There are 2 elements to apparent intelligence.
1) The rate the neurons fire and transmit between the nodes.
2) The number of connections between the nodes.
Having multiple pathways to the needed information and making
those pathways more efficient is apparently the key to having higher
intelligence. That said,intelligence is not quite the same as knowing
what to do with the information and even knowing what to do does
not always allow you to execute the actions related.
Consider things that require speed, muscle mass, or coordination.
There seems to be a tendency among higher IQ to not train their
bodies to the extent they are distracted by the need to feed their
minds. In other words, time devoted to generating the pathways
in the mind is time not spent working in the physical world.
Music (playing/dance) is one of the bridges that seems to offer
opportunities to feed both. Other artistic endeavors requiring a
certain "touch" like painting of model making likely also create
bridges.
I think we might be able to stimulate minds to create the paths,
but I'm concerned about messing with the chemistry to increase
the rate of operation. We don't want to burn out the nodes like
you can when you over clock a cpu. We need to optimize for
the "equipment" that is installed.