The effects of methylphenidate and propranolol on the interplay between induced-anxiety and working memory

Attenuation of Anxiety-Potentiated Startle After Treatment With Escitalopram or Mindfulness Meditation in Anxiety Disorders

BACKGROUND

Biological markers for anxiety disorders may further understanding of disorder pathophysiology and suggest potential targeted treatments. The fear-potentiated startle (FPS) (a measure of startle to predictable threat) and anxiety-potentiated startle (APS) (startle to unpredictable threat) laboratory paradigm has been used to detect physiological differences in individuals with anxiety disorders compared with nonanxious control individuals, and in pharmacological challenge studies in healthy adults. However, little is known about how startle may change with treatment for anxiety disorders, and no data are available regarding alterations due to mindfulness meditation training.

METHODS

Ninety-three individuals with anxiety disorders and 66 healthy individuals completed 2 sessions of the neutral, predictable, and unpredictable threat task, which employs a startle probe and the threat of shock to assess moment-by-moment fear and anxiety. Between the two testing sessions, patients received randomized 8-week treatment with either escitalopram or mindfulness-based stress reduction.

RESULTS

APS, but not FPS, was higher in participants with anxiety disorders compared with healthy control individuals at baseline. Further, there was a significantly greater decrease in APS for both treatment groups compared with the control group, with the patient groups showing reductions bringing them into the range of control individuals at the end of the treatment.

CONCLUSIONS

Both anxiety treatments (escitalopram and mindfulness-based stress reduction) reduced startle potentiation during unpredictable (APS) but not predictable (FPS) threat. These findings further validate APS as a biological correlate of pathological anxiety and provide physiological evidence for the impact of mindfulness-based stress reduction on anxiety disorders, suggesting that there may be comparable effects of the two treatments on anxiety neurocircuitry.

Muscle Quality Index is inversely associated with psychosocial variables among Chilean adolescents

A good muscle quality index (MQI) may have an inverse relationship with psychosocial variables of depression, anxiety, and stress in adolescents. Unfortunately, little scientific evidence has related MQI to psychosocial variables in this population. Therefore, this research aimed to determine the relationship between the MQI and psychosocial variables of depression, anxiety, and stress in Chilean adolescents. In this quantitative correlational design study, sixty adolescents participated voluntarily (mean ± standard deviation [SD]: age 15.11 ± 1.78 years). Anthropometric parameters, prehensile strength, MQI, and psychosocial variables were evaluated. The results showed that adolescents with high levels of MQI presented lower levels of depression (7.50 ± 6.06 vs. 10.97 ± 5.94), anxiety (5.64 ± 4.81 vs. 9.66 ± 5.12), and stress (6.79 ± 5.09 vs. 10 ± 5.58), in addition to reported lower abdominal obesity (WtHR, 0.47 ± 0.07 vs. 0.52 ± 0.07) than those with low levels of MQI. The group with high levels of MQI reported a higher prevalence of nonanxiety (81.3%, p = 0.031) and a lower prevalence of abdominal obesity (55.8%, p = 0.023). Likewise, a significant inverse association was evidenced between MQI and depression (β; -6.18, 95% CI; -10.11: -2.25, p = 0.003), anxiety (β; -6.61, 95% CI; -9.83: -3.39, p < 0.001) and stress (β; -4.90, 95% CI; -8.49: -1.32 p = 0.008). In conclusion, the results suggest that high levels of MQI are associated with a higher prevalence of nonanxiety in adolescents and a significant inverse association between MQI and levels of depression, anxiety, and stress.

