Selective involvement of superior frontal cortex during working memory for shapes

Abstract

A spatial/nonspatial functional dissociation between the dorsal and ventral visual pathways is well established and has formed the basis of domain-specific theories of prefrontal cortex (PFC). Inconsistencies in the literature regarding prefrontal organization, however, have led to questions regarding whether the nature of the dissociations observed in PFC during working memory are equivalent to those observed in the visual pathways for perception. In particular, the dissociation between dorsal and ventral PFC during working memory for locations versus object identities has been clearly present in some studies but not in others, seemingly in part due to the type of objects used. The current study compared functional MRI activation during delayed-recognition tasks for shape or color, two object features considered to be processed by the ventral pathway for perceptual recognition. Activation for the shape-delayed recognition task was greater than that for the color task in the lateral occipital cortex, in agreement with studies of visual perception. Greater memory-delay activity was also observed, however, in the parietal and superior frontal cortices for the shape than for the color task. Activity in superior frontal cortex was associated with better performance on the shape task. Conversely, greater delay activity for color than for shape was observed in the left anterior insula and this activity was associated with better performance on the color task. These results suggest that superior frontal cortex contributes to performance on tasks requiring working memory for object identities, but it represents different information about those objects than does the ventral frontal cortex.

FIG. 1.

Example trial sequence for the color-delayed recognition, shape-delayed recognition, and sensorimotor control tasks. The working-memory trials shown are both “match” trials. One representative shade from each color group of stimuli is shown.

FIG. 2.

Brain regions showing greater activity during shape than during color working-memory delays (green) and greater activity during color than during shape delays (red).

FIG. 3.

Differential activities in shape-sensitive (green) and color-sensitive (red) regions for good (solid line) and poor (dotted line) performers. A: left superior frontal sulcus. B: right middle occipital gyrus. C: left insula.