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Abstract

Hearing a groove rhythm (GR), which creates the sensation of wanting to move to the music, can also create feelings of pleasure and arousal in people, and it may enhance cognitive performance, as does exercise, by stimulating the prefrontal cortex. Here, we examined the hypothesis that GR enhances executive function (EF) by acting on the left dorsolateral prefrontal cortex (l-DLPFC) while also considering individual differences in psychological responses. Fifty-one participants underwent two conditions: 3 min of listening to GR or a white-noise metronome. Before and after listening, participants performed the Stroop task and were monitored for l-DLPFC activity with functional near-infrared spectroscopy. Our results show that GR enhanced EF and l-DLPFC activity in participants who felt a greater groove sensation and a more feeling clear-headed after listening to GR. Further, these psychological responses predict the impact of GR on l-DLPFC activity and EF, suggesting that GR enhances EF via l-DLPFC activity when the psychological response to GR is enhanced.

Introduction

A growing amount of evidence shows that physical exercise has beneficial effects on cognitive functions, especially on human executive function (EF) mainly in the prefrontal cortex (PFC). Our recent study using acute exercise with music showed that the key factor of exercise’s effect on prefrontal executive function is a positive affective response expressed the two-dimensional axis of pleasure and arousal.

Another potential stimulus which can improve EF through a positive affective response is groove rhythm (GR). GR is a musical rhythm that induces the sensation of “Wanting to move to the music” (groove sensation) accompanied by positive affective responses while listening to music. GR can be defined by the subjective score of “Wanting to move to the music” and “Good nori”. The groove sensation can be modulated by syncopation. Syncopation is a method of shifting rhythmic emphasis by manipulating the complexity of a rhythm. Rhythm with low to medium syncopation induces a higher groove sensation than does rhythm with high syncopation as evidenced by averages of mass groups in previous studies. Low-frequency components, such as the bass drum, induce entrainment of body movement and musical beat. In several previous studies, drum breaks consisting of hi-hat, snare-drum, and bass-drum sounds were used because they made it easy to control rhythmic factors, syncopation, bass sound, and tempo.

Moving the body to music is a universal phenomenon (e.g., clapping, nodding, swaying) and one of the main powers of music. Music with groove-inducing characteristics increasing in recent music popularity charts may be indicative of this. That groove music improves gait performance in Parkinson’s disease (PD) by reducing the cognitive demands of synchronizing to the beat and promoting vigorous movement shows that groove music affects the interaction between body movement and brain function. More interestingly, listening to groove music induces entrainment of body movement and musical rhythm together with positive affective responses and activates neural networks associated with motor and reward systems. Since the dopaminergic reward system projects not only to emotion-related brain areas but also to cognition-related areas such as the PFC, GR could increase prefrontal cortex (PFC) activity and lead to improved EF. However, no research has explored the effect of groove music on executive function (EF) and prefrontal activity to date. The reason for this could be that the effect of GR on EF may have large individual differences because both groove sensation and concurrent positive affective responses to groove music would have many individual differences and both responses are associated with reward system activity. Therefore, we should examine the single effects of GR on EF and its relationship with PFC activity. To examine this, consideration of the psychological responses to listening to groove rhythm (GR) as influential factors that explain individual differences and creation of an experimental model which can evaluate the effect of GR on EF and how it is related to PFC activity are necessary.

To that end, in the current study we introduce the combination of an acute experimental model that was used for the detection of exercise’s effect on cognition and prefrontal activity and a grouping analysis to explore the psychological response to GR. In our previous research, we used functional near-infrared spectroscopy (fNIRS) with the color-word-matching Stroop task (CWST), which evaluates inhibitory EF, in order to clarify the effects of an acute bout (10 min) of exercise. fNIRS is a non-invasive neuroimaging method which can monitor hemodynamic response to neural activation (neurovascular coupling) by using near-infrared light passing through tissue. Since fNIRS allows for the least restrictive measuring environment among neuroimaging modalities, it can measure regional cortical activation boosted by listening to music while minimizing possible negative environmental influences on psychological response and cognition. The CWST has been adopted in numerous neuroimaging studies including fNIRS studies, and the brain regions related with the task are well known. The DLPFC is a key region for inhibitory control of EF and responsible for CWST performance. In addition, the left hemisphere plays a key role in the processing of verbal information. Therefore, we focused on the left dorsolateral prefrontal cortex (l-DLPFC) as the region of interest (ROI). A previous study indicated that l-DLPFC activity correlated with a positive affective response and that EF changed with a single bout of exercise with music. Therefore, in the current study, the color-word-matching Stroop task (CWST) was performed before and after listening to GR while monitoring l-DLPFC activity using fNIRS. In addition to this acute model, cluster analysis using the subjective senses of both groove sensation and psychological state when listening to GR was introduced, and we tried to reveal the individual differences in the effect of listening to groove rhythm (GR) on EF and task-related l-DLPFC activity.

