Tonic vs. Phasic (IMAGE) Picower Institute at MIT Caption Tonic neurons (light green) expressed 40 times more of a gene called Wnt4 (darker green) than did phasic neurons (purple). Credit Littleton Lab/MIT Picower Institute Usage Restrictions with credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.