Contrasting visual working memory for verbal and non-verbal material with multivariate analysis of fMRI

• Published in: Brain research Vol. 1467; pp. 27 - 41
• Main Authors: Habeck, Christian, Rakitin, Brian, Steffener, Jason, Stern, Yaakov
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 27.07.2012; Elsevier
• Subjects: Anatomical correlates of behavior; Behavioral psychophysiology; Biological and medical sciences; brain; correlation; covariance; Encoding; Female; Fundamental and applied biological sciences. Psychology; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Maintenance; Male; memory; Memory, Short-Term; Memory, Short-Term - physiology; Multivariate Analysis; Neurology; Photic Stimulation; physiology; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Psychomotor Performance; Psychomotor Performance - physiology; Recognition (Psychology) - physiology; Recognition, Psychology; Verbal Learning; Verbal Learning - physiology; Visual Perception; Visual Perception - physiology; Visual working memory; Young Adult; Visual working memory; Encoding; Maintenance; Multivariate analysis; Human; Visual memory; Cognition; Nuclear magnetic resonance imaging; Verbal memory; Language; Coding; Working memory; Functional imaging
• ISSN: 0006-8993; 1872-6240; 1872-6240
• DOI: 10.1016/j.brainres.2012.05.045

We performed a Delayed-Item-Recognition task to investigate the neural substrates of non-verbal visual working memory with event-related fMRI (‘Shape task’). 25 young subjects (mean age: 24.0years; STD=3.8years) were instructed to study a list of either 1, 2 or 3 unnamable nonsense line drawings for 3s (‘stimulus phase’ or STIM). Subsequently, the screen went blank for 7s (‘retention phase’ or RET), and then displayed a probe stimulus for 3s in which subjects indicated with a differential button press whether the probe was contained in the studied shape-array or not (‘probe phase’ or PROBE). Ordinal Trend Canonical Variates Analysis (Habeck et al., 2005a) was performed to identify spatial covariance patterns that showed a monotonic increase in expression with memory load during all task phases. Reliable load-related patterns were identified in the stimulus and retention phase (p<0.01), while no significant pattern could be discerned during the probe phase. Spatial covariance patterns that were obtained from an earlier version of this task (Habeck et al., 2005b) using 1, 3, or 6 letters (‘Letter task’) were also prospectively applied to their corresponding task phases in the current non-verbal task version. Interestingly, subject expression of covariance patterns from both verbal and non-verbal retention phases correlated positively in the non-verbal task for all memory loads (p<0.0001). Both patterns also involved similar frontoparietal brain regions that were increasing in activity with memory load, and mediofrontal and temporal regions that were decreasing. Mean subject expression of both patterns across memory load during retention also correlated positively with recognition accuracy (dL) in the Shape task (p<0.005). These findings point to similarities in the neural substrates of verbal and non-verbal rehearsal processes. Encoding processes, on the other hand, are critically dependent on the to-be-remembered material, and seem to necessitate material-specific neural substrates. ► FMRI data from visual verbal and non-verbal working memory tasks were analyzed with spatial covariance analysis. ► Both tasks gave rise to activation patterns that changed monotonically with memory load. ► The activation patterns underlying encoding showed no similarity between verbal and non-verbal task. ► The activation patterns underlying maintenance showed great similarity between verbal and non-verbal task.