Neural correlates of evidence accumulation during value-based decisions revealed via simultaneous EEG-fMRI

Current computational accounts posit that, in simple binary choices, humans accumulate evidence in favour of the different alternatives before committing to a decision. Neural correlates of this accumulating activity have been found during perceptual decisions in parietal and prefrontal cortex; however the source of such activity in value-based choices remains unknown. Here we use simultaneous EEG–fMRI and computational modelling to identify EEG signals reflecting an accumulation process and demonstrate that the within- and across-trial variability in these signals explains fMRI responses in posterior-medial frontal cortex. Consistent with its role in integrating the evidence prior to reaching a decision, this region also exhibits task-dependent coupling with the ventromedial prefrontal cortex and the striatum, brain areas known to encode the subjective value of the decision alternatives. These results further endorse the proposition of an evidence accumulation process during value-based decisions in humans and implicate the posterior-medial frontal cortex in this process

Interoception across Modalities: On the Relationship between Cardiac Awareness and the Sensitivity for Gastric Functions

The individual sensitivity for ones internal bodily signals (“interoceptive awareness”) has been shown to be of relevance for a broad range of cognitive and affective functions. Interoceptive awareness has been primarily assessed via measuring the sensitivity for ones cardiac signals (“cardiac awareness”) which can be non-invasively measured by heartbeat perception tasks. It is an open question whether cardiac awareness is related to the sensitivity for other bodily, visceral functions. This study investigated the relationship between cardiac awareness and the sensitivity for gastric functions in healthy female persons by using non-invasive methods. Heartbeat perception as a measure for cardiac awareness was assessed by a heartbeat tracking task and gastric sensitivity was assessed by a water load test. Gastric myoelectrical activity was measured by electrogastrography (EGG) and subjective feelings of fullness, valence, arousal and nausea were assessed. The results show that cardiac awareness was inversely correlated with ingested water volume and with normogastric activity after water load. However, persons with good and poor cardiac awareness did not differ in their subjective ratings of fullness, nausea and affective feelings after drinking. This suggests that good heartbeat perceivers ingested less water because they subjectively felt more intense signals of fullness during this lower amount of water intake compared to poor heartbeat perceivers who ingested more water until feeling the same signs of fullness. These findings demonstrate that cardiac awareness is related to greater sensitivity for gastric functions, suggesting that there is a general sensitivity for interoceptive processes across the gastric and cardiac modality

Auditory information enhances post-sensory visual evidence during rapid multisensory decision-making

Despite recent progress in understanding multisensory decision-making, a conclusive mechanistic account of how the brain translates the relevant evidence into a decision is lacking. Specifically, it remains unclear whether perceptual improvements during rapid multisensory decisions are best explained by sensory (i.e., ‘Early’) processing benefits or post-sensory (i.e., ‘Late’) changes in decision dynamics. Here, we employ a well-established visual object categorisation task in which early sensory and post-sensory decision evidence can be dissociated using multivariate pattern analysis of the electroencephalogram (EEG). We capitalize on these distinct neural components to identify when and how complementary auditory information influences the encoding of decision-relevant visual evidence in a multisensory context. We show that it is primarily the post-sensory, rather than the early sensory, EEG component amplitudes that are being amplified during rapid audiovisual decision-making. Using a neurally informed drift diffusion model we demonstrate that a multisensory behavioral improvement in accuracy arises from an enhanced quality of the relevant decision evidence, as captured by the post-sensory EEG component, consistent with the emergence of multisensory evidence in higher-order brain areas

Isolating shape from semantics in haptic-visual priming

The exploration of a familiar object by hand can benefit its identification by eye. What is unclear is how much this multisensory cross-talk reflects shared shape representations versus generic semantic associations. Here, we compare several simultaneous priming conditions to isolate the potential contributions of shape and semantics in haptic-to-visual priming. Participants explored a familiar object manually (haptic prime) while trying to name a visual object that was gradually revealed in increments of spatial resolution. Shape priming was isolated in a comparison of identity priming (shared semantic category and shape) with category priming (same category, but different shapes). Semantic priming was indexed by the comparisons of category priming with unrelated haptic primes. The results showed that both factors mediated priming, but that their relative weights depended on the reliability of the visual information. Semantic priming dominated in Experiment 1, when participants were free to use high-resolution visual information, but shape priming played a stronger role in Experiment 2, when participants were forced to respond with less reliable visual information. These results support the structural description hypothesis of haptic-visual priming (Reales and Ballesteros in J Exp Psychol Learn Mem Cogn 25:644–663, 1999) and are also consistent with the optimal integration theory (Ernst and Banks in Nature 415:429–433, 2002), which proposes a close coupling between the reliability of sensory signals and their weight in decision making.This work was supported by a PhD scholarship to author AP from the Portuguese Fundação para a Ciência e Tecnologia (SFRH/BD/76087/2011), an Exchange Fellowship to author AAB from the Dr. Michael Quinn Memorial Fund, Department of Psychology, University of British Columbia, an NSERC (Canada) Discovery Grant to author JTE, and Grants to author SS-F from the Spanish Ministry of Science and Innovation (PSI2010-15426 and Consolider INGENIO CSD2007-00012 Grants, the Comissionat per a Universitats i Recerca del DIUE-Generalitat de Catalunya (SRG2009- 092), and the European Research Council (StG-2010 263145)