Background symmetry and interhemispheric synchrony

Criteria & assessment

• Persistent >2:1 voltage difference between homologous regions, or persistent disparity in frequency or graphoelement distribution, is abnormal asymmetry; fleeting differences may remain normal.
• A burst pair is synchronous when left and right onsets differ by <=1.5 seconds; report the percentage of synchronous bursts.
• Near-complete synchrony is expected before roughly 27-29 weeks and again near term; about 70% synchrony may occur around 29-30 weeks and some asynchrony is expected from 30-37 weeks.
• After 38 weeks PMA, substantial asynchrony is not expected; abnormal asynchrony means a clearly excessive PMA-adjusted proportion of bursts with onset difference >1.5 seconds.