Does modafinil activate the locus coeruleus in man? Comparison of modafinil and clonidine on arousal and autonomic functions in human volunteers

The beneficial effects of modafinil administration on repeat mild traumatic brain injury (RmTBI) pathology in adolescent male rats are not dependent upon the orexinergic system

The sleep-wake cycle plays an influential role in the development and progression of repeat mild traumatic brain injury (RmTBI)-related pathology. Therefore, we first aimed to manipulate the sleep-wake cycle post-RmTBI using modafinil, a wake-promoting substance used for the treatment of narcolepsy. We hypothesized that modafinil would exacerbate RmTBI-induced deficits. Chronic behavioural analyses were completed along with a 27-plex serum cytokine array, metabolomic and proteomic analyses of cerebrospinal fluid (CSF), as well as immunohistochemical staining in structures important for sleep/wake cycles, to examine orexin, melanin-concentrating hormone, tyrosine hydroxylase, and choline acetyltransferase, in the lateral hypothalamus, locus coeruleus, and basal forebrain, respectively. Contrary to expectation, modafinil administration attenuated behavioural deficits, metabolomic changes, and neuropathological modifications. Therefore, the second aim was to determine if the beneficial effects of modafinil treatment were driven by the orexinergic system. The same experimental protocol was used; however, RmTBI rats received chronic orexin-A administration instead of modafinil. Orexin-A administration produced drastically different outcomes, exacerbating anxiety-related and motor deficits, while also significantly disrupting their metabolomic and neuropathological profiles. These results suggest that the beneficial effects of modafinil administration post-RmTBI, work independently of its wake-promoting properties, as activation of the orexinergic wake-promoting system with orexin-A was detrimental. Overall, these findings highlight the complexity of sleep-wake changes in the injured brain and showcase the potential of the arousal and sleep systems in its treatment.

Impact of Stimulation Duration in taVNS-Exploring Multiple Physiological and Cognitive Outcomes

Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive neuromodulation technique that modulates the noradrenergic activity of the locus coeruleus (LC). Yet, there is still uncertainty about the most effective stimulation and reliable outcome parameters. In a double blind, sham-controlled study including a sample of healthy young individuals (N = 29), we compared a shorter (3.4 s) and a longer (30 s) stimulation duration and investigated the effects of taVNS (real vs. sham) on saliva samples (alpha amylase and cortisol concentration), pupil (pupillary light reflex and pupil size at rest) and EEG data (alpha and theta activity at rest, ERPs for No-Go signals), and cognitive tasks (Go/No-Go and Stop Signal Tasks). Salivary alpha amylase concentration was significantly increased in the real as compared to sham stimulation for the 30 s stimulation condition. In the 3.4 s stimulation condition, we found prolonged reaction times and increased error rates in the Go/No-Go task and increased maximum acceleration in the pupillary light reflex. For the other outcomes, no significant differences were found. Our results show that prolonged stimulation increases salivary alpha-amylase, which was expected from the functional properties of the LC. The finding of longer response times to short taVNS stimulation was not expected and cannot be explained by an increase in LC activity. We also discuss the difficulties in assessing pupil size as an expression of taVNS-mediated LC functional changes.

Three paradoxes related to the mode of action of pramipexole: The path from D2/D3 dopamine receptor stimulation to modification of dopamine-modulated functions

Pramipexole, a D2/D3 dopamine receptor agonist, is used to treat the motor symptoms of Parkinson's disease, caused by degeneration of the dopaminergic nigrostriatal pathway. There are three paradoxes associated with its mode of action. Firstly, stimulation of D2/D3 receptors leads to neuronal inhibition, although pramipexole does not inhibit but promotes some dopamine-modulated functions, such as locomotion and reinforcement. Secondly, another dopamine-modulated function, arousal, is not promoted but inhibited by pramipexole, leading to sedation. Thirdly, pramipexole-evoked sedation is associated with an increase in pupil diameter, although sedation is expected to cause pupil constriction. To resolve these paradoxes, the path from stimulation of D2/D3 receptors to the modification of dopamine-modulated functions has been tracked. The functions considered are modulated by midbrain dopaminergic nuclei: locomotion - substantia nigra pars compacta (SNc), reinforcement/motivation - ventral tegmental area (VTA), sympathetic activity (as reflected in pupil function) - VTA; arousal - ventral periaqueductal grey (vPAG), with contributions from VTA and SNc. The application of genetics-based molecular techniques (optogenetics and chemogenetics) has enabled tracing the chains of neurones from the dopaminergic nuclei to their final targets executing the functions. The functional neuronal circuits linked to the D2/D3 receptors in the dorsal and ventral striata, stimulated by inputs from SNc and VTA, respectively, may explain how neuronal inhibition induced by pramipexole is translated into the promotion of locomotion, reinforcement/motivation and sympathetic activity. As the vPAG may increase arousal mainly by stimulating cortical D1 dopamine receptors, pramipexole would stimulate only presynaptic D2/D3 receptors on vPAG neurones, curtailing their activity and leading to sedation.

Impact of acute psychosocial stress on attentional control in humans. A study of evoked potentials and pupillary response

Psychosocial stress has increased considerably in our modern lifestyle, affecting global mental health. Deficits in attentional control are cardinal features of stress disorders and pathological anxiety. Studies suggest that changes in the locus coeruleus-norepinephrine system could underlie the effects of stress on top-down attentional control. However, the impact of psychosocial stress on attentional processes and its underlying neural mechanisms are poorly understood. This study aims to investigate the effect of psychosocial stress on attentional processing and brain signatures. Evoked potentials and pupillary activity related to the oddball auditory paradigm were recorded before and after applying the Montreal Imaging Stress Task (MIST). Electrocardiogram (ECG), salivary cortisol, and subjective anxiety/stress levels were measured at different experimental periods. The control group experienced the same physical and cognitive effort but without the psychosocial stress component. The results showed that stressed subjects exhibited decreased P3a and P3b amplitude, pupil phasic response, and correct responses. On the other hand, they displayed an increase in Mismatch Negativity (MMN). N1 amplitude after MIST only decreased in the control group. We found that differences in P3b amplitude between the first and second oddball were significantly correlated with pupillary dilation and salivary cortisol levels. Our results suggest that under social-evaluative threat, basal activity of the coeruleus-norepinephrine system increases, enhancing alertness and decreasing voluntary attentional resources for the cognitive task. These findings contribute to understanding the neurobiological basis of attentional changes in pathologies associated with chronic psychosocial stress.

