[6] His passion for Panamanian music was further reinforced after Brenes returned to Panama in 1931 when he read Narciso Garay’s Tradiciones y cantares de Panamá.
He collected folk music of that region which led to the publication of his book Desarrollo musical de Panamá a partir de la República (Panama City) and the folk song collection Tondas del trópico niño (Panama City, 1955) which included 70 of the Panamanian songs from his research.
This latter work became widely used in public school music education programs in Panama, and some of these songs were performed and recorded by professional musicians.
[3] His research also influenced his composition writing, including his opera La cucarachita mandinga which used a libretto by Rogelio Sinan.
[7] When Juan Demóstenes Arosemena succeeded Arias Madrid as Panama's president, Brenes's employment changed, and he taught at the Escuela Normal de Santiago [es] from 1938 to 1940.
[3] In 1948 he taught in Mexico where he befriended musicologist Adolfo Salazar and composers Rodolfo Halffter, Luis Sandi, and Manuel Ponce.
[7] In 1949 Brenes returned to his hometown of David after being offered a position as associate editor of the newspaper Ecos del Valle.