Cortical activity reductions during repetition priming can result from rapid response learning

Recent observation of objects speeds up their subsequent identification and classification1,2. This common form of learning, known as repetition priming, can operate in the absence of explicit memory for earlier experiences3,4, and functional neuroimaging has shown that object classification improved in this way is accompanied by ‘neural priming’ (reduced neural activity) in prefrontal, fusiform and other cortical regions5,6,7,8,9,10. These observations have led to suggestions that cortical representations of items undergo ‘tuning’, whereby neurons encoding irrelevant information respond less as a given object is observed repeatedly10, thereby facilitating future availability of pertinent object knowledge. Here we provide experimental support for an alternative hypothesis, in which reduced cortical activity occurs because subjects rapidly learn their previous responses11. After a primed object classification (such as ‘bigger than a shoebox’), cue reversal (‘smaller than a shoebox’) greatly slowed performance and completely eliminated neural priming in fusiform cortex, which suggests that these cortical item representations were no more available for primed objects than they were for new objects. In contrast, prefrontal cortex activity tracked behavioural priming and predicted the degree to which cue reversal would slow down object classification—highlighting the role of the prefrontal cortex in executive control.