Neck muscle vibrotherapy of unilateral spatial neglect

The unilateral spatial neglect (USN) is a neuropsychological consequence of stroke and damage to neural networks, affecting spatial orientation among others. Patients do not detect stimuli located opposite to the damaged hemisphere of the brain and do not respond to them. In people with left USN, it has been shown that subjective straight-ahead (SSA) is shifted to the right, which may contribute to long-term disability. In reducing the symptoms of USN, unilateral neck muscle vibrations (NMV) are proposed, a method favorably interacting with visual-proprioceptive stimuli, but not fully tested in this context. Therefore, the aim of the French researchers was to determine the type of a feedback, in a visual or visual-proprioceptive context, associated with left-administered NMV that would produce the most intense and long-lasting beneficial effects on SSA bias in a large group of healthy people. And the context producing the greatest effect should be of importance in the treatment of patients with left-sided USN.

• For the participants of the study as a whole (regardless of the effects obtained in a given group), the median SSA, initially oriented to the right (+3.30 ± 4.10 degrees), showed a tendency to a slight deviation to the left after the interventions.
• However, only the NMV+P (vibration + visual finger pointing) group results  contributed significantly to this SSA perception correction. Compared to the baseline values, in the NMV+ P group, the SSA was significantly deviated to the left immediately after the intervention (+1.43 ± 2.13) and 30 minutes later (+2.00 ± 2.83).
• The combination of NMV vibrotherapy and visual indication may enable intermodal recalibration.
• NMV vibrotherapy may be included in the occupational therapy of USN.

Prepared on the basis of:

Perceptual post-effects of left neck muscle vibration with visuo-haptic feedback in healthy individuals: A potential approach for treating spatial neglect. Ceyte H, Beis JM, Ceyte G, Caudron S. Neurosci Lett. 2021 Jan 19;743:135557.

Study population

Healthy right-handed men (n = 48) and women (n = 39) with normal eyesight, dominant right eye, aged 21.4 ± 2.2 years, were included in the study.

Test procedure

The subjects were randomly assigned to 1 of 4 interventions lasting 15 minutes:

• blindfolded neck muscle vibration (NMV)
• neck muscle vibrations with open eyes, vision (NMV+V)
• neck muscle vibration and finger pointing (NMV+P)
• visual finger pointing and no vibration (P).

In the NMV group, the blindfolded participants did not perform any specific activities during left-sided proprioceptive neck vibration stimulation, other than an informal discussion with the researcher.

In the NMV+V group, the stimulation conditions were the same as in the NMV group, except that participants were not blindfolded.

In the NMV+P group, the participants had to point as quickly as possible with the right index finger one of the five highlighted targets at the moment, placed in front of them in a horizontal space: with a deviation from the axis “straight ahead” by 10 or 20 degrees to the left and by 10 or 20 degrees to the right, and also exactly on the “straight ahead” axis. Five 2.5-minute blocks of 50 pointing attempts were performed. Each direction was presented 10 times, in random order. There was a 30-second rest period between blocks.

In group P, participants performed the same finger pointing task as the NMV+P group, but without any vibrational stimulation. This was to test the possible effect of the training of multiple pointing alone on the end effects in the NMV+P group.

Before, immediately after, and 30 minutes after each intervention (NMV, NMV+V, NMV+P or P), the eyes-closed SSA index finger-pointing test was performed.

Use of vibration in the study

Vibration stimulators (VB115, Vibrasens®, Techno Concept, France) were mounted over the abdomen of the left and right upper trapezius muscles. A balanced head position was maintained by resting the chin on a tripod. In the NMV, NMV+V and NMV+P groups, only the left-sided vibrator was activated throughout the 15-minute session (vibration parameters: frequency 100 Hz, amplitude 0,3 mm). A right-sided vibrator was not used.

Results

Before the study, the median SSA did not differ significantly between the study groups [H (3, N = 87) = 2.38; p = 0.50]: for NMV = +3.45 ± 3.85, for NMV+V = +2.88 ± 5.10, for NMV+P = +3.63 ± 2.50 and for P = +2.53 ± 4.50 degrees.

For the study participants as a whole (regardless of the effects of a given group), the median SSA, initially oriented to the right (+3.30 ± 4.10 degrees), showed a tendency to a slight deviation to the left after the interventions (immediately after the interventions: + 2.45 ± 4.40 degrees, p = 0.024; 30 minutes later: +2.50 ± 4.85 degrees, p = 0.013).

However, only the NMV+P group significantly contributed to these results (p <0.001). In the NMV+P group, the SSA was significantly deflected to the left immediately after the intervention (+1.43 ± 2.13, p <0.001) and 30 minutes later (+2.00 ± 2.83, p <0.001). The difference between the medians of SSA immediately after the intervention and 30 minutes later did not reach statistical significance (p = 0.057).

Comment

The authors conclude that the combination of visual-proprioceptive feedback and somatosensory stimulation of the neck {by vibration; also having a proprioceptive effect; Editor’s footnote} can enable full and sustained intermodal recalibration, which can be enhanced by engaging attention during conscious pointing. The presented results also showed that the NMV technique can be easily combined with routine occupational therapy sessions to treat various aspects of USN disorders.

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