Can timing brain stimulation suppress Parkinson's beta waves?

What was the primary objective of this study regarding STN beta oscillations?

The study aimed to determine if electrical stimulation timed to a specific phase of the subthalamic nucleus (STN) LFP beta oscillation could suppress local and network-level pathological activity in Parkinson's disease.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How many patients were recorded in this study, and how many were excluded from the analysis?

Ten patients were recorded, but two were excluded (one lacked a significant beta oscillation, and the other had a stimulus-oscillation frequency difference greater than 5 Hz).

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Why was one patient excluded due to the relationship between their peak beta frequency and the stimulation frequency?

A difference of more than 5 Hz prevented consecutive stimulation cycles from occurring at the same phase of the oscillation.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What was the anatomical target of the microelectrode recording, and where was the stimulation macroelectrode positioned?

Microelectrode recording was performed within the subthalamic nucleus (STN), while stimulation was delivered to the area immediately dorsal to the STN.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What specific filter was used to remove stimulus-evoked artifacts from the LFP signals?

A Kalman filter approach was used to estimate and remove the stimulus-evoked artifact without introducing phase distortion.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What signal processing steps were used to estimate the instantaneous phase and envelope of the beta oscillation?

The signals were bandpass filtered (plus or minus 3 Hz around peak beta) using a Butterworth filter, followed by the Hilbert transform.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Did single stimulation pulses delivered at specific phases significantly suppress LFP beta amplitude?

No, single pulses grouped by phase did not produce amplitude-suppressive effects that were significantly different from natural signal variability.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What is the minimum number of consecutive stimulus pulses at the suppressing phase required to produce a significant reduction in beta amplitude compared to surrogates?

Significant suppression beyond surrogates was observed starting after the third consecutive pulse.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What was the mean percentage reduction in beta amplitude observed after five consecutive stimulus pulses at the suppressing phase?

The mean percentage reduction reached 46.8% after five consecutive pulses.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Was the optimal suppressing phase the same across all patients?

No, the specific phase bins leading to maximum suppression and amplification were patient-specific.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What was the minimum phase difference between a patient's maximum suppressing and maximum amplifying phase bins?

The difference between the suppressing and amplifying phases was always at least 90 degrees.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How did baseline spectral beta power relate to the strength of phase-dependent suppression?

The strength of suppression was inversely correlated with baseline relative spectral beta power, meaning stronger baseline oscillations were harder to modulate.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Did cumulative phase-dependent stimulation lead to significant amplification of the beta oscillation across the group?

No, group-level beta amplification was not dependent on consecutive stimuli and did not significantly exceed surrogate levels.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How did the authors rule out the possibility that suppressing epochs just happened to start during periods of naturally high or unstable beta?

They compared the starting amplitudes and phase stability of suppressing and amplifying epochs, finding no significant differences.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What are phase slips, and when did they occur significantly more often during stimulation?

Phase slips represent discontinuities in the oscillation phase, and they occurred significantly more often within 15 ms of the second and third consecutive pulses at the suppressing phase.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What does the correlation between phase slips and amplitude reduction suggest about the mechanism of suppression?

It suggests that suppression involves stimulation-induced phase advances or delays that disrupt the ongoing neural oscillation.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How did widening the phase bin from 1/4 to 1/2 of a cycle affect cumulative phase-dependent beta amplitude modulation?

Widening the phase bin to 1/2 cycle abolished the significant cumulative suppression and amplification of beta amplitude.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What is Background Unit Activity (BUA) and what does it represent in this context?

BUA represents the synchronized spiking activity of a local population of neurons, distinct from single/multiunit activity and LFP synaptic inputs.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Did stimulating at the LFP-defined suppressing phase alter the local neuronal output (BUA)?

Yes, it significantly reduced the amplitude of beta-frequency rhythmic activity in the BUA by the fourth consecutive cycle.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What effect did phase-dependent STN stimulation have on cortical beta amplitude?

It had no significant effect on cortical beta amplitude measured by midline EEG electrodes (Fz, Cz, Pz).

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How did stimulating at the suppressing phase affect corticosubthalamic phase synchronization (PSI)?

It led to a less consistent phase alignment (decreased synchronization) between the midline EEG (cortex) and the STN LFP.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Did 20 Hz stimulation overall (regardless of phase) alter the gross average firing rate of STN units?

No, stimulation did not consistently alter the average firing rate of STN units compared to the unstimulated baseline.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What was the effect of 20 Hz stimulation on overall (non-phase-dependent) LFP beta power in the majority of patients?

In 7 of 8 patients, overall peak or wideband beta power did not change relative to total power during stimulation.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Why was the BUA signal chosen to evaluate population spiking output instead of stable single units?

Because locations with strong LFP oscillations were prioritized, meaning stable single-unit recordings were not available at all locations for the full stimulation duration.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What was the effect of varying stimulus amplitude (0.5 mA vs. 1 mA) on phase-dependent suppression?

1 mA stimulation produced stronger suppression than 0.5 mA after 1, 2, or 3 consecutive pulses, but higher amplitudes tended to show plateaued or variable effects.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How does the physiological representation of LFPs compare to BUA?

LFPs are thought to reflect synchronized synaptic inputs to a population of neurons, whereas BUA reflects the population's spiking output.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Which dorsal brain structures/pathways might have been activated by the stimulation configuration in this study?

The internal capsule, zona incerta, and fields of Forel, which contain excitatory corticosubthalamic and inhibitory pallidosubthalamic fibers.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What were the stimulation parameters used in terms of total pulse width and initial phase?

The pulses were bipolar and biphasic, with a total pulse width of 200 μs (100 μs initial negative phase and 100 μs positive phase).

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Why do the authors suggest that phase-dependent DBS could be superior to current amplitude-based closed-loop strategies?

It may use less electrical energy, limit side effects, and better preserve physiological activity at timescales relevant for coding movement.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What limitation does the "phase drifting" paradigm have for behavioral testing?

It only allowed for short (50–300 ms) epochs of phase-locked stimulation, requiring real-time active phase tracking for robust behavioral testing.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How was procedural sedation managed during the microelectrode mapping and stimulation procedure?

Procedural sedation with remifentanil was stopped before the microelectrode mapping procedure, ensuring the patients were fully awake.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What clinical rating scale was used to monitor and minimize patient stress levels due to surgical prolongation?

A verbally administered numerical rating scale was used to continuously monitor patient distress.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

What clinical criteria were required of patients regarding their response to levodopa and cognitive state?

Patients had to show significant motor improvement with levodopa (UPDRS III) and no major cognitive decline (evaluated with the Mattis Dementia Rating Scale).

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

How is Phase Synchrony Index (PSI) defined in this study?

PSI is a measure ranging from 0 to 1 that represents the stability of the phase difference between two signals, in this case cortex (EEG) and STN (LFP).

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified

Why might a patient's response to phase-dependent perturbation depend on baseline network coupling strength?

A complex network's response to perturbations depends on coupling strength and plastic changes, which vary between patients and explain the different optimal suppressing phases.

Source: Phase-Dependent Suppression of Beta Oscillations in Parkinson's Disease Patients · DOI · quote verified