Abstract
Introduction. To analyze mechanisms of visual working memory and learning, we compared the brain networks involved in the processes of direct visual study, and (open-eyes) visualization from immediate memory, using previously unfamiliar material in a novel procedure to enhance memory representations. Methods. Functional MRI was run while complex spatial structures in the form of line-drawings were alternately i) visually explored to be learned, and ii) mentally visualized on a blank screen in a repeated sequence to maximize the accuracy of the memory trace. The viewing and visualization blocks were 30 s each, separated by 20 s rest periods, and repeated 3 times in each trial. The brain imaging session was followed by testing for comprehension and by direct readout of the memory trace through memory-guided drawing of the learned images. Results & Conclusions. The first response site of particular interest was the primary visual cortex (V1), which our previous studies in the blind have implicated as the neural implementation - in a supramodal form – of the ‘spatial sketchpad’ for working memory (Likova, 2012, 2013). V1 was subdivided into foveal, parafoveal, mid- and far-peripheral regions. Remarkably, direct viewing and memory visualization equally activated the mid- and far-periphery regions, whereas in the parafoveal representation the visualization signal dropped to about half of that for direct viewing, and even rapidly inverted into strong suppression throughout the extrastriate foveal confluence. Conversely, the classical visual hierarchy beyond V1 was not involved. Granger causal connectivity analysis was used to disentangle the interregional interactions within the activated networks and to provide deeper insights into cortical mechanisms of visualization from memory and its involvement in learning, including top-down causal influences to the V1-subdivisions and foveal confluence from hippocampal, parietal and frontal regions.
Acknowledgement: NSF/SL-CN & NIH/NEI ROI to LTL