Heart Rate Variability and Emotion Regulation

Not Applicable

Terminated

Conditions: Heart Rate Variability

Interventions: Behavioral: HRV training

Registration Number: NCT03458910

Lead Sponsor: University of Southern California

Brief Summary: Previous research suggests that heart rate variability (HRV) biofeedback aimed at increasing HRV can reduce anxiety and stress. However, some mental quiescence practices that reduce HRV during the practice sessions also lead to positive emotional outcomes. Thus, it is not obvious that the benefits of HRV-biofeedback accrue due to increasing HRV during the session. An alternative possibility is that the benefits arise from engaging prefrontal control over heart rate. In this study, the investigators will test two possible mechanisms of the effects of HRV on emotional health by comparing two groups. In one group, participants will be asked to engage in daily training to decrease HRV using the HRV biofeedback device. In the other group, participants will be asked to engage in daily training to increase HRV using the HRV biofeedback device. This will allow analyses to pit two possible mechanisms against each other:

1. Mechanism 1: engaging prefrontal control over heart rate is the critical factor that allows HRV biofeedback to help improve well-being. In this case, well-being should increase over time in both groups, as both training should engage prefrontal cortex to implement self-directed control over heart rate. Strengthening prefrontal control mechanisms may help improve emotion regulation in everyday life.

2. Mechanism 2: increased HRV during the training sessions leads to greater functional connectivity among brain regions associated with emotion regulation during the high HRV state. In this case, improved well-being would be specifically associated with having time each day during which there were very high HRV states, and so improved well-being should be seen only in the group in which participants get biofeedback to increase HRV.

Detailed Description: Not available

Recruitment & Eligibility

Status: TERMINATED

Sex: All

Target Recruitment: 193

Inclusion Criteria

Fluent in English
Aged between 18-35 for the younger group and aged between 55-80 for the older group
Scores on TELE indicate no current dementia
Normal or corrected-to-normal vision and hearing
People taking antidepressant, anti-anxiety medication and/or attending psychotherapy only if the treatment had been ongoing and unchanged for at least three months

Exclusion Criteria

Have a disorder that would impede performing the HRV biofeedback procedures (i.e., abnormal cardiac rhythm, heart disease including coronary artery disease, angina, and arrhythmia, cardiac pacemaker, stroke, panic attack, cognitive impairment).
Current practice of any relaxation, biofeedback, or breathing technique.
Currently taking any psychoactive drugs other than antidepressants or anti-anxiety medications
No trips that would lead them to miss any of the weekly meetings
Currently nursing, pregnant, or intend to become pregnant
Have metals in their body, as this is a scanning requirement
Have any conditions listed in the MRI Screening form (see below)

MRI screening

Cardiac pacemaker
Implanted cardiac defibrillator
Aneurysm clip or brain clip
Carotid artery vascular clamp
Neurostimulator
Insulin or infusion pump
Spinal fusion stimulator
Cochlear, otologic, ear tubes or ear implant
Prosthesis (eye/orbital, penile, etc.)
Implant held in place by a magnet
Heart valve prosthesis
Artificial limb or joint
Other implants in body or head
Electrodes (on body, head or brain)
Intravascular stents, filters, or
Shunt (spinal or intraventricular)
Vascular access port or catheters
IUD or diaphragm
Transdermal delivery system or other types of foil
patches (e.g. Nitro, Nicotine, Birth control, etc.)
Shrapnel, buckshot, or bullets
Tattooed eyeliner or eyebrows
Body piercing(s)
Metal fragments (eye, head, ear, skin)
Internal pacing wires
Aortic clips
Metal or wire mesh implants
Wire sutures or surgical staples
Harrington rods (spine)
Bone/joint pin, screw, nail, wire, plate
Wig, toupee, or hair implants
Asthma or breathing disorders
Seizures or motion disorders
Hospitalization for mental or neurological illness
Head Trauma
Migraine Headache
Panic attack
Stroke

Study & Design

Study Type: INTERVENTIONAL

Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
HRV-decrease group	HRV training	Half of the participants will be randomly assigned to this group who will undergo daily practice to decrease their HRV and heart rate.
HRV-increase group	HRV training	Half of the participants will be randomly assigned to this group who will undergo daily practice to increase their heart rate variability (HRV).

