Electroencephalogram and evoked potentials in naturally occurring scrapie in sheep

Electroencephalogram (EEG), brain stem auditory-evoked potential, and flash visual-evoked potential recordings were taken from healthy sheep and from 3 sheep with scrapie, a CNS slow virus infection. The EEG changes included semi-periodic, polyphasic, high-voltage sharp waves (bilaterally synchronous and symmetric in all channels), and a cyclic alternating pattern consisting of a high-voltage low-frequency phase, followed by a low-voltage high-frequency phase. The high-voltage phase occurred with increased arousal, and the low-voltage phase occurred with decreased arousal. Myoclonic jerks were coincident with EEG sharp waves in one sheep with scrapie. Several spontaneous focal seizures were observed. Wave-form amplitudes were greatly reduced in the brain stem auditory-evoked potential and flash visual-evoked potential; degree of reduction did not always correlate with disease severity. The EEG and evoked potential changes were seen in an exposed sheep that had not yet developed clinical signs of scrapie.