The research carried out as described in this dissertation was aimed principally at developing a multichannel CWNIRS instrument for applications in BCI. In particular a new application of optical BCI was conceptualised by the group recently in stroke rehabilitation (Ward, et al., 2007) which is considered in Chapter 7. However, one of the main areas of BCI is as a communication aid for the severely disabled for those individuals who for a number of reasons are not able to interact with their environment at all or at least in a very limited way. A review of BCI is reported in Chapter 3, most of which concern such communication aids Thus, it was felt fitting that the main debilitating disorders that these people face should be described. The principal pathological condition of "locked-in
syndrome", along with the various contributing diseases that can cause it are mentioned, in particular, amyotrophic lateral sclerosis (ALS).
2.6.1 Locked-In syndrome
Locked-In syndrome (LIS) refers to a state of paralysis of voluntary muscular control as a result of a disease causing de-efferentation of the motor system. The term 'locked-in syndrome' was first coined by Plum and Posner in 1966 which refered to a neurological condition of infarction of the ventral pons (pons in the brainstem that is). However, in a review in 1986 of 139 cases of ALS (Patterson, et al., 1986), many more etiological origins were reported, labelled as either vascular or non-vascular. Vascular origins included pontine hemorrhage, embolic phenomenon, and infarction of the midbrain. Non-vascular etiology included those caused by tumor, trauma, heroin abuse, and multiple sclerosis, to name a few. In the study, the non-vascular group were reported as having a more rapid functional recovery in its survivors compared to the vascular etiology group (Patterson, et al., 1986). Although there are various other names by which it is known such as pseudocoma, three principle varieties were identified in 1979 (Bauer, et al., 1979): Classical-, Incomplete-, and Total- locked-in syndrome.
The three catagories are identified according to the level of functional impairment the subject sustained. The classical version resembles those signs (reported by physician) and symptoms (reported by patient) as outlined in the foremost publication by Plum and Posner (Posner, et al., 1966), with manifestations of quadriplegia, lower cranial nerve paralysis, and mutism. However, the subject preserves vertical eye gaze and upper eyelid voluntary control. Incomplete locked-in syndrome includes the same manifestations and voluntary controls as the classical version except that the subject has additional remnants of volitional control apart from those of eyelid and vertical eye movement. Finally, the totally locked-in state (TLS) is a version where the patient is completely immobile, with no voluntary motor ability whatsoever.
The main subgroup that BCIs have a unique duty to establish a working communication strategy for is the TLS variety. This is because other varieties with some form of voluntary control can avail of other ultimately better techniques of control using whatever residual voluntary control they have, be it eyeblinking, eye tracking, etc. However, it has also been suggested (Naito, et al., 2007) that to increase the chances for successful communication in the TLS state, the patient in question should be 'trained' in the use of the device whilst still in the classical or incomplete state. This is because since the expectancy is that the disease will progress to the TLS variety. In the event of the patient only beginning to use the device in the TLS state, the outlook is grim (Birbaumer, 2006).
The life expectancy after diagnosis of the syndrome ranges from months to less than 15 years in the case of the aforementioned study (Patterson, et al., 1986). One neurological disorder called amyotrophic lateral sclerosis (ALS) can lead to the locked-in state and is highly reported in BCI literature. ALS is the most common neurodegenerative disease, involving progressive degeneration of motor neurons which can lead to complete paralysis of the patient, i.e. the TLS version of LIS.
2.6.1.1 Amyotrophic lateral sclerosis (ALS)
Amyotrophic lateral sclerosis (ALS) also known as Lou Gehrig's disease was first described in 1869 by Jean-Martin Charcot, a french neurologist. It is called Lou Gehrig's disease after the famous American baseball player Lou Gehrig, who retired after contracting ALS in 1939 (ALS_Association, 2008).
The term amyotrophic lateral sclerosis can be split into different segments to clarify its definition. 'A' refers to negative or no, 'Myo' refers to muscles, and 'trophic' refers to nourishment. Thus - a lack of nourishment to the muscles leading to muscular atrophy or muscles wasting away. 'Lateral' refers to the fact that ALS affects lateral areas of nerve cells in the spinal cord that signal and control the muscles. Finally, 'sclerosis' refers to the hardening of the affected areas, not unlike scarring of the skin. ALS specifically is a neurodegenerative disease which affects mostly upper (in the CNS) and lower (in the spinal cord and to the PNS) motor neurons, leaving afferent or sensory motor areas unaffected. Although the heart and digestive system are under involuntary control, and are thus not directly affected by ALS, the lung's muscular control is under threat since their associated musculature can be voluntarily controlled. Thus, a high cause of death is from pulmonary complications, mainly pneumonia, as was also demonstrated in the previously mentioned review for general LIS patients (Patterson, et al., 1986). A further high incident cause of death for those LIS patients was the extension of the brainstem lesion. In any case the ALS disease is quite variable with a spectrum of progression rates and survival times for ALS sufferers. Typically, death by respiratory failure is said to occur 2-5 years after disease onset (Schmidt, et al., 2009). Early symptoms of ALS include increasing muscle weakness especially of the arms, legs, speech related musculature, and those of breathing and swallowing.
2.6.1.1.1 Forms of ALS
In the USA, 5,600 are diagnosed with ALS each year (15 per day), with 30,000 people estimated to have the disease at any given time there (ALS_Association, 2008). It mostly affects 40-70 year olds being 20% more common in men. Apart from classification within the realm of LIS, ALS can be divided into three chief subgroups:
• Sporadic ALS (SALS); • Familial; (FALS); • And, Guamanian ALS.
Most (90-95% in the USA) of all ALS cases are of the sporadic ALS (SALS) type, meaning that it can affect anyone, anywhere, with no direct familial link. Familial ALS (FALS) occurs in 5-10% of ALS cases with an inherited predisposition to the disease. One known susceptible gene responsible is the SOD1 gene on chromosome 21, although this only accounts for 20% of the total FALS patients. The other 80% of FALS cases are caused by unknown familial linkage and so testing for FALS is not as significant an indicator as a thorough family history. Guamanian ALS occurs in Guam and the Trust Territories of the Pacific where a high occurence of ALS was found there in the 1950's (ALS_Association, 2008). ALS is not contagious and doesn't fall into any racial, socioeconomic, or ethnic boundaries. In 1995 the FDA approved the use of a drug Riluzole which is aimed at prolonging a patient's life by slowing the progression of the disease. Other efforts have been sought to aid or reduce the risk of ALS such as stem cell therapy (Lunn, et al., 2009) and intake of vitamin E with polyunsaturated fatty acids (Veldink, et al., 2007).
2.6.1.1.2 Cognitive ability in the ALS patient
A recent question being considered is whether the patient with TLS-ALS has any/enough cognitive control to take part in a communication system employing cognitive tasks in order to control an augmentative device (Hinterberger, et al., 2005, Fuchino, et al., 2008). As reported in (Kiernan, 2009) it was thought in the past that cognitive areas were completely unaffected by ALS. Kiernan then continues to cite research demonstrating that ALS sufferers can develop overt dementia syndrome, but others only manifest less severe cognitive defects. Nevertheless, some BCI studies have been performed on TLS-ALS subjects (Naito, et al., 2007) although the outlook for controlling a BCI for a TLS-ALS subject with no prior BCI training before entering that final state is, for the moment, very poor (Birbaumer, 2006).