Probing the role of the vestibular system in motivation and reward-based attention

The vestibular system has widespread connections in the central nervous system. Several activation loci following vestibular stimulations have been notably reported in deep, limbic areas that are otherwise difficult to reach and modulate in healthy subjects. Following preliminary evidence, suggesting that such stimulations might affect mood and affective processing, we wondered whether the vestibular system is also involved in motivation. Evolutionary accounts suggest that visuo-vestibular mismatches might have a role in preventing the search for and exploitation of goods that previously resulted in aversive reactions, as they would be a fine warning signal which follows the contact with or ingestion of noxious neurotoxins. The first question was thus whether vestibular stimulation alters sensitivity to reward. Secondly, we sought to assess whether attention is allocated in space differently when cued by highly motivational stimuli, and if this interplay is further modulated by the vestibular system. In order to evaluate both motivational and attentional assets, we administered a Posner-like cueing task to 30 healthy subjects concurrently receiving sham or galvanic vestibular stimulation (GVS; Left-Anodal and Right-Anodal configurations). The participants had to discriminate targets appearing in either exogenously cued or uncued locations (50% validity); cues predicted the amount of points (0, 2, or 10) and thus money that they could earn for a correct response. The results highlight a robust inhibition of return (IOR) (faster responses for invalidly-cued targets) which was not modulated by different levels of reward or GVS. Across all stimulation sessions, rewards exerted a powerful beneficial effect over performance: reaction times were faster when rewards were at stake. However, this effect was largest in sham, but greatly reduced in GVS conditions, most notably with the Right-Anodal configuration. This is the first evidence for a decreased sensitivity to rewards causally induced by a perturbation of the vestibular system. While future studies will shed light on its neural underpinnings and clinical implications, here we argue that GVS could be a safe and promising way to enrich our understanding of reward processes and eventually tackle the management of patients with aberrant sensitivity to rewards

Close is better: visual perception in peripersonal space

The neuroscientific approach to peripersonal space (PPS) stems directly from electrophysiological studies assessing the response properties of multisensory neurons in behaving non-human primates. This multisensory context fostered frameworks which i) stress the PPS role in actions (including defensive reactions) and affordances, which are optimally performed through multiple sensory convergence; and ii) largely make use of tasks that are multisensory in nature. Concurrently, however, studies on spatial attention reported proximity-related advantages in purely unisensory tasks. These advantages appear to share some key PPS features. Activations in brain areas reported to be multisensory, indeed, can also be found using unimodal (visual) paradigms. Overall, these findings point to the possibility that closer objects may benefit from being processed as events occurring in PPS. The dominant multisensory view of PPS should therefore be expanded accordingly, as perceptual advantages in PPS may be broader than previously thought

Insulin Management for Type 1 Diabetic Patients During Social Alcohol Consumption: The SPRITZ Study

BACKGROUND: There is no data available on the best insulin treatment to counteract the effects of glucose excursions due to a moderate alcohol intake associated with portions of slight fat and protein-containing food, as often the case during social happenings or "happy hours". INTRODUCTION: This study analyzes the glycemic control and quality of life in 8 adult type 1 diabetic (T1D) patients on insulin-pump therapy which were invited to consume a traditional Italian aperitif ("Spritz" and chips). METHODS: Patients consumed Spritz aperitif twice: using their habitual bolus, based on carbohydrates (CHO) counting (V1), or with a personalized, advanced bolus (V2) calculated from insulin/Kcal derived from Fats and Proteins (FPU). Post-prandial glucose was continuously monitored; glucose incremental areas (iAUC), glucose peak and time to peak, and estimated change from V1 to V2 from repeated- measures models were computed. Each patient fulfilled validated questionnaires on quality of life, knowledge about diabetes and CHO counting. RESULTS: After the educational program, a reduced iAUC (0-80 min: -306, p=ns; 40-80 min: -400, p=0.07) due to greater (p=0.03) and prolonged double-wave insulin boluses was observed. Blood glucose peak and time to peak were also reduced. Moreover, improvements in the psycho-affective dimension, as well as in the alimentary knowledge were detected. CONCLUSION: Therefore, a personalized educational program on CHO + FPU counting together with insulin bolus management can improve glycemic control during social consumption of alcohol, with positive reflections on the psycho-affective dimension. Further studies are mandatory to confirm such preliminary results

