Cortical areas supporting category learning identified using functional MRI

Abstract

Functional MRI was used to identify cortical areas involved in category learning by prototype abstraction. Participants studied 40 dot patterns that were distortions of an underlying prototype and then, while functional MRI data were collected, made yes-no category judgments about new dot patterns. The dot patterns alternated between ones mostly requiring a "yes" response and ones mostly requiring a "no" response. Activity in four cortical areas correlated with the category judgment task. A sizeable posterior occipital cortical area (BA 17/18) exhibited significantly less activity during processing of the categorical patterns than during processing of noncategorical patterns. Significant increases in activity during processing the categorical patterns were observed in left and right anterior frontal cortex (BA 10) and right inferior lateral frontal cortex (BA 44/47). Decreases in activation of visual cortex when categorical patterns were being evaluated suggest that these patterns could be processed in a more rapid or less effortful manner after the prototype had been learned. Increases in prefrontal activity associated with processing categorical patterns could be related to any of several processes involved in retrieving information about the learned exemplars.

Figure 1

Examples of study items and test items used to assess classification learning of dot patterns. The study items were high distortions of a prototype dot pattern. The test items, illustrated left to right, were presentations of the training prototype, low and high distortions of the training prototype, and random dot patterns.

Figure 2

Classification of new dot patterns after studying 40 exemplar patterns. The endorsement rate varied in accordance with how closely the test items resembled the study items. P, instances of the prototype (four patterns per test); L, low distortions of the prototype (20 patterns per test); H, high distortions of the prototype (20 patterns per test); R, random patterns (40 patterns per test). Error bars show the SEM.

Figure 3

Brain areas activated. Areas of significant signal change are shown as color overlays on the averaged axial structural images (transformed to the atlas of Talairach and Tournoux, ref. 8). Images are oriented according to radiologic convention (the right side of the brain is on the left side of the image, anterior-posterior is shown top to bottom). The distance of the displayed slice above the AC-PC line is shown below each image. Areas where activation increased when subjects processed categorical patterns are shown in red and yellow. Areas where activation decreased during the processing of categorical patterns are indicated in blue.