In acutely thiamine-deficient pigeons marked impairment of function of the central nervous system develops, associated with a characteristic and progressive series of head and neck movements and degeneration of certain neurons (Swank1; Swank and Bessey2; Swank and Prados3). The first of these movements consists of rhythmic lateral rotation of the head alone or combined with extensor thrusts of the neck and has been designated preopisthotonos. This phase may last from a few to twenty-four hours and in progressive thiamine deficiency is followed by complete opisthotonos. If the deficiency is allowed to become more severe, and death does not intervene, opisthotonos is followed by slow relaxation; the pigeon can no longer elevate its head above the horizontal and is generally listless. This final stage, enopisthotonos, is followed by death within a few hours if thiamine is not administered.
Histologic studies (Swank1; Swank and Prados3) have revealed
SWANK RL, JASPER HH. ELECTROENCEPHALOGRAMS OF THIAMINE-DEFICIENT PIGEONS. Arch NeurPsych. 1942;47(5):821–827. doi:10.1001/archneurpsyc.1942.02290050123011