Brain Activation and Single-Limb Balance following ACLR

My colleagues and I have new paper in the Clinical Neurophysiology Journal.

The Summary

What’s the context?

As rehabilitation specialists we implicitly understand the dynamic systems theory – as sensory information from our environment changes, we automatically adjust our actions to achieve a task goal.

Yet, after ACL injury the loss of a single proprioceptive ligament in the knee results in widespread and distributed changes in the nervous system. With such changes in sensory input, we believe there is a cascade of neuroplastic re-weighting influencing our patient’s ability to automatically adapt to changing environments and optimize motor control. We wanted to determine whether changes in neural control related to changes in balance control, and whether common clinical interventions (like cueing or biofeedback) have any effect.

What did we find?

Using mobile brain imaging , we found that those with ACLR demonstrated less motor and sensory cortex activity during worse single-limb balance performance. Individuals with ACLR also demonstrating higher motor planning demands, indicating a neural ‘inefficiency’ that may stem from less responsive motor activation (more inhibition).

When it came to potential treatments, visual biofeedback improved motor and sensory activation while decreasing motor planning demands in those with ACLR and controls. Visual biofeedback also improved balance performance in the ACLR group.

What does it mean?

These results demonstrate reduced sensory and motor processing, but higher motor planning demands, during single-limb balance in individuals with ACLR. Notably, external focus of attention with visual biofeedback had a transient therapeutic effect. Interventions like visual biofeedback that reduce cognitive / motor-planning demands and increase somatosensory processing may help improve balance and normalize brain activity after ACLR.

The Highlights

Experimental Set-Up

Participants performed multiple repetitions of a balance task while electrical activity from the brain and postural sway were recorded.

Brain Activity Localization

Participants’ brain activity was localized using source space reconstruction. We characterized the level of brain activity in cognitive, motor, sensory, and visual regions.

Individuals with ACLR had inhibited sensory and motor activation.

The ACLR group demonstrated higher motor planning demands, yet lower somatosensory and motor drive activity. This group effect was consistent across all conditions.

External Focus of Attention with Visual Biofeedback Improved Brain Activation

In both groups, the “Laser” condition had the broadest and most therapeutic effects. With visual biofeedback occurring as the laser oscillated on the target. We recorded higher sensory, visual, and motor processing, as well as, lower motor planning demands.

The Clinical Bottom Line

Differences in cortical activity in individuals after ACLR are reported to contribute to impairments in quadriceps muscle function (Scheurer et al. 2020) and balance strategies (Lehmann et al. 2021). These brain activation impairments may be modifiable, and thus relevant treatment targets in therapeutic rehabilitation. External focus of attention with visual biofeedback represents a widely available clinical tool. Although applied during a single session, visual biofeedback (external focus of attention on a laser pointer dot) demonstrated transient therapeutic alignment for upregulation of somatosensory and motor activations in those with ACLR. This adds support to existing literature detailing the disinhibitory effects of biofeedback on motor pathways after ACLR (Bodkin et al. 2021; Lepley et al. 2012; Luc et al. 2016; Pietrosimone et al. 2015).

Transcutaneous electrical nerve stimulation (TENS) also demonstrated a small effect on sensory and motor processing - findings are discussed in more detail in the paper.

The Full Text

The full paper is available online at Clinical Neurophysiology.

You can also reach out to me on ResearchGate.

1 - Nuccio et al. J Physiol. 2021.
2 - Bodkin et al. Clin Biomech. 2021.
3 - Luc et al. J Electromyogr Kinesiol. 2016.
4 - Pietrosimone et al. J Electromyogr Kinesiol. 2015.
5 - Lepley et al. J Strength Cond Res. 2012.
6 - Norte et al. J Sport Rehabil. 2021.