No alterations in potential indirect markers of locus coeruleus-norepinephrine function in insomnia disorder

The norepinephrine locus coeruleus system (LC NE) represents a promising treatment target in patients with insomnia disorder (ID) due to its well understood links to arousal and sleep regulation. However, consistent markers of LC NE activity are lacking. This study measured three potential indirect markers of LC NE activity - REM sleep, P3 amplitude during an auditory oddball paradigm (as a marker of phasic LC activation), and baseline pupil diameter (as a marker of tonic LC activation). The parameters were then combined in a statistical model and tested to compare LC NE activity between 20 subjects with insomnia disorder (13 female; age 44.2 ± 15.1 year) and 20 healthy, good sleeping controls (GSC; 11 female; age 45.4 ± 11.6 year). No group differences regarding the primary outcome parameters were detected. Specifically, insomnia disorder did not display the hypothesised changes in markers of LC NE function. While increased LC NE function remains an interesting speculative pathway for hyperarousal in insomnia disorder, the investigated markers do not appear closely related to each other and fail to discriminate between insomnia disorder and good sleeping controls in these samples.

Short bursts of transcutaneous auricular vagus nerve stimulation enhance evoked pupil dilation as a function of stimulation parameters

Transcutaneous auricular vagus nerve stimulation (taVNS) is a neurostimulatory technique hypothesised to enhance central noradrenaline. Currently, there is scarce evidence in support of a noradrenergic mechanism of taVNS and limited knowledge on its stimulation parameters (i.e., intensity and pulse width). Therefore, the present study aimed to test whether taVNS enhances pupil dilation, a noradrenergic biomarker, as a function of stimulation parameters. Forty-nine participants received sham (i.e., left ear earlobe) and taVNS (i.e., left ear cymba concha) stimulation in two separate sessions, in a counterbalanced order. We administered short bursts (5s) of seven stimulation settings varying as a function of pulse width and intensity and measured pupil size in parallel. Each stimulation setting was administered sixteen times in separate blocks. We expected short bursts of stimulation to elicit phasic noradrenergic activity as indexed by event-related pupil dilation and event-related temporal derivative. We hypothesised higher stimulation settings, quantified as the total charge per pulse (pulse width x intensity), to drive greater event-related pupil dilation and temporal derivative in the taVNS compared to sham condition. Specifically, we expected stimulation settings in the taVNS condition to be associated with a linear increase in event-related pupil dilation and temporal derivative. We found stimulation settings to linearly increase both pupil measures. In line with our hypothesis, the observed dose-dependent effect was stronger in the taVNS condition. We also found taVNS to elicit more intense and unpleasant sensations than sham stimulation. These results support the hypothesis of a noradrenergic mechanism of taVNS. However, future studies should disentangle whether stimulation elicited sensations mediate the effect of taVNS on evoked pupil dilation.

Pupillometric measures of altered stimulus-evoked locus coeruleus-norepinephrine activity explain attenuated social attention in preschoolers with autism spectrum disorder

Attenuated social attention has been described as a reduced preference for social compared to geometric motion in preschoolers with autism spectrum disorder (ASD). The locus coeruleus-norpinephrine (LC-NE) system modulates sensory reactivity and is a promising underlying mechanism. LC-NE activity is indexed by a stimulus-evoked pupillary response (SEPR) and partially by a luminance-adaptation pupillary response (LAPR), which were both shown to be aberrant in ASD. We examined whether SEPR and LAPR explain an attenuated social motion preference. We applied pupillometry via video-based eye tracking in young children (18-65 months) with ASD (n = 57) and typically developing (TD) children (n = 39) during a preferential looking paradigm of competing social and geometric motion and a changing light condition paradigm. We found an attenuated social motion preference in the ASD compared to the TD group. This was accompanied by atypical pupillometry showing a smaller SEPR to social motion, a larger SEPR to geometric motion and a reduced LAPR to a dark screen. SEPR but not LAPR explained the group difference in social motion preference. An ASD diagnosis was statistically predicted by the social motion preference, while this effect was mediated by the inclusion of SEPR to geometric and social motion. Our findings suggest a decreased sensory reactivity to social and increased reactivity to non-social motion in ASD, which may concurrently contribute to an attenuated social attention. The LC-NE system is supported as a promising underlying mechanism of altered social attention in young children with ASD, while the specificity of findings remains to be addressed.

Tonic and phasic effects of reward on the pupil: implications for locus coeruleus function

The locus coeruleus (LC), a nucleus in the pons of the brainstem, plays a significant role in attention and cognitive control. Here, we use an adapted auditory oddball paradigm and measured the pupil dilation response, to provide a marker of LC activity in humans. In Experiment 1, we show event-related pupil responses to rare auditory events which were further elevated by task relevant. In Experiment 2, by asking participants to silently count the number of oddballs, we demonstrated that the task-relevance elevation was not a result of the generation or execution of the manual response. In Experiment 3, we observed two separate effects of reward on the pupil response. First, we found an overall increase in pupil area in the high compared to the low-reward blocks: a sustained effect reminiscent of the tonic changes that occur in LC. Second, we found elevated event-related pupil responses to behaviourally relevant stimuli in the high-reward condition compared with the low-reward condition, consistent with phasic changes in LC in response to a stimulus. These results highlight the complexity of the relationship between the pupil response and reward, and the inferred role of LC in both top-down and bottom-up cognitive control.

Error-related Alpha Suppression: Scalp Topography and (Lack of) Modulation by Modafinil

Errors in performance trigger cognitive and neural changes that are implemented to adaptively adjust to fluctuating demands. Error-related alpha suppression (ERAS)-which refers to decreased power in the alpha frequency band after an incorrect response-is thought to reflect cognitive arousal after errors. Much of this work has been correlational, however, and there are no direct investigations into its pharmacological sensitivity. In Study 1 (n = 61), we evaluated the presence and scalp distribution of ERAS in a novel flanker task specifically developed for cross-species assessments. Using this same task in Study 2 (n = 26), which had a placebo-controlled within-subject design, we evaluated the sensitivity of ERAS to placebo (0 mg), low (100 mg), and high (200 mg) doses of modafinil, a wakefulness promoting agent. Consistent with previous work, ERAS was maximal at parieto-occipital recording sites in both studies. In Study 2, modafinil did not have strong effects on ERAS (a significant Accuracy × Dose interaction emerged, but drug-placebo differences did not reach statistical significance after correction for multiple comparisons and was absent after controlling for accuracy rate). ERAS was correlated with accuracy rates in both studies. Thus, modafinil did not impact ERAS as hypothesized, and findings indicate ERAS may reflect an orienting response to infrequent events.

Superior frontal regions reflect the dynamics of task engagement and theta band-related control processes in time-on task effects

Impairment of cognitive performance is often observed in time-on tasks. Theoretical considerations suggest that especially prefrontal cortex cognitive control functions is affected by time-on-task effects, but the role of effort/task engagement is not understood. We examine time-on-task effects in cognitive control on a neurophysiological level using a working-memory modulated response inhibition task and inter-relate prefrontal neuroanatomical region-specific theta-band activity with pupil diameter data using EEG-beamforming approaches. We show that task performance declines with time-on tasks, which was paralleled by a concomitant decreases of task-evoked superior frontal gyrus theta-band activity and a reduction in phasic pupil diameter modulations. A strong relation between cognitive control-related superior frontal theta-band activity and effort/task engagement indexed by phasic pupil diameter modulations was observed in the beginning of the experiment, especially for tasks requiring inhibitory controls and demanding high working memory. This strong relation vanished at the end of the experiment, suggesting a decoupling of cognitive control resources useable for a task and effort invested that characterizes time-on-task effects in prefrontal cortical structures.

