A small study suggests that sleep apnea patients may have impaired attention and decision-making ability, even if they are being treated with CPAP, reports Reuters.

“These individuals do not respond to treatment, and eventually will drop CPAP because they do not feel better,” said lead study author Ksdy Werli of the Federal University of Sao Paulo in Brazil.

“We chose to study this issue aiming to understand the real difficulties of these patients,” Werli said by email.