Effects of Motor Imagery and Action Observation on Upper Limb Motor Chances and Cognitive Chances in Parkinson's Disease

Parkinson's disease (PD) is degenerative, occurs slowly and progressively, is idiopathic, and involves several factors. In PD occurs the degeneration of dopamine-producing neurons (dopaminergic neurons) in the substantia nigra, within the basal ganglia. The activation of excitatory neurons then occurs, manifesting itself through the dysregulation of motor control.

PD is characterized by non-motor and motor symptoms, being causes of negative implications in quality of life, reflecting directly in several daily situations of the person with PD. Non-motor symptoms are considered as additional symptoms and are also frequent, having the prevalence of dementia and mild cognitive impairment. The most observed cognitive problems in PD are in the following domains: concentration and attention, working memory, as well as difficulties with calculations and spatial orientation activities, and executive functions. The non-motor symptoms have a negative impact on occupational performance, and may present difficulties in activities such as driving, shopping, household maintenance; as well as self-care: dressing and bathing.

The main motor symptoms are: a) resting tremor - occurs at rest and decreases when voluntary movement is attempted; b) rigidity - simultaneous increase in muscle tone, which may present a constant resistance throughout the range of motion when the movement is slow and progressive or a rhythmically resisted movement throughout the range of motion; c) akinesia - difficulty to initiate movement; d) bradykinesia - slowness to maintain movement.

The tremor in PD is an involuntary rhythmic movement, typically characterized by unilateral resting tremor, which occurs in the upper extremities, especially the hands. Resting tremor is inhibited during movement and may reappear as frequently when adopting a posture or even when moving. The essential tremor occurs more in the forearms and hands, being more problematic during voluntary movement or when maintaining the posture against gravity, which affects the performance of activities of daily living, and the most affected are: writing by hand, eating, dressing, and taking care of oneself. There are also isolated postural and kinetic tremors, with an even higher frequency (greater than 4 Hz).

In turn, rigidity is one of the cardinal symptoms of PD and includes information on severity, distribution, and whether it is present at rest and in a non-drug state. People with PD have higher rigidity values, both at rest and during passive mobilization, because there is an increased tone in the muscles. Reduced range of motion can be a debilitating consequence of PD, affecting daily activities such as writing. Regarding bradykinesia, it refers to the difficulty of adjusting body position, initiating and executing movement, and performing sequential and simultaneous movements.

People with PD generally have difficulty initiating movements, with slower movements and reduced range. This reflects with the difficulty performing most daily activities: personal care, dressing, work and leisure activities and household chores, by the relationship with fine motor coordination and dexterity, as well as bimanual coordination, hypokinesis and initiation.

Currently, there is no approved treatment that changes the progression rate of PD, and the possibilities are focused on the mitigation of symptoms since there is no known cure. The degeneration of dopaminergic neurons, triggers the changes in the basal ganglia network and is mainly treated with medication, such as levodopa or dopaminergic antagonist, being a dopamine replacement therapy, which compensates for the lack of dopamine produced endogenously.

Conventional rehabilitation, associated with other intervention possibilities, in addition physical exercise, are important for the maintenance of motor and non-motor changes, complementing the pharmacological treatment.

Motor imagery (MI) and action observation (AO) are two innovative rehabilitation approaches that are feasible in various pathological conditions. Thus, there is an investment of applying both as a tool in neurorehabilitation, and significant benefits can be induced in PD.

From a systematic review, of the 25 articles selected, there was no record of a study involving the investigation of the joint action of MI and long-term AO, and only one comparing the effect of both in a single session, but the rest dealt with the effect of OA or MI, isolated, in a single session experiment, or the effect of only OA or only MI as a long-term treatment. Another relevant note is that the use of approaches in PD are more directed to motor symptoms in lower limbs, such as balance and gait alterations.

The combination of AO and MI increases imitation in PD, being a promising therapeutic approach for helping people with PD in their activities of daily living and symptom management, since the actions are presented in the context of daily life.Thus, MI and AO used as therapeutic programs can improve motor skills by increasing proprioceptive signals normally generated during movements, or slow down the deterioration of motor skills in PD.

Motor imagery (MI) is a cognitive process that involves the ability to perform an action mentally, without the need to perform the movement itself. The perspective that the person uses to imagine can be: internal perspective (first person - imagines himself/herself), which relates to the person's view of the content of the images or to his/her kinesthetic sensation - the person imagines the movement being performed, as if feeling the movement of the action; or external perspective (third person - imagines another person), which relates to the visual imagination of scenes outside the person.

Like motor execution, MI training can induce improvements in motor performance and therefore in the motor learning processes in PD. Despite the few studies in PD, there is evidence that mental practice can reduce bradykinesia, improve mobility and gait speed, as well as improve dynamic stability, besides showing no tremor in the condition with medication during rest and mental task.

Action observation consists of watching another person acting, or doing a motor task, on video or in real-time. It is recognized that when observing another person acting, there is brain activation in the same neural structures used for the real execution of the same actions, being recruited in the brain of the observer as if performing the observed action.

The AO shows everyday actions, providing information for performing them in life contexts. AO is an effective way to learn or improve the performance of a motor skill, modifying the speed and accuracy of actions in PD. The use of AO in PD improves the spontaneous rate of self-rhythmic finger movements, which reflects in the improvement in the performance of activities of daily living.

The term Brain-Machine Interface (BMI) refers to systems that capture the individual's brain activity signals, translating them into computer commands to control external devices, which can be communication devices, functional electrical stimulation (FES), or robotic exoskeletons. BMI technology is relatively new, and it allows a person to interact with the environment through brain signals and can restore motor function by inducing brain plasticity.

To capture these brain signals, invasive and non-invasive strategies can be used. In non-invasive systems, electrodes are positioned on the skull cap, using signals collected by electroencephalography (EEG), magnetoencephalography (MEG), and functional near-infrared spectroscopy (fNIRS), being more promising than invasive strategies due to safety and ethical issues.

In typical BMI, through EEG, the person's movement intention (motor imagery or execution) is decoded in real-time through the ongoing brain electrical activity triggered by sensory feedback. BMIs are currently used mainly in two applications: in assistive technologies or movement paralysis; and in rehabilitation technologies, also called rehabilitative Brain-Machine Interface or neurofeedback that aims to promote neuroplasticity through manipulation or autoregulation of neurophysiological activity to facilitate motor recovery.

Among numerous neurofunctional dysfunctions, Parkinson's disease (PD) could benefit most from this technology. The use of BMI, through EEG with Functional Electrical Stimulation (FES), to stimulate the muscles of the upper limb during the execution phase of the AO when facing the execution of an observed motor act, may present advantages, such as improved performance, whatever the severity of the neurological impairment, such as severe PD. The literature presents different BMI employed to people with PD and, so far, there is no study evaluating the training of motor imagery and observation of the action to improve the activity of the sensorimotor cortex with EEG associated with a robotic haptic glove.