Practice improves older adults' attentional control and prospective memory more than HD-tDCS: a randomized controlled trial

Abstract

Frontal and parietal brain regions are involved in attentional control and prospective memory. It is debated, however, whether increased or decreased activity in those regions is beneficial for older adults' task performance. We therefore aimed to systematically modulate activity in those regions using high-definition transcranial direct current stimulation. We included n = 106 healthy adults (60-75 years old, 58% female) in a randomized, double-blind, and sham-controlled study. We evaluated task performance twice in the laboratory and at home and additionally assessed heart rates. Participants received cathodal, anodal, or sham stimulation of the left or right inferior frontal lobe, or the right superior parietal lobe (1 mA for 20 min). Performance improved at visit two in laboratory tasks but declined in at-home tasks. Stimulation did not modulate performance change in laboratory tasks but prevented decline in at home-tasks. Heart rates increased at visit two but only when right inferior frontal lobe activity was inhibited. Repeating a task seems more beneficial than stimulation for laboratory tasks. This might be different for at-home tasks. Inhibiting right frontal brain function increases heart rates, possibly due to a modulation of the frontal-vagal brain-heart axis.

Keywords: Ageing; Brain-heart axis; Cognitive control; Delayed intentions; Non-invasive brain stimulation.

Fig. 1

Participant flow diagram. Flow diagram of the progress through the phases of a 2-group parallel randomized controlled trial.

Fig. 2

Electrode positions and simulations of current flow through the brain. Electrodes were mounted over the right inferior frontal lobe (FC6; A), the left inferior frontal lobe (FC5; B), or the right superior parietal lobe (P4; C). Positive values (red) indicate an expected increase, negative values (blue) an expected decrease in excitability of neurons. Simulations were created with SimNIBS (version 3.2.6¹⁰⁰). Note: From Schmidt et al.. CC BY-NC.

Fig. 3

Change (visit two minus visit one) in older adults’ naturalistic prospective memory with frontal or parietal transcranial direct current stimulation or sham. Electrodes were mounted over the right inferior frontal lobe (FC6), the left inferior frontal lobe (FC5), or the right superior parietal lobe (P4). Positive values indicate an improvement, negative values indicate worsening of performance.

Fig. 4

Change in heart rate (beats per minute, bpm) between beginning and end of visit two in older adults receiving frontal or parietal high-definition transcranial direct current stimulation or sham. Electrodes were mounted over the right inferior frontal lobe (FC6), the left inferior frontal lobe (FC5), or the right superior parietal lobe (P4). Positive values indicate an increased heart rate at the end of visit two, negative values indicate a reduced heart rate.