Increase In Theta Band Power Research Articles

Human Cervical Epidural Spinal Electrogram Topographically Maps Distinct Volitional Movements.

Little is known about the electrophysiologic activity of the intact human spinal cord during volitional movement. We analyzed epidural spinal recordings from a total of five human subjects of both sexes during a variety of upper extremity movements and found that these spinal epidural electrograms contain spectral information distinguishing periods of movement, rest, and sensation. Cervical epidural electrograms also contained spectral changes time-locked with movement. We found that these changes were primarily associated with increased power in the theta (4-8 Hz) band and feature increased theta phase to gamma amplitude coupling, and this increase in theta power can be used to topographically map distinct upper extremity movements onto the cervical spinal cord in accordance with established myotome maps of the upper extremity. Our findings have implications for the development of neurostimulation protocols and devices focused on motor rehabilitation for the upper extremity, and the approach presented here may facilitate spatiotemporal mapping of naturalistic movements.

Exploring Horizontally Flipped Interaction in Virtual Reality for Improving Spatial Ability.

Virtual reality (VR) is a high-fidelity medium that can offer experiences that are close to real-life. Spatial ability plays an important role in human life, including academic achievement and advancement in work settings. Spatial ability is known to be improved by practicing relevant tasks. Mental rotation and spatial perception are among such tasks that improve spatial skills. In this research, we investigated a "mirror-reversed" interaction technique in a cup stacking task in VR and looked into its effects on spatial ability, brain activity regarding spatial processing and attention (measured with EEG), performance, and user experience in male participants. Participants stacked cups according to given patterns using direct manipulation with horizontally flipped controls, similar to looking in a mirror while performing object manipulation in real life. In a between-subjects user study, we compared this novel interaction with a baseline where the participants completed the same task with regular controls. Although there was no significant main effect of group on the mental rotation and perspective taking/spatial orientation tests scores, within-group analysis indicated a trend toward an improvement in the mirror-reversed group in spatial orientation, while both groups showed a trend toward improvement in mental rotation. Participants in both groups got better at the task over time (their task completion durations decreased). EEG data revealed significant theta band power increase in the mirror-reversed group whereas there was no difference in the alpha band power between the two groups. Our results are encouraging for exploring spatially challenging interactions in VR for spatial skills training. We share the implementation and user study results, and discuss the implications.

Temporal dynamics of oscillatory activity during nonlexical language decoding: Evidence from Morse code and magnetoencephalography.

Understanding encoded languages, such as written script or Morse code, requires nonlexical and lexical processing components that act in a parallel and interactive fashion. Decoding written script-as for example in reading-is typically very fast, making the investigation of the lexical and nonlexical components and their underlying neural mechanisms challenging. In the current study, we aimed to accomplish this problem by using Morse code as a model for language decoding. The decoding of Morse code is slower and thus allows a better and more fine-grained investigation of the lexical and nonlexical components of language decoding. In the current study, we investigated the impact of various components of nonlexical decoding of Morse code using magnetoencephalography. For this purpose, we reconstructed the time-frequency responses below 40 Hz in brain regions significantly involved in Morse code decoding and word comprehension that were identified in a previous study. Event-related reduction in beta- and alpha-band power were found in left inferior frontal cortex and angular gyrus, respectively, while event-related theta-band power increase was found at frontal midline. These induced oscillations reflect working-memory encoding, long-term memory retrieval as well as demanding cognitive control, respectively. In sum, by using Morse code and MEG, we were able to identify a cortical network underlying language decoding in a time- and frequency-resolved manner.