Time-on-task effects on working memory gating processes—A role of theta synchronization and the norepinephrine system

Performance impairment as an effect of prolonged engagement in a specific task is commonly observed. Although this is a well-known effect in everyday life, little is known about how this affects central cognitive functions such as working memory (WM) processes. In the current study, we ask how time-on-task affects WM gating processes and thus processes regulating WM maintenance and updating. To this end, we combined electroencephalography methods and recordings of the pupil diameter as an indirect of the norepinephrine (NE) system activity. Our results showed that only WM gate opening but not closing processes showed time-on-task effects. On the neurophysiological level, this was associated with modulation of dorsolateral prefrontal theta band synchronization processes, which vanished with time-on-task during WM gate opening. Interestingly, also the modulatory pattern of the NE system, as inferred using pupil diameter data, changed. At the beginning, a strong correlation of pupil diameter data and theta band synchronization processes during WM gate opening is observed. This modulatory effect vanished at the end of the experiment. The results show that time-on-task has very specific effects on WM gate opening and closing processes and suggests an important role of NE system in the time-on-task effect on WM gate opening process.

A role of the norepinephrine system or effort in the interplay of different facets of inhibitory control

Inhibitory control has multiple facets, and one possible distinction can be made between 'inhibition of interferences' and the 'inhibition of actions'. Both facets of inhibitory control show an interdependency. Even though some neurophysiological processes underlying this interdependency have been examined, the role of neuro-modulatory processes in their interplay are not understood. In the current study, we examine the role of the norepinephrine (NE) system in these processes. We did so by combining a Go/Nogo and Simon task. We recorded the EEG and pupil diameter data as an indirect index of NE system activity during the task. EEG theta band activity data and pupil diameter data were then integrated after conducting a temporal signal decomposition of the EEG data. We show that particularly theta band activity coding stimulus-response translation processes associated with middle frontal cortices, but not stimulus-driven processes are modulated by the interplay between the 'inhibition of interferences' and the 'inhibition of actions'. Modulations in stimulus-response translation processes were systematically correlated with pupil-diameter responses. The pattern of correlations suggests that phasic NE system activity particularly modulates stimulus-response mapping processes during conflict monitoring in incongruent Nogo trials, which may explain behavioral performance effects. Phasic NE system activity reflects essential modulators of the interplay between the 'inhibition of interferences' and the 'inhibition of actions'.

Stimulating meditation: a pre-registered randomised controlled experiment combining a single dose of the cognitive enhancer, modafinil, with brief mindfulness training

BACKGROUND

Mindfulness-meditation has a variety of benefits on well-being. However, individuals with primary attentional impairments (e.g. attention deficit disorder) or attentional symptoms secondary to anxiety, depression or addiction, may be less likely to benefit, and require additional mindfulness-augmenting strategies.

AIMS

To determine whether a single dose of the cognitive enhancer, modafinil, acutely increases subjective and behavioural indices of mindfulness, and augments brief mindfulness training.

METHODS

A randomised, double-blind, placebo-controlled, 2 (drug: placebo, modafinil) × 2 (strategy: mindfulness, relaxation control) experiment was conducted. Seventy-nine meditation-naïve participants were assigned to: placebo-relaxation, placebo-mindfulness, modafinil-relaxation or modafinil-mindfulness. Pre-drug, post-drug and post-strategy state mindfulness, affect and autonomic activity, along with post-strategy sustained attention and mind-wandering were assessed within a single lab session. After the session, participants were instructed to practice their assigned behavioural strategy daily for one week, with no further drug administration, after which, follow-up measures were taken.

RESULTS

As predicted, modafinil acutely increased state mindfulness and improved sustained attention. Differential acute strategy effects were found following mindfulness on autonomic activity but not state mindfulness. There were no strategy or drug effects on mind-wandering. However, exploratory analyses indicated that participants receiving modafinil engaged in more strategy practice across strategy conditions during follow-up.

CONCLUSIONS

Modafinil acutely mimicked the effects of brief mindfulness training on state mindfulness but did not enhance the effects of this training. Limitations of the current study, and recommendations for future research examining modafinil as an adjunct to mindfulness- (or relaxation-) based treatments are discussed.

The peripheral effect of direct current stimulation on brain circuits involving memory

An ongoing debate surrounding transcranial direct current stimulation (tDCS) of the scalp is whether it modulates brain activity both directly and in a regionally constrained manner enough to positively affect symptoms in patients with neurological disorders. One alternative explanation is that direct current stimulation affects neural circuits mainly indirectly, i.e., via peripheral nerves. Here, we report that noninvasive direct current stimulation indirectly affects neural circuits via peripheral nerves. In a series of studies, we show that direct current stimulation can cause activation of the greater occipital nerve (ON-tDCS) and augments memory via the ascending fibers of the occipital nerve to the locus coeruleus, promoting noradrenaline release. This noradrenergic pathway plays a key role in driving hippocampal activity by modifying functional connectivity supporting the consolidation of a memory event.

Individual differences in baseline oculometrics: Examining variation in baseline pupil diameter, spontaneous eye blink rate, and fixation stability

Individual differences in baseline oculometrics (baseline pupil diameter, spontaneous eye blink rate, fixation stability), and their relation with cognitive abilities, personality traits, and self-report assessments were examined. Participants performed a baseline eye measure in which they were instructed to stare at a fixation point onscreen for 5 min. Following the baseline eye measure, participants completed a questionnaire asking what they were thinking about during the baseline eye measure. Participants also completed various cognitive ability measures assessing working memory capacity, attention control, and off-task thinking. Finally, participants completed a number of questionnaires assessing personality, Attention Deficit/Hyperactivity Disorder symptomology, mind wandering, and morningness-eveningness. Overall, the vast majority of correlations with the baseline eye measures were weak and nonsignificant, suggesting that these associations may not be very robust. The results also demonstrated the importance of examining what participants are thinking about during the baseline measure. These results add to the growing body of findings suggesting inconsistent relations between different baseline eye measures and various individual differences constructs.

