A method to analyze low signal-to-noise ratio functional magnetic resonance imaging data

The current practice of using a single, representative hemodynamic response function (canonical HRF) to model functional magnetic resonance imaging (fMRI) data is questionable given the trial-to-trial variability of the brain's responses. In addition, the changes in blood-oxygenation level due to sensory stimulation may be small, especially when auditory stimuli are used. Here we introduce a correlation-based single trial analysis method for fMRI data analysis to deal with the low signal-to-noise (SNR) ratio and variability of the HRF in response to repeated, identical auditory stimuli. The correlation technique identifies the "active" trials, i.e., those showing a robust hemodynamic response among all single trials. Using data collected from 14 healthy subjects, it was found that the correlation method can find significant differences between brain areas and brain states in actual fMRI data. Also, the correlation-based method confirmed that the superior temporal gyrus (STG), inferior frontal gyrus (IFG), dorsolateral prefrontal cortex (DLPFC) and thalamus (THA) are involved in auditory information processing in general, and the involvement of the bilateral STG, right THA and left DLPFC in sensory gating. In contrast, conventional analysis failed to find any regions involved in sensory gating. The findings suggest that our single trial analysis method can increase the sensitivity of fMRI data analysis.

Agent-specific responses in the cingulate cortex during economic exchanges

Interactions with other responsive agents lie at the core of all social exchange. During a social exchange with a partner, one fundamental variable that must be computed correctly is who gets credit for a shared outcome; this assignment is crucial for deciding on an optimal level of cooperation that avoids simple exploitation. We carried out an iterated, two-person economic exchange and made simultaneous hemodynamic measurements from each player's brain. These joint measurements revealed agent-specific responses in the social domain ("me" and "not me") arranged in a systematic spatial pattern along the cingulate cortex. This systematic response pattern did not depend on metrical aspects of the exchange, and it disappeared completely in the absence of a responding partner.