Primary Outcome Measures

Name	Time	Method
mPFC-right Amygdala Resting-state Functional Connectivity for Younger Adults (ANOVA)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity was measured by correlation coefficients. Values represent the correlation of BOLD time-series between mPFC and the right amygdala. Higher values indicate greater connectivity.
mPFC-right Amygdala Resting-state Functional Connectivity for Older Adults (ANOVA)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity was measured by correlation coefficients. Values represent the correlation of BOLD time-series between mPFC and the right amygdala. Higher values indicate greater connectivity.
mPFC-right Amygdala Resting-state Functional Connectivity for Younger Adults (Post-Pre)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity between mPFC and the right amygdala was measured by correlation coefficients. The difference in functional connectivity between the two time points (Time 2 - Time 1) was calculated. Higher values indicate greater connectivity at Time 2 than Time 1 (or post- than pre-intervention).
mPFC-right Amygdala Resting-state Functional Connectivity for Older Adults (Post-Pre)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity between mPFC and the right amygdala was measured by correlation coefficients. The difference in functional connectivity between the two time points (Time 2 - Time 1) was calculated. Higher values indicate greater connectivity at Time 2 than Time 1 (or post- than pre-intervention).

Secondary Outcome Measures

Name	Time	Method
Emotion Regulation in Younger Adults (Behavior)	Time 1 (Baseline), Time 2 (5 weeks)	Emotional intensity ratings, which participants reported during the emotion regulation task inside MRI scanner before and after intervention. The ratings ranged from 1 through 4, and 4 represents strongest intensity.
Emotion Regulation in Older Adults (Behavior)	Time 1 (Baseline), Time 2 (5 weeks)	Emotional intensity ratings, which participants reported during the emotion regulation task inside MRI scanner before and after intervention. The ratings ranged from 1 through 4, and 4 represents strongest intensity.
Left Amygdala BOLD Activity During Emotion Regulation in Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	We measured percent changes (%) in BOLD activity in the left amygdala region during emotion down-regulation, viewing, and up-regulation before and after intervention. The viewing condition was used as a baseline during the task. The change is represented by %.
Left Amygdala BOLD Activity During Emotion Regulation in Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	We measured percent changes (%) in BOLD activity in the left amygdala region during emotion down-regulation, viewing, and up-regulation before and after intervention. The viewing condition was used as a baseline during the task. The change is represented by %.
Right Amygdala BOLD Activity During Emotion Regulation in Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	We measured percent changes (%) in BOLD activity in the right amygdala region during emotion down-regulation, viewing, and up-regulation before and after intervention. The viewing condition was used as a baseline during the task. The change is represented by %.
Right Amygdala BOLD Activity During Emotion Regulation in Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	We measured percent changes (%) in BOLD activity in the right amygdala region during emotion down-regulation, viewing, and up-regulation before and after intervention. The viewing condition was used as a baseline during the task. The change is represented by %.
Plasma Total Tau (tTau) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma tTau levels at pre- and post-intervention will be reported for HRV-increase and HRV-decrease group for younger adults.
Plasma Total Tau (tTau) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma tTau levels at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for older adults.
LC-innervated-sub Region Volume in Hippocampus for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	LC-innervated-sub region volume in hippocampus at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for younger adults .
LC-innervated-sub Region Volume in Hippocampus for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	LC-innervated-sub region volume in hippocampus at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for older adults.
Cortical Volume in Left Orbitofrontal Cortex or Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Left orbitofrontal volume at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for younger adults.
Cortical Volume in Left Orbitofrontal Cortex for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Left orbitofrontal volume at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for older adults.
Cortical Volume in Right Orbitofrontal Cortex for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Right orbitofrontal volume at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for younger adults.
Cortical Volume in Right Orbitofrontal Cortex for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Right orbitofrontal volume at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for older adults.