Pharmacological and Physiological Correlates of the Bidirectional Fear Phenotype of the Carioca Rats and Other Bidirectionally Selected Lines

The Carioca rat lines originated from the selective bidirectional breeding of mates displaying extreme defense responses to contextual conditioned fear. After three generations, two distinct populations could be distinguished: the Carioca High- and Low-conditioned Freezing rats, CHF, and CLF, respectively. Later studies identified strong anxiety-like behaviors in the CHF line, while indications of impulsivity and hyperactivity were prominent in the CLF animals. The present review details the physiological and pharmacological-related findings obtained from these lines. The results discussed here point towards a dysfunctional fear circuitry in CHF rats, including alterations in key brain structures and the serotoninergic system. Moreover, data from these animals highlight important alterations in the stress-processing machinery and its associated systems, such as energy metabolism and antioxidative defense. Finally, evidence of an alteration in the dopaminergic pathway in CLF rats is also debated. Thus, accumulating data gathered over the years, place the Carioca lines as significant animal models for the study of psychiatric disorders, especially fear-related ones like anxiety.

Emotional and sensory dysregulation as a possible missing link in attention deficit hyperactivity disorder: A review

Attention Deficit Hyperactivity Disorder (ADHD) is a common developmental disorder affecting 5-7% of adults and children. We surveyed the literature to examine ADHD through three pillars: developmental characteristics, symptomatology, and treatment strategies. Firstly, in terms of developmental characterstics, early life stress may increase the risk of developing ADHD symptoms according to animal models' research. Secondly, the current core symptoms of ADHD are comprised of inattention, hyperactivity, and impulsivity. However, the up-to-date literature indicates individuals with ADHD experience emotional and sensory dysregulation as well, which early-life stress may also increase the risk of. Finally, we discuss the therapeutic benefits of methylphenidate on both the current core ADHD symptoms and the sensory and emotional dysregulation found in those with ADHD. In summation, we surveyed the recent literature to analyze (i) the potential role of early-life stress in ADHD development, (ii) the involvement of emotional and sensory dysregulation in ADHD symptomatology and finally, (iii) the therapeutic intervention with methylphenidate, aiming to reduce the potential effect of early life stress in ADHD, and mainly emotional and sensory dysregulation. The apparent but currently less recognized additional symptoms of emotional and sensory dysregulation in ADHD call for further investigation of these possible causes and thus increasing treatments efficacy in individuals with ADHD.

Neural resources shift under Methylphenidate: A computational approach to examine anxiety-cognition interplay

The reciprocal interplay between anxiety and cognition is well documented. Anxiety negatively impacts cognition, while cognitive engagement can down-regulate anxiety. The brain mechanisms and dynamics underlying such interplay are not fully understood. To study this question, we experimentally and orthogonally manipulated anxiety (using a threat of shock paradigm) and cognition (using methylphenidate; MPH). The effects of these manipulations on the brain and behavior were evaluated in 50 healthy participants (25 MPH, 25 placebo), using an n-back working memory fMRI task (with low and high load conditions). Behaviorally, improved response accuracy was observed as a main effect of the drug across all conditions. We employed two approaches to understand the neural mechanisms underlying MPH-based cognitive enhancement in safe and threat conditions. First, we performed a hypothesis-driven computational analysis using a mathematical framework to examine how MPH putatively affects cognitive enhancement in the face of induced anxiety across two levels of cognitive load. Second, we performed an exploratory data analysis using Topological Data Analysis (TDA)-based Mapper to examine changes in spatiotemporal brain activity across the entire cortex. Both approaches provided converging evidence that MPH facilitated greater differential engagement of neural resources (brain activity) across low and high working memory load conditions. Furthermore, load-based differential management of neural resources reflects enhanced efficiency that is most powerful during higher load and induced anxiety conditions. Overall, our results provide novel insights regarding brain mechanisms that facilitate cognitive enhancement under MPH and, in future research, may be used to help mitigate anxiety-related cognitive underperformance.

