Exploring the impact of a brief mindfulness induction on motor inhibitory control

Abstract

Inhibitory control can be divided into motor and cognitive inhibition. The current research is the first study exploring the impact of brief mindfulness training on motor inhibition, measured by a stop signal task in participants without any meditation experience. Motor inhibition performance was compared before and immediately after three different conditions; a brief mindfulness induction, a resting state and an active control session in which participants listened to their favorite music. Post-test learning effect on go-reaction times was seen for the resting and mindfulness conditions, but was absent in the music session, possibly due to emotional arousal might have led slower responses. Brief mindfulness training did not significantly alter inhibitory control, although marginal improvement in stop signal reaction time following the mindfulness induction was observed. Motor inhibition appears unresponsive to either short-term or long-term mindfulness practice. Future mindfulness studies should explore a broad spectrum of cognitive functions and populations.

Introduction

Inhibitory control of an ongoing action is critical for survival. Additionally, Moffitt et al. (2011) reported children with low self-control scores experience various socioeconomic problems later in life. While increased mindfulness may potentially result in better self-control, to date, few studies have explored its effects on motor inhibition. A potentially useful task for this is the go-stop paradigm (Heeren et al., 2009). However, this has limitations, including confounds with short-term memory and a potentially high probability of having to withhold a response. An alternative, the stop signal task (Logan, 1994), has only imperative signals, such as arrows, with stop trials differing from go signals in that the imperative signal is followed by a visible indicator as the stop signal. Performance on this task is explained by a ‘horse-race’ model that assumes that there is a competition between pre-potent go and stopping responses to reach the threshold and determining the response.

Objective

A within subject, pre-test versus post-test design was employed, with effects of brief mindfulness induction compared to effects of a well-controlled resting state and an active control in which participants listened to their favorite music. It was predicted that the participants’ speed on an imperative go-signal (Go-RT) would be faster for post-test versus pre-test due to a practice effect. The primary measure of inhibitory control, stop signal reaction time (SSRT) was predicted to be shorter in the post-test condition following brief mindfulness induction in comparison to both the resting and preferred music conditions, indicating better motor inhibition facilitated by mindfulness.

Methods

Thirty participants (13 females) were recruited from the National Central University with a mean age of 23.1 (SD = 2.2) years. None had any prior meditation experience nor any neuropsychiatric disorder or current medication. All participants gave written informed consent in accordance with the Declaration of Helsinki and all experimental procedures were approved by the Institutional Review Board of National Taiwan University, Taipei, Taiwan. The stop signal task (see Figure 1) was performed by each participant in a pre-test and a post-test for three different conditions, each on different days (Figure 2). These conditions were resting state, listening to preferred music and engagement in mindfulness induction, all 20-minute duration. Resting state involved sitting idle, the music condition involved listening to their favorite music on their cellphones and for the mindfulness condition they followed instructions presented via a Power Point file (for details see Supplementary Document (dx.doi.org/10.17504/protocols.io.74ihque)).

In go trials, a central fixation cross ‘+’ was displayed for 500 milliseconds (ms) and was followed by a blank screen for 200 ms. Next, a go stimulus was presented for 1,000 ms, to which a response is typically required, with participants responding to left arrows by pressing the ‘X’ key and to right arrows by pressing the ‘M’ key on a computer keyboard with either their left or right index fingers, respectively. Each trial was followed by a blank screen inter-trial interval for a duration between 500 ms and 1,000 ms. In stop trials, a red dot was presented as a stop signal positioned above the go stimulus location, with the presentation of these trials otherwise identical to the go trials. On trials where the stop signal was presented, participants were required to withhold their responses to the go signal.

Figure 1. Stop Signal Task.

In this within-subject design, the stop signal task was performed by each participant before and after each of three different conditions. These conditions were resting state, listening to preferred music and engagement in mindfulness induction. Each condition was ‘presented’ for 20 minutes following the pre-test on three different days. The order of the conditions was counterbalanced across participants.

Figure 2. Study Design

Results

Two participants were excluded, having RTs greater than ±3SD from the mean. Two-way repeated measures ANOVA was used for Go-RTs and SSRTs. Go-RTs showed no significant effect of condition [F(2, 54) = 0.121, p = 0.886] or condition x session interaction [F(2, 54) = 1.275, p = 0.288], but a significant effect of session [F(1, 27) = 13.150, p = 0.001]. Ad hoc pair-wise t-tests showed improvement across sessions for resting and mindfulness conditions, but not for the music condition [t(27) = 1.176, p = 0.250] (Figure 3). SSRTs showed no significant effect of condition [F(2, 54) = 0.371, p = 0.692], session [F(1, 27) = 1.385, p = 0.250], or interaction between condition and session [F(2, 54) = 0.946, p = 0.395]. Ad hoc paired-tests showed the mindfulness condition resulted in lower SSRTs that approached significance for post-test versus pre-test [t(27) = 1.868, p = 0.073] (Figure 4).

Significant improvement, likely due to a practice effect, was seen post rest and mindfulness inductions, but not following listening to preferred music (error bars = standard errors of the mean).

Figure 3. Go-RTs across conditions and sessions.

The mindfulness induction was associated with a marginal reduction in SSRT, but resting and active control (music) conditions did not show any significant change in post-test sessions (error bars = standard error of the mean).

Figure 4. SSRTs across conditions and sessions.

Discussion

Post-test Go-RTs in mindfulness and resting condition showed an expected practice effect (Ando et al., 2002). However, no such speed enhancement was seen for the preferred music condition. It is possible that the music listening may have caused emotional and physiological arousal (Rickard, 2004). Droit-Volet et al. (2013) found altered time perception due to emotional effects of music, mainly regulated by the temporal dynamics of the music. A marginal trend for slower SSRTs in the post-test session for the mindfulness condition might be linked with facilitated inhibition could be due to a lack of statistical power.

Conclusion

Consistent with a prior longitudinal study comparing mindfulness meditators and matched controls (Heeren et al., 2009), no difference in motor inhibition was observed here for the mindfulness condition compared to the two control conditions. The data obtained here are consistent with motor inhibitory control being unaffected by mindfulness, irrespective of whether engagement with the technique is long or brief. Future mindfulness studies should investigate a broader spectrum of cognitive tasks and sample populations (Jaiswal et al., 2018) to test cognitive functions and population types that might be sensitive to mindfulness interventions.