> Nicotine-containing products are sometimes used for the performance-enhancing effects of nicotine on cognition.[57] A 2010 meta-analysis of 41 double-blind, placebo-controlled studies concluded that nicotine or smoking had significant positive effects on aspects of fine motor abilities, alerting and orienting attention, and episodic and working memory.[58] A 2015 review noted that stimulation of the α4β2 nicotinic receptor is responsible for certain improvements in attentional performance;[59] among the nicotinic receptor subtypes, nicotine has the highest binding affinity at the α4β2 receptor (ki=1 nM), which is also the biological target that mediates nicotine's addictive properties.[60] Nicotine has potential beneficial effects, but it also has paradoxical effects, which may be due to the inverted U-shape of the dose-response curve or pharmacokinetic features.