mPFC-left Amygdala Resting-state Functional Connectivity for Younger Adults (Post-Pre)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity between mPFC and the left amygdala was measured by correlation coefficients. The difference in functional connectivity between the two time points (Time 2 - Time 1) was calculated. Higher values indicate greater connectivity at Time 2 than Time 1 (or post- than pre-intervention).
Plasma Phosphorylated Tau 181 (pTau) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma pTau levels at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for older adults.
Decision-making for Younger Adults at Post Intervention (Behavior)	one time point: at study completion, which is the end of 5-week training	The decision-making ability was measured by multiple-choice responses during a computer-based task. Median percentage of acceptance of unfair offers and fair offers were calculated. A higher percentage of accepted both unfair and fair offers points toward more rational decision-making and likely better emotion regulation. This task was administered only at post-intervention (but not pre-intervention).
Decision-making for Younger Adults (fMRI)	one time point: at study completion, which is the end of 5-week training	We measured percent changes (%) in BOLD activity in the dorsal anterior cingulate cortex and anterior insula during a computer-based decision-making task. Higher values indicate greater activity.
Mood for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the Profile of Mood States (POMS) for younger adults. The POMS consists of 40 items that are rated on a 5-point scale ranging from "0=not at all" to "4=extremely. Total Mood Disturbance (TMD) is calculated by summing the totals for the negative items and then subtracting the totals for the positive items. A constant (i.e., 100) is added to the TMD formula in order to eliminate negative scores. Higher scores indicate more negative mood states. The scores range from 56 and 216.
Depression for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the Center for Epidemiological Studies Depression Scale (CES-D) for younger adults. The CES-D consists of 20 items that are rated on a scale of 0 to 3 (0 = Rarely or None of the Time, 1 = Some or Little of the Time, 2 = Moderately or Much of the time, 3 = Most or Almost All the Time). Possible range of scores is 0 to 60, with the higher scores indicating more depressive symptoms.
State Anxiety for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the State Anxiety Inventory (SAI) for older adults. The SAI consists of 20 items that are rated on a 4-point scale as follows: 1) not at all, 2) somewhat, 3) moderately so, and 4) very much so. Scores range from 20 to 80, with higher scores indicating greater state anxiety.
Mood for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the Profile of Mood States (POMS) for older adults. The POMS consists of 40 items that are rated on a 5-point scale ranging from "0=not at all" to "4=extremely. Total Mood Disturbance (TMD) is calculated by summing the totals for the negative items and then subtracting the totals for the positive items. A constant (i.e., 100) is added to the TMD formula in order to eliminate negative scores. Higher scores indicate more negative mood states. The scores range from 56 and 216.
Depression for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the Center for Epidemiological Studies Depression Scale (CES-D) for older adults. The CES-D consists of 20 items that are rated on a scale of 0 to 3 (0 = Rarely or None of the Time, 1 = Some or Little of the Time, 2 = Moderately or Much of the time, 3 = Most or Almost All the Time). Possible range of scores is 0 to 60, with the higher scores indicating more depressive symptoms.
State Anxiety for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the State Anxiety Inventory (SAI) for younger adults. The SAI consists of 20 items that are rated on a 4-point scale as follows: 1) not at all, 2) somewhat, 3) moderately so, and 4) very much so. Scores range from 20 to 80, with higher scores indicating greater state anxiety.
Trait Anxiety for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the Trait Anxiety Inventory (TAI) for older adults. The TAI consists of 20 items that are rated on a 4-point scale as follows: 1) not at all, 2) somewhat, 3) moderately so, and 4) very much so. Scores range from 20 to 80, with higher scores indicating greater trait anxiety.
Trait Anxiety for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Emotional well-being measured by the Trait Anxiety Inventory (TAI) for younger adults. The TAI consists of 20 items that are rated on a 4-point scale as follows: 1) not at all, 2) somewhat, 3) moderately so, and 4) very much so. Scores range from 20 to 80, with higher scores indicating greater trait anxiety.
Stress Recovery (Systolic Blood Pressure) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress recovery elicited by standard cognitive tasks, as assessed by change in systolic blood pressure from cognitive tasks to recovery rest
Stress Recovery (Systolic Blood Pressure) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress recovery elicited by standard cognitive tasks, as assessed by change in systolic blood pressure from cognitive tasks to recovery rest
Stress Recovery (Heart Rate) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress recovery elicited by standard cognitive tasks, as assessed by change in heart rate from cognitive tasks to recovery rest
Stress Recovery (Heart Rate) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress recovery elicited by standard cognitive tasks, as assessed by change in heart rate from cognitive tasks to recovery rest