Cortico-Cerebellar neurodynamics during social interaction in Autism Spectrum Disorders

BackgroundExploring neural network dynamics during social interaction could help to identify biomarkers of Autism Spectrum Disorders (ASD). A cerebellar involvement in autism has long been suspected and recent methodological advances now enable studying cerebellar functioning in a naturalistic setting. Here, we investigated the electrophysiological activity of the cerebro-cerebellar network during real-time social interaction in ASD. We focused our analysis on theta oscillations (3–8 Hz), which have been associated with large-scale coordination of distant brain areas and might contribute to interoception, motor control, and social event anticipation, all skills known to be altered in ASD. MethodsWe combined the Human Dynamic Clamp, a paradigm for studying realistic social interactions using a virtual avatar, with high-density electroencephalography (HD-EEG). Using source reconstruction, we investigated power in the cortex and the cerebellum, along with coherence between the cerebellum and three cerebral-cortical areas, and compared our findings in a sample of participants with ASD (n = 107) and with typical development (TD) (n = 33). We developed an open-source pipeline to analyse neural dynamics at the source level from HD-EEG data. ResultsIndividuals with ASD showed a significant increase in theta band power over the cerebellum and the frontal and temporal cortices during social interaction compared to resting state, along with significant coherence increases between the cerebellum and the sensorimotor, frontal and parietal cortices. However, a phase-based connectivity measure did not support a strict activity increase in the cortico-cerebellar functional network. We did not find any significant differences between the ASD and the TD group. ConclusionsThis exploratory study uncovered increases in the theta band activity of participants with ASD during social interaction, pointing at the presence of neural interactions between the cerebellum and cerebral networks associated with social cognition. It also emphasizes the need for complementary functional connectivity measures to capture network-level alterations. Future work will focus on optimizing artifact correction to include more participants with TD and increase the statistical power of group-level contrasts.

Evoked Acute Stress Alters Frontal Midline Neural Oscillations Affecting Behavioral Inhibition in College Students.

PurposeThe current research of the effect of acute stress on individual behavioral inhibition remains divergent. The present study aims to explore the effects of acute stress on behavioral inhibition in college students and to understand the neural oscillatory characteristics of their behavioral inhibition process.Patients and MethodsWe invited 27 college students (12 males and 15 females) to participate in the study. The experiment was conducted using the Trier Social Stress paradigm to evoke an acute stress state and an out-of-speech reading to set a neutral state. Participants completed a two-choice Oddball task in the acute stress state and the neutral state, respectively. We used a 64-channel EEG cap to record EEG data from university students during the experimental task. In combination with the ERO technique, we compared the reaction time, the number of errors, and the power of the alpha (8–13 Hz) and theta (4–8 Hz) frequency bands at the midline of the frontal lobe for subjects in both states. The correlation between the area under the stress area line and the alpha as well as theta frequency bands was also analyzed.ResultsWe found that in the two-choice Oddball task, the response inhibition time was shorter, the number of response errors decreased, and the alpha-band power values decreased in the acute stress state compared to the neutral state. For the standard stimulus, the theta-band power increase in the acute stress state.ConclusionOur results suggest that evoked acute stress promotes behavioral inhibition in college students by affecting their frontal midline neural oscillations.

Clinical and Electroencephalography Assessment of the Effects of Brivaracetam in the Treatment of Drug-Resistant Focal Epilepsy.

Introduction: Our aim was to evaluate the clinical and electroencephalographic effects of brivaracetam (BRV) in patients with drug-resistant focal epilepsy. BRV is a new antiepileptic drug (AED) with a high affinity for vesicle protein 2A (SV2A) and recently approved as adjunctive therapy for focal onset seizures. Methods: In this observational study of six-month duration, BRV (50-200 mg) was administered to 76 patients with drug-resistant focal epilepsy, who were ≥16-year-old and who suffered from daily, weekly, monthly and yearly recurrent seizures. At baseline and after six months of follow-up, we performed a neurological visit, neuropsychological tests: Quality of life in epilepsy-31 (QOLIE31), Epworth Sleepiness Scale (ESS), Intrapersonal Emotional Quotient (IEQ) and an electroencephalogram (EEG; inspective and quantitative analysis). Twenty-four patients underwent an overnight switch from levetiracetam (LEV) to BRV. Results: Seizure frequency of the 54 patients remaining at six months was reduced >50% in 29.6% of cases (responders), <50% in 31.5% (non-responders 1), while it remained unchanged in 38.8% (non-responders 2). Twenty-nine percent of patients early discontinued BRV because of lack of efficacy or minor adverse effects (AEs) like irritability, asthenia or headache. Neuropsychological tests in 28 patients demonstrated a significant improvement in I-EPI scores (p=0.04). Comparable results have been found in the subgroup of patients who switched from LEV to BRV. The EEG quantitative analysis showed a significant reduction of alpha absolute power at six months (p=0.03). Theta band power resulted significantly superior in non-responders than in responders (p=0.03). Furthermore, the δ+θ/α+β index resulted more elevated in patients with AEs than in patients without. Conclusions: BRV showed discrete results in terms of efficacy, safety and tolerability, with a good behavioural profile. BRV reduces the power of the alpha band, in correlation with its sedative effects but not with its minor efficacy. Furthermore, the increase in theta band power can be considered as a predictor of scarce response to treatment, while an increase in the δ+θ/α+β index could be a possible predictor of AEs occurrence.

