Phase-locking of Neural Activity to the Envelope of Speech in the Delta Frequency Band Reflects Differences between Word Lists and Sentences.

The envelope of a speech signal is tracked by neural activity in the cerebral cortex. The cortical tracking occurs mainly in two frequency bands, theta (4-8 Hz) and delta (1-4 Hz). Tracking in the faster theta band has been mostly associated with lower-level acoustic processing, such as the parsing of syllables, whereas the slower tracking in the delta band relates to higher-level linguistic information of words and word sequences. However, much regarding the more specific association between cortical tracking and acoustic as well as linguistic processing remains to be uncovered. Here, we recorded EEG responses to both meaningful sentences and random word lists in different levels of signal-to-noise ratios (SNRs) that lead to different levels of speech comprehension as well as listening effort. We then related the neural signals to the acoustic stimuli by computing the phase-locking value (PLV) between the EEG recordings and the speech envelope. We found that the PLV in the delta band increases with increasing SNR for sentences but not for the random word lists, showing that the PLV in this frequency band reflects linguistic information. When attempting to disentangle the effects of SNR, speech comprehension, and listening effort, we observed a trend that the PLV in the delta band might reflect listening effort rather than the other two variables, although the effect was not statistically significant. In summary, our study shows that the PLV in the delta band reflects linguistic information and might be related to listening effort.

Acute dosing of vortioxetine strengthens event-related brain activity associated with engagement of attention and cognitive functioning in rats.

Studies of the antidepressant vortioxetine have demonstrated beneficial effects on cognitive dysfunction associated with depression. To elucidate how vortioxetine modulates neuronal activity during cognitive processing we investigated the effects of vortioxetine (3 and 10mg/kg) in rats performing an auditory oddball (deviant target) task. We investigated neuronal activity in target vs non-target tone responses in vehicle-treated animals using electroencephalographic (EEG) recordings. Furthermore, we characterized task performance and EEG changes in target tone responses of vortioxetine vs controls. Quantification of event-related potentials (ERPs) was supplemented by analyses of spectral power and inter-trial phase-locking. The assessed brain regions included prelimbic cortex, the hippocampus, and thalamus. As compared to correct rejection of non-target tones, correct target tone responses elicited increased EEG power in all regions. Additionally, neuronal synchronization was increased in vehicle-treated rats during both early and late ERP responses to target tones. This indicates a significant consistency of local phases across trials during high attentional load. During early sensory processing, vortioxetine increased both thalamic and frontal synchronized gamma band activity and EEG power in all brain regions measured. Finally, vortioxetine increased the amplitude of late hippocampal P3-like ERPs, the rodent correlate of the human P300 ERP. These findings suggest differential effects of vortioxetine during early sensory registration and late endogenous processing of auditory discrimination. Strengthened P3-like ERP response may relate to the pro-cognitive profile of vortioxetine in rodents. Further investigations are warranted to explore the mechanism by which vortioxetine increases network synchronization during attentive and cognitive processing.

Adapted wavelet transform improves time-frequency representations: a study of auditory elicited P300-like event-related potentials in rats.

OBJECTIVE: Active auditory oddball paradigms are simple tone discrimination tasks used to study the P300 deflection of event-related potentials (ERPs). These ERPs may be quantified by time-frequency analysis. As auditory stimuli cause early high frequency and late low frequency ERP oscillations, the continuous wavelet transform (CWT) is often chosen for decomposition due to its multi-resolution properties. However, as the conventional CWT traditionally applies only one mother wavelet to represent the entire spectrum, the time-frequency resolution is not optimal across all scales. To account for this, we developed and validated a novel method specifically refined to analyse P300-like ERPs in rats. APPROACH: An adapted CWT (aCWT) was implemented to preserve high time-frequency resolution across all scales by commissioning of multiple wavelets operating at different scales. First, decomposition of simulated ERPs was illustrated using the classical CWT and the aCWT. Next, the two methods were applied to EEG recordings obtained from prefrontal cortex in rats performing a two-tone auditory discrimination task. MAIN RESULTS: While only early ERP frequency changes between responses to target and non-target tones were detected by the CWT, both early and late changes were successfully described with strong accuracy by the aCWT in rat ERPs. Increased frontal gamma power and phase synchrony was observed particularly within theta and gamma frequency bands during deviant tones. SIGNIFICANCE: The study suggests superior performance of the aCWT over the CWT in terms of detailed quantification of time-frequency properties of ERPs. Our methodological investigation indicates that accurate and complete assessment of time-frequency components of short-time neural signals is feasible with the novel analysis approach which may be advantageous for characterisation of several types of evoked potentials in particularly rodents.

