 subjects) or an auditory stimulus (music: 4 subjects). Because the mute sequence delivers fewer images per unit time than a fast echo planar imaging (EPI) sequence, we explored our data using a parametric ANOVA test and a non-parametric Wilcoxon-Mann-Whitney test in addition to performing a cross-correlation analysis. All three methods were in close agreement regarding the location of the BOLD contrast signal change. We demonstrated that, using appropriate statistical analysis, functional MRI using an MR sequence that is acoustically inaudible to the subject is feasible. Furthermore compared with the "silent" event-related procedures involving an EPI protocol, our mGE protocol compares favourably with respect to experiment time and the BOLD signal.

Functional MR imaging in pediatrics.

Functional magnetic resonance (fMR) imaging can show neuronal structures underlying specific perceptual and cognitive processes. With the aid of fMR imaging, the development of brain functions can be followed, and deviation from the normal pattern can be established quickly. This article discusses the unique issues of fMR imaging in the pediatric population (e.g., the occurrence of a negative blood oxygenation-level dependent [BOLD] signal during visual stimulation in the age group in whom the synaptic density is the highest; in older children, when synaptic pruning has proceeded, the BOLD signal takes on the positive characteristics seen in adults). fMR imaging also suggests prospectively important applications in the diagnostic workup of children: an early diagnosis of functional deficit can reduce residual deficits to a minimum because remediation, such as specialized training, can be started at an early stage.

Processing of kinetically defined boundaries in areas V1 and V2 of the macaque monkey.

We recorded responses in 107 cells in the primary visual area V1 and 113 cells in the extrastriate visual area V2 while presenting a kinetically defined edge or a luminance contrast edge. Cells meeting statistical criteria for responsiveness and orientation selectivity were classified as selective for the orientation of the kinetic edge if the preferred orientation for a kinetic boundary stimulus remained essentially the same even when the directions of the two motion components defining that boundary were changed by 90 degrees. In area V2, 13 of the 113 cells met all three requirements, whereas in V1, only 4 cells met the criteria of 107 that were tested, and even these demonstrated relatively weak selectivity. Correlation analysis showed that V1 and V2 populations differed greatly (P < 1.0 x 10(-6), Student's t-test) in their selectively for specific orientations of kinetic edge stimuli. Neurons in V2 that were selective for the orientation of a kinetic boundary were further distinguished from their counterparts in V1 in displaying a strong, sharply tuned response to a luminance edge of the same orientation. We concluded that selectivity for the orientation of kinetically defined boundaries first emerges in area V2 rather than in primary visual cortex. An analysis of response onset latencies in V2 revealed that cells selective for the orientation of the motion-defined boundary responded about 40 ms more slowly, on average, to the kinetic edge stimulus than to a luminance edge. In nonselective cells, that is, those presumably responding only to the local motion in the stimulus, this difference was only about 20 ms. Response latencies for the luminance edge were indistinguishable in KE-selective and -nonselective neurons. We infer that while responses to luminance edges or local motion are indigenous to V2, KE-selective responses may involve feedback entering the ventral stream at a point downstream with respect to V2.

Anatomic MR images obtained with silent sequences.

The authors evaluated silent magnetic resonance (MR) imaging sequences for their suitability in providing high-spatial-resolution anatomic images that are of sufficient quality to be useful in a clinical setting. The authors compared the images obtained with a silent rapid acquisition with relaxation enhancement (RARE) sequence to its standard counterpart with respect to signal-to-noise ratio, distribution of gray level, and spatial resolution. No real differences were observed between the standard and the silent RARE MR images. Anatomic images were also acquired with a silent spin-echo sequence. Acoustic noise levels with the silent sequences were at least 22 dB (A-weighted scale) lower than those with standard sequences, without loss of image quality.

Effect of pentobarbital on visual processing in man.

To investigate the effect of sedative agents on visual processing in humans, we analysed the BOLD contrast signal response to a visual stimulation paradigm in 15 healthy, adult volunteers using functional magnetic resonance imaging. The subjects were tested during alert state and under sedation following intravenous administration of pentobarbital. The injection of pentobarbital not only significantly reduced the response signal strength but the reduction in BOLD contrast signal was related to the ratio of amount of sedative administered and the subject's body weight. The three subjects with the highest relative sedative dosage even displayed an inverted (negative) BOLD contrast signal. A significant reduction in the number of positively correlating pixels was found 15 min after administration of pentobarbital. All measured parameters returned to near pre-sedative levels by the end of the experimental session. The relative dosage dependence of the strength of the BOLD signal the negative BOLD signal in the three subjects with the highest relative sedative dosage indicates that pentobarbital had a more pronounced effect on cerebral blood flow than on cerebral oxidative metabolism.

Response latency of macaque area MT/V5 neurons and its relationship to stimulus parameters.

