Functional connectivity and cognitive changes after donepezil treatment in healthy participants

RATIONALE

Donepezil is a potent, noncompetitive, reversible, clinically effective acetylcholinesterase inhibitor. The effects of this drug on healthy brains have seldom been investigated.

OBJECTIVES

The primary objective of the present study was to identify possible functional connectivity markers of the effect of donepezil in healthy young adult volunteers.

METHODS

The study had a double-blind, randomized, crossover design. 30 healthy adult volunteers underwent resting-state MRI scans during 15 days of donepezil or placebo treatment, in accordance with the design.

RESULTS

Results showed significant differences in intrinsic functional connectivity between donepezil and placebo, mainly in the right executive control network (RECN). More specifically, we found a decrease in the connectivity of the right inferior parietal node with other RECN nodes. Analysis using the cingulate cortex and parahippocampal regions as seeds also revealed complex modulation of functional connectivity in the donepezil condition.

CONCLUSIONS

In conclusion, donepezil treatment for 15 days may result in reorganization of resting-state networks, compared with placebo.

Sleep deprivation and Modafinil affect cortical sources of resting state electroencephalographic rhythms in healthy young adults

OBJECTIVE

It has been reported that sleep deprivation affects the neurophysiological mechanisms underpinning the vigilance. Here, we tested the following hypotheses in the PharmaCog project (www.pharmacog.org): (i) sleep deprivation may alter posterior cortical delta and alpha sources of resting state eyes-closed electroencephalographic (rsEEG) rhythms in healthy young adults; (ii) after the sleep deprivation, a vigilance enhancer may recover those rsEEG source markers.

METHODS

rsEEG data were recorded in 36 healthy young adults before (Pre-sleep deprivation) and after (Post-sleep deprivation) one night of sleep deprivation. In the Post-sleep deprivation, these data were collected after a single dose of PLACEBO or MODAFINIL. rsEEG cortical sources were estimated by eLORETA freeware.

RESULTS

In the PLACEBO condition, the sleep deprivation induced an increase and a decrease in posterior delta (2-4 Hz) and alpha (8-13 Hz) source activities, respectively. In the MODAFINIL condition, the vigilance enhancer partially recovered those source activities.

CONCLUSIONS

The present results suggest that posterior delta and alpha source activities may be both related to the regulation of human brain arousal and vigilance in quiet wakefulness.

SIGNIFICANCE

Future research in healthy young adults may use this methodology to preselect new symptomatic drug candidates designed to normalize brain arousal and vigilance in seniors with dementia.

Adaptability and reproducibility of a memory disruption rTMS protocol in the PharmaCog IMI European project

Transcranial magnetic stimulation (TMS) can interfere with cognitive processes, such as transiently impairing memory. As part of a multi-center European project, we investigated the adaptability and reproducibility of a previously published TMS memory interfering protocol in two centers using EEG or fMRI scenarios. Participants were invited to attend three experimental sessions on different days, with sham repetitive TMS (rTMS) applied on day 1 and real rTMS on days 2 and 3. Sixty-eight healthy young men were included. On each experimental day, volunteers were instructed to remember visual pictures while receiving neuronavigated rTMS trains (20 Hz, 900 ms) during picture encoding at the left dorsolateral prefrontal cortex (L-DLPFC) and the vertex. Mixed ANOVA model analyses were performed. rTMS to the L-DLPFC significantly disrupted recognition memory on experimental day 2. No differences were found between centers or between fMRI and EEG recordings. Subjects with lower baseline memory performances were more susceptible to TMS disruption. No stability of TMS-induced memory interference could be demonstrated on day 3. Our data suggests that adapted cognitive rTMS protocols can be implemented in multi-center studies incorporating standardized experimental procedures. However, our center and modality effects analyses lacked sufficient statistical power, hence highlighting the need to conduct further studies with larger samples. In addition, inter and intra-subject variability in response to TMS might limit its application in crossover or longitudinal studies.

Translational Challenge Models in Support of Efficacy Studies: Neurobehavioral and Cognitive Changes Induced by Transcranial Magnetic Stimulation in Healthy Volunteers

Transcranial Magnetic Stimulation (TMS) was proposed as a neurophysiological tool almost three decades ago. It now encompasses a very wide range of applications including clinical research and the treatment of psychiatric, neurologic and medical conditions such as depression, schizophrenia, addictions, post-traumatic stress disorders, pain, migraine, stroke, Alzheimer's disease, autism, multiple sclerosis and Parkinson's disease. By inducing electrical brain responses through the administration of magnetic pulses, TMS is in a unique position to painlessly modulate cortical regions and offers good spatial resolution and excellent temporal resolution, particularly when applied using single pulses. However, despite the impressive number of papers describing the use of TMS to modulate cognitive functions, the mechanisms underlying the behavioral changes observed after stimulation have not been fully identified. Here we present a review of the ability of TMS to transiently compromise brain function in humans. The primary aim was to investigate its capacity for use as a 'cognitive challenge model' in human pharmacological studies. The data reviewed include findings on executive function, attention and episodic memory. For each cognitive process, the convergent and divergent results are discussed in terms of paradigm differences and in order to define the optimal methodology for obtaining the desired effects.

