(C) Locked in state # Locked-in syndrome is a rare neuropsychological disorder.> Locked-in syndrome (LIS) is a condition in which a patient is aware but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in the body except for the eyes.> Its primary features are quadriplegia and paralysis of the cranial nerves except for those responsible for vertical eye movements.> Site of lesion: 1. Lateral 2/3rd of cerebral peduncle bilaterally. 2. Basis pontis bilaterally sparing tegmentum. 3. Ventral aspect of medulla bilaterally sparing tegmentum,> Characteristic features: Conscious, alert and awake as the tegmental ascending reticular activating system (ARAS) concerned with arousal is intact, so be careful with your bedside comments. Blinking movements of the eyes are preserved; hence patient is able to communicate in a telegraphic pattern ("on or off' movements of eye lids). Vertical movements are intact as it is controlled by the interstitial nucleus of cajal and the rostral part of the medial longitudinal fasciculus (MLF), which is situated in the teg-mentum of the midbrain, which is spared in the locked in syndrome. Horizontal movements of eyes are lost especially when the ventral part of the basis pontis is involved, leading to involvement of the 6th cranial nerve fascicle. Patient may be aphonic because of the involvement of the corticobulbar fibers and motor nucleus of the lower cranial nerves especially the 7th, 9th, 10th, 12th cranial nerves. Patient is quadriplegic due to involvement of pyramidal fibers in the lateral 2/3rd of cerebral peduncle of the midbrain or the basis pontis or the ventral aspect of the medulla. "Fourier de prodromique" - Pathologically characteristic sudden onset of laugh at the onset of quadriparesis due to involvement of bilateral pyramidal system, producing psuedobulbar palsy like state before the onset of brainstem symptoms.# Etiology for locked in syndrome: 1. Lacunar infarcts. 2. Demyelination (central pontine myelinolysis) 3. Haemmorhage. 4. Trauma. 5. Tumours.> Pseudo-Locked in states: 1. Gullain Barre syndrome 2. Acute polyneuritis 3. Myasthenia gravis 4. Poliomyelitis.