Abstract
BackgroundDorsolateral prefrontal cortex (DLPFC), posterior parietal cortex, and regions in the occipital cortex have been identified as neural sites for visual working memory (WM). The exact involvement of the DLPFC in verbal and non-verbal working memory processes, and how these processes depend on the time-span for retention, remains disputed.MethodsWe used functional MRI to explore the neural correlates of the delayed discrimination of Gabor stimuli differing in orientation. Twelve subjects were instructed to code the relative orientation either verbally or non-verbally with memory delays of short (2 s) or long (8 s) duration.ResultsBlood-oxygen level dependent (BOLD) 3-Tesla fMRI revealed significantly more activity for the short verbal condition compared to the short non-verbal condition in bilateral superior temporal gyrus, insula and supramarginal gyrus. Activity in the long verbal condition was greater than in the long non-verbal condition in left language-associated areas (STG) and bilateral posterior parietal areas, including precuneus. Interestingly, right DLPFC and bilateral superior frontal gyrus was more active in the non-verbal long delay condition than in the long verbal condition.ConclusionThe results point to a dissociation between the cortical sites involved in verbal and non-verbal WM for long and short delays. Right DLPFC seems to be engaged in non-verbal WM tasks especially for long delays. Furthermore, the results indicate that even slightly different memory maintenance intervals engage largely differing networks and that this novel finding may explain differing results in previous verbal/non-verbal WM studies.
Highlights
Dorsolateral prefrontal cortex (DLPFC), posterior parietal cortex, and regions in the occipital cortex have been identified as neural sites for visual working memory (WM)
A memory system related to the visuo-spatial sketchpad component of WM is perceptual memory, which has been described as a low-level memory process that is comprised of a series of independent parallel mechanisms for various basic stimulus dimensions
Behavioural results The computation of each individual's performance revealed that all participants were able to discriminate the relevant stimuli reasonably well
Summary
Dorsolateral prefrontal cortex (DLPFC), posterior parietal cortex, and regions in the occipital cortex have been identified as neural sites for visual working memory (WM). A memory system related to the visuo-spatial sketchpad component of WM is perceptual memory, which has been described as a low-level memory process that is comprised of a series of independent parallel mechanisms for various basic stimulus dimensions. These attributes, such as spatial frequency, contrast, or orientation, are thought to be the building blocks of visual images [4]. According to this theory, each attribute is stored with high precision in separate perceptual stores [5]. These models of sensory-based WM emphasize the delay-related signals in sensory cortex and the reciprocal projections of these areas to parietal and prefrontal cortex [6]
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