Bifidobacterium longum 1714™ Strain Modulates Brain Activity of Healthy Volunteers During Social Stress.

OBJECTIVES:Accumulating evidence indicates that the gut microbiota communicates with the central nervous system, possibly through neural, endocrine, and immune pathways, and influences brain function. B. longum 1714™ has previously been shown to attenuate cortisol output and stress responses in healthy subjects exposed to an acute stressor. However, the ability of B. longum 1714™ to modulate brain function in humans is unclear.METHODS:In a randomized, double-blinded, placebo-controlled trial, the effects of B. longum 1714™ on neural responses to social stress, induced by the “Cyberball game,” a standardized social stress paradigm, were studied. Forty healthy volunteers received either B. longum 1714™ or placebo for 4 weeks at a dose of 1 × 109 cfu/d. Brain activity was measured using magnetoencephalography and health status using the 36-item short-form health survey.RESULTS:B. longum 1714™ altered resting-state neural oscillations, with an increase in theta band power in the frontal and cingulate cortex (P < 0.05) and a decrease in beta-3 band in the hippocampus, fusiform, and temporal cortex (P < 0.05), both of which were associated with subjective vitality changes. All groups showed increased social stress after a 4-week intervention without an effect at behavioral level due to small sample numbers. However, only B. longum 1714™ altered neural oscillation after social stress, with increased theta and alpha band power in the frontal and cingulate cortex (P < 0.05) and supramarginal gyrus (P < 0.05).DISCUSSION:B. longum 1714™ modulated resting neural activity that correlated with enhanced vitality and reduced mental fatigue. Furthermore, B. longum 1714™ modulated neural responses during social stress, which may be involved in the activation of brain coping centers to counter-regulate negative emotions.

Neuronal networks underlying the conjoint modulation of response selection by subliminal and consciously induced cognitive conflicts.

Goal-directed behavior has been shown to be affected by consciously and subliminally induced conflicts. Both types of conflict conjointly modulate behavioral performance, but the underlying neuronal mechanisms have remained unclear. While cognitive control is linked to oscillations in the theta frequency band, there are several mechanisms via which theta oscillations may enable cognitive control: via the coordination and synchronization of a large and complex neuronal network and/or via local processes within the medial frontal cortex. We, therefore, investigated this issue with a focus on theta oscillations and the underlying neuronal networks. For this purpose, n = 40 healthy young participants performed a conflict paradigm that combines conscious and subliminal distractors while an EEG was recorded. The data show that separate processes modulate the theta-based activation and organization of cognitive control networks: EEG beamforming analyses showed that variations in theta band power generated in the supplementary motor area reflected the need for control and task-relevant goal shielding, as both conflicts as well as their conjoint effect on behavior increased theta power. Yet, large networks were not modulated by this and graph theoretical analyses of the efficiency (i.e. small worldness) of theta-driven networks did not reflect the need for control. Instead, theta network efficiency was decreased by subliminal conflicts only. This dissociation suggests that while both kinds of conflict require control and goal shielding, which are induced by an increase in theta band power and modulate processes in the medial frontal cortex, only non-conscious conflicts diminish the efficiency of theta-driven large-scale networks.

