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Abstract:
We previously reported that naming an object once leads to
immediate and long-lasting (3 days) decreases in activity in
posterior regions, concurrent with slower developing changes in
anterior regions of the object naming system. Here, we used
event-related fMRI to examine how these changes are modulated by
the spacing and number of object repetitions. Ten subjects named
pictures of objects 3 times; 3 days, 6 hours, and 1 hour prior to
scanning (spaced practiced). During scanning, subjects named these
pictures again, intermixed with novel pictures. These novel
pictures were also repeated 3 times at 30 sec time intervals
(massed practice). Pictures were presented randomly intermixed, for
200 msec, one every 2.5 seconds. Whole brain images were collected
on a 3.0T scanner. Relative to a visual-noise baseline, naming
objects increased activity in bilateral ventral occipitotemporal,
left inferior frontal (Broca's area), and left insular cortices.
Both massed and spaced repetitions led to decreased activity in
occipitotemporal and left inferior cortices, and these decreases
got larger with multiple repetitions. Importantly, whereas in
occipitotemporal cortex decreases were greater after massed
practice, in Broca's area decreases were significantly greater when
repetitions were spread out over the course of three days. This
difference in time course suggests that the experience-related
changes in neural activity in posterior and anterior regions
reflect distinct types of learning.
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