Recognition memory, primacy vs. recency effects, and time perception in the online version of the fear of scream paradigm

Anxiety disorders are characterized by cognitive dysfunctions which contribute to the patient’s profound disabilities. The threat of shock paradigm represents a validated psychopathological model of anxiety to measure the impact of anxiety on cognitive processes. We have developed an online version of the threat of scream paradigm (ToSP) to investigate the impact of experimental anxiety on recognition memory. Two animated passive walkthrough videos (either under threat of scream or safety conditions) were shown to healthy participants. Recognition memory, primacy vs. recency effects, and subjective estimations of the length of encoding sessions were assessed. Subjective anxiety, stress, and emotional arousal ratings indicated that experimental anxiety could successfully be induced (Safe-Threat) or reversed (Threat-Safe) between the two passive walkthrough sessions. Participants exposed to distress screams showed impaired retrieval of complex information that has been presented in an animated environment. In the threat condition, participants failed to recognize details related to the persons encountered, their spatial locations, as well as information about the temporal order and sequence of encounters. Participant groups, which received a threat announcement prior to the first walkthrough session (Threat-Threat vs. Safety-Safety and Threat-Safety vs. Safety-Threat) showed poorer recognition memory as compared to the groups that received a safety announcement (P = 0.0468 and P = 0.0426, respectively; Mann–Whitney U test, Cohen’s d = 0.5071; effect size r = 0.2458). In conclusion, experimental anxiety induced by the online version of the ToSP leads to compromised recognition memory for complex multi-dimensional information. Our results indicate that cognitive functions of vulnerable populations (with limited mobility) can be evaluated online by means of the ToSP.

Haloperidol and methylphenidate alter motor behavior and responses to conditioned fear of Carioca Low-conditioned Freezing rats

Animal models are important tools for studying neuropsychological disorders. Considering their limitations, a more extensive translational research must encompass data that are generated from several models. Therefore, a comprehensive characterization of these models is needed in terms of behavior and neurophysiology. The present study evaluated the behavioral responses of Carioca Low-conditioned Freezing (CLF) rats to haloperidol and methylphenidate. The CLF breeding line is characterized by low freezing defensive responses to contextual cues that are associated with aversive stimuli. CLF rats exhibited a delayed response to haloperidol at lower doses, needing higher doses to reach similar levels of catatonia as control randomly bred animals. Methylphenidate increased freezing responses to conditioned fear and induced motor effects in the open field. Thus, CLF rats differ from controls in their responses to both haloperidol and methylphenidate. Because of the dopamine-related molecular targets of these drugs, we hypothesize that dopaminergic alterations related to those of animal models of hyperactivity and attention disorders might underlie the observed phenotypes of the CLF line of rats.

β-Adrenergic Contributions to Emotion and Physiology During an Acute Psychosocial Stressor

OBJECTIVE

β-Adrenergic receptor signaling, a critical mediator of sympathetic nervous system influences on physiology and behavior, has long been proposed as one contributor to subjective stress. However, prior findings are surprisingly mixed about whether β-blockade (e.g., propranolol) blunts subjective stress, with many studies reporting no effects. We reevaluated this question in the context of an acute psychosocial stressor with more comprehensive measures and a larger-than-typical sample. We also examined the effects of β-blockade on psychophysiological indicators of sympathetic and parasympathetic nervous system reactivity, given that β-blockade effects for these measures specifically under acute psychosocial stress are not yet well established.

METHODS

In a double-blind, randomized, placebo-controlled study, 90 healthy young adults received 40 mg of the β-blocker propranolol or placebo. Participants then completed the Trier Social Stress Test, which involved completing an impromptu speech and difficult arithmetic in front of evaluative judges. Self-reported emotions and appraisals as well as psychophysiology were assessed throughout.

RESULTS

Propranolol blunted Trier Social Stress Test preejection period reactivity (b = 9.68, p = .003), a marker of sympathetic nervous system activity, as well as salivary α-amylase reactivity (b = -0.50, p = .006). Critically, propranolol also blunted negative, high arousal emotions in response to the stressor (b = -0.22, p = .026), but cognitive appraisals remained intact (b values < -0.17, p values > .10).

CONCLUSIONS

These results provide updated experimental evidence that β-adrenergic blockade attenuates negative, high arousal emotions in response to a psychosocial stressor while also blunting sympathetic nervous system reactivity. Together, these findings shed light on the neurophysiological mechanisms by which stressors transform into the subjective experience we call "stress."Trial Registration: ClinicalTrials.gov Identifier: NCT02972554.