Bilateral cortical representation of tactile roughness

Roughness is the most important feature for texture discrimination. Here we investigate how the bilateral cortical representation of touch is modulated by tactile roughness by analyzing the neural responses elicited by stimuli with various coarseness levels ranging from fine to medium.A prolonged stimulation was delivered to 10 healthy subjects by passively sliding tactile stimuli under the fingertip while recording the EEG to study the modulation of Somatosensory Evoked Potentials (SEPs) as well as activity in the theta and alpha bands. Elicited long-latency SEPs, namely bilateral P100-N140 and frontal P240 were consistent across stimuli. On the contrary, the temporal lag N140 – P240 was nonlinearly modulated both in contralateral and ipsilateral sides, in agreement with literature.Using a time-frequency analysis approach, we identified a theta band power increase in the [0 0.5]s interval and a partially overlapped power decrease in the alpha band which lasted throughout the stimulation. The estimated time these two phenomena were overlapped was comparable across stimuli, whereas a linear decrease in alpha band amplitude was reported when increasing the stimulus roughness in both contralateral and ipsilateral sides.This study showed that the selected tactile stimuli generated physiological bilateral responses that were modulated in a diversified way according to the stimulus roughness and side. Specifically, we identified sensory processing features (i.e., theta and alpha time overlap) invariant to the stimulus roughness (i.e., associated to a basic cortical mechanism of touch) and roughness-dependent cortical outputs comparable in the contralateral and ipsilateral sides that confirm a bilateral processing of tactile information.

Prior Expectation Modulates Repetition Suppression without Perceptual Awareness

Stimulus repetition induces attenuated brain responses. This phenomenon, termed repetition suppression (RS), is classically held to stem from bottom-up neuronal adaptation. However, recent studies suggest that RS is driven by top-down predictive mechanisms. It remains controversial whether these top-down mechanisms of RS rely on conscious strategies, or if they represent a more fundamental aspect of perception, coding for physical properties of the repeated feature. The presence of top-down effects in the absence of perceptual awareness would indicate that conscious strategies are not sufficient to explain top-down mechanisms of RS. We combined an unconscious priming paradigm with EEG recordings and tested whether RS can be modulated by the probability of encountering a repetition, even in the absence of awareness. Our results show that both behavioural priming and RS near occipital areas are modulated by repetition probability, regardless of prime awareness. This contradicts previous findings that have argued that RS modulation is a by-product of conscious strategies. In contrast, we found that the increase in theta-band power following unrepeated trials – an index of conflict detection – is modulated only by expectations during conscious primes, implicating the use of conscious strategies. Together, our results suggest that the influence of predictions on RS can be either automatic in sensory brain regions or dependent on conscious strategies.

Switching direction affects switching costs: Behavioral, ERP and time-frequency analyses of intra-sentential codeswitching

Bilinguals have the unique ability to produce utterances that switch between languages. Most language switching research has focused on isolated, unrelated items, which emphasizes separation of the languages. Fewer studies examined the cognitive and neural mechanisms of switching languages in natural discourse. The present study examined the effect of codeswitching direction on the comprehension of intra-sentential codeswitching in Spanish-English bilinguals, using self-paced reading behavioral measurements (Experiment 1) and electroencephalography (EEG) measurements (Experiment 2), analyzed via both event-related potentials (ERPs) and time-frequency analysis (TFR). Reading times showed a significant switching cost for codeswitched sentences in both codeswitching directions, though switching costs were somewhat higher into the dominant language than into the weaker language. ERPs showed that codeswitched as compared to non-switched words elicited a late positivity, but only when switching from the dominant into the weaker language, not in the reverse direction. TFRs showed complementary and converging results: switches into the weaker language resulted in a power decrease in lower beta band while switches into the dominant language resulted in a power increase in theta band. These multi-method findings provide novel insights into neurocognitive resources engaged in the comprehension of intra-sentential codeswitches related to sentence-level restructuring processes to activate and access the weaker language.

