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Visual imagery – similar to visual perception – activates feature-specific and category-specific visual areas. This is frequently observed in experiments where the instruction is to imagine stimuli that have been shown immediately before the imagery task. Hence, feature-specific activation could be related to the short-term memory retrieval of previously presented sensory information. Here, we investigated mental imagery of stimuli that subjects had not seen before, eliminating the effects of short-term memory. We recorded brain activation using fMRI while subjects performed a behaviourally controlled guided imagery task in predefined retinotopic coordinates to optimize sensitivity in early visual areas. Whole brain analyses revealed activation in a parieto-frontal network and lateral–occipital cortex. Region of interest (ROI) based analyses showed activation in left hMT/V5+. Granger causality mapping taking left hMT/V5+ as source revealed an imagery-specific directed influence from the left inferior parietal lobule (IPL). Interestingly, we observed a negative BOLD response in V1–3 during imagery, modulated by the retinotopic location of the imagined motion trace. Our results indicate that rule-based motion imagery can activate higher-order visual areas involved in motion perception, with a role for top-down directed influences originating in IPL. Lower-order visual areas (V1, V2 and V3) were down-regulated during this type of imagery, possibly reflecting inhibition to avoid visual input from interfering with the imagery construction. This suggests that the activation in early visual areas observed in previous studies might be related to short- or long-term memory retrieval of specific sensory experiences.

PubMed ID: 22886737 Standard text reading involves frequent eye movements that go against normal reading order. The function of these "regressions" is still largely unknown. The most obvious explanation is that regressions allow for the rereading of previously fixated words. Alternatively, physically returning the eyes to a word's location could cue the reader's memory for that word, effectively aiding the comprehension process via location priming (the "deictic pointer hypothesis"). In Experiment 1, regression frequency was reduced when readers knew that information was no longer available for rereading. In Experiment 2, readers listened to auditorily presented text while moving their eyes across visual placeholders on the screen. Here, rereading was impossible, but deictic pointers remained available, yet the readers did not make targeted regressions in this experiment. In Experiment 3, target words in normal sentences were changed after reading. Where the eyes later regressed to these words, participants generally remained unaware of the change, and their answers to comprehension questions indicated that the new meaning of the changed word was what determined their sentence representations. These results suggest that readers use regressions to reread words and not to cue their memory for previously read words. Publisher's Version

International audience; Neuroimaging studies investigating the neural correlates of verbal fluency (VF) focused on sex differences without taking into account behavioural variation. Nevertheless, group differences in this verbal ability might account for neurocognitive differences elicited between men and women. The aim of this study was to test sex and performance level effects and the combination of these on cerebral activation. Four samples of 11 healthy Students (N = 44) selected on the basis of sex and contrasted VF scores, high fluency (HF) versus low fluency (LF), performed a covert phonological VF task during scans. Within-nd between-group analyses were conducted. Consistent with previous studies, for each sample, the whole-group analysis reported activation in the inferior frontal gyrus (IFG), insula, anterior cingulate cortex (ACC), medial frontal gyrus (mFG), superior (SPL) and inferior parietal lobules (IPL), inferior visual areas, cerebellum, thalamus and basal ganglia. Between-group analyses showed an interaction between sexes and performances in the right precuneus, left ACC, right IFG and left dorsolateral prefrontal cortex (dlPFC). HF men showed more activation than LF ones in the right precuneus and left dlPFC. LF men showed more activation in the right IFG than HF ones and LF women elicited more activation in the left ACC than HF ones. A sex main effect was found regardless of performance in the left inferior temporal gyrus (ITG), cerebellum, anterior and posterior cingulate cortexes and in the right superior frontal gyrus (SFG) and dlPFC, lingual gyrus and ACC, with men eliciting significantly greater activations than women. A performance main effect was found for the left ACC and the left cerebellum regardless of sex. LF subjects had stronger activations than HF ones in the ACC whereas HF subjects showed stronger activations in the cerebellum. Activity in three discrete subregions of the ACC is related to sex, performance and their interaction, respectively. Our findings emphasize the need to consider sex and performance level in functional imaging studies of VF. (c) 2007 Elsevier Srl. All rights reserved.