Methylphenidate modulates interactions of anxiety with cognition

While a large body of literature documents the impairing effect of anxiety on cognition, performing a demanding task was shown to be effective in reducing anxiety. Here we explored the mechanisms of this anxiolytic effect by examining how a pharmacological challenge designed to improve attentional processes influences the interplay between the neural networks engaged during anxiety and cognition. Using a double-blind between-subject design, we pharmacologically manipulated working memory (WM) using a single oral dose of 20 mg methylphenidate (MPH, cognitive enhancer) or placebo. Fifty healthy adults (25/drug group) performed two runs of a WM N-back task in a 3 T magnetic resonance imaging scanner. This task comprised a low (1-Back) and high (3-Back) WM load, which were performed in two contexts, safety or threat of shocks (induced-anxiety). Analyses revealed that (1) WM accuracy was overall improved by MPH and (2) MPH (vs. placebo) strengthened the engagement of regions within the fronto-parietal control network (FPCN) and reduced the default mode network (DMN) deactivation. These MPH effects predominated in the most difficult context, i.e., threat condition, first run (novelty of the task), and 3-Back task. The facilitation of neural activation can be interpreted as an expansion of cognitive resources, which could foster both the representation and integration of anxiety-provoking stimuli as well as the top-down regulatory processes to protect against the detrimental effect of anxiety. This mechanism might establish an optimal balance between FPCN (cognitive processing) and DMN (emotion regulation) recruitment.

Norepinephrine as a spatial memory reset signal

Contextual information is represented in the hippocampus (HPC) partially through the recruitment of distinct neuronal ensembles. It is believed that reactivation of these ensembles underlies memory retrieval processes. Recently, we showed that norepinephrine input from phasic locus coeruleus activation induces hippocampal plasticity resulting in the recruitment of new neurons and disengagement from previously established representations. We hypothesize that norepinephrine may provide a neuromodulatory mnemonic switch signaling the HPC to move from a state of retrieval to encoding in the presence of novelty, and therefore, plays a role in memory updating. Here, we tested whether bilateral dorsal dentate gyrus (dDG) infusions of the β-adrenergic receptor (BAR) agonist isoproterenol (ISO), administered prior to encoding or retrieval, would impair spatial working and reference memory by reverting, the system to encoding (thereby recruiting new neurons) potentially interfering with the retrieval of the previously established spatial ensemble. We also investigated whether dDG infusions of ISO could promote cognitive flexibility by switching the system to encoding when it is adaptive (ie, when new information is presented, eg, reversal learning). We found that intra-dDG infusions of ISO given prior to retrieval caused deficits in working and reference memory which was blocked by pretreatment with the BAR-antagonist, propranolol (PRO). In contrast, ISO administered prior to reversal learning led to improved performance. These data support our hypothesis that norepinephrine serves as a novelty signal to update HPC contextual representations via BAR activation-facilitated recruitment of new neurons. This can be both maladaptive and adaptive depending on the situation.

Neurophysiological contributors to advantageous risk-taking: an experimental psychopharmacological investigation

The ability to learn from experience is critical for determining when to take risks and when to play it safe. However, we know little about how within-person state changes, such as an individual's degree of neurophysiological arousal, may impact the ability to learn which risks are most likely to fail vs succeed. To test this, we used a randomized, double-blind, placebo-controlled design to pharmacologically manipulate neurophysiological arousal and assess its causal impact on risk-related learning and performance. Eighty-seven adults (45% female, Mage = 20.1 ± 1.46 years) took either propranolol (n = 42), a beta-adrenergic receptor blocker that attenuates sympathetic nervous system-related signaling, or a placebo (n = 45). Participants then completed the Balloon Emotional Learning Task, a risk-taking task wherein experiential learning is necessary for task success. We found that individuals on propranolol, relative to placebo, earned fewer points on the task, suggesting that they were less effective risk-takers. This effect was mediated by the fact that those on propranolol made less optimal decisions in the final phase of the task on trials with the greatest opportunity for advantageous risk-taking. These findings highlight that neurophysiological arousal supports risk-related learning and, in turn, more advantageous decision-making and optimal behavior under conditions of risk.