Theta and high-beta networks for feedback processing: a simultaneous EEG\u2013fMRI study in healthy male subjects

The reward system is important in assessing outcomes to guide behavior. To achieve these purposes, its core components interact with several brain areas involved in cognitive and emotional processing. A key mechanism suggested to subserve these interactions is oscillatory activity, with a prominent role of theta and high-beta oscillations. The present study used single-trial coupling of simultaneously recorded electroencephalography and functional magnetic resonance imaging data to investigate networks associated with oscillatory responses to feedback during a two-choice gambling task in healthy male participants (n=19). Differential associations of theta and high-beta oscillations with non-overlapping brain networks were observed: Increase of high-beta power in response to positive feedback was associated with activations in a largely subcortical network encompassing core areas of the reward network. In contrast, theta-band power increase upon loss was associated with activations in a frontoparietal network that included the anterior cingulate cortex. Trait impulsivity correlated significantly with activations in areas of the theta-associated network. Our results suggest that positive and negative feedback is processed by separate brain networks associated with different cognitive functions. Communication within these networks is mediated by oscillations of different frequency, possibly reflecting different modes of dopaminergic signaling.

Anchors as Semantic Primes in Value Construction: An EEG Study of the Anchoring Effect.

Previous research regarding anchoring effects has demonstrated that human judgments are often assimilated to irrelevant information. Studies have demonstrated that anchors influence the economic valuation of various products and experiences; however, the cognitive explanations of this effect remain controversial, and its neural mechanisms have rarely been explored. In the current study, we conducted an electroencephalography (EEG) experiment to investigate the anchoring effect on willingness to accept (WTA) for an aversive hedonic experience and the role of anchors in this judgment heuristic. The behavioral results demonstrated that random numbers affect participants’ WTA for listening to pieces of noise. The participants asked for higher pay after comparing their WTA with higher numbers. The EEG results indicated that anchors also influenced the neural underpinnings of the valuation process. Specifically, when a higher anchor number was drawn, larger P2 and late positive potential amplitudes were elicited, reflecting the anticipation of more intensive pain from the subsequent noise. Moreover, higher anchors induced a stronger theta band power increase compared with lower anchors when subjects listened to the noises, indicating that the participants felt more unpleasant during the actual experience of the noise. The levels of unpleasantness during both anticipation and experience were consistent with the semantic information implied by the anchors. Therefore, these data suggest that a semantic priming process underlies the anchoring effect in WTA. This study provides proof for the robustness of the anchoring effect and neural evidence of the semantic priming model. Our findings indicate that activated contextual information, even seemingly irrelevant, can be embedded in the construction of economic value in the brain.

3D Cortical electrophysiology of ballistic upper limb movement in humans

Precise motor control requires the ability to scale the parameters of movement. Theta oscillations across the cortex have been associated with changes in memory, attention, and sensorimotor processing. What has proven more elusive is pinpointing the region-specific frequency band oscillations that are associated with specific parameters of movement during the acceleration and deceleration phases. We report a study using 3D analytic techniques for high density electroencephalography that examines electrocortical dynamics while participants produce upper limb movements to different distances at varying rates. During fast ballistic movements, we observed increased theta band activity in the left motor area contralateral to the moving limb during the acceleration phase of the movement, and theta power correlated with the acceleration of movement. In contrast, beta band activity scaled with the type of movement during the deceleration phase near the end of the movement and correlated with movement time. In the ipsilateral motor and somatosensory area, alpha band activity decreased with the type of movement near the end of the movement, and gamma band activity in visual cortex increased with the type of movement near the end of the movement. Our results suggest that humans use distinct lateralized cortical activity for distance and speed dependent arm movements. We provide new evidence that a temporary increase in theta band power relates to movement acceleration and is important during movement execution. Further, the theta power increase is coupled with desychronization of beta band power and alpha band power which are modulated by the task near the end of movement.