Neurobehavioral and Cognitive Changes Induced by Hypoxia in Healthy Volunteers

The early assessment of new symptomatic drugs against Alzheimer's disease remains difficult because of the lack of a predictive end-point. The use of a battery including different parameters could improve this early development. In order to test the reverse effect of symptomatic drugs in healthy volunteers, scientists have developed new experimental paradigms to artificially induce transient cognitive impairments in healthy volunteers akin to those observed in Alzheimer's disease, i.e. Cognitive Challenge Models. In this context, transient hypoxia could be a relevant Cognitive Challenge Model. The deleterious effects of hypoxia on cognition, as described in the literature, should be considered carefully since they are usually assessed with different populations that do not have the same hypoxic sensitivity. Hypoxia can be obtained by the means of two different methods: normobaric and hypobaric hypoxia. In both designs, cognitive changes can be directly modulated by the severity of hypoxic levels. The purpose of this review is to gather existing support on the application of hypoxia within different cognitive domains and to highlight the scientific interests of such a model to predict and select promising drug candidates. We aimed at reviewing in detail the methods, designs and cognitive paradigms used in non-pharmacological hypoxia studies. Probing the four main cognitive functions will allow identifying the extent to which different hypoxia designs selectively compromise cognitive functioning. For each cognitive process, the convergent and divergent results are discussed in terms of paradigm differences whereas we will focus on defining the optimal methodology for obtaining the desired effects.

A 15-day course of donepezil modulates spectral EEG dynamics related to target auditory stimuli in young, healthy adult volunteers

OBJECTIVE

To identify possible electroencephalographic (EEG) markers of donepezil's effect on cortical activity in young, healthy adult volunteers at the group level.

METHODS

Thirty subjects were administered a daily dose of either 5mg donepezil or placebo for 15days in a double-blind, randomized, cross-over trial. The electroencephalogram during an auditory oddball paradigm was recorded from 58 scalp electrodes. Current source density (CSD) transformations were applied to EEG epochs. The event-related potential (ERP), inter-trial coherence (ITC: the phase consistency of the EEG spectrum) and event-related spectral perturbation (ERSP: the EEG power spectrum relative to the baseline) were calculated for the target (oddball) stimuli.

RESULTS

The donepezil and placebo conditions differed in terms of the changes in delta/theta/alpha/beta ITC and ERSP in various regions of the scalp (especially the frontal electrodes) but not in terms of latency and amplitude of the P300-ERP component.

CONCLUSION

Our results suggest that ITC and ERSP analyses can provide EEG markers of donepezil's effects in young, healthy, adult volunteers at a group level.

SIGNIFICANCE

Novel EEG markers could be useful to assess the therapeutic potential of drug candidates in Alzheimer's disease in healthy volunteers prior to the initiation of Phase II/III clinical studies in patients.

Skin conductance biofeedback training in adults with drug-resistant temporal lobe epilepsy and stress-triggered seizures: a proof-of-concept study

The present proof-of-concept study investigated the feasibility of skin conductance biofeedback training in reducing seizures in adults with drug-resistant temporal lobe epilepsy (TLE), whose seizures are triggered by stress. Skin conductance biofeedback aims to increase levels of peripheral sympathetic arousal in order to reduce cortical excitability. This might seem somewhat counterintuitive, since such autonomic arousal may also be associated with increased stress and anxiety. Thus, this sought to verify that patients with TLE and stress-triggered seizures are not worsened in terms of stress, anxiety, and negative emotional response to this nonpharmacological treatment. Eleven patients with drug-resistant TLE with seizures triggered by stress were treated with 12 sessions of biofeedback. Patients did not worsen on cognitive evaluation of attentional biases towards negative emotional stimuli (P>.05) or on psychometric evaluation with state anxiety inventory (P = .059); in addition, a significant improvement was found in the Negative Affect Schedule (P = .014) and in the Beck Depression Inventory (P = .009). Biofeedback training significantly reduced seizure frequency with a mean reduction of -48.61% (SD = 27.79) (P = .005). There was a correlation between the mean change in skin conductance activity over the biofeedback treatment and the reduction of seizure frequency (r(11) = .62, P = .042). Thus, the skin conductance biofeedback used in the present study, which teaches patients to achieve an increased level of peripheral sympathetic arousal, was a well-tolerated nonpharmacological treatment. Further, well-controlled studies are needed to confirm the therapeutic value of this nonpharmacological treatment in reducing seizures in adults with drug-resistant TLE with seizures triggered by stress.

