Biofeedback

Biofeedback is a technique which helps individuals to learn to control physiological functions, such as blood pressure, heart rate, muscle tension and balance, by giving the individual access to information pertaining to these systems. This process is typically

mediated by sensors, often from surface mounted electrodes attached to the skin. For example, an ECG can relay feedback about the electrical and muscular activity of the heart, which in conjunction with manipulation of breathing can be used to decisively control heart rate.

Biofeedback has been extensively applied to treat a wide variety of illnesses and disorders, including but not limited to; speech disorders and to improve speech per- formance (i.e. phonatory disorders) [232], urinary incontinence [119], gastrointestinal disorders [233], Bruxism (a condition in which you grind, gnash or clench your teeth) [158], Dysgraphia (deficiency in the ability to write) [160], primary Raynaud’s phe- nomenon (excessively reduced blood flow in response to cold or emotional stress) [178], peak performance training in sport [297] and for stroke rehabilitation [262]. From the latter perspective, that of stroke rehabilitation, biofeedback has been applied to numer- ous aspects of the rehabilitation process. Many extensive literature reviews of the use of biofeedback in stroke rehabilitation have been conducted, for a comprehensive in-depth discussion the reader is referred to [118, 262, 404]. The following section gives a brief overview of the relevant literature, giving context to the utility of biofeedback for stroke.

3.5.1.1 EMG Biofeedback

EMG biofeedback for neuromuscular re-education was one of the initial biofeedback technologies applied to stroke rehabilitation for individuals with hemiparesis. EMG uses surface electrodes to detect a change in skeletal muscle activity, which is then fed back to the user usually by a visual or auditory signal. Following a stroke, normal regulation of muscle tone is disrupted, as is the ability to in-act direct specific control over target muscles, as a result of neuronal damage to the motor circuits. However, typically some of the motor circuits survive and are partially left intact. The theory behind EMG biofeedback is that through feedback, individuals may be able to learn how to use these preserved pathways, which over time might help to strengthen and rebuild the damaged pathways and hence the recovery of motor function. EMG feedback is particularly suitable in the earlier stages of stroke recovery or when paresis is more severe, when the individual’s ability to generate movement is small and less easily observable kinesthetically. There has been a series of independent meta-analyses conducted to investigate the effectiveness of EMG biofeedback for stroke.

An analysis by Schleenbaker et al. including 8 studies, with a total of 192 patients, found that EMG biofeedback improves functional outcomes in patients with hemiplegic stroke [323].

A meta-analysis was conducted by Moreland and Thomson, containing 6 studies and examined the efficacy of electromyographic biofeedback compared with conventional physical therapy for upper-extremity [251]. This study found small effect size increases with biofeedback therapy compared to conventional physical therapy [251].

A later meta-analysis by Moreland, including 8 studies on the effects of EMG biofeed- back for improving lower extremity function after stroke indicates that EMG biofeedback is superior to conventional therapy for improving ankle dorsiflexion muscle strength [252]. A more recent Cochrane review by Woodford and Price was conducted on the use of EMG biofeedback for the recovery of motor function after stroke. 13 trials, involv- ing 269 individuals with stroke were included. All trials compared EMG biofeedback plus standard physiotherapy to standard physiotherapy either alone or with sham EMG biofeedback. The review suggests that there was a small amount of evidence to suggest that EMG biofeedback had a beneficial effect when used with standard physiotherapy techniques [404].

3.5.1.2 Force Platform Biofeedback

The body maintains a sense of balance through a complex set of sensory-motor control systems, primarily using input from the vestibular system (motion, equilibrium, spa- tial orientation) but also sensory input from vision (sight) and proprioception (touch). Damaged caused by stroke to any of the subsequent control areas of the brain can result in a reduced sense of stability and balance. Difficulty with balance is therefore very common after stroke and as a result approximately 40% of stroke survivors have serious falls within a year of their stroke [391]. Much effort has thus been allocated to improving balance during stroke rehabilitation. One method for improving balance is to provide additional information to an individual during training that can help reinforce informa- tion coming from the bodies correctly functioning intrinsic balance apparatus. Force platform biofeedback is one such method for providing an individual with information about the location of their center of gravity with reference to the location of their feet. A Cochrane review, containing seven trials and 246 participants, which assessed the use of force platform biofeedback, found that biofeedback significantly improved stance symmetry [24].

3.5.1.3 Mirror Biofeedback

Although technically a form of visual feedback, mirror feedback is more aptly categorised as a form of bio-feedback. Mirror box therapy was first described by [299] for the relief of phantom limb pain, a phenomenon common in individuals who have had a limb abruptly amputated. It occurs because the nerve endings at the amputation site still send messages to the brain which preserves a sense of that limb within the CNS. The principal behind mirror feedback is that vivid kinaesthetic sensations of movement can be evoked by observing movement of the healthy hand or arm in a mirror. It is suggested that observing such movement causes additional neural activity in motor areas located in the affected hemisphere, which should eventually result in cortical reorganization and improved function [319]. In practise, during mirror box therapy the amputated limb is obscured by a mirror box, which projects a virtual inverted copy of their healthy limb back to the patient. The patient then attempts to move both limbs while watching the reflection in the mirror. The mirror essentially leads the brain to perceive the missing limb is intact and responding correctly to their motor command and subsequently relays this sensorimotor information to the contralateral portion of the brain and closes the motor feedback loop. This motor-sensory information stimulates the otherwise dormant cortex region and in turn elevates the phantom pain.

Since its initial discovery, application of the mirror box therapy technique has also been successfully reported in patients with other pain syndromes and in sensory re- education of severe hyperaesthesia after hand injury [307]. For motor recovery after stroke, mirror therapy might provide patients with sensorimotor feedback which substi- tutes for the lack of, or decreased proprioceptive input from a paretic limb.

Altschuler et al. performed an initial proof of concept study of mirror therapy for recovery of hempiparesis in chronic stroke patients. The patient were randomly assigned to one of two groups, a mirror group or transparent plastic group (control). Patients practised using either a mirror or transparent plastic sheet, for 15 min, twice a day, 6 days a week, moving both hands or arms symmetrically (moving the affected arm as best they could) while watching the good arm in the mirror. During practise patient performance was assessed by two graders. After competition of the trials, both graders found that substantially more patients improved from the mirror group compared to the control group [8].

Sathian et al. describe the successful application of mirror therapy to the post-stroke rehabilitation of a patient with poor functional use of an upper extremity. Although small and not sufficiently controlled, the results of this study are promising, reporting

improved range of motion (ROM), speed and accuracy of arm movement after mirror therapy [320].

Michielsen et al. showed that in patients with chronic stroke, unsupervised home- based practise with a mirror resulted in statistically significant improvements in upper extremity motor function and that mirror therapy caused a shift in activation balance M1 toward the lesioned hemisphere, suggesting neural reorganisation [246].

More recent studies, [408] and [88] conducted high-quality, randomized control trials which both reported mirror therapy-improved motor function in patient with acute and sub-acute stroke.