Strokes are one of the leading causes of long-term motor disability among adults. Current rehabilitative interventions often don’t help patients with severe motor impairment. Brain computer interfaces (BCI) can provide an alternative approach for neuro-rehabilitation, particularly for severely impaired stroke patients.
But first let’s start defining what a stroke is. Strokes happen when the blood flow to your brain stops. Within minutes, brain cells begin to die. There are two kinds of stroke:
- The more common kind, called ischemic stroke, is caused by a blood clot that blocks or plugs a blood vessel in the brain.
- The other kind, called hemorrhagic stroke, is caused by a blood vessel that breaks and bleeds into the brain. As a result, the affected area of the brain cannot function, which might result in an inability to move one or more limbs on one side of the body, inability to understand or formulate speech, or an inability to see one side of the visual field.
Brain computer interfaces allow the direct translation of brain activity into control signals of external devices or computers. BCI applications have been successfully used in the past for communication or control of robotic devices. Depending on the aim of the BCI use in rehabilitation, two major approaches can be distinguished:
- Assistive BCI systems aim at high dimensional control of robotic limbs or functional electric stimulation that specifically activate paralyzed muscles to substitute lost motor functions.
- Restorative BCI aims at selective induction of use-dependent neuroplasticity to facilitate motor recovery.
In this post we are going to focus on restorative brain computer interfaces. To understand how restorative BCIs work it is necessary first to explain what brain plasticity is. A plastic material is moldable or changeable in structure and so is the brain. Brain plasticity refers to the brain’s ability to change throughout life. The brain has the amazing ability of reorganizing itself by forming new connections between neurons. A consequence of neuroplasticity is that the brain activity associated with a given function can move to a different location. It is therefore able to compensate damage by reorganizing and forming new connections between intact neurons. In order to reconnect, the neurons need to be stimulated through activity, and here is where BCI’s role comes in.
One of the most common types of BCI techniques is motor imagery (MI). Motor imagery can be defined as a dynamic state during which an individual mentally simulates a given action. This type of phenomenal experience implies that the subject feels himself performing the action. Stroke patients can be asked to imagine moving their left or right hand or foot. MI tasks induce neural plasticity and thus can be used to enhance motor rehabilitation.
The challenge for patients with motor disabilities during MI therapy (they can have not moved the limb under training in years) is to know whether they are performing the task correctly or not. MI tasks generate specific patterns of brain activity in the EEG signal that can be detected and interpreted. During the imagery tasks the patient’s EEG is analyzed in real time and a visual feedback of the task under training is delivered. That is, think about a patient imagining he/she’s grasping an object with his right hand. Every time the action is detected in the patient’s EEG, an image of a right hand grasping something is shown to the patient helping him to visualize the movement and encouraging him to repeat the action in the same way in the following trials.
Today there is sufficient evidence that suggests that using a rehabilitation protocol involving motor imagery (MI) practice of goal-directed rehabilitation tasks leads to enhanced functional recovery of paralyzed limbs among stroke sufferers. EEG-based BCI motor imagery task feedback is definitely a necessary tool to help the patient focus better on the task and learn how to perform it. Even if it is still a technique currently under study, there have been a large number of reported evidences in which MI along with BCI feedback helped stroke patients to fully or partially regain motor functions, such as grasping objects. The power of reorganizing your brain is there!!
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