Near infrared spectroscopy (NIRS) is an increasingly popular technology for studying brain function. NIRS presents several advantages relative to functional magnetic resonance imaging (fMRI), such as measurement of concentration changes in both oxygenated- and deoxygenated hemoglobin, finer temporal resolution, and ease of administration, as well as disadvantages, most prominently inferior spatial resolution and decreased signal-to-noise ratio (SNR). While fMRI has become the gold standard for in vivo imaging of the human brain, in practice NIRS is a more convenient and less expensive technology than fMRI. It is therefore of interest to many researchers how NIRS compares to fMRI in studies of brain function. In the present study we scanned participants with simultaneous NIRS and fMRI on a battery of cognitive tasks, placing NIRS probes over both frontal and parietal brain regions. We performed detailed comparisons of the signals in both temporal and spatial domains. We found that NIRS signals have significantly weaker SNR, but are nonetheless often highly correlated with fMRI measurements. Both SNR and the distance between the scalp and the brain contributed to variability in the NIRS/fMRI correlations. In the spatial domain, we found that a photon path forming an ellipse between the NIRS emitter and detector correlated most strongly with the BOLD response. Taken together these findings suggest that, while NIRS can be an appropriate substitute for fMRI for studying brain activity related to cognitive tasks, care should be taken when designing studies with NIRS to ensure that: 1) the spatial resolution is adequate for answering the question of interest and 2) the design accounts for weaker SNR, especially in brain regions more distal from the scalp.

We used Near-Infrared Spectroscopy (NIRS) to simultaneously measure brain activity in two people while they played a computer-based cooperation game side by side. Inter-brain activity coherence was calculated between the two participants. We found that the coherence between signals generated by participants right superior frontal cortices increased during cooperation, but not during competition. Increased coherence was also associated with better cooperation performance. To our knowledge, this work represents the first use of a single NIRS instrument for simultaneous measurements of brain activity in two people. This study demonstrates the use of NIRS-based hyperscanning in studies of social interaction in a naturalistic environment.

Near infrared spectroscopy (NIRS) is a promising technology for functional brain imaging which measures hemodynamic signals from the cortex, similar to functional magnetic resonance imaging (fMRI), but does not require the participant to lie motionless in a confined space. NIRS can therefore be used for more naturalistic experiments, including face to face communication, or natural body movements, and is well suited for real-time applications that may require lengthy training. However, improving signal quality and reducing noise, especially noise induced by head motion, is challenging, particularly for real time applications. Here we study the properties of head motion induced noise, and find that motion noise causes the measured oxygenated and deoxygenated hemoglobin signals, which are typically strongly negatively correlated, to become more positively correlated. Next, we develop a method to reduce noise based on the principle that the concentration changes of oxygenated and deoxygenated hemoglobin should be negatively correlated. We show that despite its simplicity, this method is effective in reducing noise and improving signal quality, for both online and offline noise reduction.

To judge causality, organisms must determine the temporal order of their actions and sensations. However, this judgment may be confounded by changing delays in sensory pathways, suggesting the need for dynamic temporal recalibration. To test for such a mechanism, we artificially injected a fixed delay between participants' actions (keypresses) and subsequent sensations (flashes). After participants adapted to this delay, flashes at unexpectedly short delays after the keypress were often perceived as occurring before the keypress, demonstrating a recalibration of motor-sensory temporal order judgments. When participants experienced illusory reversals, fMRI BOLD signals increased in anterior cingulate cortex/medial frontal cortex (ACC/ MFC), a brain region previously implicated in conflict monitoring. This illusion-specific activation suggests that the brain maintains not only a recalibrated representation of timing, but also a less-plastic representation against which to compare it.

When asked to imagine a visual scene, such as an ant crawling on a checkered table cloth toward a jar of jelly, individuals subjectively report different vividness in their mental visualization. We show that reported vividness can be correlated with two objective measures: the early visual cortex activity relative to the whole brain activity measured by functional magnetic resonance imaging (fMRI) and the performance on a novel psychophysical task. These results show that individual differences in the vividness of mental imagery are quantifiable even in the absence of subjective report.