Patients with anxiety disorders rely on bilateral dlPFC activation during verbal working memory

One of the hallmarks of anxiety disorders is impaired cognitive control, affecting working memory (WM). The dorsolateral prefrontal cortex (dlPFC) is critical for WM; however, it is still unclear how dlPFC activity relates to WM impairments in patients. Forty-one healthy volunteers and 32 anxiety (general and/or social anxiety disorder) patients completed the Sternberg WM paradigm during safety and unpredictable shock threat. On each trial, a series of letters was presented, followed by brief retention and response intervals. On low- and high-load trials, subjects retained the series (five and eight letters, respectively) in the original order, while on sort trials, subjects rearranged the series (five letters) in alphabetical order. We sampled the blood oxygenation level-dependent activity during retention using a bilateral anatomical dlPFC mask. Compared to controls, patients showed increased reaction time during high-load trials, greater right dlPFC activity and reduced dlPFC activity during threat. These results suggest that WM performance for patients and controls may rely on distinct patterns of dlPFC activity with patients requiring bilateral dlPFC activity. These results are consistent with reduced efficiency of WM in anxiety patients. This reduced efficiency may be due to an inefficient allocation of dlPFC resources across hemispheres or a decreased overall dlPFC capacity.

Intrinsic connections between thalamic sub-regions and the lateral prefrontal cortex are differentially impacted by acute methylphenidate

BACKGROUND

The thalamus is a major target of dopaminergic projections and is densely connected with the prefrontal cortex. A better understanding of how dopamine changes thalamo-cortical communication may shed light on how dopamine supports cognitive function. Methylphenidate has been shown to facilitate cognitive processing and reduce connectivity between the thalamus and lateral prefrontal cortex.

AIMS

The thalamus is a heterogeneous structure, and the present study sought to clarify how the intrinsic connections of thalamic sub-regions are differentially impacted by acute dopamine transporter blockade.

METHODS

Sixty healthy volunteers were orally administered either 20 mg of methylphenidate (N = 29) or placebo (N = 31) in a double-blind, randomized, between-subject design. Multi-echo fMRI was used to assess intrinsic functional connectivity of sub-regions of the thalamus during a resting state scan. An N-back working-memory paradigm provided a measure of cognitive performance.

RESULTS

Acute methylphenidate significantly reduced connectivity of the lateral prefrontal cortex with the motor and somatosensory sub-regions of the thalamus and reduced connectivity with the parietal and visual sub-regions at a trend level. Connectivity with the premotor, prefrontal, and temporal sub-regions was not impacted. The intrinsic connectivity between the thalamus and the lateral prefrontal cortex was not associated with working-memory performance.

CONCLUSIONS

Methylphenidate decreases functional connections between the lateral prefrontal cortex and thalamus broadly, while sparing intrinsic connectivity with thalamic sub-regions involved with working-memory and language related processes. Collectively, our results suggest that the dopamine transporter regulates functional connections between the prefrontal cortex and non-cognitive areas of the thalamus.

Better cognitive efficiency is associated with increased experimental anxiety

There is increased interest in the development of cognitive training targeting working memory (WM) to alleviate anxiety symptoms, but the effectiveness of such an approach is unclear. Improved understanding of the effect of cognitive training on anxiety may facilitate the development of more effective cognitive training treatment for anxiety disorders. This study uses an experimental approach to examine the interplay of WM and anxiety following WM training. Previous studies show that increased demand on WM reduces concurrent anxiety evoked by threat of shock (induced anxiety). However, improving WM pharmacologically or via exercise prevents this anxiolytic effect. Conceivably, improving WM frees up cognitive resources to process threat information, thereby increasing anxiety. The present study tested the hypothesis that practicing a high load WM (i.e., increased demand) task would improve WM, and thus, free cognitive resources to process threat of shock, resulting in more anxiety (i.e., greater startle) during a subsequent WM task. Participants were randomly assigned to two training groups. The active-training group (N = 20) was trained on a 1- (low load) & 3-back (high load) WM task, whereas the control-training group (N = 20) performed a 0-back WM task. The experimental phase, similar in both groups, consisted of a 1- & 3-back WM task performed during both threat of shock and safety. As predicted, active training improved WM accuracy and increased anxiety during the experimental 3-back WM task. Therefore, improving WM efficiency can increase anxiety, possibly by freeing WM resources to process threat information.