GR elicits groove sensation and concurrent positive affective response, but it is not known whether it enhances inhibitory executive function (EF) with dorsolateral prefrontal cortex (l-DLPFC) activity as a result. The purpose of this study is to determine whether GR enhances EF and l-DLPFC activity, focusing on individual differences in psychological responses to GR. Our working hypothesis is that GR presented as drum breaks with low to medium syncopation enhances CWST performance with task-related l-DLPFC activation. Furthermore, the effects can be remarkable in participants who experience a higher groove sensation and positive psychological state. This study will allow us to look ahead to new aspects of the effect of GR, for example a potential cumulative effect with exercise.

Results

Physical load and psychological measures

Physical load and psychological measures for each experimental condition for all participants are shown. Paired t tests were conducted over condition (WM, GR). We confirmed that there were no differences in HR between conditions. GR elicited significantly higher scores compared to WM in these items: “Good nori”, “Wanting to move to the music”, “Feeling like my body is resonating with the rhythm”, “Having fun”, “Excited”, and “Feeling clear-headed”. WM elicited significantly higher scores compared to GR in these items: “Struggling to synchronize with the beat”, “Bored”, “Wanting to stop listening”, and “Feeling discomfort”.

Discussion

The purpose of this study was to determine whether GR enhances EF and DLPFC activity, focusing on individual differences in psychological responses to GR. To achieve this purpose, the current study tested the hypothesis that GR presented as drum breaks with low to medium syncopation enhances CWST performance with task-related l-DLPFC activation, and that the effects can be remarkable in participants who show higher groove sensation and positive psychological state. To our knowledge, this study presents the first experimental evidence for the enhancing effects of GR on EF and l-DLPFC activity in only participants for whom listening to GR largely augments both groove sensation and feeling clear-headed. In addition, these psychological responses to listening to GR were shown to predict EF and l-DLPFC activity.

First, as a precondition of the experiment, we confirmed that drum breaks with a low to medium degree of syncopation (GR) induced groove sensation (e.g., “Wanting to move to the music”, “Good nori”) and positive affective response (e.g., “Having fun”, “Excited”) compared with the WM by comparing average values. This agreed with previous studies showing that drum breaks with a low to medium degree of syncopation induce higher groove sensation. To make the rhythm more interesting to listeners and to thus induce groove sensation and the related positive affective responses, a balance between expectation and violation of the rhythm is thought to be important. This is supported by the hypothesis that prediction error (deviation from predicted rhythm) is a requisite for music to activate the reward system in the brain. Since the validity of our experimental design was confirmed, we proceeded to the detection of the effect of GR on cognitive function.

Regarding EF and l-DLPFC activity, we confirmed that there was Stroop interference in both Stroop task performance and l-DLPFC activity. However, there were no significant differences between experimental conditions. One possible reason for this is extensive individual differences in psychological response to groove rhythm (GR). Thus, we conducted a sub-group analysis to consider the influences of individual differences in psychological response. Using the k-means clustering method in which “Good nori” and “Feeling clear-headed” were the variables, participants were divided into three clusters. The results show that only in participants who felt a high groove sensation and a high feeling clear-headed (“Groove-familiar” cluster), listening to GR significantly enhanced executive function (EF) and l-DLPFC activity compared to the WM condition. Conversely, GR significantly decreased EF in the participants who felt a relatively low groove sensation and a low feeling clear-headed (“Groove-unfamiliar” cluster). Furthermore, using path analysis, we detected a potential causal relationship between groove sensation, psychological state, dorsolateral prefrontal cortex (l-DLPFC) activity, and EF. The model described that groove sensation influenced both psychological state and l-DLPFC activity and that psychological state influenced EF and l-DLPFC activity. When interpreting neural activity, it should be considered together with task performance. With regard to improved task performance, neural activity may decrease, remain unchanged, or increase. A decrease or no change in neural activity despite an improvement in task performance can be interpreted as an increase in neural efficiency. Gender, task difficulty, and training are known to be influential factors of neural efficiency. On the other hand, if neural activity increases with improved task performance, it can be interpreted as an increase in neural activity to achieve higher task performance. In the present study, increased l-DLPFC neural activity was positively correlated with better color-word-matching Stroop task (CWST) performance, suggesting that the l-DLPFC neural activity led to higher EF. This interpretation has also been validated by other previous studies including our own. These results suggest that groove sensation and psychological state are important predictors, and these factors influence the effect of GR not only positively but also negatively.

