Material specific lateralization of medial temporal lobe function: An fMRI investigation

Abstract

The theory of material specific lateralization of memory function posits that left and right MTL regions are asymmetrically involved in mnemonic processing of verbal and nonverbal material respectively. Lesion and functional imaging (fMRI) studies provide robust evidence for a left MTL asymmetry in the verbal memory domain. Evidence for a right MTL/nonverbal asymmetry is not as robust. A handful of fMRI studies have investigated this issue but have generally utilised nonverbal stimuli which are amenable to semantic elaboration. This fMRI study aimed to investigate the neural correlates of recognition memory processing in 20 healthy young adults (mean age = 26 years) for verbal stimuli and nonverbal stimuli that were specifically designed to minimize verbalisation. Analyses revealed that the neural correlates of recognition memory processing for verbal and nonverbal stimuli were differentiable and asymmetrically recruited the left and right MTL respectively. The right perirhinal cortex and hippocampus were preferentially involved in successful recognition memory of items devoid of semantic information. In contrast, the left anterior hippocampus was preferentially involved in successful recognition memory of stimuli which contained semantic meaning. These results suggest that the left MTL is preferentially involved in mnemonic processing of verbal/semantic information. In contrast, the right MTL is preferentially involved in visual/non-semantic mnemonic processing. We propose that during development, the left MTL becomes specialised for verbal mnemonic processing due to its proximity with left lateralised cortical language processing areas while visual/non-semantic mnemonic processing gets 'crowded out' to become predominantly, but not completely, the domain of the right MTL.

Keywords: fMRI; material specific lateralization of function; medial temporal lobes.

Figure 1

Three examples of the symbol pairs used in the nonverbal task.

Figure 2

Recognition memory performance for each stimulus condition on the verbal and nonverbal tasks. The bar chart shows the percent correct response for each condition (old and new). Error bars represent the standard error of the mean. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 3

Regions of significant difference in BOLD response associated with recognition memory (old vs. new) for verbal (red) and nonverbal (blue) stimuli. Bar charts indicate mean percent signal change associated with each memory condition (verbal old and nonverbal old) within each significant cluster. See Table 1 for the coordinates and cluster sizes of relevant regions. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]