Speed = meth?

and so keep them shut = and so keep their tubes shut?

Context:

Snails on speed shed light on human memory
12:41 28 May 2010 by Jessica Hamzelou
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Pond snails make unlikely speed freaks. But dosing the gastropods on methamphetamine is helping us understand how certain "pathological memories" form in human addicts.

Meth users develop long-term memories of their highs, which is why the sight of places and people connected with a high can cause recovering addicts to relapse into taking the drug. "It's hard to get rid of those memories in addicts," says Barbara Sorg at Washington State University in Pullman. So potent is meth's effect on memory that, in low doses, the drug can be used as a "cognitive enhancer" in kids with attention-deficit hyperactivity disorder.

To probe the drug's effect on memory, Sorg's team placed pond snails in two pools of low-oxygen water, one of which was laced with meth. In low-oxygen conditions snails will surface and use their breathing tubes to access more oxygen. By poking the snails, Sorg's team trained them to associate using the tubes with an unpleasant experience, and so keep them shut. Only the snails on speed remembered their training the following morning, and in a separate experiment it took longer for them to "unlearn" the memory.

Humans are obviously more complicated, says Sorg, but "the snails still provide a model of how meth affects memory". The team's goal is to work out how to diminish specific memories, helping addicts recover.