Dissociation between Conceptual and Perceptual Implicit Memory: Evidence from Patients with Frontal and Occipital Lobe Lesions

Abstract

The latest neuroimaging studies about implicit memory (IM) have revealed that different IM types may be processed by different parts of the brain. However, studies have rarely examined what subtypes of IM processes are affected in patients with various brain injuries. Twenty patients with frontal lobe injury, 25 patients with occipital lobe injury, and 29 healthy controls (HC) were recruited for the study. Two subtypes of IM were investigated by using structurally parallel perceptual (picture identification task) and conceptual (category exemplar generation task) IM tests in the three groups, as well as explicit memory (EM) tests. The results indicated that the priming of conceptual IM and EM tasks in patients with frontal lobe injury was poorer than that observed in HC, while perceptual IM was identical between the two groups. By contrast, the priming of perceptual IM in patients with occipital lobe injury was poorer than that in HC, whereas the priming of conceptual IM and EM was similar to that in HC. This double dissociation between perceptual and conceptual IM across the brain areas implies that occipital lobes may participate in perceptual IM, while frontal lobes may be involved in processing conceptual memory.

Keywords: brain injury; explicit memory; frontal lobes; implicit memory; occipital lobes; priming.

Figure 1

The overlaying maps of brain injury in patient groups. (A,B) The main injured regions in patients with frontal lobe injury; (C,D) the main injured regions in patients with occipital lobe injury. The color bar reflects the number of injured patients; purple color represents one patient while yellow color represents nine patients injured in this area. X and Z represent the Montreal Neurological Institute space (MNI) coordinates in the brain.

Figure 2

The correlation between verbal fluency test and conceptual priming in patients with frontal lobe injury.