Dynamic causal modelling of auditory surprise during disconnected consciousness: The role of feedback connectivity

The neural mechanisms through which individuals lose sensory awareness of their environment during anesthesia remains poorly understood despite being of vital importance to the field. Prior research has not distinguished between sensory awareness of the environment (connectedness) and consciousness itself. In the current study, we investigated the neural correlates of sensory awareness by contrasting neural responses to an auditory roving oddball paradigm during consciousness with sensory awareness (connected consciousness) and consciousness without sensory awareness (disconnected consciousness). These states were captured using a serial awakening paradigm with the sedative alpha2 adrenergic agonist dexmedetomidine, chosen based on our published hypothesis that suppression of noradrenaline signaling is key to induce a state of sensory disconnection. High-density electroencephalography was recorded from 18 human subjects before and after administration of dexmedetomidine. By investigating event-related potentials and taking advantage of advances in Dynamic Causal Modeling (DCM), we assessed alterations in effective connectivity between nodes of a previously established auditory processing network. We found that during disconnected consciousness, the scalp-level response to standard tones produced a P3 response that was absent during connected consciousness. This P3 response resembled the response to oddball tones seen in connected consciousness. DCM showed that disconnection produced increases in standard tone feedback signaling throughout the auditory network. Simulation analyses showed that these changes in connectivity, most notably the increase in feedback from right superior temporal gyrus to right A1, can explain the new P3 response. Together these findings show that during disconnected consciousness there is a disruption of normal predictive coding processes, so that all incoming auditory stimuli become similarly surprising.

The protective effects of escitalopram on synaptic plasticity in the CA1 region of chronically stressed and non-stressed male rats

INTRODUCTION

Stress impairs cognitive processes and escitalopram affects them in various ways. The present study has compared the protective effects of two escitalopram doses on neural excitability and synaptic plasticity in the CA1 region of chronically stressed and non-stressed male rats.

METHODS

Forty-nine rats were randomly allocated into seven groups: control (Co), stress (St), sham (Sh), escitalopram 10 and 20 mg/kg (Esc10 & Esc20), stress-escitalopram 10 and 20 mg/kg (St-Esc10 & St-Esc20). Induction of restraint stress (6 h/day) and escitalopram injections were performed for 14 days. The fEPSP slope and amplitude were measured according to input-output functions and after the LTP induction in the hippocampal CA1 region. Also, serum corticosterone levels were evaluated in all experimental groups.

RESULTS

The fEPSP slope and amplitude decreased significantly in the St group and increased significantly in the Esc10 group compared to the Co group. In non-stressed states, significant increases in slope and amplitude occurred in the Esc10 group compared to the Esc20 group. Notably, these values were also significantly enhanced by both escitalopram doses under stressed conditions. Moreover, serum corticosterone levels significantly elevated in the St group although its levels decreased in both St-Esc groups compared to the St.

CONCLUSION

Stress significantly attenuated neural excitability and long-term plasticity in the CA1 area. Only escitalopram 10 mg/kg improved synaptic excitability, as well as LTP induction and maintenance in non-stressed subjects even more than normal levels. However, under stress conditions, both escitalopram doses enhanced neural excitability and memory probably due to reduced serum corticosterone levels.

Distinct EEG signatures differentiate unconsciousness and disconnection during anaesthesia and sleep

BACKGROUND

How conscious experience becomes disconnected from the environment, or disappears, across arousal states is unknown. We sought to identify the neural correlates of sensory disconnection and unconsciousness using a novel serial awakening paradigm.

METHODS

Volunteers were recruited for sedation with dexmedetomidine i.v., propofol i.v., or natural sleep with high-density EEG monitoring and serial awakenings to establish whether subjects were in states of disconnected consciousness or unconsciousness in the preceding 20 s. The primary outcome was classification of conscious states by occipital delta power (0.5-4 Hz). Secondary analyses included derivation (dexmedetomidine) and validation (sleep/propofol) studies of EEG signatures of conscious states.

