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Title: The influence of attention on kinesthetic and visual motor imagery: combined results from transcranial magnetic stimulation and eye movement registration
Authors: Ceux, Tanja
Herrygers, Hilde
Hannes, Dennis
Heremans, Elke
Feys, Peter
Buekers, Mart
Helsen, Werner
Wenderoth, Nicole #
Issue Date: 28-Oct-2009
Conference: ACAPS edition:13 location:Lyon date:28-30 October 2009
Abstract: The influence of attention on kinesthetic and visual motor imagery: combined results from transcranial magnetic stimulation and eye movement registration.

Tanja Ceux1, Hilde Herrygers1, Dennis Hannes1, Elke Heremans1, Peter Feys1,2, Mart Buekers1, Werner Helsen1 & Nici Wenderoth1
1Department of Biomedical Kinesiology, Katholieke Universiteit Leuven, Belgium
2REVAL research institute, PHL/UHasselt
Tanja.Ceux@faber.kuleuven.be

The present study combines two different approaches to quantify motor imagery by means of transcranial magnetic stimulation (TMS) and the registration of eye movements (electro-oculography). We wanted to explore the difference between kinesthetic and visual motor imagery while imagine performing a unimanual task with a specific spatial and temporal component. The role of attention was implemented as an additional research question.
Key words: Kinesthetic motor imagery, Visual motor imagery, Transcranial magnetic stimulation, Electro-oculography (EOG), Dual task.

Introduction
Motor imagery can be defined as a dynamic state during which a representation of a given motor act is internally rehearsed in working memory without any overt motor output (Decety and Grezes, 1999). This concept became important for improving motor performance in the sport context, but also for rehabilitation of neurological disorders such as stroke. Motor imagery strategies can be divided into kinesthetic motor imagery and visual motor imagery (Hall et al., 1985). Kinesthetic motor imagery involves that the subject imagines the feeling of performing a movement (i.e., the somatosensory representation), while during visual motor imagery the subject imagines seeing himself performing a task (i.e., the visual representation). Stinear et al. (2006) demonstrated that only kinesthetic but not visual motor imagery of a phasic thumb movement facilitated corticomotor excitability above resting levels. It is important to note, however, that the spatial component of this thumb tapping task was rather limited. In the present study we compared kinesthetic versus visual imagery of a unimanual task involving the grasping, lifting and placing of an object. In particular, we were interested in the explicit contribution of attention during motor imagery. Therefore, both types of motor imagery were executed either alone or in combination with an auditory dual task. The effect of motor imagery was quantified by changes in corticomotor excitability as measured by TMS (Stinear & Byblow, 2003) as well as by electro-oculography (EOG) measuring eye movements (Heremans et al., 2008).

Methods
Fourteen right-handed volunteers participated in this study. Subjects were seated comfortably on a chair with their right hand resting on a table in front of them. Surface electromyography (EMG) was recorded from their right abductor pollicis brevis (APB) and first dorsal interosseus (FDI) following standard skin preparation techniques. Single pulse transcranial magnetic stimuli were delivered using a MagStim stimulator 200 (MagStim Company, Dyfed, UK), via a figure-of-eight coil. The coil was positioned over the left motor cortex, at the optimal site of producing responses in the resting APB muscle (test stimulus intensity of 130% rMT). Horizontal and vertical movements of the right eye were quantified by the electro-oculographic signal as measured by means of a Porti 7 device (Twente Medical Systems International, Enschede, the Netherlands) with a sample frequency of 1024 Hz. Subjects had to close the eyes but did not receive any instruction about making eye movements. For the motor imagery task, a computer voice instructed the subject to (1) be ready, (2) grasp an object and (3) place it either at a left or right target, 30 cm away from the start position. The cognitive dual task consisted of two short sequences of rhythmic tones which were either identical or different and had to be discriminated by the subject. This result was reported to the test leader after each trial. The participants had to perform six randomly presented experimental conditions consisting of three motor imagery conditions (Rest, KinImag and VisImag) each performed with and without a dual task (Single, Dual). Mean peak to peak amplitudes (mV) in APB and FDI were determined for each subject under each experimental task condition. Surprisingly, subjects exhibited different behavior such that half of them exhibited higher corticomotor responses for the kinesthetic than the visual imagery condition, whereas the other half exhibited the reverse relation. Therefore, subjects were divided in two subgroups (Kinesthetic, Visual) based on their results on the kinesthetic and visual motor imagery conditions. A repeated measures analysis of variance (ANOVA) was conducted to explore the effect of Group (KinGroup, VisGroup), Muscle (APB, FDI), Imagery condition (Rest, KinImag, VisImag) and Dual task (Single, Dual).

Results
Preliminary analyses revealed that corticomotor excitability was significantly increased during Kinesthetic as well as Visual Imagery as compared to Rest (p < 0.05). Moreover, a significant Group x Imagery x Dual task interaction was found (F(2,24) = 4.33; p = 0.02). In the Single task condition, MEP amplitudes were significantly higher in the Visual Imagery than the Kinesthetic Imagery condition for the Visual Group and in the Kinesthetic Imagery than Visual Imagery condition for the Kinesthetic Group. However, in the Dual task condition, this difference between the preferred and non-preferred Imagery conditions disappeared. Additional analyses revealed that the lack of imagery specific differences in MEP amplitudes did not result from a ceiling effect of corticomotor excitability. Additionally, eye movements occurred regularly when the imagery conditions were executed as a Single task, but were less frequent in the Dual task condition.

Conclusion
Our results indicated that both visual and kinesthetic motor imagery could increase the corticomotor excitability of the primary motor cortex during a grasp and place task. However, individual differences were large such that approximately half of our subjects responded more strongly to kinesthetic imagery whereas the other half responded more strongly to visual imagery. Interestingly differences between both imagery types disappeared when a dual task was added. This suggests that during the execution of a second task cognitive resources were insufficient to perform the motor imagery task at the same time. We conclude that motor imagery is an effortful process which requires increased attention control. This finding might have implications for the use of motor imagery in the context of rehabilitation, for example, when patients suffer from attentional deficits.

References
Decety, J. (1996). Do imagined and executed actions share the same neural substrate? Cognitive Brain Research, 3, 87-93.
Hall, C., Pongrac, J. & Buckholz, E. (1985). The measurement of imagery stability. Human Movement Science, 4, 107-118.
Heremans, E., Helsen, W. F., & Feys, P. (2008). The eyes as a mirror of our thoughts: Quantification of motor imagery of goal-directed movements through eye movement registration. Behavioural Brain Research, 187, 351-360.
Stinear, C. M., & Byblow, W. D. (2003). Motor imagery of phasic thumb abduction temporally and spatially modulates corticospinal excitability. Clinical Neurophysiology, 114, 909-914.
Stinear, C. M., Byblow, W. D., Steyvers, M., Levin, O., & Swinnen, S. P. (2006). Kinesthetic, but not visual, motor imagery modulates corticomotor excitability. Experimental Brain Research, 168, 157-164.
Publication status: published
KU Leuven publication type: IMa
Appears in Collections:Department of Kinesiology - miscellaneous
Movement Control & Neuroplasticity Research Group
Research Group for Neuromotor Rehabilitation
Policy in Sports & Physical Activity Research Group
# (joint) last author

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