How our hearts beat together: a study on physiological synchronization based on a self-paced joint motor task

Cardiac physiological synchrony is regarded as an important component of social interaction due to its putative role in prosocial behaviour. Yet, the processes underlying physiological synchrony remain unclear. We aim to investigate these processes. 20 dyads (19 men, 21 women, age range 18-35) engaged in a self-paced interpersonal tapping synchronization task under different levels of tapping synchrony due to blocking of sensory communication channels. Applying wavelet transform coherence analysis, significant increases in heart rate synchronization from baseline to task execution were found with no statistically significant difference across conditions. Furthermore, the control analysis, which assessed synchrony between randomly combined dyads of participants showed no difference from the original dyads' synchrony. We showed that interindividual cardiac physiological synchrony during self-paced synchronized finger tapping resulted from a task-related stimulus equally shared by all individuals. We hypothesize that by applying mental effort to the task, individuals changed into a similar mental state, altering their cardiac regulation. This so-called psychophysiological mode provoked more uniform, less variable fluctuation patterns across all individuals leading to similar heart rate coherence independent of subsequent pairings. With this study, we provide new insights into cardiac physiological synchrony and highlight the importance of appropriate study design and control analysis

Systemic physiology augmented functional near-infrared spectroscopy hyperscanning: a first evaluation investigating entrainment of spontaneous activity of brain and body physiology between subjects.

Significance: Functional near-infrared spectroscopy (fNIRS) enables measuring the brain activity of two subjects while they interact, i.e., the hyperscanning approach. Aim: In our exploratory study, we extended classical fNIRS hyperscanning by adding systemic physiological measures to obtain systemic physiology augmented fNIRS (SPA-fNIRS) hyperscanning while blocking and not blocking the visual communication between the subjects. This approach enables access brain-to-brain, brain-to-body, and body-to-body coupling between the subjects simultaneously. Approach: Twenty-four pairs of subjects participated in the experiment. The paradigm consisted of two subjects that sat in front of each other and had their eyes closed for 10 min, followed by a phase of 10 min where they made eye contact. Brain and body activity was measured continuously by SPA-fNIRS. Results: Our study shows that making eye contact for a prolonged time causes significant changes in brain-to-brain, brain-to-body, and body-to-body coupling, indicating that eye contact is followed by entrainment of the physiology between subjects. Subjects that knew each other generally showed a larger trend to change between the two conditions. Conclusions: The main point of this study is to introduce a new framework to investigate brain-to-brain, body-to-body, and brain-to-body coupling through a simple social experimental paradigm. The study revealed that eye contact leads to significant synchronization of spontaneous activity of the brain and body physiology. Our study is the first that employed the SPA-fNIRS approach and showed its usefulness to investigate complex interpersonal physiological changes

Effects of contact with a dog on prefrontal brain activity: A controlled trial

BACKGROUND There is a broad range of known effects of animal contact on human mental and physical health. Neurological correlates of human interaction with animals have been sparsely investigated. We investigated changes in frontal brain activity in the presence of and during contact with a dog. METHODS Twenty-one healthy individuals each participated in six sessions. In three sessions, participants had contact with a dog, and in three control sessions they interacted with a plush animal. Each session had five two-minute phases with increasing intensity of contact to the dog or plush animal from the first to the fourth phase. We measured oxygenated, deoxygenated, and total hemoglobin and oxygen saturation of the blood in the frontal lobe/frontopolar area with functional near-infrared spectroscopy (SenSmart Model X-100) to assess brain activity. FINDINGS In both conditions, the concentration of oxygenated hemoglobin increased significantly from the first to the fourth phase by 2.78 μmol/l (CI = 2.03-3.53, p < .001). Oxygenated hemoglobin concentration was 0.80 μmol/l higher in the dog condition compared to in the control condition (CI = 0.27-1.33, p = .004). Deoxygenated-hemoglobin concentration, total hemoglobin concentration, and oxygen saturation showed similar patterns. CONCLUSION Prefrontal brain activation in healthy subjects increased with the rise in interaction closeness with a dog or a plush animal. Moreover, interaction with a dog stimulated more brain activity compared to the control condition, suggesting that interactions with a dog can activate stronger attentional processes and elicit more emotional arousal than interacting with a nonliving stimulus

