In the 1960s, Mauricio Rosenbaum and colleagues showed that lesions placed at specific locations in the fan like divisions of the left bundle caused specific abnormalities that they referred to as āhemiblocksā and that are now referred to as āfascicular blocksā. Lesions placed in the anterior fascicle caused the pattern labeled left anterior hemiblock (or left anterior fascicular block), and lesions placed in the posterior fascicle, the pattern labeled left posterior hemiblock (or left posteror fascicular block).