Component processes in free-viewing visual search: Insights from fixation-aligned pupillary response averaging

Pupil size changes during a visual search may reflect cognitive processes, such as effort and memory accumulation, but methodological confounds and the general lack of literature in this area leave the reliability of findings open to question. We used a novel synthesis of experimental methods and averaging techniques to explore how cognitive processing unfolds during free-viewing visual search for multiple targets. Twenty-seven participants completed 152 searches across two separate 1-hour sessions. The number of targets present (Targets: 0, 1, 2, and 3) in each trial was the main manipulation and the task was to "find all of the targets" and report the total via mouse-click at the end of the trial. Search time lasted for 10 seconds or until the participant purported to have found all of the targets, in which case they could terminate the search via keypress. Whole-trial pupil analysis revealed a significant effect of button pressing as well as a significant main effect of targets for trials that were not self-terminated via button press. Fixation-aligned pupil responses revealed transient modulations in pupil size following initial fixations on targets but not distractors and refixations on both targets and distractors. Owing to rigorous control over experimental confounds and a detailed analysis and correction of eye-movement-related measurement error, we confidently discuss these findings in terms of task-related processing and underlying brain activity.

Bidirectional pharmacological perturbations of the noradrenergic system differentially affect tactile detection

The brain neuromodulatory systems heavily influence behavioral and cognitive processes. Previous work has shown that norepinephrine (NE), a classic neuromodulator mainly derived from the locus coeruleus (LC), enhances neuronal responses to sensory stimuli. However, the role of the LC-NE system in modulating perceptual task performance is not well understood. In addition, systemic perturbation of NE signaling has often been proposed to specifically target the LC in functional studies, yet the assumption that localized (specific) and systemic (nonspecific) perturbations of LC-NE have the same behavioral impact remains largely untested. In this study, we trained mice to perform a head-fixed, quantitative tactile detection task, and administered an α2 adrenergic receptor agonist or antagonist to pharmacologically down- or up-regulate LC-NE activity, respectively. We addressed the outstanding question of how bidirectional perturbations of LC-NE activity affect tactile detection, and tested whether localized and systemic drug treatments exert the same behavioral effects. We found that both localized and systemic suppression of LC-NE impaired tactile detection by reducing motivation. Surprisingly, while locally activating LC-NE enabled mice to perform in a near-optimal regime, systemic activation impaired behavior by promoting impulsivity. Our results demonstrate that localized silencing and activation of LC-NE differentially affect tactile detection, and that localized and systemic NE activation induce distinct behavioral changes.

A literature review on the neurophysiological underpinnings and cognitive effects of transcutaneous vagus nerve stimulation: challenges and future directions

Brain stimulation approaches are important to gain causal mechanistic insights into the relevance of functional brain regions and/or neurophysiological systems for human cognitive functions. In recent years, transcutaneous vagus nerve stimulation (tVNS) has attracted considerable popularity. It is a noninvasive brain stimulation technique based on the stimulation of the vagus nerve. The stimulation of this nerve activates subcortical nuclei, such as the locus coeruleus and the nucleus of the solitary tract, and from there, the activation propagates to the cortex. Since tVNS is a novel stimulation technique, this literature review outlines a brief historical background of tVNS, before detailing underlying neurophysiological mechanisms of action, stimulation parameters, cognitive effects of tVNS on healthy humans, and, lastly, current challenges and future directions of tVNS research in cognitive functions. Although more research is needed, we conclude that tVNS, by increasing norepineprine (NE) and gamma-aminobutyric acid (GABA) levels, affects NE- and GABA-related cognitive performance. The review provides detailed background information how to use tVNS as a neuromodulatory tool in cognitive neuroscience and outlines important future leads of research on tVNS.

Moving beyond belief: A narrative review of potential biomarkers for transcutaneous vagus nerve stimulation

Transcutaneous vagus nerve stimulation (tVNS) is a non-invasive neurostimulation technique that is currently being tested as a potential treatment for a myriad of neurological and psychiatric disorders. However, the working mechanisms underlying tVNS are poorly understood and it remains unclear whether stimulation activates the vagus nerve for every participant. Finding a biological marker of tVNS is imperative, as it can help guide research on clinical applications and can inform researchers on optimal stimulation sites and parameters to further optimize treatment efficacy. In this narrative review, we discuss five potential biomarkers for tVNS and review currently available evidence for these markers for both invasive and tVNS. While some of these biomarkers hold promise from a theoretical perspective, none of the potential biomarkers provide clear and definitive indications that tVNS increases the vagal activity or augments activity in the locus coeruleus-noradrenaline network. We conclude the review by providing several recommendations for how to tackle the challenges and opportunities when researching potential biomarkers for the effects of tVNS.

Properties of lower level processing modulate the actions of the norepinephrine system during response inhibition

We ask whether actions of the norepinephrine (NE) system during response inhibition are affected by properties of lower level sensory stimulus processing. We used a somato-sensory Go/Nogo task and combined ERP recordings with pupil diameter recordings as an index of NE system activity. The Go/Nogo task was designed to achieve processing of tactile stimuli predominantly over primary somatosensory (SI) and secondary somatosensory (SII) areas. The data show that response inhibition was better when stimuli were processed via SII, compared to SI areas. This was reflected by variations in the Nogo-N2/P3 associated with anterior cingulate structures. Correlations with the pupil diameter data, indicting modulations of the NE system during inhibitory control processes, were only evident when SI sensory areas were involved. These dissociable modulatory effects were associated with activations in the superior frontal gyrus. Actions of the NE system during response inhibition are modulated by properties of lower level processing.

On the interrelation of 1/f neural noise and norepinephrine system activity during motor response inhibition

Several lines of evidence suggest that there is a close interrelation between the degree of noise in neural circuits and the activity of the norepinephrine (NE) system, yet the precise nexus between these aspects is far from being understood during human information processing and cognitive control in particular. We examine this nexus during response inhibition in n = 47 healthy participants. Using high-density EEG recordings, we estimate neural noise by calculating "1/f noise" of those data and integrate these EEG parameters with pupil diameter data as an established indirect index of NE system activity. We show that neural noise is reduced when cognitive control processes to inhibit a prepotent/automated response are exerted. These neural noise variations were confined to the theta frequency band, which has also been shown to play a central role during response inhibition and cognitive control. There were strong positive correlations between the 1/f neural noise parameter and the pupil diameter data within the first 250 ms after the Nogo stimulus presentation at centro-parietal electrode sites. No such correlations were evident during automated responding on Go trials. Source localization analyses using standardized low-resolution brain electromagnetic tomography show that inferior parietal areas are activated in this time period in Nogo trials. The data suggest an interrelation of NE system activity and neural noise within early stages of information processing associated with inferior parietal areas when cognitive control processes are required. The data provide the first direct evidence for the nexus between NE system activity and the modulation of neural noise during inhibitory control in humans. NEW & NOTEWORTHY This is the first study showing that there is a nexus between norepinephrine system activity and the modulation of neural noise or scale-free neural activity during inhibitory control in humans. It does so by integrating pupil diameter data with analysis of EEG neural noise.