Stress Recovery (Breathing Rate) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress recovery elicited by standard cognitive tasks, as assessed by change in breathing rate from cognitive tasks to recovery rest
Stress Reactivity (Systolic Blood Pressure) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress reactivity elicited by standard cognitive tasks, as assessed by change in systolic blood pressure from rest to cognitive tasks
Stress Reactivity (Systolic Blood Pressure) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress reactivity elicited by standard cognitive tasks, as assessed by change in systolic blood pressure from rest to cognitive tasks
Stress Recovery (Breathing Rate) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress recovery elicited by standard cognitive tasks, as assessed by change in breathing rate from cognitive tasks to recovery rest
Stress Reactivity (Heart Rate) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress reactivity elicited by standard cognitive tasks, as assessed by change in heart rate from rest to cognitive tasks
Stress Reactivity (Heart Rate) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress reactivity elicited by standard cognitive tasks, as assessed by change in heart rate from cognitive tasks to recovery rest
Stress Reactivity (Breathing Rate) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress reactivity elicited by standard cognitive tasks, as assessed by change in breathing rate from rest to cognitive tasks
Stress Reactivity (Breathing Rate) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Difference in stress reactivity elicited by standard cognitive tasks, as assessed by change in breathing rate from rest to cognitive tasks
Arterial Spin Labeling (ASL) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Cerebral blood flow was measured at pre-training resting state and post-training paced-breathing.
Arterial Spin Labeling (ASL) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Cerebral blood flow was measured at pre-training resting state and post-training paced-breathing.
High Frequency (HF) HRV for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	HRV measured by high frequency (HF) HRV for younger adults. HF-HRV is quantified as the spectral power of interbeat interval variability within the high frequency range (typically 0.15-0.40 Hz), which reflects parasympathetic (vagal) activity. In this study, HF-HRV was obtained using photoplethysmography (PPG) methods. During a standardized resting condition, the device continuously records interbeat intervals. These data are then processed via spectral analysis to calculate the power in the high frequency band. Measurements are expressed in units of milliseconds squared (ms²). Higher HF-HRV values indicate increased parasympathetic modulation and are generally associated with improved autonomic regulation and better cognitive performance.
High Frequency (HF) HRV for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	HRV measured by high frequency (HF) HRV for older adults. HF-HRV is quantified as the spectral power of interbeat interval variability within the high frequency range (typically 0.15-0.40 Hz), which reflects parasympathetic (vagal) activity. In this study, HF-HRV was obtained using photoplethysmography (PPG) methods. During a standardized resting condition, the device continuously records interbeat intervals. These data are then processed via spectral analysis to calculate the power in the high frequency band. Measurements are expressed in units of milliseconds squared (ms²). Higher HF-HRV values indicate increased parasympathetic modulation and are generally associated with improved autonomic regulation and better cognitive performance.
Plasma Amyloid Beta 42 (Aβ42) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma Aβ42 levels at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for older adults.
Plasma Phosphorylated Tau 181 (pTau) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma pTau levels at pre- and post-intervention will be reported for HRV-increase and HRV-decrease group for younger adults.
Low Frequency (LF) HRV for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	HRV measured by low frequency (LF) HRV for younger adults. LF-HRV is quantified as the spectral power of interbeat interval variability within the low frequency range (typically 0.04-0.15 Hz), which reflects the combined influences of sympathetic and parasympathetic activity. In this study, LF-HRV was obtained using photoplethysmography (PPG) methods. During a standardized resting condition, the device continuously records interbeat intervals. These data are then processed via spectral analysis to calculate the power in the low frequency band. Measurements are expressed in units of milliseconds squared (ms²). Although LF-HRV reflects contributions from both branches of the autonomic nervous system, higher LF-HRV values can indicate enhanced autonomic modulation, with interpretation made in the context of overall autonomic balance.
