A Method for Using Video Presentation to Increase Cortical Region Activity during Motor Imagery Tasks in Stroke Patients

Abstract

Previous studies have reported that stroke patients have difficulty recalling the motor imagery (MI) of a task, also known as MI vividness. Research on combining MI with action observation is gaining importance as a method to improve MI vividness. We enrolled 10 right-handed stroke patients and compared MI vividness and cortical activity under different presentation methods (no inverted image, inverted image of another individual’s hand, and an inverted image of the patient’s nonparalyzed hand) using near-infrared spectroscopy. Images of the nonparalyzed upper limb were inverted to make the paralyzed upper limb appear as if it were moving. Three tasks (non inverted image, AO + MI (other hand), AO + MI (own hand)) were randomly performed on 10 stroke patients. MI vividness was significantly higher when the inverted image of the nonparalyzed upper limb was presented compared to the other conditions (p < 0.01). The activity of the cortical regions was also significantly enhanced (p < 0.01). Our study highlights the potential application of inverted images of a stroke patient’s own nonparalyzed hand in mental practice to promote the motor recovery of stroke patients. This technique achieved higher levels of MI vividness and cortical activity when performing motor tasks.

Keywords: inverse video; motor imagery vividness; near-infrared spectroscopy; stroke.

Figure 1

Motor imagery (MI) task of the paralyzed upper limb grasping a cup on a desk. The MI task consisted of a first-person viewpoint of reaching forward with the paralyzed upper limb to grasp a cup on a desk. This was performed while in a seated position without moving the trunk. Then, the movement proceeds with lifting the cup, returning the cup to the place on the desk, releasing the hand, and returning the paralyzed upper limb to its starting position in front of the trunk.

Figure 2

Inverted MI task images. We took images of the movements of a stroke patient’s nonparalyzed upper limb and inverted the images to make the paralyzed upper limb seem as if it were moving.

Figure 3

The experimental protocol. Participants were given three MI tasks: an MI task without an inverted image (MI only), an MI task with an inverted image of another person’s hand (other hand action observation [AO] + MI), and an MI task with an inverted image of their own hand (own hand AO + MI). The subjective MI vividness was assessed immediately after the MI tasks were completed using the recorded NIRS measurements.

Figure 4

Near-infrared spectroscopy (NIRS). NIRS measurements were performed using an optical topography system. NIRS probes were positioned at the Cz position (midpoint of the crown of the head) according to the international 10–20 method in a 4 × 4 probe set. As for the baseline, the data were averaged over the 5 s immediately prior to the start of the MI task and the 5 s following its completion. The data recorded 5 s following the start of the MI task until 20 s following its completion (15 s of data) were used.

Figure 5

All regions of interest (ROI) during three MI tasks. Cortical activity was observed for all three MI task conditions.

Figure 6

Comparison of oxygenated hemoglobin (oxy-Hb) (Z-score) during the MI of paralyzed upper limbs. Oxy-Hb in the cortical region was significantly higher in own hand AO + MI than in MI only or other hand AO + MI.

Figure 7

MI vividness. MI vividness was evaluated using visual analog scale (VAS) following NIRS measurements, and the effect observed showed a mean of 48.2 ± 9.7 mm for MI only, 56.7 ± 13.3 mm for other hand AO + MI and 82.2 ± 11.2 mm for own hand AO + MI.