A stroke is a major cause of death but in non-lethal cases it causes significant damage to the brain. One of the most bizarre one is the locked-in syndrome. This is caused by the lesion to the brain stem ventral pons and was termed the “locked in syndrome” by Plum and Posner in 1966. There are other names for this : De-efferented state, pseudocoma, ventral pontine syndrome, cereberomedullospinal disconnection, pontepseudocoma, pontine disconnection syndrome, or pontine locked in syndrome.
Locked-in syndrome is a condition in which the person in aware of the environment around him and can see and hear but cannot respond with any motor function. This syndrome occurs in various grades from mild impairment of movement to total impairment. Surprisingly the eyes seem to be unaffected in many of the patients and are often used as communication devices through eye movement or blinking but the lack of speech (aphonia) is due to the lack of coordination between breathing and voice even though the vocal cords are functional.
There are several characteristics that differentiate it from a coma and the critical two among them is : Sustained eye opening and preserved higher cortical functions.
Since the sensation is often preserved, it is possible that the patient be made comfortable.
There are many ways that patients can communicate:
- Eye tracking
- Sniffing
- Measurement of brain EEG patterns.
- Electromyogram based technologies
Here are a few examples of technology being used for locked-in patients.
Neuroswitch made by Control Bionics (www.controlbionics.com) has coupled innovative software to electromyogram hardware and made a device that works surprisingly well if they can get a EMG signal.
Eyewriter was an innovative Kickstarter project (www.eyewriter.org) that created a eye tracking software and glasses as an open source project to enable capture of eye movements of an artist with ALS.
Anton Plotkin and Lee Sela at the Weizmann institute of Science discovered that they could help a patient communicate by using the pattern of sniffs. It takes some training to gain control but it has been shown to be very effective in communication for Locked-in patients that do not have the luxury of eye movements. http://www.pnas.org/content/107/32/14413
The striking feature of EEG has been that the EEG looks apparently very normal in most patients. It is responsive to the waking state and stimuli. EEG has been used extensively but the data is confusing. In general lockedin patients show a reactive EEG patterns with a reactive alpha and theta rhythm consistent with consciousness. However, as exception, in some locked-in patients that could communicate by other means were in alpha rhythm with EEG. This alpha EEG rhythm would have classified them being in vegetative state but that was not true. (http://www.ncbi.nlm.nih.gov/pubmed/2297946} . The training of the patient is required before EEG has been used as a brain-computer interface connection.