RESULTS

Occipital delta power differentiated disconnected and unconscious states for dexmedetomidine (area under the curve [AUC] for receiver operating characteristic 0.605 [95% confidence interval {CI}: 0.516; 0.694]) but not for sleep/propofol (AUC 0.512 [95% CI: 0.380; 0.645]). Distinct source localised signatures of sensory disconnection (AUC 0.999 [95% CI: 0.9954; 1.0000]) and unconsciousness (AUC 0.972 [95% CI: 0.9507; 0.9879]) were identified using support vector machine classification of dexmedetomidine data. These findings generalised to sleep/propofol (validation data set: sensory disconnection [AUC 0.743 {95% CI: 0.6784; 0.8050}]) and unconsciousness (AUC 0.622 [95% CI: 0.5176; 0.7238]). We identified that sensory disconnection was associated with broad spatial and spectral changes. In contrast, unconsciousness was associated with focal decreases in activity in anterior and posterior cingulate cortices.

CONCLUSIONS

These findings may enable novel monitors of the anaesthetic state that can distinguish sensory disconnection and unconsciousness, and these may provide novel insights into the biology of arousal.

CLINICAL TRIAL REGISTRATION

NCT03284307.

Association between a history of child neglect, abuse and the suicidal patient: a cross-sectional study

Objective: People with a significant childhood history of abuse may exhibit emotional dysregulations and psychiatric disorders and, in some cases, present suicidal ideation. Methods: In this descriptive-analytical and cross-sectional study data were collected from suicidal patients referred to two grand hospitals in 2019. One hundred ninety-five participants were evaluated concerning child abuse and neglect history. Data were reported as mean, SD, frequency, and percent. T-test and chi-square tests were used for statistical analyses accordingly. Results: Child abuse regarding suicidal people were to the following order, neglect (n=103), child emotional abuse (n=102), child physical abuse (n=101), malnutrition (n=96), and child sexual abuse (n=87). Suicide was different between the two genders, but it was not different based on parents’ education and marital status. Conclusion: The harassed child is not equipped with proper behavioral skills and is subjected to low self-esteem due to incorrect training. Therefore, he/she may commit suicide in adolescence by facing some problems and failures. In this regard, community plays an important role, parents must be informed and use the right culture to reward the child.

Association between plasma tau and postoperative delirium incidence and severity: a prospective observational study

BACKGROUND

Postoperative delirium is associated with increases in the neuronal injury biomarker, neurofilament light (NfL). Here we tested whether two other biomarkers, glial fibrillary acidic protein (GFAP) and tau, are associated with postoperative delirium.

METHODS

A total of 114 surgical patients were recruited into two prospective biomarker cohort studies with assessment of delirium severity and incidence. Plasma samples were sent for biomarker analysis including tau, NfL, and GFAP, and a panel of 10 cytokines. We determined a priori to adjust for interleukin-8 (IL-8), a marker of inflammation, when assessing associations between biomarkers and delirium incidence and severity.

RESULTS

GFAP concentrations showed no relationship to delirium. The change in tau from preoperative concentrations to postoperative Day 1 was greater in patients with postoperative delirium (P<0.001) and correlated with delirium severity (ρ=0.39, P<0.001). The change in tau correlated with increases in IL-8 (P<0.001) and IL-10 (P=0.0029). Linear regression showed that the relevant clinical predictors of tau changes were age (P=0.037), prior stroke/transient ischaemic attack (P=0.001), and surgical blood loss (P<0.001). After adjusting for age, sex, preoperative cognition, and change in IL-8, tau remained significantly associated with delirium severity (P=0.026). Using linear mixed effect models, only tau (not NfL or IL-8) predicted recovery from delirium (P<0.001).

