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...ad actually been created during the task. with the three-dimensional version of SPMs (Friston et al., 1995). The original brain images were transformed into the standard stereotactic Talairach space (=-=Talairach and Tournoux, 1988-=-). Global differences in the NrCBF within and between subjects were removed by scaling, and comparisons across conditions were made by way of t statistics. As indicated above, the experimental protoco...

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... is upheld on-line so that the object is assembled correctly. The role of the visuospatial sketch pad, one of the working memory components, is to maintain visuospatial information in the short term (=-=Baddeley, 1992-=-). Its involvement in the CONS task could result in the simultaneous activation of the parietal cortex and the premotor lateral cortex. In fact, coupled activations of the parietal and premotor cortic...

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... some mental imagery tasks may not involve any significant participation of early visual areas. Key words: spatial mental imagery; dorsal visual pathway; frontal cortex; parietal cortex; occipital cortex; precuneus; position emission tomography; cerebral blood flow The significance of mental imagery in human cognition results from the capacity of this process to reactivate previous visual experience in a quasi-perceptual format. Visual images reflecting objects or spatial configurations are accessible to conscious inspection and can be externalized in particular in the form of verbal reports (Paivio, 1986). A recently emphasized feature of visual imagery is its capacity to build mental representations of objects that have never been experienced perceptually but have been described verbally. In such cases, the generation of visual images does not result from the reactivation of previously stored memories but does result from on-line construction of internal representations on the basis of the processing of verbal instructions and their encoding in a visuospatial format. Although such images may lack detail or vividness, they have been shown to reflect properties similar to those of images based ...

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...t the category of spatial words could be processed by motor and spatial systems, namely the premotor and occipitoparietal cortex, rather than by classical language areas (Landau and Jackendoff, 1993; =-=Jeannerod, 1994-=-). The CONS and LIST conditions elicited very different patterns of decreases when compared with REST. Although the physiological significance remains unclear, the medial frontal and posterior cingula...

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...otomy that was evidenced in the visual system between dorsal and ventral anatomo-functional pathways respectively specialized in the processing of spatial and figurative attributes of visual stimuli (=-=Mishkin et al., 1983-=-; Haxby et al., 1991, 1994). It remains to be seen whether a highly specialized visual treatment route can be mobilized by an acoustico-verbal input. This should provide additional insight into the br...

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...3). It has been suggested that the category of spatial words could be processed by motor and spatial systems, namely the premotor and occipitoparietal cortex, rather than by classical language areas (=-=Landau and Jackendoff, 1993-=-; Jeannerod, 1994). The CONS and LIST conditions elicited very different patterns of decreases when compared with REST. Although the physiological significance remains unclear, the medial frontal and ...

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...d in visuospatial tasks, such as spatial localization (Haxby et al., 1994) or shifting of spatial attention (Corbetta et al., 1993), and in situations explicitly involving the spatial working memory (=-=Jonides et al., 1993-=-; Courtney et al., 1996). They were described recently in a study on the execution of prelearned sequences of eye saccades in total darkness (Petit et al., 1996), in which it was emphasized that this ...

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... representation. This implication of the visual memory may be reflected by the inferior temporal activation; this region is known to be involved in visual memory processes in both humans and monkeys (=-=Miyashita, 1993-=-). Moreover, there have been several reports of activation of inferior temporal lobes during PET studies on mental imagery (Kosslyn et al., 1993; Roland and Gulyas, 1995), which indicates that this st...

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...unclear, the medial frontal and posterior cingulate deactivation observed during CONS were close to those observed previously during visual matching tasks (Haxby et al., 1994) or visual memory tasks (=-=Moscovitch et al., 1995-=-; Courtney et al., 1996), in agreement with the visuospatial nature of our task. On the other hand, the NrCBF decreases evidenced during the LIST condition were located in the visual associative areas...

