I know this is a news article but the journal mentioned is PLOS one, while the study is malaysian.
The study itself :
Modafinil Increases the Latency of Response in the Hayling Sentence Completion Test in Healthy Volunteers: A Randomised Controlled Trial
This study demonstrated that administration of single 200 mg doses of modafinil to healthy individuals increased the latency of responses in the performance of the HSCT, a task that is highly sensitive to prefrontal executive function, without enhancing accuracy of performance. This finding may provide important clues to defining the limitations of modafinil as a putative cognitive enhancer.
It may be that Mod is detrimental to some aspects of brain functioning while enhancing others.
Many other test prove its efficacy and highlight its positive effects. But the picture can't all be rosy, can it?