Can brain stimulation reduce anxiety long-term?

What are "oscillopathies" as described in the paper?

"Oscillopathies" refer to aberrations in brain oscillations observed across a host of neuropsychiatric disorders, potentially underpinning their underlying pathophysiology.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

What is the typical frequency range and primary generator of alpha oscillations in the human brain?

Alpha oscillations range from 8 to 12 Hz, are posteriorly distributed in the awake restful brain, and are thought to be generated in the thalamo-cortical network.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How do alpha oscillations modulate cognitive processes such as attention and sensory perception?

Alpha oscillations exert a largely inhibitory modulation, where heightened pre-stimulus alpha power reduces perceptual sensitivity and attenuated alpha power enhances visual attention.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How does alpha connectivity mediate information flow between sensory and frontal regions?

Alpha oscillations mediate inhibitory bottom-up information flow from the sensory cortex to frontal regions via long-range, posterior-to-frontal projections to influence global neural activity.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How is resting-state alpha activity typically correlated with the Default Mode Network (DMN) and the Salience Network (SN)?

Alpha activity is positively correlated with DMN activity and negatively correlated with SN activity, helping maintain a state of restful alertness.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

What specific alpha rhythm deficits did the authors previously identify in patients with PTSD?

The authors identified deficits in resting-state alpha power and posterior-to-frontal alpha connectivity, with reduced connectivity correlating with greater hypervigilance.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

What are the proposed mechanisms for the short-term versus long-term plastic effects of tACS?

Short-term effects are driven by the entrainment of local neuronal firing synchrony, while long-term plastic effects arise from strengthened oscillatory circuits via spike-timing-dependent plasticity (STDP) and long-term potentiation (LTP) at the synapse.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Why do single-session tACS alpha power enhancements typically fail to persist over long durations?

Single-session tACS effects represent a labile, early-phase LTP, and the deep subcortical/thalamic generators of the thalamo-cortical circuit act to reset cortical alpha oscillations back to baseline.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Why did the authors hypothesize that inter-cortical connectivity plasticity would persist longer than local cortical alpha power after tACS?

Because inter-cortical connectivity is relatively independent of the deep subcortical thalamic drives that reset local alpha oscillations, allowing its synaptic changes to outlast local entrainment.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

What were the two main hypotheses tested in this study?

First, α-tACS would generate lasting enhancement of alpha power and long-range connectivity (specifically posterior-to-frontal). Second, these neural changes would be accompanied by lasting anxiety reduction.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

How many healthy volunteers participated, and how were they allocated to experimental groups?

There were 38 healthy volunteers, randomly assigned to an Active stimulation group (N=21) or a Sham control group (N=17).

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

What behavioral metrics and sensory modalities were used to assess anxiety and stimulus perception in the study?

Subjective units of anxious arousal (rated on a 0-100 scale) and perceived pleasantness ratings of auditory (sounds) and olfactory (odors) stimuli presented at three intensities.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

What specific electrode configuration and montage was used to deliver tACS in this study?

A 4x1 High-Definition (HD) tACS montage placed over occipitoparietal sites, with the central electrode receiving current from four surrounding electrodes to target the cuneus/precuneus.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

According to current flow modeling, what was the peak electric field intensity in the target area versus the frontal regions?

The peak electric field intensity was 0.21 V/m in the right dorsal occipital cortex, while it did not exceed 0.02 V/m in frontal regions.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How was the stimulation frequency determined for each individual participant?

It was tuned to each participant's individual peak alpha frequency (PAF) within the 8–12 Hz range, identified during baseline resting EEG recordings.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

What was the current intensity and duration of active tACS applied per session?

A ±2 mA sinusoidal current was administered with eyes open for 30 minutes.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How did the authors design the sham stimulation protocol to ensure participant blinding?

The current ramped up to 2 mA over 10 seconds, was immediately discontinued, and was reintroduced only during the last 10 seconds of the 30-minute block.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

What was the multi-session schedule of the study across days?

