Eye blinking is a type of reflex action that means our body does it automatically. As part of it, we can also do it under our control. Babies and children generally blink around 2-3 times per minute. But this frequency increases to 14 to 17 times every minute in adults and stays at the same number till life. Blinking is beneficial to lubricate and clean our eyes with the help of our tears which spread over the surface. Excessive blinking or lessor blinking is when you blink less or more than you want to. There are a lot of things which can cause excessive blinking. Problem on the surface of the eye is the most frequent happening. Excessive blinking can irritate you, and also can cause some serious neurological syndrome and symptoms. We blink more when we are nervous, talking, have some brain injuries, under stress, anxiety or depression or in pain and blink less when in danger or reading anything.
After any severe brain injury, specific diagnosis of disorders of consciousness, that is Unresponsive Wakefulness Syndrome/Vegetative State and Minimally Conscious State, is important for optimizing patient management. Till now, diagnosis of disorders of consciousness is based on clinical interpretation of patients’ voluntary responses to multi-sensory stimulation and spontaneous behavior. It could be, however, obstructed by sensory-motor and cognitive impairments. Several research studies indicated that a diagnosis based on clinical interpretation might lead to a little wrong or misdiagnosis with a rate of 30–40%. Therefore, it is of very crucial to identify reliable and accurate diagnostic markers of consciousness and not completely relying on patients’ voluntary responses.
It was suggested that spontaneous eye blink rate (EBR) can be a possible index of patients’ consciousness level and can be easy to detect in clinical practice. Eye blink rate is thought to be associated with the activity of the spinal tri-geminal complex (STC). Dopaminergic activity in the basal ganglia modulated the STC excitability. According to a hypothesis (Meso-circuit) which is well-established, dopaminergic projections which are present within striato-thalamo-cortical circuits possibly play a crucial role in conscious processes regulation. Dopaminergic projections are also a target for therapeutic intervention and can be related to recovery of consciousness. A relative sparing of thalamo-cortical neuronal assemblies were earlier reported in Minimally Conscious State compared to Unresponsive Wakefulness Syndrome/Vegetative State. Moreover, beyond the requirement for corneal lubrication, EBR is also modulated by cognitive variables such as fatigue, level of vigilance , and task demand. During an auditory oddball paradigm, spontaneous EBR increases as a part of cognitive load in healthy individuals, i.e. the cognitive resources required to perform a job or task.
To establish easy-to-detect markers to improve specificity and accuracy in diagnosis in disorders of consciousness patients it was hypothesized that patients in Minimally Conscious State might present a higher spontaneous eye blink rate as compared to patients in Unresponsive Wakefulness Syndrome/Vegetative State.That changes in spontaneous eye blink rate as a function of cognitive load could also be seen in patients with a higher responsiveness level, i.e. in Minimally Conscious State but not in Vegetative State/Unresponsive Wakefulness Syndrome.
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