Effects of contact with a dog on prefrontal brain activity: a controlled trial

Background There is a broad range of known effects of animal contact on human mental and physical health. Neurological correlates of human interaction with animals have been sparsely inves- tigated. We investigated changes in frontal brain activity in the presence of and during con- tact with a dog. Methods Twenty-one healthy individuals each participated in six sessions. In three sessions, partici- pants had contact with a dog, and in three control sessions they interacted with a plush ani- mal. Each session had five two-minute phases with increasing intensity of contact to the dog or plush animal from the first to the fourth phase. We measured oxygenated, deoxygenated, and total hemoglobin and oxygen saturation of the blood in the frontal lobe/frontopolar area with functional near-infrared spectroscopy (SenSmart Model X-100) to assess brain activity. Findings In both conditions, the concentration of oxygenated hemoglobin increased significantly from the first to the fourth phase by 2.78 μmol/l (CI = 2.03-3.53, p < .001). Oxygenated hemoglo- bin concentration was 0.80 μmol/l higher in the dog condition compared to in the control con- dition (CI = 0.27-1.33, p = .004). Deoxygenated-hemoglobin concentration, total hemoglobin concentration, and oxygen saturation showed similar patterns. Conclusion Prefrontal brain activation in healthy subjects increased with the rise in interaction closeness with a dog or a plush animal. Moreover, interaction with a dog stimulated more brain activity compared to the control condition, suggesting that interactions with a dog can activate stron- ger attentional processes and elicit more emotional arousal than interacting with a nonliving stimulus

Neural response during temporal - and spatial luminance contrast processing and its manifestation in the blood-oxygen-level-dependent-signal in striate and extra-striate cortex

The primate visual system has been the prime site for investigating the relationship between stimulus property, neural response and blood-oxygen-level-dependent (BOLD)-signal; yet this relationship remains ill-understood. Electrophysiological studies have shown that the ability to visualise a neural response is determined by stimulus property and presentation paradigm. The neural response in the human visual cortex consists of a phasic response processing temporal and tonic response processing spatial luminance contrast. We investigated their influence on the BOLD signal from the visual cortex. To do so, we compared BOLD signal amplitude from BA17 and BA18 of 15 human volunteers to visual patterns varying the size of the active neural population and the discharge activity of this population. The BOLD signal amplitude in both areas reflected the discharge activity of the active neural population but not the size of the active neural population. For identical stimuli, BOLD signal amplitude in BA17 exceeded than that of BA18. This indicates that the BOLD signal reflects the tonic neural neuronal response during spatial luminance contrast processing. The difference in BOLD signal amplitude between BA17 and BA18 is accounted for by differences in neurophysiological and cytoarchitectonic differences between the two areas. Our findings offer an understanding of the relationship between stimulus property, neural response and the BOLD signal by considering the cytoarchitectonic, and neurophysiological make-up between different cortical areas and the influence of a phasic and tonic neural response on local deoxyhaemoglobin concentration. Conversely, differences in BOLD signal between brain structures and stimuli provide cues to the influence of different neurophysiological mechanisms on the neural response

Modulation of the neuronal response in human primary visual cortex by re-entrant projections during retinal input processing as manifest in the visual evoked potential

Initial deflections in the visual evoked potential (VEP) reflect the neuronal process of extracting features from the retinal input; a process not modulated by re-entrant projections. Later deflections in the VEP reflect the neuronal process of combining features into an object, a process referred to as 'object closure' and modulated by re-entrant projections. Our earlier work indicated that the VEP reflects independent neuronal responses processing temporal - and spatial luminance contrast and that these responses arise from an interaction between forward and re-entrant input. In this earlier work, changing the temporal luminance contrast property of a stimulus altered its spatial luminance contrast property. We recorded the VEP in 12 volunteers viewing image pairs of a windmill, regular dartboard or an RMS dartboard rotated by either Π/4, Π/2, 3Π/4 or Π radians with respect to each other. The windmill and regular dartboard had identical white to black ratio, while the two dartboards identical contrast edges per unit area. Rotation varied temporal luminance contrast of a stimulus without affecting its spatial luminance contrast. N75, P100, N135 and P240 amplitude and latency were compared and a source localisation and temporal frequency analysis performed. P100 amplitude signals a neuronal response processing temporal luminance contrast that is modulated by re-entrant projections with fast axonal conduction velocities. N135 and P240 signal the neuronal response processing spatial luminance contrast and is modulated by re-entrant projections with slow axonal conduction velocities. The dorsal stream is interconnected by fast axonal conduction velocities, the ventral stream by slow axonal conduction velocities

Stimuli to differentiate the neural response at successive stages of visual processing using the VEP from human visual cortex

BACKGROUND: Clarifying the enigmatic relationship between stimulus property, neural response and the evoked potential is essential if non-invasive functional imaging is to make a meaningful contribution to the understanding of how maturational or degenerative processes influence brain activity. Visual cortex has proven a favourite target to elucidate this relationship. However, to date most studies involving the visual system have yielded inconsistent results or have been strongly criticised. NEW METHOD: We developed a set of three visual stimuli, two of which either had the same low- or high spatial frequency characteristic. Adult volunteers viewed these as pattern reversing stimuli while the scalp electric potential was recorded using a 10-10 array of electrodes. RESULTS: Established processing mechanisms of the primate visual system enabled us to link the amplitude of the N75 and P100 to the size of the neural population processing the temporal luminance contrast, and the amplitude of the N135 and P240 to the size of the neural processing the spatial luminance contrast in our stimuli. Calculating the distribution of current source density enabled us to identify the neural source of each VEP component. CONCLUSIONS: Demonstrating a direct relationship between the temporal- and spatial luminance contrast properties of our stimuli and the size of the neural population involved provides a better understanding of the nature of the relationship between stimulus property, neural response and the VEP. It also shows that EEG can contribute in a significant manner to the study of the influence of maturational or degenerative processes on brain activity