Standards in Pupillography

The number of research groups studying the pupil is increasing, as is the number of publications. Consequently, new standards in pupillography are needed to formalize the methodology including recording conditions, stimulus characteristics, as well as suitable parameters of evaluation. Since the description of intrinsically photosensitive retinal ganglion cells (ipRGCs) there has been an increased interest and broader application of pupillography in ophthalmology as well as other fields including psychology and chronobiology. Color pupillography plays an important role not only in research but also in clinical observational and therapy studies like gene therapy of hereditary retinal degenerations and psychopathology. Stimuli can vary in size, brightness, duration, and wavelength. Stimulus paradigms determine whether rhodopsin-driven rod responses, opsin-driven cone responses, or melanopsin-driven ipRGC responses are primarily elicited. Background illumination, adaptation state, and instruction for the participants will furthermore influence the results. This standard recommends a minimum set of variables to be used for pupillography and specified in the publication methodologies. Initiated at the 32nd International Pupil Colloquium 2017 in Morges, Switzerland, the aim of this manuscript is to outline standards in pupillography based on current knowledge and experience of pupil experts in order to achieve greater comparability of pupillographic studies. Such standards will particularly facilitate the proper application of pupillography by researchers new to the field. First we describe general standards, followed by specific suggestions concerning the demands of different targets of pupil research: the afferent and efferent reflex arc, pharmacology, psychology, sleepiness-related research and animal studies.

Anodal tDCS affects neuromodulatory effects of the norepinephrine system on superior frontal theta activity during response inhibition

Medial and superior frontal theta oscillations are important for response inhibition. The norepinephrine (NE) system has been shown to modulate these oscillations possibly via gain control mechanisms, which depend on the modulation of neuron membrane potentials. Because the latter are also modulated by tDCS, the interrelation of tDCS and NE effects on superior frontal theta band activity needs investigation. We test the hypothesis that anodal tDCS affects modulatory effects of the NE system on theta band activity during inhibitory control in superior frontal regions. Using EEG beamforming, theta band activity in the superior frontal gyrus (SFG) was integrated (correlated) with the pupil diameter data as an indirect index of NE activity. In a within-subject design, healthy participants completed a response inhibition task in two sessions in which they received 2 mA anodal tDCS over the vertex, or sham stimulation. There were no behavioral effects of anodal tDCS. Yet, tDCS affected correlations between SFG theta band activity time course and the pupil diameter time course. Correlations were evident after sham stimulation (r = .701; p < .004), but absent after anodal tDCS. The observed power of this dissociation was above 95%. The data suggest that anodal tDCS may eliminate neuromodulatory effects, likely of the NE system, on theta band activity during response inhibition in a structure of the response inhibition network. The NE system and tDCS seem to target similar mechanisms important for cognitive control in the prefrontal cortex. The results provide a hint why tDCS often fails to induce overt behavioral effects and shows that neurobiological systems, which may exert similar effects as tDCS on neural processes should closely be monitored in tDCS experiments.

Functional Organization of the Sympathetic Pathways Controlling the Pupil: Light-Inhibited and Light-Stimulated Pathways

Pupil dilation is mediated by a sympathetic output acting in opposition to parasympathetically mediated pupil constriction. While light stimulates the parasympathetic output, giving rise to the light reflex, it can both inhibit and stimulate the sympathetic output. Light-inhibited sympathetic pathways originate in retina-receptive neurones of the pretectum and the suprachiasmatic nucleus (SCN): by attenuating sympathetic activity, they allow unimpeded operation of the light reflex. Light stimulates the noradrenergic and serotonergic pathways. The hub of the noradrenergic pathway is the locus coeruleus (LC) containing both excitatory sympathetic premotor neurones (SympPN) projecting to preganglionic neurones in the spinal cord, and inhibitory parasympathetic premotor neurones (ParaPN) projecting to preganglionic neurones in the Edinger-Westphal nucleus (EWN). SympPN receive inputs from the SCN via the dorsomedial hypothalamus, orexinergic neurones of the latero-posterior hypothalamus, wake- and sleep-promoting neurones of the hypothalamus and brain stem, nociceptive collaterals of the spinothalamic tract, whereas ParaPN receive inputs from the amygdala, sleep/arousal network, nociceptive spinothalamic collaterals. The activity of LC neurones is regulated by inhibitory α₂-adrenoceptors. There is a species difference in the function of the preautonomic LC. In diurnal animals, the α₂-adrenoceptor agonist clonidine stimulates mainly autoreceptors on SymPN, causing miosis, whereas in nocturnal animals it stimulates postsynaptic α₂-arenoceptors in the EWN, causing mydriasis. Noxious stimulation activates SympPN in diurnal animals and ParaPN in nocturnal animals, leading to pupil dilation via sympathoexcitation and parasympathetic inhibition, respectively. These differences may be attributed to increased activity of excitatory LC neurones due to stimulation by light in diurnal animals. This may also underlie the wake-promoting effect of light in diurnal animals, in contrast to its sleep-promoting effect in nocturnal species. The hub of the serotonergic pathway is the dorsal raphe nucleus that is light-sensitive, both directly and indirectly (via an orexinergic input). The light-stimulated pathways mediate a latent mydriatic effect of light on the pupil that can be unmasked by drugs that either inhibit or stimulate SympPN in these pathways. The noradrenergic pathway has widespread connections to neural networks controlling a variety of functions, such as sleep/arousal, pain, and fear/anxiety. Many physiological and psychological variables modulate pupil function via this pathway.

Arousal Effects on Pupil Size, Heart Rate, and Skin Conductance in an Emotional Face Task

Arousal level changes constantly and it has a profound influence on performance during everyday activities. Fluctuations in arousal are regulated by the autonomic nervous system, which is mainly controlled by the balanced activity of the parasympathetic and sympathetic systems, commonly indexed by heart rate (HR) and galvanic skin response (GSR), respectively. Although a growing number of studies have used pupil size to indicate the level of arousal, research that directly examines the relationship between pupil size and HR or GSR is limited. The goal of this study was to understand how pupil size is modulated by autonomic arousal. Human participants fixated various emotional face stimuli, of which low-level visual properties were carefully controlled, while their pupil size, HR, GSR, and eye position were recorded simultaneously. We hypothesized that a positive correlation between pupil size and HR or GSR would be observed both before and after face presentation. Trial-by-trial positive correlations between pupil diameter and HR and GSR were found before face presentation, with larger pupil diameter observed on trials with higher HR or GSR. However, task-evoked pupil responses after face presentation only correlated with HR. Overall, these results demonstrated a trial-by-trial relationship between pupil size and HR or GSR, suggesting that pupil size can be used as an index for arousal level involuntarily regulated by the autonomic nervous system.