Impact of Sheetali and Sheetkari Pranayama on the Topographic Mapping of the Brain Waves

Pranayama is yogic breathing technique which is known to improve the physical and mental well-being. The tremendous impact of yoga on the functioning of nervous system, attenuation of stress and promotion of relaxation is well known. Sheetali and Sheetkari pranayama also produce similar effects but, in addition, they also cool down the body and the brain. However, the impact of these pranayama on electroencephalogram (EEG) is not explored so far. For this study, 20 male volunteers were recruited and divided into two equal groups namely yoga group (YG) who underwent the practice of these pranayama for two months and non-yoga group (NYG) who did not do any type of breathing technique. In both the groups, EEG topographic mapping was recorded and the results were compared. The mapping revealed an increase in the delta (red bands) and alpha band power (green bands) in the frontal and occipital regions and an increase in theta band power (yellow bands) in the frontal region with a marked decrease in beta band power (blue bands) almost throughout the entire hemisphere after two months’ of Sheetali and Sheethkari pranayama practice indicating that the brain (mind) was calm and quiet in relaxed state with less anxiety.

Abnormal patterns of theta frequency oscillations during the temporal evolution of freezing of gait in Parkinson’s disease

ObjectiveWe sought to characterize the electrophysiological signature of Freezing of gait in Parkinson’s disease. MethodsWe examined 24 patients with idiopathic Parkinson’s disease and significant freezing of gait as they performed a series of timed up-and-go tasks in their ‘off’ state while electroencephalographic data was collected from four scalp leads. Fast Fourier Transformation was utilized to explore the power spectral density between periods of normal walking and periods of freezing, as well as during the transition between the two states. In addition, Cross Spectrum and Cross Frequency analyses were used to explore the role of impaired temporal and spatial connectivity. ResultsWhen compared to walking, episodes of freezing were associated with a significant increase in theta band power within the central and frontal leads. The transition from normal walking to freezing of gait was also associated with increased theta frequency coupling between the central and frontal leads, along with an increase in cross-frequency coupling in the central lead. ConclusionsEpisodes of freezing of gait in Parkinson’s disease are associated with abnormal oscillatory activity in the brain. SignificanceThese results provide novel insights into the pattern of spatiotemporal dynamics underlying freezing of gait and may provide a potential means for therapeutic prediction and alleviation of freezing episodes in susceptible patients.

Loss of balance during balance beam walking elicits a multifocal theta band electrocortical response

Determining the neural correlates of loss of balance during walking could lead to improved clinical assessment and treatment for individuals predisposed to falls. We used high-density electroencephalography (EEG) combined with independent component analysis (ICA) to study loss of balance during human walking. We examined 26 healthy young subjects performing heel-to-toe walking on a treadmill-mounted balance beam as well as walking on the treadmill belt (both at 0.22 m/s). ICA identified clusters of electrocortical EEG sources located in or near anterior cingulate, anterior parietal, superior dorsolateral-prefrontal, and medial sensorimotor cortex that exhibited significantly larger mean spectral power in the theta band (4-7 Hz) during walking on the balance beam compared with treadmill walking. Left and right sensorimotor cortex clusters produced significantly less power in the beta band (12-30 Hz) during walking on the balance beam compared with treadmill walking. For each source cluster, we also computed a normalized mean time/frequency spectrogram time locked to the gait cycle during loss of balance (i.e., when subjects stepped off the balance beam). All clusters except the medial sensorimotor cluster exhibited a transient increase in theta band power during loss of balance. Cluster spectrograms demonstrated that the first electrocortical indication of impending loss of balance occurred in the left sensorimotor cortex at the transition from single support to double support prior to stepping off the beam. These findings provide new insight into the neural correlates of walking balance control and could aid future studies on elderly individuals and others with balance impairments.