An investigation into the relationship between stimulus property, neural response and its manifestation in the visual evoked potential involving retinal resolution

The visual evoked potential (VEP) has been shown to reflect the size of the neural population activated by a processing mechanism selective to the temporal - and spatial luminance contrast property of a stimulus. We set out to better understand how the factors determining the neural response associated with these mechanisms. To do so we recorded the VEP from 14 healthy volunteers viewing two series of pattern reversing stimuli with identical temporal-and spatial luminance contrast properties. In one series the size of the elements increased towards the edge of the image, in the other it decreased. In the former element size was congruent with receptive field size across eccentricity, in the later it was incongruent. P100 amplitude to the incongruent series exceeded that obtained to the congruent series. Using electric dipoles due the excitatory neural response we accounted for this using dipole cancellation of electric dipoles of opposite polarity originating in supra- and infragranular layers of V1. The phasic neural response in granular lamina of V1 exhibited magnocellular characteristics, the neural response outside of the granular lamina exhibited parvocellular characteristics and was modulated by re-entrant projections. Using electric current density, we identified areas of the dorsal followed by areas of the ventral stream as the source of the re-entrant signal modulating infragranular activity. Our work demonstrates that the VEP does not signal reflect the overall level of a neural response but is the result of an interaction between electric dipoles originating from neural responses in different lamina of V1

Shades of grey; Assessing the contribution of the magno- and parvocellular systems to neural processing of the retinal input in the human visual system from the influence of neural population size and its discharge activity on the VEP

Introduction: Retinal input processing in the human visual system involves a phasic and tonic neural response. We investigated the role of the magno- and parvocellular systems by comparing the influence of the active neural population size and its discharge activity on the amplitude and latency of four VEP components. Method: We recorded the scalp electric potential of 20 human volunteers viewing a series of dartboard images presented as a pattern reversing and pattern on-/offset stimulus. These patterns were designed to vary both neural population size coding the temporal- and spatial luminance contrast property and the discharge activity of the population involved in a systematic manner. Results: When the VEP amplitude reflected the size of the neural population coding the temporal luminance contrast property of the image, the influence of luminance contrast followed the contrast response function of the parvocellular system. When the VEP amplitude reflected the size of the neural population responding to the spatial luminance contrast property the image, the influence of luminance contrast followed the contrast response function of the magnocellular system. The latencies of the VEP components examined exhibited the same behavior across our stimulus series. Conclusions: This investigation demonstrates the complex interplay of the magno- and parvocellular systems on the neural response as captured by the VEP. It also demonstrates a linear relationship between stimulus property, neural response, and the VEP and reveals the importance of feedback projections in modulating the ongoing neural response. In doing so, it corroborates the conclusions of our previous study

Reorganization in secondary somatosensory cortex in chronic low back pain patients

STUDY DESIGN: A cross-sectional comparative study between chronic low back pain (CLBP) patients and healthy control subjects. OBJECTIVE: The aim of this study was to investigate reorganization in the sensory cortex by comparing cortical activity due to mechanosensory stimulation of the lumbar spine in CLBP patients versus a control group by using functional magnetic resonance imaging (fMRI). SUMMARY OF BACKGROUND DATA: LBP is now the number 1 condition across the world in terms of years living with a disability. There is growing evidence that maladaptive changes in the processing of sensory input by the central nervous system are central to understanding chronic (back) pain. METHODS: Nonpainful, posterior-anterior (PA) movement pressure was applied manually to lumbar vertebrae at L1, L3, and L5 in 13 healthy subjects and 13 CLBP patients. The manual pressure (30 N) was monitored and controlled using sensors. A randomized stimulation protocol was used consisting of 51 pressure stimuli of 5 seconds duration. fMRI data analysis was performed for the group activation within the primary and secondary sensory cortices (S1 and S2, respectively) and the representation of the individual vertebrae was extracted and statistically analyzed. RESULTS: Nonpainful PA pressure revealed no cortical reorganization in S1. In contrast, the extent of S2 activation in the CLBP group was significantly reduced in both hemispheres. In the control group, a somatotopy was identified for the lumbar vertebrae between L1 and L3, respectively, and L5 in S2 of the right hemisphere. Most importantly, a blurring of the somatotopic representation of the lumbar spine in S2 was observed in the patient group. CONCLUSION: Together, these maladaptive changes suggest a reorganization of higher-order processing for sensory information in CLBP patients that might have implications for a decreased sensory acuity, also related to body perception and subsequent altered functioning of the lumbar spine. LEVEL OF EVIDENCE: 2