The experiment consisted of four sessions, with each session separated by 24 hours.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How did the experimental procedures differ between Days 1/4 and Days 2/3?

Days 1 and 4 included resting EEG recordings and pleasantness ratings (pre/post tACS), while Days 2 and 3 included only tACS and pre/post-stimulation anxious arousal ratings.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

What mathematical method was used to compute directional posterior-to-frontal alpha connectivity?

Granger causality (GC) analysis was performed on current source density data derived from the surface Laplacian algorithm.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

What covariate was included in the ANOVA for subjective anxiety ratings, and why?

Behavioral Inhibition Scale (BIS) scores were used as a covariate to control for individual differences in trait anxiety, which can influence state anxiety over repeated measures.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

What effect did α-tACS have on local posterior alpha power?

It induced immediate and short-term (30 minutes post-stimulation) power increases in the Active group, but failed to induce a long-term (24-hour) baseline shift.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Was the alpha power increase broad-spectrum or band-specific?

The power increase was highly specific to the targeted alpha band (specifically 8–10.5 Hz) and did not occur in other frequency bands.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How did posterior-to-frontal alpha connectivity change over the course of the 4-day study in the Active group?

Right-hemisphere posterior-to-frontal connectivity increased both immediately and showed a long-term, 24-hour baseline shift from the initial to the final session.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Did the left hemisphere exhibit the same connectivity changes as the right hemisphere?

No, the left hemisphere showed only a trend toward immediate connectivity increase during the initial session and did not exhibit a long-term baseline shift.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

What were the behavioral effects of α-tACS on subjective anxious arousal across the four days?

The Active group experienced consistently lowered anxious arousal, showing lasting baseline shifts (decreased anxiety) on Days 2, 3, and 4 relative to Day 1.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

How did Day 1 posterior-to-frontal connectivity (GC) changes relate to subsequent anxious arousal?

Day 1 Granger causality (GC) enhancement predicted a reduction in baseline anxious arousal marginally on Day 2 and significantly on Day 3, but not on Day 4.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How did α-tACS affect the perceived pleasantness of auditory stimuli?

It led to immediate and short-term increases in pleasantness ratings after the initial session, which developed into a sustained, long-term increase by the final session.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI

How did the effects of α-tACS on olfactory pleasantness differ from its effects on auditory pleasantness?

Olfactory changes (for negative odors) were purely transient (immediate and 30-minute post-stimulation) and did not result in a long-term baseline shift.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Why did the authors argue that local posterior alpha power returned to baseline despite repeated stimulation?

Because local alpha power is regulated by a highly integrated subcortical pacemaker (thalamo-cortical network) that acts to restore endogenous oscillation levels after stimulation ceases.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Why did posterior-to-frontal connectivity display long-term plasticity while local power did not?

Inter-cortical connectivity operates outside the subcortical thalamo-cortical loops that constrain local power, making its tACS-induced synaptic modifications more resistant to resetting.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Why did the authors argue that directional connectivity measures (like Granger Causality) were vital in this study?

Because alpha connectivity increases were highly directional (only posterior-to-frontal showed effects), which would have been obscured by non-directional connectivity metrics.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

What limitation of using healthy participants did the authors note regarding the potential "ceiling effect" in anxiety reduction?

Healthy participants already have low baseline anxious arousal, leaving modest room for improvement compared to clinical patients who have greater alpha deficits and higher baseline anxiety.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

How did the authors rule out experimenter bias and non-specific electrical stimulation effects?

They conducted a smaller-scale, double-blind, single-session replication study using random noise stimulation (RNS) as a control condition.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified

Why is targeting connectivity via tACS deemed more therapeutically advantageous for neuropsychiatric disorders than targeting local power?

Because psychiatric disorders (such as PTSD) are often conceptualized as large-scale circuit/network anomalies rather than local aberrations, and connectivity changes correlate better with symptom severity.

Source: Lasting connectivity increase and anxiety reduction via transcranial alternating current stimulation · DOI · quote verified