Pikudei Hashem

Question: I was taught that due to our state of mourning on Tisha B’Av, we are not allowed to learn or discuss Torah – a topic that makes us happy and weakens our mournful state. Why, then, are we allowed to read from the Torah at Shacharit and Mincha on Tisha B’Av? Also, does the halacha of not learning apply to a regular mourner as well? Menachem (Via E-Mail)