Modulating Prospective Memory in Older Adults With Non-invasive Brain Stimulation

Study Overview
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Brief Summary
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Prospective memory is the ability to remember to carry out intentions with a certain delay (e.g. remember to buy stamps when passing a postal office). Prospective memory tasks require a large degree of self-initiated retrieval and in the absence of a prompt to recall, people must 'remember to remember' by their own volition. Thus, prospective memory is a challenge - especially in old age with increasing health-related prospective memory demands. Previous studies reported links between neural activity in specific brain regions and prospective memory performance. Yet, the mere occurrence of a change in brain activity in concomitance with performance of a behavioral task is not sufficient to confirm a causal relationship between the two phenomena. Therefore, this study aims to apply non-invasive brain stimulation to facilitate or inhibit activity in different brain regions presumed to be functionally associated with prospective memory. Additional to the prospective memory tasks, the investigators will implement control tasks (i.e., attention) to assess whether stimulation will specifically enhance prospective memory performance or whether other cognitive functions will be modulated additionally. It is hypothesized that stimulation will lead to changes in prospective memory functioning. Further, the investigators expect that facilitation of attentional processes might be linked to prospective memory improvements.

Detailed Description
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This study aims to modulate neural activity in the left and right inferior frontal lobe as well as in the right superior parietal lobe via high-definition transcranial direct current stimulation (HD-tDCS) in older adults. There is evidence from functional magnetic resonance imaging (fMRI) studies that these areas are involved in prospective memory performance in younger and older adults but a causal relation between activity in these areas and responses in prospective memory tasks has not been established so far. A double blind, sham-controlled, parallel group design will be applied. Healthy older adults (n=105) will participate in two separate sessions: During the first baseline session, no stimulation is applied. For the second session, participants will then be randomly assigned to one of seven experimental groups (cathodal vs. anodal right inferior frontal lobe (rIFL); cathodal vs. anodal left inferior frontal lobe (lIFL); cathodal vs. anodal right superior parietal lobe (rSPL); or sham). Real stimulation will be applied during 20 minutes with one Milliamp (mA). In case of sham stimulation (i.e., control intervention), the electrode positions and the attachment procedures correspond to those of real tDCS but the electrical current will only be ramped up to one mA and switched off completely after 30 s of stimulation. The primary objective of this study is the modulation of prospective memory performance in a computer-based task via tDCS. Further, this study aims to clarify the role of attentional control for prospective memory performance, as both processes seem to recruit similar neural structures. Additionally, naturalistic and self-rated prospective memory performance will be assessed. It is hypothesized that stimulation of the right inferior frontal lobe will lead to changes in prospective memory performance and attentional processes. Whether cathodal or anodal stimulation will enhance performance is not clear yet, since previous fMRI studies were inconsistent about activity changes in older adults. Further, the investigators expect that anodal stimulation of the left inferior frontal cortex may lead to faster responses to prospective memory stimuli, whereas cathodal stimulation of the same area may lead to prolonged reaction times. It is hypothesized that attentional control will not be affected by stimulation of the left inferior frontal lobe. Finally, the investigators expect that anodal stimulation of the right superior parietal cortex will lead to better prospective memory and attentional control performance, whereas cathodal stimulation will have detrimental effects on both functions.

Official Title
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Modulating Prospective Memory in Older Adults With Noninvasive Brain Stimulation

Conditions
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Healthy Aging

Intervention / Treatment
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* Device: Non-invasive brain stimulation
* Device: Sham stimulation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: No cognitive impairments Fluent in German Right-handed Normal or corrected-to-normal vision Non-smokers Written informed consent Exclusion Criteria: Current/lifetime severe psychiatric or neurological disorder Metal implants in the head area Psychotropic medication Dermatosis Current/lifetime alcohol abuse Magnetisable implants