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...presentations In the CONS condition, the subjects used acoustico-verbal information to assemble units into three-dimensional objects that had no physical counterparts. Because verbal and visual representations are different cognitive entities (Paivio, 1986), this operation implies on-line translation of the semantic content of verbal stimuli into picture-like representations. The flow increases in the superior and middle gyri observed during both the CONS and the LIST conditions likely reflect the lexico-semantic treatment required in these two cases (Petersen et al., 1988; Wise et al., 1991; Price et al., 1992; Guaraglia et al., 1993; Mazoyer et al., 1993). The locations and intensities of these activations were remarkably similar in these two conditions. Although it requires the semantic processing of the word, the CONS task did not implicate language areas in a more extensive manner than the LIST did. Rather, an activation of Broca’s area was detected during LIST conditions, congruent with previous PET studies (Mazoyer et al., 1993), with no equivalent during CONS conditions. The lack of Broca’s area activation during the latter task could be related to the nature of the words that were used. Onl...

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... CONS condition, the subjects used acoustico-verbal information to assemble units into three-dimensional objects that had no physical counterparts. Because verbal and visual representations are different cognitive entities (Paivio, 1986), this operation implies on-line translation of the semantic content of verbal stimuli into picture-like representations. The flow increases in the superior and middle gyri observed during both the CONS and the LIST conditions likely reflect the lexico-semantic treatment required in these two cases (Petersen et al., 1988; Wise et al., 1991; Price et al., 1992; Guaraglia et al., 1993; Mazoyer et al., 1993). The locations and intensities of these activations were remarkably similar in these two conditions. Although it requires the semantic processing of the word, the CONS task did not implicate language areas in a more extensive manner than the LIST did. Rather, an activation of Broca’s area was detected during LIST conditions, congruent with previous PET studies (Mazoyer et al., 1993), with no equivalent during CONS conditions. The lack of Broca’s area activation during the latter task could be related to the nature of the words that were used. Only a few spatial words ex...

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...m (Baddeley, 1992). Its involvement in the CONS task could result in the simultaneous activation of the parietal cortex and the premotor lateral cortex. In fact, coupled activations of the parietal and premotor cortices have been described in visuospatial tasks, such as spatial localization (Haxby et al., 1994) or shifting of spatial attention (Corbetta et al., 1993), and in situations explicitly involving the spatial working memory (Jonides et al., 1993; Courtney et al., 1996). They were described recently in a study on the execution of prelearned sequences of eye saccades in total darkness (Petit et al., 1996), in which it was emphasized that this frontoparietal interaction is not dependent on a perceptual activity. Our results demonstrate that an exchange of information between the premotor and the parietal areas is also necessary when the visuospatial stimulus is processed only mentally. They also mean that this interaction is independent from the execution of a motor activity. It is likely that the parietal “perceptual” pole and the frontal “motor” pole systematically exchange spatial information, whether a motor action is envisioned or not, thus executing the encoding of a spatial environment i...

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...ublic Cyceron, Boulevard Becquerel, BP 5229, F-14074 Caen Cedex, France. Copyright � 1996 Society for Neuroscience 0270-6474/96/166504-09$05.00/0 imagery (Kosslyn et al., 1993; Le Bihan et al., 1993; =-=Mellet et al., 1995-=-; Roland and Gulyas, 1995; Kosslyn et al., 1996). They have shown that images generated from previously memorized percepts activate regions engaged in visual perception, giving anatomical support to t...

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...not result from the reactivation of previously stored memories but does result from on-line construction of internal representations on the basis of the processing of verbal instructions and their encoding in a visuospatial format. Although such images may lack detail or vividness, they have been shown to reflect properties similar to those of images based on perceptual experience. In particular, cognitive operations performed on images, such as mental scanning or distance comparisons, exhibit chronometric patterns similar to those executed on images that reactivate stored visual information (Denis et al., 1995; De Vega et al., 1996). Previous functional neuroanatomy studies using either positron emission tomography (PET) or functional magnetic resonance imaging (FMRI) have considered the brain regions involved in mental imagery (Kosslyn et al., 1993; Le Bihan et al., 1993; Mellet et al., 1995; Roland and Gulyas, 1995; Kosslyn et al., 1996). They have shown that images generated from previously memorized percepts activate regions engaged in visual perception, giving anatomical support to the analogies between perception and its mental equivalent. Moreover, in a recent report, we showed that mental e...