CONCLUSIONS

The change in plasma tau was associated with delirium incidence and severity, and resolved over time in parallel with delirium features. The impact of this putative perioperative neuronal injury biomarker on long-term cognition merits further investigation.

CLINICAL TRIAL REGISTRATION

NCT02926417 and NCT03124303.

Postoperative delirium is associated with increased plasma neurofilament light

While delirium is associated with cognitive decline and dementia, there is limited evidence to support causality for this relationship. Clarification of how delirium may cause cognitive decline, perhaps through evidence of contemporaneous neuronal injury, would enhance plausibility for a causal relationship. Dose-dependence of neuronal injury with delirium severity would further enhance the biological plausibility for this relationship. We tested whether delirium is associated with neuronal injury in 114 surgical patients recruited to a prospective biomarker cohort study. Patients underwent perioperative testing for changes in neurofilament light, a neuronal injury biomarker, as well as a panel of 10 cytokines, with contemporaneous assessment of delirium severity and incidence. A subset of patients underwent preoperative MRI. Initially we confirmed prior reports that neurofilament light levels correlated with markers of neurodegeneration [hippocampal volume (ΔR2 = 0.129, P = 0.015)] and white matter changes including fractional anisotropy of white matter (ΔR2 = 0.417, P < 0.001) with similar effects on mean, axial and radial diffusivity) in our cohort and that surgery was associated with increasing neurofilament light from preoperative levels [mean difference (95% confidence interval, CI) = 0.240 (0.178, 0.301) log10 (pg/ml), P < 0.001], suggesting putative neuronal injury. Next, we tested the relationship with delirium. Neurofilament light rose more sharply in participants with delirium compared to non-sufferers [mean difference (95% CI) = 0.251 (0.136, 0.367) log10 (pg/ml), P < 0.001]. This relationship showed dose-dependence, such that neurofilament light rose proportionately to delirium severity (ΔR2 = 0.199, P < 0.001). Given that inflammation is considered an important driver of postoperative delirium, next we tested whether neurofilament light, as a potential marker of neurotoxicity, may contribute to the pathogenesis of delirium independent of inflammation. From a panel of 10 cytokines, the pro-inflammatory cytokine IL-8 exhibited a strong correlation with delirium severity (ΔR2 = 0.208, P < 0.001). Therefore, we tested whether the change in neurofilament light contributed to delirium severity independent of IL-8. Neurofilament light was independently associated with delirium severity after adjusting for the change in inflammation (ΔR2 = 0.040, P = 0.038). These data suggest delirium is associated with exaggerated increases in neurofilament light and that this putative neurotoxicity may contribute to the pathogenesis of delirium itself, independent of changes in inflammation.

Cohort study of electroencephalography markers of amyloid-tau-neurodegeneration pathology

Electroencephalography signatures of amyloid-β, tau and neurodegenerative pathologies would aid in screening for, tracking progression of, and critically, understanding the pathogenesis of dementia. We hypothesized that slowing of the alpha peak frequency, as a signature of hyperpolarization-activated cyclic nucleotide gated ‘pacemaker’ channel activity, would correlate with amyloid and tau pathology burden measured by amyloid (Pittsburgh Compound B) and tau (MK-6240) positron emission tomography or CSF biomarkers. We also hypothesized that EEG power would be associated with neurodegeneration (CSF neurofilament light and hippocampal volume). Wakeful high-density EEG data were collected from 53 subjects. Both amyloid-β and tau pathology were associated with slowing in the alpha peak frequency [Pittsburgh Compound B (+) vs. Pittsburgh Compound B (−) subjects, P = 0.039 and MK-6240 (+) vs. MK-6240 (−) subjects, P = 0.019]. Furthermore, slowing in the peak alpha frequency correlated with CSF Aβ_42/40 ratio (r² = 0.270; P = 0.003), phosphoTau (pTau₁₈₁, r² = 0.290; P = 0.001) and pTau₁₈₁/Aβ₄₂ (r² = 0.343; P < 0.001). Alpha peak frequency was not associated with neurodegeneration. Higher CSF neurofilament light was associated with lower total EEG power (r² = 0.136; P = 0.018), theta power (r² = 0.148; P = 0.014) and beta power (r² = 0.216; P = 0.002); the latter was also associated with normalized hippocampal volume (r² = 0.196; P = 0.002). Amyloid-tau and neurodegenerative pathologies are associated with distinct electrophysiological signatures that may be useful as mechanistic tools and diagnostic/treatment effect biomarkers in clinical trials.