The participants who were grouped in the “Groove-familiar” cluster experienced positive effects of GR on EF and l-DLPFC activity. Successful entrainment and body movement to a musical beat (rhythmic entrainment, sensorimotor synchronization) could be among the important factors for promoting the positive effects of GR. Generally, music induces positive affective responses and concurrently increases dopamine release and brain activation related to the reward system including the basal ganglia (BG), midbrain, and orbitofrontal cortex, whereas rhythmic entrainment reinforces both groove sensation and positive affective responses and recruits brain regions related to both the motor and reward systems through BG activity, which plays a key role in the connection of rhythmic entrainment and positive affective responses. That groove music recruits not only the reward system, but also the motor system indicates that the body and musical entrainment are the bases of inducing a positive affective response. In addition to recruiting the dopaminergic reward system, high-groove music also induces physiological arousal related to the noradrenergic system, which is part of the catecholamine system, inducing brain activation. A positive affective response involving the catecholamine system can trigger the enhancement of executive function (EF) and related DLPFC activity. Considering that both groove sensation and positive affective responses were together correlated with BG activity in a previous study and that the current data shows that both groove sensation and feeling clear-headed are influential factors in the effect on dorsolateral prefrontal cortex (l-DLPFC) activity and EF, we could postulate a relationship between rhythmic entrainment, psychological responses, the catecholamine system, and prefrontal function. Thus, “Groove-familiar” participants may have achieved successfully entrainment to GR, enhanced groove sensation and positive psychological states, and these psychological response may have triggered the release of neurotransmitters resulting in l-DLPFC activation and EF enhancement.

Conversely, the participants grouped in the “Low feeling clear-headed” and “Groove-unfamiliar” clusters experienced no or negative effects of GR on EF and l-DLPFC activity. One potential inhibiting factor is low beat-processing ability in those individuals. It is possible that participants who have a low beat-processing ability were forced to pay extra attention to the beat while listening to the GR. This may have resulted not only in inducing failure to become entrained, but also in reduced mental resources, which limited attention, motivation, and cognitive performance. In the current experiment, the average scores for the beat-processing ability test among participants in both the “Low feeling clear-headed” and “Groove-unfamiliar” clusters were relatively low compared to the participants in the “Groove-familiar” cluster, but not significantly so. Since the beat alignment test used in the current study was a simple battery test to evaluate beat processing ability, further studies using battery tests with a higher sensitivity are needed to detect the influence of inhibiting factors.

This study has several limitations. First, widespread individual differences in psychological responses to the rhythm were demonstrated in the current results. Various potential factors such as musical training experience, music reward sensitivity, beat processing ability, familiarity with groove music/dance, body morphology and cultural background could influence psychological responses to the rhythm. Though more than 50 students participated in the current experiment, the sample size was insufficient for conducting sub-analyses to seek the effects of these potential influential factors. Future studies should plan to compare the effects between participants grouped by these potential influential factors. Second, in the auditory stimulus, we used rhythm with a low to medium degree of syncopation as the GR stimulus and a white-noise metronome as the control stimulus. We could control tempo, but could not control the type and number of sounds. Further studies are needed to try to detect the influence of other acoustic specifications by using different patterns for the groove rhythm (GR) and control stimuli. Third, in the measurement of the brain’s neural activation, the current study focused on only cortical, specifically the l-DLPFC, activity. We should use fMRI and PET to examine brain activity in broader and deeper regions that are involved with motor, reward, and cognitive systems, their networks, and released neurotransmitters.

In conclusion, listening to a rhythm with low to medium syncopation enhanced executive function (EF) and dorsolateral prefrontal cortex (l-DLPFC) activity in only groove-familiar participants, which supports our hypothesis. These results suggest that individual differences in psychological responses to GR are one of the key factors in predicting the effects of listening to GR on prefrontal EF. This study raises the potential that GR can enhance human cognitive performance like exercise.

 

Source: nature.com, Takemune Fukuie, Kazuya Suwabe, Satoshi Kawase, Takeshi Shimizu, Genta Ochi, Ryuta Kuwamizu, Yosuke Sakairi & Hideaki Soya

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