Threat-of-shock decreases emotional interference on affective stroop performance in healthy controls and anxiety patients

Patients with anxiety disorders suffer from impaired concentration, potentially as a result of stronger emotional interference on attention. Studies using behavioural measures provide conflicting support for this hypothesis. Elevated state anxiety may be necessary to reliably document differences in emotional interference in patients versus healthy controls. The present study examines the effect of experimentally induced state anxiety (threat-of-shock) on attention interference by emotional stimuli. Anxiety patients (n = 36) and healthy controls (n = 32) completed a modified affective Stroop task during periods of safety and threat-of-shock. Results indicated that in both patients and controls, threat decreased negative, but not positive or neutral, emotional interference on attention (both p < .001). This finding supports a threat-related narrowing of attention whereby a certain level of anxiety decreases task-irrelevant processing.

A probabilistic model of startle response reveals opposite effects of acute versus chronic Methylphenidate treatment

BACKGROUND

The startle response is considered as the major physio-behavioral indication of anxiety in health and disease conditions. However, due to different protocols of stimulation and measurement, the magnitude as well as the appearance of the startle response is inconsistent.

NEW METHOD

We postulate that the startle probability and not merely the amplitude may bare information that will form a consistent physiological measure of anxiety.

RESULTS

To examine the proof-of-concept of our suggested probability model, we evaluated the effects of acute (single) versus chronic (14 days) MPH administration on both startle amplitude and probability. We found that both acute and chronic MPH administration has yielded similar effects on startle amplitude. However, acute MPH increased the startle's probability while chronic MPH decreased it. Next, we evaluated the effects of acute versus chronic stress on the startle's parameters and found a complementary effect. Explicitly, acute stress increased the startle's probability while chronic stress increased the startle amplitude. In contrast, enriched environment had no significant effects. Finally, to further validate the probability measure, we show that Midazolam had significant anxiolytic effects. In the second part, we investigated the acoustic startle response parameters (e.g. background noise and pulse duration), to better understand the interplay between these parameters and the startle amplitude versus probability.

CONCLUSIONS

We show that the probabilistic element of the startle response does not only point to deeper physiologic relationships but may also serve as "hidden variables" congruent but not entirely identical to the commonly researched amplitude of the startle response.

Exercise modulates the interaction between cognition and anxiety in humans

Despite interest in exercise as a treatment for anxiety disorders the mechanism behind the anxiolytic effects of exercise is unclear. Two observations motivate the present work. First, engagement of attention control during increased working memory (WM) load can decrease anxiety. Second, exercise can improve attention control. Therefore, exercise could boost the anxiolytic effects of increased WM load via its strengthening of attention control. Anxiety was induced by threat of shock and was quantified with anxiety-potentiated startle (APS). Thirty-five healthy volunteers (19 male, age M = 26.11, SD  = 5.52) participated in two types of activity, exercise (biking at 60-70% of heart rate reserve) and control-activity (biking at 10-20% of heart rate reserve). After each activity, participants completed a WM task (n-back) at low- and high-load during safe and threat. Results were not consistent with the hypothesis: exercise vs. control-activity increased APS in high-load (p = .03). However, this increased APS was not accompanied with threat-induced impairment in WM performance (p = .37). Facilitation of both task-relevant stimulus processing and task-irrelevant threat processing, concurrent with prevention of threat interference on cognition, suggests that exercise increases cognitive ability. Future studies should explore how exercise affects the interplay of cognition and anxiety in patients with anxiety disorders.