Ages Eligible for Study
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Minimum Age: 60 Years
Maximum Age: 80 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: anodal stimulation of the rIFL<br>Anodal stimulation over the right inferior frontal lobe | Device: Non-invasive brain stimulation<br>* Stimulation will be applied once per subject with one mA for 20 minutes over either the left inferior frontal lobe, the right inferior frontal lobe or the right superior parietal lobe.<br>* Other names: Soterix medical;|
| Experimental: cathodal stimulation of the rIFL<br>Cathodal stimulation over the right inferior frontal lobe | Device: Non-invasive brain stimulation<br>* Stimulation will be applied once per subject with one mA for 20 minutes over either the left inferior frontal lobe, the right inferior frontal lobe or the right superior parietal lobe.<br>* Other names: Soterix medical;|
| Experimental: anodal stimulation of the lIFL<br>Anodal stimulation over the left inferior frontal lobe | Device: Non-invasive brain stimulation<br>* Stimulation will be applied once per subject with one mA for 20 minutes over either the left inferior frontal lobe, the right inferior frontal lobe or the right superior parietal lobe.<br>* Other names: Soterix medical;|
| Experimental: cathodal stimulation of the lIFL<br>Cathodal stimulation over the left inferior frontal lobe | Device: Non-invasive brain stimulation<br>* Stimulation will be applied once per subject with one mA for 20 minutes over either the left inferior frontal lobe, the right inferior frontal lobe or the right superior parietal lobe.<br>* Other names: Soterix medical;|
| Experimental: anodal stimulation of the rSPL<br>Anodal stimulation over the right superior parietal lobe | Device: Non-invasive brain stimulation<br>* Stimulation will be applied once per subject with one mA for 20 minutes over either the left inferior frontal lobe, the right inferior frontal lobe or the right superior parietal lobe.<br>* Other names: Soterix medical;|
| Experimental: cathodal stimulation of the rSPL<br>Cathodal stimulation over the right superior parietal lobe | Device: Non-invasive brain stimulation<br>* Stimulation will be applied once per subject with one mA for 20 minutes over either the left inferior frontal lobe, the right inferior frontal lobe or the right superior parietal lobe.<br>* Other names: Soterix medical;|
| Sham Comparator: sham stimulation<br>Sham stimulation over either of the three real stimulation areas | Device: Sham stimulation<br>* The electrode positions and the attachment procedures correspond to those of real tDCS but the electrical current will only be ramped up to 1 mA and switched off completely after 30 s of stimulation.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Prospective memory performance | Assessed with a computer task. Number of correct answers given to prospective memory stimuli. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), fixed to 14 minutes | 
| Prospective memory reaction time | Assessed with a computer task. Reaction times of answers given to prospective memory stimuli. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), fixed to 14 minutes | 
| Executive controlling functioning | Assessed with a computer task (ANT - Attentional Network Task). Interference between answers given to congruent and incongruent stimuli. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), task fixed to 6 minutes | 
| Flexibility performance | Assessed with a computer task (TAP- Test of Attentional Performance). Number of correct answers. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: directly after intervention), 3 minutes | 
| Inhibition errors | Assessed with a computer task (Test of Attentional Performance). Sum of incorrect responses to no-go stimuli. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: directly after intervention), 2 minutes | 
| Divided attention misses | Assessed with a computer task (TAP - Test of Attentional Performance). Sum of missed target stimuli. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: directly after intervention), 3 minutes 30 seconds | 
| Flexibility reaction-time | Assessed with a computer task (TAP - Test of Attentional Performance). Mean/ median of reactions times of correct responses. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: directly after intervention), 3 minutes | 
| Inhibition reaction time | Assessed with a go/no-go computer task (TAP -Test of Attentional Performance). Mean/ median of reactions times to correct responses. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: directly after intervention), 2 minutes | 
| Divided attention reaction time | Assessed with a computer-based task (Test of Attentional Performance). Median reaction time of correct answers. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: directly after stimulation), 3 minutes 30 seconds | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Alerting network functioning | Assessed with a computer task (ANT - Attentional Network Task). Contrasting reaction times of answers given to stimuli with alerting cues to those without alerting cues. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), task fixed to 6 minutes | 
| Orienting network functioning | Assessed with a computer task (ANT - Attentional Network Task). Contrasting reaction times of answers given to stimuli with reliable spatial cues to those without spatial cues. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), task fixed to 6 minutes | 
| Ongoing-task performance | Assessed with a computer task. Number of correctly answered ongoing task stimuli in the course of the prospective memory task. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), fixed to 14 minutes | 
| Ongoing-task reaction time | Assessed with a computer task. Mean/median response time of correct ongoing task answers in the course of the prospective memory task. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), fixed to 14 minutes | 
| Ongoing-task intra-individual coefficient of variation | Assessed with a computer task. Variability of response times (i.e., within-person fluctuation in response latency) to ongoing task stimuli in the course of the prospective memory task. Change from baseline to intervention session, difference between intervention groups. | During both sessions (for stimulation session: during intervention), fixed to 14 minutes |