Investigating the Neural Correlates of Pathological Cortical Networks in Alzheimer's Disease Using Heterogeneous Neuronal Models

This paper describes an investigation into the pathophysiological causes of abnormal cortical oscillations in Alzheimer's disease (AD) using two heterogeneous neuronal network models. The effect of excitatory circuit disruption on the beta band power (13-30 Hz) using a conductance-based network model of 200 neurons is assessed. Then, the neural correlates of abnormal cortical oscillations in different frequency bands based on a larger network model of 1000 neurons consisting of different types of cortical neurons are also analyzed. EEG studies in AD patients have shown that beta band power (13-30 Hz) decreased in the early stages of the disease with a parallel increase in theta band power (4-7 Hz). This abnormal change progresses with the later stages of the disease but with decreased power spectra in other fast frequency bands plus an increase in delta band power (1-3 Hz). Our results show that, despite the heterogeneity of the network models, the beta band power is significantly affected by excitatory neural and synaptic loss. Second, the results of modeling a functional impairment in the excitatory circuit shows that beta band power exhibits the most decrease compared with other bands. Previous biological experiments on different types of cultural excitatory neurons show that cortical neuronal death is mediated by dysfunctional ionic behavior that might specifically contribute to the pathogenesis of β-amyloid-peptide-induced neuronal death in AD. Our study also shows that beta band power was the first affected component when the modeled excitatory circuit begins to lose neurons and synapses.

Beta-amyloid induced changes in A-type K+ current can alter hippocampo-septal network dynamics

Alzheimer's disease (AD) progression is usually associated with memory deficits and cognitive decline. A hallmark of AD is the accumulation of beta-amyloid (Aβ) peptide, which is known to affect the hippocampal pyramidal neurons in the early stage of AD. Previous studies have shown that Aβ can block A-type K(+) currents in the hippocampal pyramidal neurons and enhance the neuronal excitability. However, the mechanisms underlying such changes and the effects of the hyper-excited pyramidal neurons on the hippocampo-septal network dynamics are still to be investigated. In this paper, Aβ-blocked A-type current is simulated, and the resulting neuronal and network dynamical changes are evaluated in terms of the theta band power. The simulation results demonstrate an initial slight but significant theta band power increase as the A-type current starts to decrease. However, the theta band power eventually decreases as the A-type current is further decreased. Our analysis demonstrates that Aβ blocked A-type currents can increase the pyramidal neuronal excitability by preventing the emergence of a steady state. The increased theta band power is due to more pyramidal neurons recruited into spiking mode during the peak of pyramidal theta oscillations. However, the decreased theta band power is caused by the spiking phase relationship between different neuronal populations, which is critical for theta oscillation, is violated by the hyper-excited pyramidal neurons. Our findings could provide potential implications on some AD symptoms, such as memory deficits and AD caused epilepsy.

Computational study of hippocampal-septal theta rhythm changes due to β-amyloid-altered ionic channels.

Electroencephagraphy (EEG) of many dementia patients has been characterized by an increase in low frequency field potential oscillations. One of the characteristics of early stage Alzheimer’s disease (AD) is an increase in theta band power (4–7 Hz). However, the mechanism(s) underlying the changes in theta oscillations are still unclear. To address this issue, we investigate the theta band power changes associated with β-Amyloid (Aβ) peptide (one of the main markers of AD) using a computational model, and by mediating the toxicity of hippocampal pyramidal neurons. We use an established biophysical hippocampal CA1-medial septum network model to evaluate four ionic channels in pyramidal neurons, which were demonstrated to be affected by Aβ. They are the L-type Ca2+ channel, delayed rectifying K+ channel, A-type fast-inactivating K+ channel and large-conductance Ca2+-activated K+ channel. Our simulation results demonstrate that only the Aβ inhibited A-type fast-inactivating K+ channel can induce an increase in hippocampo-septal theta band power, while the other channels do not affect theta rhythm. We further deduce that this increased theta band power is due to enhanced synchrony of the pyramidal neurons. Our research may elucidate potential biomarkers and therapeutics for AD. Further investigation will be helpful for better understanding of AD-induced theta rhythm abnormalities and associated cognitive deficits.