The role of the vestibular system in value attribution to positive and negative reinforcers

Somatic inputs originating from bioregulatory processes can guide cognition and behavior. One such bodily signal, mostly overlooked so far, is represented by visuo-vestibular coupling and its alteration, which in extreme cases may result in motion sickness. We argued that the inherently perturbed interoceptive state that follows can be a powerful determinant of human motivated behavior, resulting in a blunted response to appetitive stimuli and an exaggerated response to noxious ones. We sought to assess such differential impact of visuo-vestibular mismatches on value through a task involving conflict monitoring. We therefore administered to 42 healthy participants a modified version of the Flankers task, in which distractors (arrows, pointing in either a congruent or incongruent direction) signaled the availability of monetary incentives (gains, losses, or neutral trials). While performing the task, participants received either galvanic vestibular stimulation (GVS), or sham stimulation. We have found impaired behavioral performances when value, which was attached to task-irrelevant information, was at stake. Gains and losses, interestingly, dissociated, and only the latter caused enhanced interference costs in the task, suggesting that negative incentives may be more effective in capturing human attention than positive ones. Finally, we have found some weak evidence for GVS to further increase the processing of losses, as suggested by even larger interference costs in this condition. Results were, however, overall ambiguous, and suggest that much more research is needed to better understand the link between the vestibular system and motivation

Evaluation of prostaglandin analogue effects on corneal keratocyte density using scanning laser confocal microscopy

Purpose: To determine if treatment with prostaglandin (PG) analogues affects keratocyte density as an indirect measure of extracellular matrix in the corneal stroma. Patients and Methods: In this case control study, 129 eyes from 68 patients were examined: 52 eyes had only PG analogue therapy for at least 3 years, 37 eyes had only [beta]-adrenergic blocker therapy for at least 3 years, and 40 control eyes were without therapy. Scanning laser confocal microscopy was carried out, and each corneal stroma was subdivided into the anterior, midstroma, and posterior stroma. Keratocyte density was determined from the images by manual counting. Results: Keratocyte densities in the entire stroma and in 2 stromal layers were significantly higher in patients with PG analogue therapy compared with control patients (entire stroma, P<0.001; anterior stroma, P=0.001; posterior stroma, P=0.016). Keratocyte density in the PG analogue therapy patients was also greater compared with the [beta]-adrenergic blocker patients (entire stroma, P<0.001; anterior stroma, P<0.001; mid-stroma P=0.023, posterior stroma P=0.007). There were no significant differences between the control and [beta]-adrenergic blocker groups. Overall, the density increase for the PG analogue group was greatest in the anterior stroma. Conclusions: PG analogue therapy increased the keratocyte density in each layer of corneal stroma, but more significantly in the anterior stroma than in the midstroma or the posterior stroma. The increased keratocyte density might be the result of diminished extracellular matrix, possibly owing to the known activation of matrix metalloproteinases and inhibition of tissue inhibitors of the metalloproteinases

Mind the Depth: Visual Perception of Shapes Is Better in Peripersonal Space

Closer objects are invariably perceived as bigger than farther ones and are therefore easier to detect and discriminate. This is so deeply grounded in our daily experience that no question has been raised as to whether the advantage for near objects depends on other features (e.g., depth itself). In a series of five experiments (N = 114), we exploited immersive virtual environments and visual illusions (i.e., Ponzo) to probe humans\u2019 perceptual abilities in depth and, specifically, in the space closely surrounding our body, termed peripersonal space. We reversed the natural distance scaling of size in favor of the farther object, which thus appeared bigger, to demonstrate a persistent shape-discrimination advantage for close objects. Psychophysical modeling further suggested a sigmoidal trend for this benefit, mirroring that found for multisensory estimates of peripersonal space. We argue that depth is a fundamental, yet overlooked, dimension of human perception and that future studies in vision and perception should be depth aware