Wernicke&;s encephalopathy is due to deficiency of

The commonest cause of the organic amnestic syndrome is chronic alcohol dependence. It is also called as Wernicke-korasakoff syndrome. Wernicke&;s encephalopathy is the acute phase of delirium proceeding to the organic amnestic syndrome, while korasakoff&;s syndrome is the chronic phase of the amnestic syndrome. (Ref: a sho textbook of psychiatry, Niraj Ahuja,7th edition, pg no. 27)