CORTICAL ACTIVITY REDUCTIONS DURING
REPETITION
Recent observation of objects speeds up
their subsequent identification and classification. This common form of
learning, known as repetition priming, can operate in the absence of explicit
memory for earlier experiences, 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 regions.
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 repeatedly, thereby facilitating future
availability of pertinent object knowledge. Jan Dobbins, David Schnyer, Mieke
Verfaellie and Daniel Schacter (Cortical activity reductions during
repetition priming can result from rapid response learning. Nature 428, 316-319, March, 18, 2004) provide experimental support for an
alternative hypothesis, in which reduced cortical activity occurs because
subjects rapidly learn their previous responses. 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.
BM&L-April 2004