HGSDPres Flashcards
Intro slide - (2)
Good morning, everyone, thank you for taking the time to listen to my presentation.
Today, I will discuss some of the results from my preliminary single-unit analysis, which demonstrate that phases of the cardiac cycle modulate the auditory cortex’s excitability.
Background - Systole and Diastole - (4)
Each cardiac cycle is composed of two primary phases: 1) systole and 2) diastole.
As a general recap, the systole phase is where the ventricles of the heart contract and eject blood onto great vessels that leave the heart.
During this period, there is increased activation of baroreceptors (stretch and pressure sensors) that sends afferent information regarding the timing and strength of each individual heartbeat
On the other hand, in the diastole phase where the ventricles relax and fill with blood, the baroreceptors are inactive
Background - Baroreceptor Hypothesis
During the 1970s, Lacey and Lacey proposed the ‘Baroreceptor Hypothesis’ which states that when the baroreceptor is most active during systole, it induces cortical inhibition (Lacey and Lacey 1978).
Background - Cardiac Afferent Signals Impact Many Functions - (7)
In congruent with the hypothesis, many studies have shown that stimuli presentation at systole (baroreceptor activity is high) than diastole (when they are quiet), significantly reduces:
Memory for emotional words
Startle response
Perception of painful stimuli
Perception of visual stimuli
Perception of tactile stimuli
Perception of auditory stimuli
Limitations, Aim and Hypothesis - (6)
There are limitations of previous research:
Firstly, majority of them are behavioral
Secondly, few have assessed neural responses but only using EEG which has although high temporal resolution but lacks temporal resolution
Thirdly, there is a lack of research comparing how systole and diastole influence auditory processing relative to other sensory modalities (e.g., visual)
Therefore, we aim to overcome these limitations by using single unit recordings (which has high spatial and temporal resolution) to examine whether the responses to sound in HG is modulated by the cardiac cycle by comparing its activity during systole and diastole.
We hypothesis that the unit responses to sound in HG will be modulated by cardiac cycle, specifically with reduced activity during systole and more increased activity during diastole.
Methods - Participants and Experimental Design - (3)
Single Units were recorded from one region of interest: Heschel’s Gyrus (HG) as well as continuous EKG recording across 10 participants, participants starting from 622 onwards till 764 whilst they underwent the basic tone mapping block.
During this block, participants were passively listening to a series of tones of varying frequencies (250 Hz to 8000 Hz), represented by the blue rectangles in the figure.
Each tone lasted for 300ms and had an inter-stimulus interval of 2 seconds
Methods - Data Analysis - (3)
Each participant underwent 300 trials of the task, with approximately 150 trials of where sound onsets occurring during systole (just right after the R peak) and 150 trials of sound onsets occurring during diastole (just before the next R peak starts) so roughly equal number of trials for each phase.
Observed the activity of single units in HG during systole and diastole after tone onset.
It’s important to note that in our analysis, we did not focus/consider on whether the responses differed based on the frequency of the tones.
Results - Units in HG More Diastole than Systole - (9)
I’m going to show a couple of examples of the outputs of my analysis
So, this the example of activity of two units in HG.
The top graphs are the raster plots that plots spikes every time the unit fires whilst bottom graphs show firing rate.
As a reminder, the graphs on the left only show the unit’s activity during systole (150 trials) whilst the middle graph shows the same unit’s activity during diastole phase (150 trials) and the graph on the right shows the same unit’s activity regardless of systole and diastole throughout the entire task (300 trials)
0 is the tone onset
As we can see here, unit 1 same unit has higher firing rate (~20 times a second) and more clustering of spikes in raster plot couple of moments after tone onset during diastole compared to same unit during systole only firing ~ 11/12 times a second and less clustering of spikes in raster plot.
Also unit 2 firing rate of 23 times a second shortly after tone onset and more clustering of spikes in raster plot compared to same unit during systole only firing around 15 times a second shortly after tone onset.
Majority of the units in HG like these two have shown to strongly respond during diastole.
Thus, these findings are aligning with my hypothesis so far.
Results - Unit More in Systole Than Diastole - (2)
Although some results align with my hypothesis , there are some units in HG that respond more strongly during systole than diastole like this one here:
As we can see that the same unit has a higher firing rate (around 78 Hz, fires 78 times per second shortly after tone onset) as compared to during the diastole phase where the unit only firing around 60 Hz (60 times a second).