Dysfunctional effort-based decision-making underlies apathy in genetic cerebral small vessel disease

Apathy is a syndrome of reduced motivation that commonly occurs in patients with cerebral small vessel disease, including those with the early onset form, CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy). The cognitive mechanisms underlying apathy are poorly understood and treatment options are limited. We hypothesized that disrupted effort-based decision-making, the cognitive process by which potential rewards and the effort cost required to obtain them is integrated to drive behaviour, might underlie the apathetic syndrome. Nineteen patients with a genetic diagnosis of CADASIL, as a model of 'pure' vascular cognitive impairment, and 19 matched controls were assessed using two different behavioural paradigms and MRI. On a decision-making task, participants decided whether to accept or reject sequential offers of monetary reward in return for exerting physical effort via handheld dynamometers. Six levels of reward and six levels of effort were manipulated independently so offers spanned the full range of possible combinations. Choice, decision time and force metrics were recorded. Each participant's effort and reward sensitivity was estimated using a computational model of choice. On a separate eye movement paradigm, physiological reward sensitivity was indexed by measuring pupillary dilatation to increasing monetary incentives. This metric was related to apathy status and compared to the behavioural metric of reward sensitivity on the decision-making task. Finally, high quality diffusion imaging and tract-based spatial statistics were used to determine whether tracts linking brain regions implicated in effort-based decision-making were disrupted in apathetic patients. Overall, apathetic patients with CADASIL rejected significantly more offers on the decision-making task, due to reduced reward sensitivity rather than effort hypersensitivity. Apathy was also associated with blunted pupillary responses to incentives. Furthermore, these independent behavioural and physiological markers of reward sensitivity were significantly correlated. Non-apathetic patients with CADASIL did not differ from controls on either task, whilst actual motor performance of apathetic patients in both tasks was also normal. Apathy was specifically associated with reduced fractional anisotropy within tracts connecting regions previously associated with effort-based decision-making. These findings demonstrate behavioural, physiological and anatomical evidence that dysfunctional effort-based decision-making underlies apathy in patients with CADASIL, a model disorder for sporadic small vessel disease. Reduced incentivization by rewards rather than hypersensitivity to effort costs drives this altered pattern of behaviour. The study provides empirical evidence of a cognitive mechanism for apathy in cerebral small vessel disease, and identifies a promising therapeutic target for interventions to improve this debilitating condition.

Cortico-Amygdala-Striatal Activation by Modafinil/Flecainide Combination

Background

Modafinil, a nonamphetaminic wake-promoting compound, is prescribed as first line therapy in narcolepsy, an invalidating disorder characterized by excessive daytime sleepiness and cataplexy. Although its mode of action remains incompletely known, recent studies indicated that modafinil modulates astroglial connexin-based gap junctional communication as administration of a low dose of flecainide, an astroglial connexin inhibitor, enhanced the wake-promoting and procognitive activity of modafinil in rodents and healthy volunteers. The aim of this study is to investigate changes in glucose cerebral metabolism in rodents, induced by the combination of modafinil+flecainide low dose (called THN102).

Methods

The impact of THN102 on brain glucose metabolism was noninvasively investigated using 18F-2-fluoro-2-deoxy-D-glucose Positron Emission Tomography imaging in Sprague-Dawley male rats. Animals were injected with vehicle, flecainide, modafinil, or THN102 and further injected with 18F-2-fluoro-2-deoxy-D-glucose followed by 60-minute Positron Emission Tomography acquisition. 18F-2-fluoro-2-deoxy-D-glucose Positron Emission Tomography images were coregistered to a rat brain template and normalized from the total brain Positron Emission Tomography signal. Voxel-to-voxel analysis was performed using SPM8 software. Comparison of brain glucose metabolism between groups was then performed.

Results

THN102 significantly increased regional brain glucose metabolism as it resulted in large clusters of 18F-2-fluoro-2-deoxy-D-glucose uptake localized in the cortex, striatum, and amygdala compared with control or drugs administered alone. These regions, highly involved in the regulation of sleep-wake cycle, emotions, and cognitive functions were hence quantitatively modulated by THN102.

Conclusion

Data presented here provide the first evidence of a regional brain activation induced by THN102, currently being tested in a phase II clinical trial in narcoleptic patients.

Modafinil Reduces Parasympathetic Activity but Does Not Influence Autonomic Reactivity to Orthostatic Load in Narcolepsy Type 1

INTRODUCTION

Modafinil may affect autonomic functions in healthy subjects. The aim of the study was to assess the long-term modafinil administration influence on the cardiac autonomic reactivity to orthostatic load in patients with narcolepsy type 1.

METHODS

In 15 patients (4 male; 11 female; median age, 47 years; range, 18-70 years) with narcolepsy type 1 treated with modafinil in daily dose of 100 to 300 mg, the short-term spectral analysis of heart rate variability (HRV) in supine-standing-supine test was performed before and after 72 hours of modafinil discontinuation.

RESULTS

The sympathovagal reactivity to orthostatic load was not modified by modafinil treatment; nevertheless, the parasympathetic activity expressed by length of R-R interval and high-frequency component of HRV is reduced in supine position in patients taking modafinil.

CONCLUSIONS

We conclude that long-term use of modafinil does not influence the cardiac autonomic reactivity to orthostatic load expressed by the HRV changes in supine-standing-supine test in narcolepsy type 1 patients, but the parasympathetic cardiac activity may be reduced in quiet supine position in patients with narcolepsy taking modafinil.

Lost in Time and Space: States of High Arousal Disrupt Implicit Acquisition of Spatial and Sequential Context Information

Biased cognition during high arousal states is a relevant phenomenon in a variety of topics: from the development of post-traumatic stress disorders or stress-triggered addictive behaviors to forensic considerations regarding crimes of passion. Recent evidence indicates that arousal modulates the engagement of a hippocampus-based "cognitive" system in favor of a striatum-based "habit" system in learning and memory, promoting a switch from flexible, contextualized to more rigid, reflexive responses. Existing findings appear inconsistent, therefore it is unclear whether and which type of context processing is disrupted by enhanced arousal. In this behavioral study, we investigated such arousal-triggered cognitive-state shifts in human subjects. We validated an arousal induction procedure (three experimental conditions: violent scene, erotic scene, neutral control scene) using pupillometry (Preliminary Experiment, n = 13) and randomly administered this method to healthy young adults to examine whether high arousal states affect performance in two core domains of contextual processing, the acquisition of spatial (spatial discrimination paradigm; Experiment 1, n = 66) and sequence information (learned irrelevance paradigm; Experiment 2, n = 84). In both paradigms, spatial location and sequences were encoded incidentally and both displacements when retrieving spatial position as well as the predictability of the target by a cue in sequence learning changed stepwise. Results showed that both implicit spatial and sequence learning were disrupted during high arousal states, regardless of valence. Compared to the control group, participants in the arousal conditions showed impaired discrimination of spatial positions and abolished learning of associative sequences. Furthermore, Bayesian analyses revealed evidence against the null models. In line with recent models of stress effects on cognition, both experiments provide evidence for decreased engagement of flexible, cognitive systems supporting encoding of context information in active cognition during acute arousal, promoting reduced sensitivity for contextual details. We argue that arousal fosters cognitive adaptation towards less demanding, more present-oriented information processing, which prioritizes a current behavioral response set at the cost of contextual cues. This transient state of behavioral perseverance might reduce reliance on context information in unpredictable environments and thus represent an adaptive response in certain situations.

