Biomedical Engineering Reference
In-Depth Information
17.5.2 BCI in Movement restoration
BCIs could be used to activate devices for assisting movements. In addition to using
brain signals to control wheelchairs (Rebsamen et al. 2007; Galán et al. 2008; Iturrate et al.
2009; Millán et al. 2010), a challenge is to use them to control devices that could assist the
movements of the limbs.
Functional reorganization of the motor cortex plays either an adaptive or a maladaptive
role in modifying the intact cortical tissue (Nudo et al. 2001). Since the first successful
attempt to train a tetraplegic patient to control a device applied to hand muscles using the
mu rhythm (Pfurtscheller et al. 2000), BCIs have been considered possible rehabilitation
devices (Dobkin 2007). The use of BCIs in motor retraining was extended to other techniques
using invasive methods with implanted electrodes in tetraplegic patients (Hochberg et al.
2006) or noninvasive MEG-modulated mu rhythms to control a hand orthosis (Birbaumer
2006; Buch et al. 2008).
By recording the brain activity, it is possible to detect cortical activity originating
from the sensorimotor areas; this activity varies between 8 and 12 Hz and is present if
subjects are not engaged in processing motor information or in producing or imagining
movement. Sensorimotor rhythm (SMR) is produced during inactivity and is caused by
thalamo-cortical circuits. Such rhythms have different terms (Wolpaw et al. 2003). By
using event-related synchronization (ERS) (mu-increase) and desynchronization (ERD)
(mu-decrease), Pfurtscheller and colleagues trained a patient to operate a hand orthosis
by imagination of specific motor commands. Afterward, they convincingly demonstrated
the potential usefulness of SMR-BCIs for motor restoration of hand grasp functions
(Pfurtscheller et al. 2003a, 2003b). Using the beta oscillations generated by patients
while imagining foot movement, Pfurtscheller and colleagues were able to analyze and
classify the EEG with a BCI and to use the output signal to control a functional electrical
stimulation (FES) device. A FES device is a system that uses electrical stimulation to
stimulate peripheral nerves controlling specific muscles, or groups of them, to activate
lost bodily functions such as grasping, walking and standing, and bowel and bladder
management. Generally, FES systems for grasping are limited by the fact that only the
patients who maintain voluntary control of the shoulder and elbow are able to use these
devices (Millán et al. 2010). Thus, showing the feasibility of the combination of a BCI and
an FES device, Pfurtscheller's work gave an important impulse to the BCI community
(Pfurtscheller et al. 2003a, 2003b). In this study, a tetraplegic patient after a long training
period was able to trigger the FES device by imagining foot movements. Stimulating
the forearm nerves, the FES device activated the required movements to grasp with the
paralyzed hand a cylinder placed in front of the patient.
The use of an MEG-BCI was exploited, showing as proof of concept successful BCI
control of grasping functions in healthy subjects (Mellinger et al. 2007) and in stroke
patients (Buch et al. 2008). The system used the activity of three of the 275 MEG sensors
to control the orthosis; the patient opened the hand by increasing the mu rhythm, and
by decreasing the mu rhythm the patient closed the hand. Patients with chronic hand
plegia resulting from stroke participated in 13-22 training sessions to gain control
of the orthosis. At the end of the training, they were able to control the opening and
closing functions of an orthosis attached to the plegic hand, but no one showed clinical
improvements in the completely paralyzed hands without the prosthetic device. An
important effect of the training was the refocusing of MEG activity, which provided the
first evidence that training with a BCI may result in cortical reorganization (Birbaumer
et al. 2009). As a further evidence of brain reorganization after BCI training, Caria and
