Role of prefrontal and parietal cortices in associative learning

Abstract

Two studies were performed that compared a "Paired" condition in which participants studied paired associates with a "Generated" condition in which participants completed word fragments to produce paired associates. In both tasks, participants were responsible for memory of the material either studied or generated. The experiments revealed significant differences between the responses of a predefined prefrontal region and a predefined parietal region. The parietal region responded more in the Generated condition than the Paired condition, whereas there was no difference in the prefrontal region. On the other hand, the prefrontal region responded to the delay between study and test in both the Paired and Generated conditions, whereas the parietal region only responded to delay in the Generated condition. This pattern of results is consistent with the hypothesis that the parietal region is responsive to changes in problem representation and the prefrontal region to retrieval operations. An information-processing model embodying these assumptions was fit to the blood oxygen level-dependent responses in these regions.

Figure 1

A comparison of the procedures in the Paired and Generated conditions.

Figure 2

Behavioral results from Experiment 1: (a) Probability of correct recall; (b) Latency of correct recall.

Figure 3

fMRI results from Experiment 1: (a) BOLD response in the predefined posterior parietal region; (b) BOLD response in the predefined prefrontal region.

Figure 4

Behavioral results from Experiment 2: (a) Probability of correct recall; (b) Latency of correct recall.

Figure 5

fMRI results from Experiment 2: (a) BOLD response in the predefined posterior parietal region; (b) BOLD response in the predefined prefrontal region.

Figure 6

A representation of the sequence of module activity in different conditions of the experiment. Blue denotes activity in the visual module, green in the imaginal (parietal) module, red in the declarative retrieval (prefrontal) module, and yellow in the manual module. The retrieval boxes and delays between activity are not drawn to scale.

Figure 7

Predictions of the model for latencies and observed latencies, averaging over the 2 experiments.

Figure 8

Predictions of the information-processing model for parietal and prefrontal regions of interest for the 2 experiments. Dotted lines connect the data points and solid lines are the predictions of the model.

Figure 9

Response in the prefrontal region for each delay condition. Dotted lines connect the data points and solid lines are the predictions of the model.