Low Frequency (LF) HRV for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	HRV measured by low frequency (LF) HRV for older adults. LF-HRV is quantified as the spectral power of interbeat interval variability within the low frequency range (typically 0.04-0.15 Hz), which reflects the combined influences of sympathetic and parasympathetic activity. In this study, LF-HRV was obtained using photoplethysmography (PPG) methods. During a standardized resting condition, the device continuously records interbeat intervals. These data are then processed via spectral analysis to calculate the power in the low frequency band. Measurements are expressed in units of milliseconds squared (ms²). Although LF-HRV reflects contributions from both branches of the autonomic nervous system, higher LF-HRV values can indicate enhanced autonomic modulation, with interpretation made in the context of overall autonomic balance.
The Root Mean Squared Successive Differences (RMSSD) HRV for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	HRV measured by the root mean square of successive differences (RMSSD) for younger adults. RMSSD (Root Mean Square of Successive Differences) is a time-domain measure that quantifies the variability between successive interbeat intervals, primarily reflecting parasympathetic (vagal) activity. In this study, RMSSD was obtained using photoplethysmography (PPG) methods. During a standardized resting condition, the device continuously records interbeat intervals, and RMSSD is computed as the square root of the mean of the squared differences between consecutive interbeat intervals. Measurements are expressed in milliseconds (ms). Higher RMSSD values indicate increased parasympathetic modulation, generally associated with improved autonomic regulation and better cardiovascular and cognitive performance.
The Root Mean Squared Successive Differences (RMSSD) HRV for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	HRV measured by the root mean square of successive differences (RMSSD) for older adults. RMSSD (Root Mean Square of Successive Differences) is a time-domain measure that quantifies the variability between successive interbeat intervals, primarily reflecting parasympathetic (vagal) activity. In this study, RMSSD was obtained using photoplethysmography (PPG) methods. During a standardized resting condition, the device continuously records interbeat intervals, and RMSSD is computed as the square root of the mean of the squared differences between consecutive interbeat intervals. Measurements are expressed in milliseconds (ms). Higher RMSSD values indicate increased parasympathetic modulation, generally associated with improved autonomic regulation and better cardiovascular and cognitive performance.
Inflammation Measured by C-reactive Protein for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary C-reactive protein (CRP) for younger adults
Inflammation Measured by C-reactive Protein for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary C-reactive protein (CRP) for older adults
Inflammation Measured by IL-1b Levels for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary IL-1b levels for younger adults
Inflammation Measured by IL-1b Levels for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary IL-1b levels for older adults
Inflammation Measured by IL-6 Levels for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary IL-6 levels for younger adults
Inflammation Measured by IL-6 Levels for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary IL-6 levels for older adults
Inflammation Measured by IL-8 Levels for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary IL-8 levels for younger adults
Inflammation Measured by IL-8 Levels for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary IL-8 levels for older adults
Inflammation Measured by TNF-a Levels for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary TNF-a levels for younger adults
Inflammation Measured by TNF-a Levels for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Inflammation measured by salivary TNF-a levels for older adults
Plasma Amyloid Beta 40 (Aβ40) for Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma Aβ40 levels at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for younger adults.
Plasma Amyloid Beta 40 (Aβ40) for Older Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma Aβ40 levels at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for older adults.
Plasma Amyloid Beta 42 (Aβ42) Younger Adults	Time 1 (Baseline), Time 2 (5 weeks)	Plasma Aβ42 levels at pre- and post-intervention will be compared between HRV-increase and HRV-decrease group for younger adults.
mPFC-left Amygdala Resting-state Functional Connectivity for Older Adults (Post-Pre)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity between mPFC and the left amygdala was measured by correlation coefficients. The difference in functional connectivity between the two time points (Time 2 - Time 1) was calculated. Higher values indicate greater connectivity at Time 2 than Time 1 (or post- than pre-intervention).
mPFC-left Amygdala Resting-state Functional Connectivity for Younger Adults (ANOVA)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity was measured by correlation coefficients. Values represent the correlation of BOLD time-series between mPFC and the left amygdala. Higher values indicate greater connectivity.
mPFC-left Amygdala Resting-state Functional Connectivity for Older Adults (ANOVA)	Time 1 (Baseline), Time 2 (5 weeks)	The strength of resting-state functional connectivity was measured by correlation coefficients. Values represent the correlation of BOLD time-series between mPFC and the left amygdala. Higher values indicate greater connectivity.