Evaluation of symptomatic drug effects in Alzheimer's disease: strategies for prediction of efficacy in humans

In chronic diseases such as Alzheimer's disease (AD), the arsenal of biomarkers available to determine the effectiveness of symptomatic treatment is very limited. Interpretation of the results provided in literature is cumbersome and it becomes difficult to predict their standardization to a larger patient population. Indeed, cognitive assessment alone does not appear to have sufficient predictive value of drug efficacy in early clinical development of AD treatment. In recent years, research has contributed to the emergence of new tools to assess brain activity relying on innovative technologies of imaging and electrophysiology. However, the relevance of the use of these newer markers in treatment response assessment is waiting for validation. This review shows how the early clinical assessment of symptomatic drugs could benefit from the inclusion of suitable pharmacodynamic markers. This review also emphasizes the importance of re-evaluating a step-by-step strategy in drug development.

Cognitive and metabolic correlates of emotional vulnerability in patients with temporal lobe epilepsy

BACKGROUND

Recent investigations have suggested that the occurrence of epileptic seizures is not completely random. In particular, various types of psychological changes or life events may act as triggering factors.

OBJECTIVE

To identify a possible link between self-perception of the impact of affective precipitants, cognitive responses modulated by aversive information and brain metabolic modifications in patients with temporal lobe epilepsy (TLE).

METHODS

The extent to which seizures were elicited or not by emotional precipitants was estimated using a self-reported scale, allowing distinction of two groups: 'Emo-TLE' group (patients reporting to have seizures triggered by emotional events) and 'Other-TLE' group, which were compared with healthy individuals ('control' group). Attentional biases were investigated using the probe detection paradigm, using negative and neutral stimuli. Interictal brain metabolism was studied using FDG-PET, and comparison was made between controls, Emo-TLE and Other-TLE groups.

RESULTS

Patients with emotional vulnerability (Emo-TLE) disclosed specific attentional biases towards negative stimuli compared with the Other-TLE and control groups. Patients with Emo-TLE also exhibited specific hypometabolism in the anterior temporal lobe, including amygdala and hippocampus. The degree of attentional biases correlated with decreased metabolism in these regions.

CONCLUSIONS

This investigation shows that the impact of affective events is the result of self-perception and also that it might be determined by specific cognitive and brain metabolic modifications in TLE.

How do cognition, emotion, and epileptogenesis meet? A study of emotional cognitive bias in temporal lobe epilepsy

Emotional distress is one of the most frequently reported seizure precipitants in epilepsy, but little is known about its causes and processes. Interestingly, it is now accepted that emotional distress, such as anxiety, may be accompanied by evolutionary adaptation, or abnormal attentional vigilance toward threatening stimuli. The goal of this research was to study the link between emotional seizure precipitants and pathological attention-related biases toward threat in temporal lobe epilepsy (TLE). To this aim, patients were asked to report the extent to which seizures were elicited or not by emotional precipitants, allowing distinction of two groups: "Emo-TLE" group and "Other-TLE" group. Attentional biases were investigated by comparing patients' emotional Stroop and dot detection paradigms with those of healthy individuals (control group). We found that the Emo-TLE group was characterized by attentional bias toward threatening stimuli compared with neutral stimuli and compared with the other two groups. We thus hypothesize that attentional biases related to threat in patients with TLE may sustain emotional vulnerability and seizure occurrence.

Emotion induction after direct intracerebral stimulations of human amygdala

Very few studies in humans have quantified the effect obtained after direct electrical stimulation of the amygdala, in terms of both emotional and physiological responses. We tested patients with drug-resistant partial epilepsies who were explored with intracerebral electrodes in the setting of presurgical evaluation. We assessed the effects of direct electric stimulations in either the right or the left amygdala on verbally self-reported emotions (Izard scale) and on psychophysiological markers of emotions by recording skin conductance responses (SCRs) and by measuring the electromyographic responses of the corrugator supercilii (EMGc). According to responses on Izard scales, electrical stimulations of the right amygdala induced negative emotions, especially fear and sadness. In contrast, stimulations of the left amygdala were able to induce either pleasant (happiness) or unpleasant (fear, anxiety, sadness) emotions. Unpleasant states induced by electrical stimulations were accompanied by an increase in EMGc activity. In addition, when emotional changes were reported after electrical stimulation, SCR amplitude for the positively valenced emotions was larger than for the negative ones. These findings provide direct in vivo evidence that the human amygdala is involved in emotional experiences and strengthen the hypothesis of a functional asymmetry of the amygdala for valence and arousal processing.