Results - Summary Plot
This is the summary of my single-unit analysis showing out of the total 57 units in HG, 74% of auditory units in HG show no change in response between systole and diastole, 21% showing higher activity during diastole and only 5% of units showing higher activity during systole.
Conclusion and Next Steps - (5)
So, my conclusion of my analysis is that overall units in HG’s response to sound is modulated by phases of cardiac cycle, with most modulated (respond more strongly) during diastole than systole
This finding supports the Baroreceptor Hypothesis by Lacey and Lacey as the processing of auditory stimuli is more pronounced and stronger during diastole where there is no cortical inhibition as its during baroreceptor inactivity than systole where there is cortical inhibition due to baroreceptor activity.
The next steps of this project is to employ some sort of statistical analysis to observe whether the response to sound in HG significantly differ between systole and diastole.
Also currently working at with Hugo Critchley’s PhD Student on developing system where we could present stimuli exactly at systole or diastole while conducting the experiment would be great as more highly accurate rather than trying to offline processing of data to separating data by phase which this analysis has done which is less precise.
Also we could instead of tones, present more complex auditory stimuli such as speech or naturalistic sounds to examine the broader impact of cardiac phase on auditory perception.
How does cardiac signals reach HG? - (4)
- This question I know has not been answered yet
- I know that cardiac afferent signals during systole when active reach viscerosensory cortices like insula, amygdala and cingulate cortex through projections to brainstem and thalamus.
- So PI is may connect to HG so may receive the cardiac signal.
- But this question is yet to be answered
- What is the evidence for baroreceptor hypothesis – Bonvallet 1954 and Dworkin et al., 1994 - (2)
- Bonvallet 1954 - They did this in cats where they stimulated the carotid baroreceptors and found it induces cortical inhibition as it induces immobility as well as slow-wave activity.
- Dworkin et al., 1994 – Stimulated carotid baroreceptors where participants fitted with neck cuff and during baroreceptor stimulation (cuff is suctioned to neck during systole) and baroreceptor inhibition (cuff is loosened) – found pain ratings is reduced.
- What did Garfinkel et al., (2013) do during study finding memory for emotional words is reduced? - (2)
Mix of emotional and neutral words were presented at high speeds and the participants had to identify the two emotional words that appeared at each trial and a free recall after the experiment is ended
The memory for emotional words were less during systole than diastole – no main effect of emotion.
- How did Schulz et al., 2009 and Nyklicek et al., found startle response is reduced during systole than diastole?
- They both had participants had EMG (assess electrical activity of facial muscles) and EKG whilst startle stimuli were presented via headphones (usually bursts of whitenoise) and respond with button press as soon as they heard the sound
- What did Wilkinson et al., (2013) do showing pain sensation is reduced during systole than diastole? - (3)
THye had participants hand stimulated and asked whether they perceived stimulation as painful or not
The experiments were continuously increasing the stimulation to find the participants threshold for pain
Found pain thresholds were higher during systole than diastole.
- How did they find perception of visual stimuli reduced during systole than diastole – Salomon et al., 2016
- (2)
- Participants had to detect a visual target that randomly flashed during the trials and had to press a button whenever they detected it
- They found detection was less during systole than diastole
- How did they find perception of tactile stimulus was impacted during systole than diastole – Grund et al., 2022? - (4)
Stimuli were electrical pulses delivered via a steel wire ring electrode to left index finger
Had to say whether or not perceive electrical pulse with yes or no
Before experiment, participants familiarized with electrical finger nerve stimulated and had threshold assessment (where they could detect it 50% of the time)
Found detection of stimulus whether or not they perceived it was highest during diastole than systole.
- Is there a case where there is highest activity during systole than diastole? - (3)
Diastole is best during perception of external stimuli than systole
Some research showing that although systole is sub-optimal for external perception, it is optimal for action
e.g.., higher saccades during visual search, active information sampling, motor excitability.
- How did they find perception of auditory stimuli less during systole than diastole – Sandman 1982 - (2)
- They found sounds (tones) showed attenuated auditory evoked potentials during systole than diastole.
- The N1 component was larger during diastole than systole which reflects auditory processing than systole.
- Is the data cleaned?
- Joel has extracted the data for us so may used some techniques to reduce artifact but need to clarify
- Where are baroreceptors located?
- Aortic arch and carotid arteries
Other study ideas - (2)
- How does neuromodulation to sound change between primary (HG) and secondary auditory cortex?
- Action tasks during systole
