> If isolation with a net connection for a few months dropped multiple IQ points, then all the shut-ins who do nothing but hang around on the Internet all day would be losing multiple tens of IQ points a year and would be functionally disabled by now.You're assuming the effect is both permanent and cumulative.
An analogous effect: Clinical depression is also known to lower IQ in a subset of sufferers (for some oddballs, it's actually their main symptom). But the effect is neither permanent, nor cumulative. When the depression lifts, so does IQ (usually with a bit of delay).
So I would surmise that the same may be true of IQ deficits caused by prolonged isolation.