Perceived mental effort correlates with changes in tonic arousal during attentional tasks

Abstract

Background: It has been suggested that perceived mental effort reflects changes in arousal during tasks of attention. Such changes in arousal may be tonic or phasic, and may be mediated by the locus-coeruleus norepinephrine (LC-NE) system. We hypothesized that perceived mental effort during attentional tasks would correlate with tonic changes in cortical arousal, as assessed by relative electroencephalogram (EEG) band power and theta/beta ratio, and not with phasic changes in cortical arousal, assessed by P300 amplitude and latency.

Methods: Forty-six healthy individuals completed tasks that engage the anterior and posterior attention networks (continuous performance task, go/no-go task, and cued target detection task). During completion of the three attentional tasks a continuous record of tonic and phasic arousal was taken. Cortical measures of arousal included frequency band power, theta/beta ratios over frontal and parietal cortices, and P300 amplitude and latency over parietal cortices. Peripheral measures of arousal included skin conductance responses, heart rate and heart rate variance. Participants reported their perceived mental effort during each of the three attentional tasks.

Results: First, changes in arousal were seen from rest to completion of the three attentional tasks and between the attentional tasks. Changes seen between the attentional tasks being related to the task design and the attentional network activated. Second, perceived mental effort increased when demands of the task increased and correlated with left parietal beta band power during the three tasks of attention. Third, increased mental effort during the go/no-go task and the cued target detection task was inversely related to theta/beta ratios.

Conclusion: These results indicate that perceived mental effort reflects tonic rather than phasic changes in arousal during tasks of attention. We suggest that perceived mental effort may reflect in part tonic activity of the LC-NE system in healthy individuals.

Figure 1

Relative EEG band power during stages of the testing session. Relative EEG band power during various stages of the testing session: resting eyes open (REO), continuous performance task (CPT), go/no-go task (GNG), and cued target detection task (CTD). Relative band power reported: theta (θ, 4-7 Hz), alpha (α, 7-14 Hz), and beta (β, 15-30 Hz) for frontal (F3 & F4) and parietal (P3 & P4) electrodes. a) *Left frontal (F3) α band power was higher during REO and GNG than CPT and CTD. ^@β band power was higher during CTD than REO, CPT, and GNG. b) *Right frontal (F4) α band power was higher during REO than CPT and CTD. ^#α band power was higher during GNG than CTD. ^@β band power was higher during CTD than CPT and GNG. c) *Left parietal (P3) θ band power was lower during REO than CPT and CTD. ^#β band power was lower during GNG than REO, CPT, and CTD. d) *Right parietal (P4) θ band power was lower during REO than CPT and CTD. ^#α band power was higher during REO and GNG than during CTD (p < 0.0125, n = 46, mean ± SEM).

Figure 2

Relative theta/beta (θ/β) ratio for frontal (F3 & F4) and parietal (P3 & P4) electrodes for the stages of the testing session. Relative theta/beta (θ/β) ratio for frontal (F3 & F4) and parietal (P3 & P4) electrodes for the various stages of the testing session: resting eyes open (REO), continuous performance task (CPT), go/no-go task (GNG), and cued target detection task (CTD). *θ/β ratio for F3 and F4 was greater during GNG than during CTD (p < 0.0125, n = 46, mean ± SEM).

Figure 3

Grand mean event-related potentials (ERPs) for parietal electrodes (P3 and P4) during the three attentional tasks. Grand mean event-related potentials (ERPs) for parietal electrodes (P3 and P4) during the three attentional tasks: continuous performance task (CPT), go/no-go task (go and no-go conditions; GNG), and cued target detection task (CTD).

Figure 4

Latency and amplitude of the event-related potentials (ERPs) of parietal electrodes (P3 & P4) during the three attentional tasks. Latency and amplitude of the event-related potentials (ERPs) of parietal electrodes (P3 & P4) during the three attentional tasks: continuous performance task (CPT), go/no-go task (go and no-go conditions; GNG), and cued target detection task (CTD). a) For left parietal P300 latency the *CPT was shorter than GNG and CTD, ^#GNG go condition P300 latency was shorter than GNG no-go condition and CTD ^@GNG no-go condition P300 latency was shorter than CTD b) For right parietal P300 latency the *CPT was shorter than GNG and CTD, ^#GNG go condition P300 latency was shorter than GNG no-go condition and CTD. ^@GNG no-go condition P300 latency was shorter than CTD. c) For left parietal P300 amplitude the *CPT and GNG go condition were smaller than GNG no-go condition and greater than CTD. The ^#GNG no-go condition P300 amplitude was greater than CTD. d) The right parietal P300 amplitude *CPT and GNG go condition was smaller than GNG no-go condition and was greater than CTD. The ^#GNG no-go condition P300 amplitude was greater than CTD.

Figure 5

Skin conductance responses and their duration during stages of the testing session. a) Skin conductance responses recorded during resting eyes open (REO), continuous performance task (CPT), go/no-go task (GNG), and cued target detection task (CTD). *The number of skin conductance responses during REO were fewer than at all other stages. ^#CPT responses were fewer than responses made during the GNG and greater than responses made during the CTD. ^@GNG responses were greater than during the CTD. b) Duration of skin conductance responses. *The duration of responses during REO was shorter than at all other stages. ^#CPT duration of response was shorter than the duration of responses during the GNG and CTD (p < 0.0125, n = 46, mean ± SEM).

Figure 6

Heart rate and heart rate variance parameters during stages of the testing session. a) Heart rate and heart rate variance parameters during: resting eyes open (REO), continuous performance task (CPT), go/no-go task (GNG), and cued target detection task (CTD). *Heart rate during REO was lower than during CPT, GNG, and CTD tasks (p < 0.0125, n = 46, mean ± SEM). ^#Heart rate during GNG was higher than during the CTD task (p < 0.0125, n = 46, mean ± SEM), b) *The high frequency range during REO was greater than during the GNG task (p < 0.0125, n = 46, mean ± SEM). c) No differences were found in the low frequency range. d) No differences were found in the low frequency/high frequency ratio of heart rate variance parameters.

Figure 7

Perceived mental effort during the three attentional tasks. a) Perceived mental effort during the three attentional tasks: continuous performance task (CPT), go/no-go task (GNG), and cued target detection task (CTD). *Perceived mental effort was higher during the GNG task than during the CPT and the CTD. b) Strong positive correlations were observed between perceived mental effort during the three attentional tasks (p < 0.01667, n = 46, mean ± SEM).