Differences of sympathetic and parasympathetic modulation in major depression

Inconsistent results have been reported with respect to cardiac autonomic function in major depression. The aim of our study was to investigate autonomic function in various branches of the autonomic nervous system in order to better understand parasympathetic and sympathetic modulation in the disease. We investigated 29 unmedicated patients suffering from major depression (MD) in comparison to matched control subjects (gender, age, BMI). The autonomic assessment at rest included values of heart rate variability (HRV), blood pressure variability (BPV), baroreflex sensitivity (BRS), respiration, skin conductance (SC) as well as the calculation of pupillary diameter and the unrest index (PUI). Results were compared by means of a multivariate analysis of variance. In a classification analysis, we identified suitable parameters for patient - control separation. Finally, to analyze interrelations of pupillometric parameters and autonomic indices, we estimated Pearson correlation coefficients and fitted a linear regression model. Apart from a significantly increased heart rate (75±12 vs. 65±6min^-1, p<0.001) and decreased BRS (14±13 vs. 20±15ms/mmHg, p<0.05), we observed a lack of significant differences in HRV and BPV analysis between patients and controls. However, pupillary diameter (left: 4.3±0.9 vs. 3.8±0.6, p<0.01; right: 4.3±0.9 vs. 3.7±0.6mm, p<0.01) and PUI (left: 14.8±6.0 vs. 10.7±4.5mm/min, p<0.01; right: 14.1±5.5 vs. 10.7±4.8mm/min, p<0.01), as well as the level (left: 7.3±6.2 vs. 4.3±4.4 μS, p<0.05) and fluctuations of skin conductance (left: 4.2±4.1 vs. 2.5±3.6, p<0.05; right: 4.2±4.4 vs. 2.6±3.2, p<0.05) were significantly different. The classification accuracy was 88.5% with high specificity (e=92.9%) and sensitivity (s=83.3%) including heart rate, PUI and skin conductance. HRV indices correlated to PUI in controls but not in patients. Our data add evidence to the current debate on autonomic function in major depression. We suggest that diverse results are mainly caused by methodological shortcomings, in particular by the application of HRV assessment only, which misses changes of sympathetic modulation. The application of broader analyzing tools will clarify the pattern of autonomic function in depression and ultimately its role in cardiac morbidity and mortality.

Decreased salivary alpha-amylase levels are associated with performance deficits during sleep loss

During sleep deprivation, neurobehavioral functions requiring sustained levels of attention and alertness are significantly impaired. Discrepancies between subjective measures of sleepiness and objective performance during sustained operations have led to interest in physiological monitoring of operator performance. Alertness, vigilance, and arousal are modulated by the wake-promoting actions of the central noradrenergic system. Salivary alpha-amylase (sAA) has been proposed as a sensitive peripheral measure of noradrenergic activity, but limited research has investigated the relationship between sAA and performance. In a laboratory-controlled environment, we investigated the relationship between sAA levels, subjective sleepiness, and performance during two days (50h) of total sleep deprivation. Beginning at 09:00, twelve healthy participants (5 females) aged 22.5±2.5years (mean±SD) provided saliva samples, recorded ratings of subjective sleepiness, completed a brief 3-min psychomotor vigilance task (PVT-B) and performed a 40-min simulated driving task, at regular 3h intervals during wakefulness. Ratings of subjective sleepiness exhibited a constant linear increase (p<0.001) during sleep deprivation. In contrast, sAA levels showed a marked diurnal profile, with levels increasing during the day (p<0.001) and steadily declining in the evening and early-morning (p<0.001). PVT-B (mean reaction time and mean slowest 10% reaction time) and simulated driving performance (speed deviation and lane deviation) also exhibited diurnal profiles across the two days of sleep deprivation. Performance peaked in the afternoon (p<0.001) and then steadily worsened as wakefulness continued into the evening and early-morning (p<0.001). Further analysis revealed that higher sAA levels in the hour preceding each performance assessment were associated with better PVT-B and driving performance (p<0.001). These findings suggest that sAA measures may be suitable indicators of performance deficits during sustained wakefulness and highlight the potential for sAA to be considered for physiological monitoring of performance. In operational environments sAA levels, as part of a panel of physiological measures, may be useful for assessing fitness-for-duty prior to safety being compromised or when performance deficits are unknown.

TENS effects on salivary stress markers: A pilot study

Transcutaneous electrical nerve stimulation (TENS) is extensively used as pain relief through endorphins release. Moreover, recent findings showed a role in the activation of the autonomic nervous system (ANS); it was evidenced by modification in the heart rate variability and ANS-related marker. The objective of this pilot study is to evaluate salivary alpha amylase (sAA) as a marker of stress in two groups of healthy subjects, one receiving ultra-low frequency transcutaneous electrical nerve stimulation (ULF-TENS) and one without stimulation. Sixty healthy people were enrolled. The test group consisted of 30 participants (15 men, 15 women). The control group consisted of 30 participants (15 men, 15 women). Statistical analysis showed that sAA levels were statistically different between men and women independently from TENS; we hypothesize that treatment could influence sAA levels because it is thought to activate μ opioid receptors. The results of this study seem to indicate that the analysis of sAA, through a non-invasive saliva sample, could be an efficient aid for understanding the functions of the autonomic nervous system.

The norepinephrine system shows information-content specific properties during cognitive control - Evidence from EEG and pupillary responses

The ability to exert cognitive control is a major function of the prefrontal cortex, the efficiency of which depends on the phasic release of norepinephrine (NE) at particular time points. However, different aspects of information are simultaneously processed at any given moment. This raises the question of whether the norepinephrine system is also capable of specifically modulating selected aspects of all ongoing information processing, especially when several of those processes are carried out by the same functional neuroanatomical structure at the same time. We examine this question in humans using a flanker paradigm by integrating neurophysiological (EEG) and pupil diameter data using novel signal processing techniques including Residue Iteration Decomposition (RIDE) and source localization. We show that during conflict monitoring, motor response-related processes are more strongly modulated by the NE system than stimulus-related processes or central decision processes between stimulus and response. This was the case even though these processes occurred at the same time point and were mediated by overlapping medial frontal cortical structures. The results indicate that the NE system exerts specific modulatory effects for different informational contents that are simultaneously processed in the medial frontal cortex.

