Emotional susceptibility trait modulates insula responses and functional connectivity in flavor processing.

The present study aimed at investigating the relationship between Emotional Susceptibility (ES), an aspect of the personality trait Neuroticism, and individual differences in the neural responses in anterior insula to primary sensory stimuli colored by affective valence, i.e., distasting or pleasantly tasting oral stimuli. In addition, it was studied whether intrinsic functional connectivity patterns of brain regions characterized by such differential responses could be related to ES. To this purpose 25 female participants underwent functional magnetic resonance imaging scanning, while being involved in a flavor experiment. During the experiment, flavor stimuli were administered consisting of small amounts of liquid with a different affective valence: neutral, pleasant, unpleasant. The results showed that individual differences in ES trait predicted distinct neural activity patterns to the different stimulus conditions in a region of left anterior insula that a previous meta-analysis revealed to be linked with olfacto-gustatory processing. Specifically, low ES was associated with enhanced neural responses to both pleasant and unpleasant stimuli, compared to neutral stimuli. By contrast, high ES participants showed equally strong neural responses to all types of stimuli without differentiating between the neutral and affective stimuli. Finally, during a task-free state, high ES trait appeared also to be related to decreased intrinsic functional connectivity between left anterior insula and left cerebellum. Our findings show that individual differences in ES are associated with differential anterior insula responses to primary sensory (flavor) stimuli as well as to intrinsic functional cortico-cerebellar connectivity, the latter suggesting a basis in the brain intrinsic functional architecture of the regulation of emotional experiences.

Selective improvement of anosognosia for hemiplegia during transcranial direct current stimulation: a case report.

Right brain damage patients may not complain of a left sided paralysis up to the point of denying it or even claiming of having just moved an otherwise paralyzed limb. This condition is known as anosognosia for hemiplegia (AHP). Recent behavioural experiments suggest that some residual intentionality might be preserved in patients with anosognosia and that the false belief of having moved originates from a failure to notice discrepancies between movement expectancies and the actual state of the motor system. This failure may be caused by a lack of afferent sensory information concerning the movement or alternatively by a direct dysfunction of the brain regions involved in actions' motor monitoring (i.e., the comparator system). Here we examined the effect of anodal transcranial direct current stimulation (tDCS) of the right premotor cortex in a patient with a bilateral lesion, involving predominantly the right hemisphere, and a dense unawareness for his left hemiplegia. During sham or anodal tDCS the patient was requested to judge his ability to perform simple motor actions (i) without actually executing the movement itself ("offline" condition) and after having performed a series of verbally cued finger opposition movements ("online" condition) with (i) eyes-closed or (ii) eyes-open. We found that anodal tDCS induces a significant remission of the false experience of movement only when the patient is requested to actually perform the movement with eyes open. Conversely, the patient's awareness does not improve in both the "offline" condition (in which the patient does not attempt to perform the movement) and in the "online" condition, when vision is precluded ("online" condition, eyes-closed). We conclude that the stimulation of the premotor cortex by tDCS activates brain regions involved in motor monitoring, temporary restoring the ability of the motor comparator system to correctly appreciate afferent information and build up a veridical motor awareness.

Modulation of spontaneous alpha brain rhythms using low-intensity transcranial direct-current stimulation.

Transcranial direct-current stimulation (tDCS) is a form of neurostimulation in which a constant, low current is delivered directly to the brain area of interest by small electrodes. The overall aim of this study was to examine and monitor the modulation of brain activity by electroencephalogram (EEG) in the frequency domain during tDCS in the resting state. To this end, we considered the modulation of spontaneous EEG to be a marker of the perturbation that was induced through the direct current (1.5 mA for 15 min). In all conditions (anodal, cathodal, and sham), an active electrode was placed over the right posterior parietal cortex, and a reference electrode was placed on the ipsilateral deltoid muscle. The EEG was recorded using a 64-channel system. The effect of tDCS was limited to the alpha rhythm, and the anodal stimulation significantly affected the alpha rhythm, whereas the cathodal stimulation did not elicit any modifications. Further, we observed modulation of alpha activity in areas that were stimulated directly through tDCS and in anterior noncontiguous areas. Finally, the anodal effect peaked 7.5 min after stimulation and decreased gradually over time. Our study demonstrates that in the resting brain, monocephalic anodal tDCS over posterior parietal areas alters ongoing brain activity, specifically in the alpha band rhythm. Our data can be used to fine-tune tDCS protocols in neurorehabilitation settings.