A total of 310 MT/V5 single cells were tested in anesthetized, paralyzed macaque monkeys with moving random-dot stimuli. At optimum stimulus parameters, latencies ranged from 35 to 325 ms with a mean of 87+/-45 (SD) ms. By examining the relationship between latency and response levels, stimulus parameters, and stimulus selectivities, we attempted to isolate the contributions of these factors to latency and to identify delays representing intervening synapses (circuitry) and signal processing (flow of information through that circuitry). First, the relationship between stimulus parameters and latency was investigated by varying stimulus speed and direction for individual cells. Resulting changes in latencies were explainable in terms of response levels corresponding to how closely the actual stimulus matched the preferred stimulus of the cell. Second, the relationship between stimulus selectivity and latency across the population of cells was examined using the optimum speed and direction of each neuron. A weak tendency for cells tuned for slow speeds to have longer latencies was explainable by lower response rates among slower-tuned neurons. In contrast, sharper direction tuning was significantly associated with short latencies even after taking response rate into account, (P = 0.002, ANCOVA). Accordingly, even the first 10 ms of the population response fully demonstrates direction tuning. A third study, which examined the relationship between antagonistic surrounds and latency, revealed a significant association between the strength of the surround and the latency that was independent of response levels (P < 0.002, ANCOVA). Neurons having strong surrounds exhibited latencies averaging 20 ms longer than those with little or no surround influence, suggesting that neurons with surrounds represent a later stage in processing with one or more intervening synapses. The laminar distribution of latencies closely followed the average surround antagonism in each layer, increasing with distance from input layer IV but precisely mirroring response levels, which were highest near the input layer and gradually decreased with distance from input layer IV. Layer II proved the exception with unexpectedly shorter latencies (P< 0.02, ANOVA) yet showing only modest response levels. The short latency and lack of strong direction tuning in layer II is consistent with input from the superior colliculus. Finally, experiments with static stimuli showed that latency does not vary with response rate for such stimuli, suggesting a fundamentally different mode of processing than that for a moving stimulus.

Visual processing in infants and children studied using functional MRI.

We studied the development of visual processing in 58 children, ranging from 1 d to 12 y of age (median age 29 mo), using functional magnetic resonance imaging. All but nine children had either been sedated using chloral hydrate (n = 12) or pentobarbital (n = 28). Nine children were studied under a full halothane/ N2O:O2 anesthesia. In the first postnatal month, 30% of the neonates showed a positive blood oxygenation level-dependent (BOLD) contrast signal, whereas, for infants between the ages of 1 mo and 1 y, 27% did so. Thirty-one percent of children between 1 and 6 y of age and 71% of children aged 6 y and above showed a positive BOLD contrast signal change to our visual stimulation paradigm. Besides the usual positive BOLD contrast signal change, we also noted that a large portion of the children measured displayed a negative BOLD contrast signal change. This negative BOLD contrast signal change was observed in 30% of children up to 1 mo of age, in 27% between 1 mo and 1 y of age, in 47% between 1 and 6 y of age, and in 14% of children 6 y and older. In the children in which we observed a negative correlating BOLD contrast signal change, the locus was more anterior and more lateral than the positive BOLD contrast signal, placing it in the secondary visual cortical area. The results indicate that when using functional magnetic resonance imaging on children, the primary visual cortical area does not respond functionally in the same manner as that of the adult until 1.5 y of age. This supports earlier clinical and electrophysiologic findings that different cortical mechanisms seem to contribute to visual perception at different times postnatally.

Comparing the visual deficits of a motion blind patient with the visual deficits of monkeys with area MT removed.

The performance of a 'motion blind' patient on a series of tasks in which the perception of motion played an essential or no role was compared with that of a human subject with normal vision and with that of macaque monkeys in which cortical visual area MT had been removed and adjacent areas damaged. The patient experienced difficulties on those tasks in which the perception of motion was essential, but was unimpaired on those tasks that did not require it. Similarly, the tasks which the 'motion blind' patient found impossible or difficult were precisely those tasks on which monkeys lacking area MT performed poorly. Similarly, the tasks on which the patient performed well also presented no difficulties for the animals lacking cortical area MT. The close correlation between the pattern of visual perceptual impairments in the patient and monkeys indicates that the patient's inability to perceive most forms of visual movement is attributable to total loss of, or extensive damage to, a cortical visual area that is the human equivalent of area MT and perhaps its adjacent areas.

Size and shape of receptive fields in the medial superior temporal area (MST) of the macaque.

