Neural correlates of expectations-induced effects of caffeine intake on executive functions.

Placebo effects are defined as the beneficial subjective or behavioral outcomes of an intervention that are not attributable to its inherent properties; Placebo effects thus follow from individuals' expectations about the effects of the intervention. The present study aimed at examining how expectations influence neurocognitive processes. We addressed this question by contrasting three double-blinded within-subjects experimental conditions in which participants were given decaffeinated coffee, while being told they had received caffeinated (condition i) or decaffeinated coffee (ii), and given caffeinated coffee while being told they had received decaffeinated coffee (iii). After each of these three interventions, performance and electroencephalogram was recorded at rest as well as during sustained attention Rapid Visual Information Processing task (RVIP) and a Go/NoGo motor inhibitory control task. We first aimed to confirm previous findings for caffeine-induced enhancement on these executive components and on their associated electrophysiological indexes (The Attention-P3 component, response conflict NoGo-N2 and inhibition NoGo-P3 components (ii vs iii contrast); and then to test the hypotheses that expectations also induce these effects (i vs ii), although with a weaker amplitude (i vs iii). We did not confirm any of our hypotheses for caffeine-induced behavioral improvements and thus did not test the effect of caffeine-related expectations. At the electrophysiological level, however, we confirmed that caffeine increased the Attention-P3 and NoGo-P3 components amplitude but did not confirm an effect on the response-conflict N2 component. We did not confirm that expectations influence any of the investigated electrophysiological indices, but we confirmed that the Attention-P3 Global Field Power values were larger for the caffeine compared to the expectations conditions. We conclude that previously identified behavioral effect size of caffeine and of the related expectations for sustained attention and inhibitory control may have been overestimated, and that caffeine primarily influences the cognitive processes and brain areas supporting attention allocation. Finally, we confirm that caffeine-related expectations induce smaller effects than the substance itself.

The right thalamic ventral posterolateral nucleus seems to be determinant for macrosomatognosia: a case report.

BACKGROUND: Macrosomatognosiais the illusory sensation of a substantially enlarged body part. This disorder of the body schema, also called "Alice in wonderland syndrome" is still poorly understood and requires careful documentation and analysis of cases. The patient presented here is unique owing to his unusual macrosomatognosia phenomenology, but also given the unreported localization of his most significant lesion in the right thalamus that allowed consistent anatomo-clinical analysis. CASE PRESENTATION: This 45-years old man presented mainly with long-lasting and quasi-delusional macrosomatognosia associated to sensory deficits, both involving the left upper-body, in the context of a right thalamic ischemic lesion most presumably located in the ventral posterolateral nucleus. Fine-grained probabilistic and deterministic tractography revealed the most eloquent targets of the lesion projections to be the ipsilateral precuneus, superior parietal lobule,but also the right primary somatosensory cortex and, to a lesser extent, the right primary motor cortex. Under stationary neurorehabilitation, the patient slowly improved his symptoms and could be discharged back home and, later on, partially return to work. CONCLUSION: We discuss deficient neural processing and integration of sensory inputs within the right ventral posterolateral nucleus lesion as possible mechanisms underlying macrosomatognosia in light of observed anatomo-clinical correlations. On the other hand, difficulty to classify this unique constellation of Alice in wonderland syndrome calls for an alternative taxonomy of cognitive and psychic aspects of illusory body-size perceptions.