The impact of yohimbine-induced arousal on facets of behavioural impulsivity

Rationale State-dependent changes in physiological arousal may influence impulsive behaviours. Objectives To examine the relationship between arousal and impulsivity, we assessed the effects of yohimbine (an α2-adrenergic receptor antagonist, which increases physiological arousal via noradrenaline release) on performance on established laboratory-based impulsivity measures in healthy volunteers. Methods Forty-three participants received a single dose of either yohimbine hydrochloride or placebo before completing a battery of impulsivity measures. Blood pressure and heart rate were monitored throughout the study. Results Participants in the yohimbine group showed higher blood pressure and better response inhibition in the Stop Signal Task, relative to the placebo group. Additionally, individual changes in blood pressure were associated with performance on Delay Discounting and Information Sampling tasks: raised blood pressure following drug ingestion was associated with more far-sighted decisions in the Delay Discounting Task (lower temporal impulsivity) yet reduced information gathering in the Information Sampling Task (increased reflection impulsivity). Conclusions These results support the notion that impulsive behaviour is dependent upon state physiological arousal; however, distinct facets of impulsivity are differentially affected by physiological changes

Binge drinking is associated with attenuated frontal and parietal activation during successful response inhibition in fearful context

Binge drinking is associated with increased impulsivity and altered emotional processing. The current study investigated, in a group of university students who differed in their level of binge drinking, whether the ability to inhibit a pre-potent response and to delay gratification is disrupted in the presence of emotional context. We further tested whether functional connectivity within intrinsic resting-state networks was associated with alcohol use. Higher incidence of binge drinking was associated with enhanced activation of the lateral occipital cortex, angular gyrus, the left frontal pole during successful response inhibition irrespective of emotional context. This observation suggests a compensatory mechanism. However, higher binge drinking attenuated frontal and parietal activation during successful response inhibition within a fearful context, indicating the selective emotional facilitation of inhibitory control. Similarly, higher binge drinking was associated with attenuated frontopolar activation when choosing a delayed reward over an immediate reward within the fearful, relative to the neutral, context. Resting-state functional data analysis revealed that binge drinking decreased coupling between right supramarginal gyrus and Ventral Attention Network, indicating alcohol-associated disruption of functional connectivity within brain substrates directing attention. Together, our results suggest that binge drinking makes response inhibition more effortful, yet emotional (more arousing) contexts may mitigate this; disrupted functional connectivity between regions underlying adaptive attentional control, is a likely mechanism underlying these response inhibition effects associated with binge drinking

The role of emotions and physiological arousal in modulating impulsive behaviour

Impulsivity refers to both a stable personality trait and a set of behaviours which undergo momentary changes depending on the current circumstances. Impulsivity plays a vital role in daily life as well as clinical practice as it is associated with drug misuse and certain neuropsychiatric conditions. Because of its great health and well-being importance, it is crucial to understand factors which modulate impulsive behaviours. The current studies investigated the role of emotions and physiological arousal as modulators of impulsive actions and decisions in healthy individuals. A set of experiments was conducted using a variety of methods including behavioural testing, physiological recordings, psychopharmacology and neuroimaging. Studies 1 and 2 clarified the influence of emotional states on distinct dimensions of impulsive behaviours. Study 3 investigated the neural correlates behind the impact of emotions on impulsive actions. Finally, studies 4 and 5 focused on the relationship between physiological arousal and behavioural and trait impulsivity. Our findings demonstrate that a degree to which one’s internal (emotional or physiological) state changes, is associated with behavioural impulsivity level. Importantly, distinct dimensions of impulsivity are differentially sensitive to those changes. Namely, increased state level of physiological arousal is associated with decreased motor ‘stopping’ impulsivity, enhanced subjective ratings and objective measurements of arousal are also related to decreased temporal impulsivity. Increased ratings of stress and increased physiological arousal, however, are associated with higher reflection impulsivity. At the neural level, successful response inhibition requires enhanced activation of prefrontal and parietal areas in impulsive individuals, particularly in negative emotional context, suggesting that behavioural control might be more effortful for highly impulsive individuals. In conclusion, changes in internal bodily state are related to behavioural impulsivity level. Staying more attuned to those changes and finding adaptive ways to adjust behaviour according to bodily needs might be vital to reducing impulsivity levels

