Higher IQ scores do not necessarily make people think faster, according to an experiment from the Berlin Institute of Health at Charité and colleagues from Barcelona. Although those with higher scores were quicker at simple tasks, they took longer to solve more challenging ones than their lower-scoring peers. Personalised brain scans on 650 participants showed that those attempting to solve simple problems were less synchronised between brain regions and effectively jumped to conclusions rather than waiting for more logical, considered steps. Slow solvers tended to have more synchronised brains, holding off on decisions longer than those less well coordinated.
https://www.bihealth.org/en/notices/intelligent-brains-take-longer-to-solve-difficult-problems