Inequality signals in dorsolateral prefrontal cortex inform social preference models.

Humans typically display inequality aversion in social situations, which manifests itself as a preference for fairer distributions of resources. However, people differ in the degree to which they dislike being worse off [disadvantageous inequality (DI) aversion] or better off [advantageous inequality (AI) aversion] than others. Competing models explain such behavior by focusing on aversion to payoff differences, maximization of total payoff or reciprocity. Using functional near-infrared spectroscopy, we asked which of these theories could better explain dorsolateral prefrontal cortex (dlPFC) activity while participants accepted or punished fair vs unfair monetary transfers in an anonymous norm compliance task. We found that while all participants exhibited DI aversion, there were substantial differences in preferences for AI, which were strongly predicted by dlPFC activation. Model comparisons revealed that both punishment behavior and prefrontal activity were best explained by a model that allowed for AI seeking rather than imposing aversion. Moreover, enhancing this model by taking into account behavioral response times, as a proxy for choice difficulty, further improved model fits. Our data provide evidence that the dlPFC encodes subjective values of payoff inequality and that this representation is richer than envisaged by standard models of social preferences.

Comparison of functional near-infrared spectroscopy and electrodermal activity in assessing objective versus subjective risk during risky financial decisions.

Risk is an important factor impacting financial decisions. Risk can be processed objectively, e.g. as variance across possible outcomes of a choice option or subjectively, e.g. as value of that variance to a given individual. The aim of the present study was to test the potential of functional near-infrared spectroscopy (fNIRS) in assessing these different ways of processing risk while subjects decided between either high or low risk financial options or a safe (risk-free) option. For comparison we simultaneously measured electrodermal activity (EDA), a well-established method in decision-making research and a core measure of affective processes. FNIRS showed that lateral prefrontal cortex responses to high risk were enhanced relative to low risk only in risk-seeking individuals but reduced relative to low risk in risk-averse individuals. This is in-line with individual-specific risk processing reflecting the subjective value of risk. By contrast, EDA showed enhanced responses to high risk, independent of individual risk attitude, in-line with the notion of objective risk processing. The dissociation between the two measures arose even though they overall were equally sensitive to detect individual risk-related differences and even though there was an increased, risk attitude-independent, temporal coherence between the two measures during high-risk conditions. Our results suggest that hemodynamic responses in lateral prefrontal cortex as measured by fNIRS reflect the subjective value of risk, whereas EDA may index the objective amount of risk people are presented with. The findings suggest that fNIRS could be a useful method for studying risk behavior in financial decisions.

An extended drawing test for the assessment of arm and hand function with a performance invariant for healthy subjects.

Impaired hand motor function resulting from neurological, psychiatric or orthopaedic disorders affects patients of all ages. Existing hand function assessment methods, e.g. rating scales, accelerometers and electromyographical devices, are often time-consuming to administer, subjective in interpretation and/or expensive. Graphonomic tests are gaining popularity as a way of avoiding these drawbacks while relating directly to writing and drawing. Here we present a computerized Extended Drawing Test (EDT), which improves on an earlier Drawing Test for stroke patients in three ways. First, it assesses isolated proximal arm movement using a graphics pen in a puck-like pen holder, and in addition combined arm and finger dexterity in movements using a normal writing grip. Secondly, we calibrated our test against 186 healthy subjects (3-70 years), finding significant age- and handedness-related differences in both speed and accuracy of drawing. Thirdly, to simplify assessment we devised an overall performance measure using a variant of Fitts' Law combining speed and accuracy, which we found to be age-independent for healthy subjects above 3 years of age. This result enables us to provide age-independent performance norms using both hands, with and without the pen holder. These norms may assist quantification of specific arm dysfunction by comparing patient performance with the healthy norms, and also by comparing within-patient performance in the dominant and non-dominant hands with and without the pen holder. Using our freely available software, this new test will allow clinicians to rapidly assess arm and hand function across a wide range of patient categories and ages.