Profile of toll-like receptor mRNA expression in the choroid plexus in adult ewes

The blood-cerebrospinal fluid barrier (BCSFB) located in the epithelial cells of the choroid plexus (CP) forms the interface between the cerebrospinal fluid (CSF) and pathogen components circulating in the blood. The CP is also implicated in the passage of peripheral immune signals and circulation of immune cells into the central nervous system. Toll-like receptors (TLRs) are patternrecognition receptors that play a crucial role in the recognition of pathogens and triggering of the innate immune response. In sheep, ten members of the TLR family have been identified and cloned. We used real-time PCR analyses to examine the profiles of TLR mRNA expression in the CP of cerebral ventricles in healthy adult ewes. The transcripts for all ten TLRs except TLR8 were present; however, we observed a high variation in the degree of expression of the TLR5 and TLR1 genes (coefficient of variation: 61% and 46%, respectively) as well as a moderate variation in the expression of the TLR4 (34%), TLR2 (27%) and TLR6 (26%) genes. The TLR9, TLR7, TLR3 and TLR10 genes were the four receptors with relatively invariable expression levels (coefficient of variation: 7%, 8%, 16% and 17%, respectively) across the six adult ewes. The concentration of cortisol in blood collected prior to sacrificing the ewes ranged from 0.18 to 78.9 ng/ml. There was no correlation between cortisol concentration and mRNA expression of any of the examined TLRs. These data suggest that the CP has the potential to sense the presence of many bacterial and viral components and mediate responses for the elimination of invading microorganisms, thereby protecting the brain

Patterning of graphene on silicon-on-insulator waveguides through laser ablation and plasma etching

We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method. This loss contribution is measured to be 0.132 dB/μm

Alterations in amygdala-prefrontal functional connectivity account for excessive worry and autonomic dysregulation in generalized anxiety disorder

Background: Generalized anxiety disorder (GAD) is characterized by the core symptom of uncontrollable worry. Functional magnetic resonance imaging studies link this symptom to aberrant functional connectivity between the amygdala and prefrontal cortex. Patients with GAD also display a characteristic pattern of autonomic dysregulation. Although frontolimbic circuitry is implicated in the regulation of autonomic arousal, no previous study to our knowledge combined functional magnetic resonance imaging with peripheral physiologic monitoring in these patients to test the hypothesis that core symptoms of worry and autonomic dysregulation in GAD arise from a shared underlying neural mechanism. Methods: We used resting-state functional magnetic resonance imaging and the measurement of parasympathetic autonomic function (heart rate variability) in 19 patients with GAD and 21 control subjects to define neural correlates of autonomic and cognitive responses before and after induction of perseverative cognition. Seed-based analyses were conducted to quantify brain changes in functional connectivity with the right and left amygdala. Results: Before induction, patients showed relatively lower connectivity between the right amygdala and right superior frontal gyrus, right paracingulate/anterior cingulate cortex, and right supramarginal gyrus than control subjects. After induction, such connectivity patterns increased in patients with GAD and decreased in control subjects, and these changes tracked increases in state perseverative cognition. Moreover, decreases in functional connectivity between the left amygdala and subgenual cingulate cortex and between the right amygdala and caudate nucleus predicted the magnitude of reduction in heart rate variability after induction. Conclusions: Our results link functional brain mechanisms underlying worry and rumination to autonomic dyscontrol, highlighting overlapping neural substrates associated with cognitive and autonomic responses to the induction of perseverative cognitions in patients with GAD