Acupuncture for Pain in Chronic Pancreatitis: A Single-Blinded Randomized Crossover Trial.

OBJECTIVES: Many patients with painful chronic pancreatitis (CP) have insufficient effect of treatment, and the prevalence of adverse effects is high. Consequently, alternatives to conventional management are needed. We aimed to study the effect of acupuncture in painful CP. METHODS: This was a prospective, single-blinded, randomized crossover trial. Fifteen patients with CP were assigned to a session of acupuncture followed by sham stimulation or vice versa. Patients rated clinical pain scores daily on a 0 to 10 visual analogue scale (VAS) and completed the Patient Global Impression of Change. For mechanistic linkage, resting state electroencephalograms were recorded and quantified by spectral power analysis to explore effects on central pain processing. RESULTS: Acupuncture, compared with sham stimulation, caused more pain relief (2.0 ± 1.5 VAS vs 0.7 ± 0.8 VAS; P = 0.009). The effect, however, was short, and after 1-week follow-up, there was no difference in clinical pain scores between groups (P = 1.0) or the rating of Patient Global Impression of Change (P = 0.8). Electroencephalogram spectral power distributions between sham and acupuncture were comparable between groups (all P > 0.6). CONCLUSIONS: The study presents proof-of-concept for the analgesic effect of acupuncture in pancreatic pain. Although the effect was short lasting, the framework may be used to conceptualize future trials of acupuncture in visceral pain.

A New Method for Sham-Controlled Acupuncture in Experimental Visceral Pain - a Randomized, Single-Blinded Study.

OBJECTIVE: Acupuncture is increasingly used as an alternative to medical therapy for various pain conditions. To study the effect of acupuncture in experimental and clinical studies, a control condition with sham acupuncture is needed. However, as such models have not been established in assessment of acupunctures effect against visceral pain, this study aimed to validate a new method for blinded sham acupuncture in experimental rectal pain. METHODS: Fifteen subjects underwent a sequence of either sham or real acupuncture in randomized order. In the sham arm, a hollow inner tube with a sharp tip was fitted into an outer tube and subjects were blinded to the stimulations. Before and after the intervention, pain was induced by rectal stimulation with an inflatable balloon distended until the subjects' pain threshold was reached. The resting electroencephalogram (EEG) was quantified by spectral power analysis to explore the central nervous system effects objectively. Additionally, after the second study day, the subject was asked to indicate the sequence of interventions. RESULTS: A significant increase in rectal balloon volume was observed after sham 12 ± 21 mL (P = 0.049) and acupuncture 17 ± 30 mL (P = 0.046). However, the change in volume was not different between groups (P = 0.6). No differences in EEG spectral power distributions between sham and acupuncture were seen (all P > 0.6). The correct sequence of sham and acupuncture was indicated by 36% of the subjects (P = 0.4). CONCLUSIONS: The presented sham procedure provides a valid method for blinding of "sham acupuncture" and may be used in future blinded controlled trials of acupuncture for visceral pain.

Abnormal brain processing in hepatic encephalopathy: evidence of cerebral reorganization?

BACKGROUND AND AIM: Hepatic encephalopathy (HE) is a severe and frequent complication of liver cirrhosis characterized by abnormal cerebral function. Little is known about the underlying neural mechanisms in HE and human data are sparse. Electrophysiological methods such as evoked brain potentials after somatic stimuli can be combined with inverse modeling of the underlying brain activity. Thereby, information on neuronal dynamics and brain activity can be studied in vivo. The aim of this study was to investigate the sensory brain processing in patients with HE. PATIENTS AND METHODS: Twelve patients with minimal or overt HE and 26 healthy volunteers were included in the study. Cerebral sensory processing was investigated as (i) an auditory reaction time task; (ii) visual and somatosensory evoked brain potentials, and (iii) reconstruction of the underlying brain activity. RESULTS: Somatosensory evoked potentials were reproducible (all P>0.05), whereas flash evoked potentials were not reproducible (all P<0.05). Compared with healthy volunteers, the patient group had a prolonged reaction time index (P=0.03) along with increasing prolongation of latencies of median nerve evoked potentials (P<0.03). Reconstruction of the underlying brain sources showed a lateral shift in source localization of the P45 (P<0.001) and N60 components (P=0.02). A correlation between the psychometric hepatic encephalopathy score and the dipole shift corresponding to the N60 (P=0.003) component was seen. CONCLUSION: HE patients have evidence of prolonged intracerebral nerve conduction, along with lateralization of brain activity following median nerve stimulation. This possibly represents cortical reorganization and may be important in our understanding of this condition.