Presentations Flashcards
Intro slide - (1)
Today, I’ll be sharing my findings on the effects of low-intensity focused ultrasound on heartbeat-evoked potentials (HEPs) and heart rate variability (HRV), measured before, during, and after ultrasound stimulation.
Paradgim - (4)
The ultrasound paradigm was as follows:
5 minutes of baseline where the patient did not receive any ultrasound stimulation, and no transducer was placed.
Then there was ultrasound stimulation of the right ACC for 82 seconds and left ACC for 80 seconds
Then there was post-stimulation lasting roughly 29 minutes.
Analysis Steps and Key Terms - (8)
I extracted the EKG signal and LFP data across the entire block.
From the EKG, we detected R-peaks and measured the time between consecutive R-peaks—this is called the inter-beat interval, or IBI (point to figure).
Using these IBIs, we calculated heart rate (HR) and heart rate variability (HRV).
HRV reflects the balance between the body’s ‘fight or flight’ (sympathetic) and ‘rest and digest’ (parasympathetic) systems, which are regulated by the autonomic nervous system (ANS).
There are different ways to measure HRV. In the time domain, we used SDNN—the standard deviation of the IBIs—which gives us a measure of overall heart rate variability.
In the frequency domain, computed power spectrum density (PSD – using FFT) of the IBI time series then computed average power in the low-frequency band (0.04-0.10 Hz) and high-frequency band (0.15-0.40Hz) and computed ratio of LHF/HF ratio
LF/HF ratio, which reflects the balance between sympathetic and parasympathetic activity.
A higher ratio indicates sympathetic dominance, while a lower ratio suggests high parasympathetic dominance
We also extracted heartbeat-evoked potentials (HEPs) from the LFP data, time-locked to each R-peak.
All of these metrics—IBI, HR, SDNN, LF/HF ratio, and HEPs—were computed across the baseline, ultrasound stimulation, and post-stimulation periods.”
Results - HR - (4)
We see in terms of HR that
During baseline HR declines rapidly from 85 bpm to 70 bpm
But more importantly during stimulation periods, HR decreases ever so slightly during left and right ACC stimulation
Following 4 minutes after left ACC HR increases to 80 bpm then declines and stablises.
Results - Overall HRV (SDNN) - (3)
In terms of SDNN, however, there is a noticeable increase in SDNN (larger HRV) following right anterior cingulate cortex (ACC)stimulation, almost sky rockets.
Left ACC stimulation also appears to increase SDNN, though the effect is less pronounced compared to right-sided stimulation.
Possible interpretation since this is an excitatory US protocol that right ACC is modulated structures involved in HRV, research it is proposed its vmpfc controlling HRV, may inhibit these and this then becomes disinhibited after US stim.
Results - LF/HF Ratio - (3)
Graph on left: I took 80s of baseline period and compared to 80s of left and right US of left and right ACC
Graph of right: Whereas took 230s of baseline, 230s right after right and left ACC stim.
These both show the ratio is higher during baseline (greater than 1)than during stimulation and post meaning more sympathetic domanience during baseline and more parasympathetic (ratio less than 1) during and post stimulation periods.
Results - HEPs PI - (4)
For HEPs in terms of Posterior Insula, it’s clearly showing HEP during the baseline condition – without stimulation makes sense as PI is primary interoceptive cortex that generates HEPs which what we expected.
But interestingly, its showing HEP peaks earlier (shifting peak of HEP much earlier) than baseline during right ACC stimulation and showing sustained erp – left ACC is not showing much
But this HEP during right ACC diminishes post right ACC stimulation
But on the other hand when stimulating left ACC does not show a HEP but when you stop stimulating left ACC – post HEP appears.
Results HEP Right Amygdala - (2)
On the other hand for the amygdala, its showing stronger HEP higher erp magnitude during stimulation periods than baseline and more for left ACC stimulation than right
But the is lack of HEPs post-stimulation for both right and left ACC
Potential Things to Consider - (4)
There are some potential things to consider for the ultrasound paradigm we run on upcoming and future participants
Consider adding a sham condition where transducer placed on brain site without US or a control brain site, flipping transducer to control confounding factors
We could also increase time gap between left and right stimulations to better understand how these metrics like HRV certainly differ between left and right ACC
We could also add GSR as it’s a measure of the sympathetic nervous system and theres an idea by Craig that left is parasympathetic and right is sympathetic and we could see during stimulation and post how GSR changes