Ninety-one single units were recorded in area MSTd of anesthetized and paralyzed macaques. Receptive fields (RFs) were mapped quantitatively using small patches of moving random dots in 25 different positions (the two-dimensional position test, or P2D). The dimensions of the receptive fields (RFs) were estimated by fitting P2D data with a generalized Gaussian function. The half-height areas of the RFs in MSTd were found to average 1085 deg2 and were not dependent upon eccentricity, in contrast to those in MT/V5 (n = 295) which averaged 31 deg2 at the fovea but at the periphery approached the RFs of MSTd in size. The RFs of some MSTd neurons extended 30-40 degrees into the ipsilateral hemifield. In comparison, the overlap was only 10-15 degrees in area MT/V5.

Selectivity of macaque MT/V5 neurons for surface orientation in depth specified by motion.

Area MTN5 in the macaque brain is one of the major cortical regions involved in the analysis of retinal image motion. The majority of the neurons in this cortical area have non-uniform antagonistic surrounds as components of their receptive field complexes. Theoretical studies indicate that such asymmetrical surrounds should enable neurons to extract orientation in depth from motion. Here we show that nearly half of the MTN5 neurons encode the tilt component of the orientation in depth of a plane specified by motion. Furthermore, we show that such selectivity for depth from motion depends on the presence of an asymmetrical surround and on the speed tuning of those asymmetrical surround influences.

Shape and spatial distribution of receptive fields and antagonistic motion surrounds in the middle temporal area (V5) of the macaque.

The spatial organization of receptive fields in the middle temporal (MT) area of anaesthetized and paralysed macaque monkeys was studied. In all, 288 neurons were successfully recorded. The size and shape of the receptive field (RF) was mapped with small patches of translating random dots and the resulting data were fitted with a generalized Gaussian. Results show that the RF area increases with eccentricity, and is larger in lamina 5 than in other layers. Most of these RFs are elongated, and the axis of elongation tends to be orthogonal to the preferred direction of motion. The direction selectivity is maintained in all positions in the RF, but layer 5 cells are less direction-selective than cells in other layers. In a second series of experiments, radial dimensions of the classical RF and the antagonistic surround were estimated from area summation tests. These data were fitted with the difference of the integrals of two Gaussians. Surrounds were weakest in layer 4 and strongest in layer 2. Optimal stimulus diameters, also estimated from the area summation curve, were larger in the infragranular layers than in the other layers. The maximum sensitivity of the surround was clearly displaced from the classical RF (CRF) centre, indicating that the surround is not concentric with the CRF. This radial offset and the extent of the surround were largest in layers 2 and 5 and smallest in 3a. The extent of the surround half-height equalled, on average, 3-4 times that of the CRF. These results suggest that antagonistic surrounds are constructed in MT, probably through horizontal connections, and that a strong vertical organization exists in area MT, as has been shown for V1.

Processing of kinetically defined boundaries in the cortical motion area MT of the macaque monkey.

1. Electrophysiological recordings of 68 cells in the middle temporal area MT were made in paralyzed and anesthetized macaque monkeys. 2. Testing with our kinetic boundary stimuli always occurred under optimized conditions. To this end, the preferred direction, speed, stimulus position, and stimulus size of each cell were determined by quantitative tests. 3. The orientation selectivity to stationary luminance contrast edges served as a reference by which a response to kinetic boundaries could be compared. We found cells in area MT to be less selective to the orientation of luminance contrast stimuli than to the direction of motion. We confirmed the presence of neurons with preferred orientation aligned with their preferred direction. 4. The responses to kinetic edges defined by motion vectors moving in opposite directions, kinetic gratings with motion vectors in opposite directions, kinetic edges containing coherent motion and a stationary complementary field or coherent motion and a complementary field containing visual dynamic noise were compared. Kinetic boundaries were generated so that the motion vectors moved either parallel or orthogonal to the orientation of the discontinuity. For a cell to be considered as responding to the orientation of a kinetic boundary, it had to exhibit the same preferred orientation when the local motion vectors changed from parallel to orthogonal to the orientation of the kinetic boundary. 5. All cells in area MT changed their preferred orientation by 90 degrees when the coherent motion vectors changed from moving parallel to moving orthogonal to the boundary. This was the case independent of the types of kinetic boundary tested. We concluded that cells in area MT appear to respond to the motion vector over their classical receptive field (CRF) only and were unable to code the orientation of the kinetic boundary. 6. In those cells exhibiting an antagonistic surround, we examined the ability of the cell to code the position of a kinetic boundary. None of the cells tested signaled the position of a kinetic boundary. The side preference of the stimulus of the cells changed from left to right as the motion vectors in the stimulus reversed. This indicates that the cells were only selective for the motion vectors present over their CRF. 7. We found that the directional sensitivity of cells in area MT remained unaltered by the presence of additional motion vectors within the CRF. This suggests that cells in area MT extract a specific motion vector from a spatial configuration of vectors.(ABSTRACT TRUNCATED AT 400 WORDS)