Unifying Evidence on Delay Discounting: Open Task, Analysis Tutorial, and Normative Data from an Italian Sample

Despite the widespread use of the delay discounting task in clinical and non-clinical contexts, several task versions are available in the literature, making it hard to compare results across studies. Moreover, normative data are not available to evaluate individual performances. The present study aims to propose a unified version of the delay discounting task based on monetary rewards and it provides normative values built on an Italian sample of 357 healthy participants. The most used parameters in the literature to assess the delay discount rate were compared to find the most valid index to discriminate between normative data and a clinical population who typically present impulsivity issues, i.e., patients with a lesion to the medial orbitofrontal cortex (mOFC). In line with our hypothesis, mOFC patients showed higher delay discounting scores than the normative sample and the normative group. Based on this evidence, we propose that the task and indexes here provided can be used to identify extremely high (above the 90th percentile for hyperbolic k or below the 10th percentile for AUC) or low (below the 10th percentile for hyperbolic k or above the 90th percentile for AUC) delay discounting performances. The complete dataset, the R code used to perform all analyses, a free and modifiable version of the delay discounting task, as well as the R code that can be used to extract all indexes from such tasks and compare subjective performances with the normative data here presented are available as online materials.

Dissociation between Private and Social Counterfactual Value Signals Following Ventromedial Prefrontal Cortex Damage

Individuals learn by comparing the outcome of chosen and unchosen actions. A negative counterfactual value signal is generated when this comparison is unfavorable. This can happen in private as well as in social settings—where the foregone outcome results from the choice of another person. We hypothesized that, despite sharing similar features such as supporting learning, these two counterfactual signals might implicate distinct brain networks. We conducted a neuropsychological study on the role of private and social counterfactual value signals in risky decision-making. Patients with lesions in the ventromedial prefrontal cortex (vmPFC), lesion controls, and healthy controls repeatedly chose between lotteries. In private trials, participants could observe the outcomes of their choices and the outcomes of the unselected lotteries. In social trials, participants could also see the other player's choices and outcome. At the time of outcome, vmPFC patients were insensitive to private counterfactual value signals, whereas their responses to social comparison were similar to those of control participants. At the time of choice, intact vmPFC was necessary to integrate counterfactual signals in decisions, although amelioration was observed during the course of the task, possibly driven by social trials. We conclude that if the vmPFC is critical in processing private counterfactual signals and in integrating those signals in decision-making, then distinct brain areas might support the processing of social counterfactual signals.

Pulvinar Lesions Disrupt Fear-Related Implicit Visual Processing in Hemianopic Patients

The processing of emotional stimuli in the absence of awareness has been widely investigated in patients with lesions to the primary visual pathway since the classical studies on affective blindsight. In addition, recent evidence has shown that in hemianopic patients without blindsight only unseen fearful faces can be implicitly processed, inducing enhanced visual encoding (Cecere et al., 2014) and response facilitation (Bertini et al., 2013, 2017) to stimuli presented in their intact field. This fear-specific facilitation has been suggested to be mediated by activity in the spared visual subcortical pathway, comprising the superior colliculus (SC), the pulvinar and the amygdala. This suggests that the pulvinar might represent a critical relay structure, conveying threat-related visual information through the subcortical visual circuit. To test this hypothesis, hemianopic patients, with or without pulvinar lesions, performed a go/no-go task in which they had to discriminate simple visual stimuli, consisting in Gabor patches, displayed in their intact visual field, during the simultaneous presentation of faces with fearful, happy, and neutral expressions in their blind visual field. In line with previous evidence, hemianopic patients without pulvinar lesions showed response facilitation to stimuli displayed in the intact field, only while concurrent fearful faces were shown in their blind field. In contrast, no facilitatory effect was found in hemianopic patients with lesions of the pulvinar. These findings reveal that pulvinar lesions disrupt the implicit visual processing of fearful stimuli in hemianopic patients, therefore suggesting a pivotal role of this structure in relaying fear-related visual information from the SC to the amygdala.

Stuck in the here and now: Construction of fictitious and future experiences following ventromedial prefrontal damage

There is increasing interest in uncovering the cognitive and neural bases of episodic future thinking (EFT), the ability to imagine events relevant to one's own future. Recent functional neuroimaging evidence shows that the ventromedial prefrontal cortex (vmPFC) is engaged during EFT. However, vmPFC is also activated during imagination of fictitious, atemporal experiences. Therefore, its role in EFT is currently unclear. To test (1) whether vmPFC is critical for EFT, and (2) whether it supports EFT specifically, or, rather, construction of any complex experience, patients with focal lesions to vmPFC (vmPFC patients), control patients with lesions not involving vmPFC, and healthy controls were asked to imagine personal future experiences and fictitious experiences. Compared to the control groups, vmPFC patients were impaired at imagining both future and fictitious experiences, indicating a general deficit in constructing novel experiences. Unlike the control groups, however, vmPFC patients had more difficulties in imagining future compared to fictitious experiences. Exploratory correlation analyses showed that general construction deficits correlated with lesion volume in BA 11, whereas specific EFT deficits correlated with lesion volume in BA 32 and BA 10. Together, these findings indicate that vmPFC is crucial for EFT. We propose, however, that different vmPFC subregions may support different component processes of EFT: the most ventral part, BA 11, may underlie core constructive processes needed to imagine any complex experience (e.g., scene construction), whereas BA 10 and BA 32 may mediate simulation of those specific experiences that likely await us in the future.

Improving memory following prefrontal cortex damage with the PQRST method

We tested (1) whether the PQRST method, involving Preview (P), Question (Q), Read (R), State (S), and Test (T) phases, is effective in enhancing long-term memory in patients with mild memory problems due to prefrontal cortex lesions, and (2) whether patients also benefit from a more self-initiated version of the PQRST. Seven patients with prefrontal lesions encoded new texts under three different conditions: the Standard condition, requiring to read texts repeatedly, the PQRST-Other condition, in which the experimenter formulated questions about the text (Q phase), and the PQRST-Self condition, in which patients formulated the relevant questions on their own. Compared to the Standard condition, both the PQRST-Other and the PQRST-Self condition resulted in higher immediate and delayed recall rates, as well as a higher ability to answer questions about the texts. Importantly, the two PQRST conditions did not differ in efficacy. These results confirm that the PQRST method is effective in improving learning of new material in brain-injured populations with mild memory problems. Moreover, they indicate that the PQRST proves effective even under conditions with higher demands on patients’ autonomy and self-initiation, which encourages its application to real-life situations.