Cohort study into the neural correlates of postoperative delirium: the role of connectivity and slow-wave activity

BACKGROUND

Delirium frequently affects older patients, increasing morbidity and mortality; however, the pathogenesis is poorly understood. Herein, we tested the cognitive disintegration model, which proposes that a breakdown in frontoparietal connectivity, provoked by increased slow-wave activity (SWA), causes delirium.

METHODS

We recruited 70 surgical patients to have preoperative and postoperative cognitive testing, EEG, blood biomarkers, and preoperative MRI. To provide evidence for causality, any putative mechanism had to differentiate on the diagnosis of delirium; change proportionally to delirium severity; and correlate with a known precipitant for delirium, inflammation. Analyses were adjusted for multiple corrections (MCs) where appropriate.

RESULTS

In the preoperative period, subjects who subsequently incurred postoperative delirium had higher alpha power, increased alpha band connectivity (MC P<0.05), but impaired structural connectivity (increased radial diffusivity; MC P<0.05) on diffusion tensor imaging. These connectivity effects were correlated (r²=0.491; P=0.0012). Postoperatively, local SWA over frontal cortex was insufficient to cause delirium. Rather, delirium was associated with increased SWA involving occipitoparietal and frontal cortex, with an accompanying breakdown in functional connectivity. Changes in connectivity correlated with SWA (r²=0.257; P<0.0001), delirium severity rating (r²=0.195; P<0.001), interleukin 10 (r²=0.152; P=0.008), and monocyte chemoattractant protein 1 (r²=0.253; P<0.001).

CONCLUSIONS

Whilst frontal SWA occurs in all postoperative patients, delirium results when SWA progresses to involve posterior brain regions, with an associated reduction in connectivity in most subjects. Modifying SWA and connectivity may offer a novel therapeutic approach for delirium.

CLINICAL TRIAL REGISTRATION

NCT03124303, NCT02926417.

Inhibition of lipolysis by adenosine is potentiated with age

The ability of a variety of hormones to activate cells declines with age. We have investigated the mechanism for the reduced ability of beta adrenergic stimulation to activate lipolysis in fat cells from older rats. Previously, we have found that these cells have an intact lipolytic response to a cAMP analogue but diminished cAMP accumulation after isoproterenol stimulation, suggesting that the blunted cAMP response is rate limiting. In the present study we have tested the hypothesis that enhanced inhibition of lipolysis by endogenously released adenosine accounts for the diminished lipolysis. Adenosine deaminase was added to media containing the adipocytes from older rats to remove endogenous adenosine. Under these conditions beta adrenergic stimulation of lipolysis is intact in fat cells from older rats. The adenosine analogue N6-phenylisopropyladenosine more effectively inhibited lipolysis in the older group (77 +/- 6%) than in the younger group (46 +/- 5%), suggesting that enhanced efficacy of endogenous adenosine may account for the reduced lipolytic response to catecholamines. When pertussis vaccine was used to functionally inactivate adenosine receptors in adipocytes from the younger and older rats, the ability of isoproterenol to activate lipolysis was restored in the older group. All the data are consistent with the hypothesis that enhanced inhibitory effects of adenosine explain the diminished ability of beta adrenergic agonists to activate lipolysis. It is possible that enhanced inhibitory pathways may be involved in blunting responses to stimulatory hormones in other tissues from older animals.