The norepinephrine system affects specific neurophysiological subprocesses in the modulation of inhibitory control by working memory demands

Inhibitory control processes are known to be modulated by working memory demands. However, the neurobiological mechanisms behind these modulations are inconclusive. One important system to consider in this regard is the locus coeruleus (LC) norepinephrine (NE) system. In the current study the role of the LC-NE system by means of pupil diameter recordings that are integrated with neurophysiological (EEG) and source localization data were examined. A combined mental-rotation Go/Nogo task was used. The results show that increases in working memory load complicate response inhibition processes. On a neurophysiological level these effects were reflected by specific modulations in event-related potentials (ERPs) reflecting motor inhibition processes (i.e., Nogo-P3). Attentional selection processes (reflected by the P1 and N1) as well as pre-motor inhibition or conflict monitoring processes (reflected by the Nogo-N2) were not affected. Activity of the LC-NE systems, as indexed by the pupil diameter data, predicted neurophysiological processes selectively in the Nogo-P3 time range. Source localization analyses suggest that this modulation occurs in the right middle and inferior frontal gyrus. The study provides evidence that the LC-NE system is an important neurobiological system modulating the effects of working memory load on response inhibition processes. More specifically, it modulates a subset of dissociable cognitive processes that are related to prefrontal cortical regions. Hum Brain Mapp 38:68-81, 2017. © 2016 Wiley Periodicals, Inc.

Association between striatal dopamine D2/D3 receptors and brain activation during visual attention: effects of sleep deprivation

Sleep deprivation (SD) disrupts dopamine (DA) signaling and impairs attention. However, the interpretation of these concomitant effects requires a better understanding of dopamine's role in attention processing. Here we test the hypotheses that D2/D3 receptors (D2/D3R) in dorsal and ventral striatum would distinctly regulate the activation of attention regions and that, by decreasing D2/D3, SD would disrupt these associations. We measured striatal D2/D3R using positron emission tomography with [(11)C]raclopride and brain activation to a visual attention (VA) task using 4-Tesla functional magnetic resonance imaging. Fourteen healthy men were studied during rested wakefulness and also during SD. Increased D2/D3R in striatum (caudate, putamen and ventral striatum) were linearly associated with higher thalamic activation. Subjects with higher D2/D3R in caudate relative to ventral striatum had higher activation in superior parietal cortex and ventral precuneus, and those with higher D2/D3R in putamen relative to ventral striatum had higher activation in anterior cingulate. SD impaired the association between striatal D2/D3R and VA-induced thalamic activation, which is essential for alertness. Findings suggest a robust DAergic modulation of cortical activation during the VA task, such that D2/D3R in dorsal striatum counterbalanced the stimulatory influence of D2/D3R in ventral striatum, which was not significantly disrupted by SD. In contrast, SD disrupted thalamic activation, which did not show counterbalanced DAergic modulation but a positive association with D2/D3R in both dorsal and ventral striatum. The counterbalanced dorsal versus ventral striatal DAergic modulation of VA activation mirrors similar findings during sensorimotor processing (Tomasi et al., 2015) suggesting a bidirectional influence in signaling between the dorsal caudate and putamen and the ventral striatum.

Diverse autonomic regulation of pupillary function and the cardiovascular system during alcohol withdrawal

BACKGROUND

Previous research indicated the complexity of autonomic dysfunction during acute alcohol withdrawal. This study aimed to investigate the pupillary light reflex as an indicator of midbrain and brainstem regulatory systems in relation to cardiovascular autonomic function.

METHODS

Thirty male patients were included in the study. They were investigated during acute alcohol withdrawal syndrome and 24h later during clomethiazole treatment and compared to healthy controls. Parameters of pupillary light reflex of both eyes as well as heart rate variability, blood pressure variability and baroreflex sensitivity (BRS) were studied.

RESULTS

We observed significantly reduced sympathetic (small diameter, e.g., left eye: 5.00 in patients vs. 5.91 mm in controls) and vagal modulation (e.g., prolonged latencies, left eye: 0.28 vs. 0.26 ms) regarding both pupils during acute alcohol withdrawal syndrome. Cardiovascular parameters showed reduced vagal modulation (e.g., b-slope of BRS: 7. 57 vs. 13.59 ms/mm Hg) and mixed results for sympathetic influence. After 24h, autonomic dysfunction improved significantly, both for the pupils (e.g., left diameter: 5.38 mm) and the heart (e.g., b-slope of BRS: 9.34 ms/mm Hg). While parameters obtained from the pupil correlated with cardiac autonomic function (e.g, BRS and left diameter: r=0.564) in healthy controls, no such pattern was observed in patients.

CONCLUSION

Results obtained from the pupil during acute alcohol withdrawal do not simply mirror autonomic dysfunction regarding the heart. Pupillary and cardiovascular changes after 24h indicate state dependencies of the results. The findings are discussed with respect to autonomic mechanisms and potentially involved brain regions.

Relationships between Pupil Diameter and Neuronal Activity in the Locus Coeruleus, Colliculi, and Cingulate Cortex

Changes in pupil diameter that reflect effort and other cognitive factors are often interpreted in terms of the activity of norepinephrine-containing neurons in the brainstem nucleus locus coeruleus (LC), but there is little direct evidence for such a relationship. Here, we show that LC activation reliably anticipates changes in pupil diameter that either fluctuate naturally or are driven by external events during near fixation, as in many psychophysical tasks. This relationship occurs on as fine a temporal and spatial scale as single spikes from single units. However, this relationship is not specific to the LC. Similar relationships, albeit with delayed timing and different reliabilities across sites, are evident in the inferior and superior colliculus and anterior and posterior cingulate cortex. Because these regions are interconnected with the LC, the results suggest that non-luminance-mediated changes in pupil diameter might reflect LC-mediated coordination of neuronal activity throughout some parts of the brain.

Modafinil for cognitive neuroenhancement in healthy non-sleep-deprived subjects: A systematic review

Modafinil is an FDA-approved eugeroic that directly increases cortical catecholamine levels, indirectly upregulates cerebral serotonin, glutamate, orexin, and histamine levels, and indirectly decreases cerebral gamma-amino-butrytic acid levels. In addition to its approved use treating excessive somnolence, modafinil is thought to be used widely off-prescription for cognitive enhancement. However, despite this popularity, there has been little consensus on the extent and nature of the cognitive effects of modafinil in healthy, non-sleep-deprived humans. This problem is compounded by methodological discrepancies within the literature, and reliance on psychometric tests designed to detect cognitive effects in ill rather than healthy populations. In order to provide an up-to-date systematic evaluation that addresses these concerns, we searched MEDLINE with the terms "modafinil" and "cognitive", and reviewed all resultant primary studies in English from January 1990 until December 2014 investigating the cognitive actions of modafinil in healthy non-sleep-deprived humans. We found that whilst most studies employing basic testing paradigms show that modafinil intake enhances executive function, only half show improvements in attention and learning and memory, and a few even report impairments in divergent creative thinking. In contrast, when more complex assessments are used, modafinil appears to consistently engender enhancement of attention, executive functions, and learning. Importantly, we did not observe any preponderances for side effects or mood changes. Finally, in light of the methodological discrepancies encountered within this literature, we conclude with a series of recommendations on how to optimally detect valid, robust, and consistent effects in healthy populations that should aid future assessment of neuroenhancement.