Advances in Neural Signal Processing
24
4. Discussion
Diagonal rhythmical bilateral movements have previously been suggested to
promote improvement in motor and cognitive functions [1, 3]. The diagonal axis
has the role of a metaphorical rule breaker in relation to the way of thinking, as suggested by the definition of “diagonal thinking” as a mixture of logical (i.e., vertical)
and creative (i.e., lateral) thinking [47]. Diagonal movements are widely used in
disciplines based on whole-body movements such as Asian martial arts (i.e., aikido,
Tai Chi, Qigong) or modern and contemporary dance.
Yet, no study that we are aware of has actually examined electrophysiological changes during diagonal movements. Consequently, in the present study, we
wanted to examine cerebral activity during diagonal arm movements in comparison
to vertical arm movements. Previous literature has suggested that diagonal movements promote neuroplasticity along frontoparietal pathways through an increase
in alpha and beta power [5]. For this reason, we focused our analysis on spectral
power changes during the actual execution of movements in the theta, alpha, and
beta bands.
Time-frequency analysis was conducted in order to observe how power in
specific frequencies changes over time during movement execution.
4.1 Theta: attention, navigation, and computation
Comparing vertical to diagonal movement, we observed an increase of theta
power during the first stage of diagonal movement over frontal electrodes, especially
over Fz. This increment of frontal theta can be explained in three interrelated ways,
including attentional effort [12, 19], navigational computation [13], and integration
of information from different brain regions [16, 17]. First, it reflects greater attentional effort required for diagonal movement. In fact, diagonal movements are more
complex and less automatic than vertical movements, and subjects must be more
focused and pay more attention in order to perform correctly the movement. Second,
it could reflect navigational computation. In both diagonal and vertical movements,
the arms swing in peripersonal space, requiring the computation of the trajectory
of both arms. However, it is only in diagonal movements that the arms go across the
sagittal body midline and reach the other peripersonal hemispace. This kind of crossing requires more complex spatial computation than during movements that do not
involve both hemispaces. Third, theta has previously been related to the integration of
different information from distant cerebral regions [17]. Other studies have suggested
that theta increase is related to a general mechanism of recall and integration of information from different domains supported by a central executive module [19, 48].
Finally, the state of focused attention on movement execution, together with the
navigational computation necessary for the performance and the external sound,
could evoke an absorption state in subjects. In fact, the role of frontal midline theta
has been previously related to meditation, internalized attention, and integration of
sensory information into executive control components of complex motor behavior
[12, 15, 49].
4.2 Alpha: internalized attention and movement
While greater theta activity was related to the diagonal movements, we observed
a biphasic modulation of alpha activity during the second part of vertical movements. Keeping in mind that each movement was composed of two parts (forward
period and comeback period), we observed a biphasic response in the comeback
period during vertical movement.
24
4. Discussion
Diagonal rhythmical bilateral movements have previously been suggested to
promote improvement in motor and cognitive functions [1, 3]. The diagonal axis
has the role of a metaphorical rule breaker in relation to the way of thinking, as suggested by the definition of “diagonal thinking” as a mixture of logical (i.e., vertical)
and creative (i.e., lateral) thinking [47]. Diagonal movements are widely used in
disciplines based on whole-body movements such as Asian martial arts (i.e., aikido,
Tai Chi, Qigong) or modern and contemporary dance.
Yet, no study that we are aware of has actually examined electrophysiological changes during diagonal movements. Consequently, in the present study, we
wanted to examine cerebral activity during diagonal arm movements in comparison
to vertical arm movements. Previous literature has suggested that diagonal movements promote neuroplasticity along frontoparietal pathways through an increase
in alpha and beta power [5]. For this reason, we focused our analysis on spectral
power changes during the actual execution of movements in the theta, alpha, and
beta bands.
Time-frequency analysis was conducted in order to observe how power in
specific frequencies changes over time during movement execution.
4.1 Theta: attention, navigation, and computation
Comparing vertical to diagonal movement, we observed an increase of theta
power during the first stage of diagonal movement over frontal electrodes, especially
over Fz. This increment of frontal theta can be explained in three interrelated ways,
including attentional effort [12, 19], navigational computation [13], and integration
of information from different brain regions [16, 17]. First, it reflects greater attentional effort required for diagonal movement. In fact, diagonal movements are more
complex and less automatic than vertical movements, and subjects must be more
focused and pay more attention in order to perform correctly the movement. Second,
it could reflect navigational computation. In both diagonal and vertical movements,
the arms swing in peripersonal space, requiring the computation of the trajectory
of both arms. However, it is only in diagonal movements that the arms go across the
sagittal body midline and reach the other peripersonal hemispace. This kind of crossing requires more complex spatial computation than during movements that do not
involve both hemispaces. Third, theta has previously been related to the integration of
different information from distant cerebral regions [17]. Other studies have suggested
that theta increase is related to a general mechanism of recall and integration of information from different domains supported by a central executive module [19, 48].
Finally, the state of focused attention on movement execution, together with the
navigational computation necessary for the performance and the external sound,
could evoke an absorption state in subjects. In fact, the role of frontal midline theta
has been previously related to meditation, internalized attention, and integration of
sensory information into executive control components of complex motor behavior
[12, 15, 49].
4.2 Alpha: internalized attention and movement
While greater theta activity was related to the diagonal movements, we observed
a biphasic modulation of alpha activity during the second part of vertical movements. Keeping in mind that each movement was composed of two parts (forward
period and comeback period), we observed a biphasic response in the comeback
period during vertical movement.