ABSTRACT
The retina is one of the best known quantum detectors with rods able to reliably respond to single photons. However, estimates on the number of photons eliciting conscious perception, based on signal detection theory, are systematically above these values after discounting by retinal losses. One possibility is that there is a trade-off between the limited motor resources available to living systems and the excellent reliability of the visual photoreceptors. On this view, the limits to sensory thresholds are not set by the individual reliability of the receptors within each sensory modality (as often assumed) but rather by the limited central processing and motor resources available to process the constant inflow of sensory information. To investigate this issue, we reproduced the classical experiment from Hetch aimed to determine the sensory threshold in human vision. We combined a careful physical control of the stimulus parameters with high temporal/spatial resolution recordings of EEG signals and behavioral variables over a relatively large sample of subjects (12). Contrarily to the idea that the limits to visual sensitivity are fully set by the statistical fluctuations in photon absorption on retinal photoreceptors we observed that the state of ongoing neural oscillations before any photon impinges the retina helps to determine if the responses of photoreceptors have access to central conscious processing. Our results suggest that motivational and attentional off-retinal mechanisms play a major role in reducing the QE efficiency of the human visual system when compared to the efficiency of isolated retinal photoreceptors. Yet, this mechanism might subserve adaptive behavior by enhancing the overall multisensory efficiency of the whole system composed by diverse reliable sensory modalities.
ABSTRACT
Disappointment, the emotion experienced when faced to reward prediction errors (RPEs), considerably impacts decision making (DM). Individuals tend to modify their behavior in an often unpredictable way just to avoid experiencing negative emotions. Despite its importance, disappointment remains much less studied than regret and its impact on upcoming decisions largely unexplored. Here, we adapted the Trust Game to effectively elicit, quantify, and isolate disappointment by relying on the formal definition provided by Bell's in economics. We evaluated the effects of experienced disappointment and elation on future cooperation and trust as well as the rationality and utility of the different behavioral and neural mechanisms used to cope with disappointment. All participants in our game trusted less and particularly expected less from unknown opponents as a result of disappointing outcomes in the previous trial but not necessarily after elation indicating that behavioral consequences of positive and negative RPEs are not the same. A large variance in the tolerance to disappointment was observed across subjects, with some participants needing only a small disappointment to impulsively bias their subsequent decisions. As revealed by high-density EEG recordings the most tolerant individuals - who thought twice before making a decision and earned more money - relied on different neural generators to contend with neutral and unexpected outcomes. This study thus provides some support to the idea that different neural systems underlie reflexive and reflective decisions within the same individuals as predicted by the dual-system theory of social judgment and DM.
ABSTRACT
The authors evaluated the feasibility, clinical yield, and localization precision of high-resolution EEG source imaging of interictal epileptic activity. A consecutive series of 44 patients with intractable epilepsy of various causes, who underwent a comprehensive presurgical epilepsy evaluation, were subjected to a 128-channel EEG recording. A standardized source imaging procedure constrained to the individual gray matter was applied to the averaged spikes of each patient. In 32 patients, the presurgical workup identified a focal epileptogenic area. The 128-channel EEG source imaging correctly localized this area in 30 of these patients (93.7%). Imprecise localization was explained by simplifications of the recordings and analysis procedure, which was accepted for the benefit of speed and standardization. In a subgroup of 24 patients who underwent operations, the sublobar precision of the 128-channel EEG source imaging was evaluated by calculating the distance of the source maximum to the resected area. This analysis revealed zero distance in 19 cases (79%). The authors conclude that high-resolution interictal EEG source imaging is a valuable noninvasive functional neuroimaging technique. The speed, ease, flexibility, and low cost of this technique warrant its use in clinical practice.