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... versus CONS comparison and the REST versus LIST comparison. We believed that it would be worthwhile to compare the results of the present study with data on mental spatial exploration reported recently from our laboratory (Mellet et al., 1995). In the previous study, the mental imagery task consisted of the mental exploration of the visual image of a previously presented spatial configuration. Subjects were asked to execute this task in total darkness without any time constraint, in contrast to the classic mental scanning paradigm that also calls for mental exploration (Kosslyn et al., 1978; Denis and Cocude, 1992). The control condition was the condition described above as REST. This study was carried out with another sample of eight subjects with high visuospatial abilities and with the same PET and data acquisition scheme; however, PET data were analyzed using a region-of-interest analysis method. To compare the two mental spatial imagery tasks properly, these previous data were thus reanalyzed using the same SPM approach as that used in the present report. RESULTS CONS task execution It is noteworthy that the subjective details of the imagery activity during the construction of mental objects differ...

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... the superior and middle gyri observed during both the CONS and the LIST conditions likely reflect the lexico-semantic treatment required in these two cases (Petersen et al., 1988; Wise et al., 1991; =-=Price et al., 1992-=-; Guaraglia et al., 1993; Mazoyer et al., 1993). The locations and intensities of these activations were remarkably similar in these two conditions. Although it requires the semantic processing of the...

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...and amer (sour). Therefore, subjects listened to the exact same number of phonetically equivalent words presented at the same rate during both the CONS and the LIST conditions. Control task 2: REST. In the second control condition (REST), no instructions were given to the subjects except that they were not to move. This baseline control condition is the usual reference condition used in our laboratory. Image data acquisition. For each NrCBF measurement, thirty-one 3.375-mm-thick contiguous brain slices were acquired simultaneously on an ECAT 953B/31 PET camera with a 5 mm in-plane resolution (Mazoyer et al., 1991). A black chamber was set up all around the PET tomograph so that PET data were acquired in total darkness, with subjects’ eyes closed, in all conditions. To assess eye movements, horizontal electro-oculograms were recorded for each subject, using external electrodes placed at the external canthi and a right ear reference electrode. Emission data were acquired with septa extended. Tasks were started 30 sec before the intravenous bolus injection of 60 mCi of 15O-labeled water. A single 80 sec scan was acquired and reconstructed (including a correction for head attenuation using a measured trans...

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...of Spatial Mental Imagery J. Neurosci., October 15, 1996, 16(20):6504–6512 6511 ment of the primary visual areas (PVAs) in mental imagery tasks performed in total darkness (Kosslyn and Ochsner, 1994; =-=Moscovitch et al., 1994-=-; Roland and Gulyas, 1994). In short, the REST condition used as a reference condition by the groups that do not evidence activation of PVA is suspected to be the cause of this absence of activation. ...

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...ddle gyri observed during both the CONS and the LIST conditions likely reflect the lexico-semantic treatment required in these two cases (Petersen et al., 1988; Wise et al., 1991; Price et al., 1992; =-=Guaraglia et al., 1993-=-; Mazoyer et al., 1993). The locations and intensities of these activations were remarkably similar in these two conditions. Although it requires the semantic processing of the word, the CONS task did...

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...agery and verbal representations In the CONS condition, the subjects used acoustico-verbal information to assemble units into three-dimensional objects that had no physical counterparts. Because verbal and visual representations are different cognitive entities (Paivio, 1986), this operation implies on-line translation of the semantic content of verbal stimuli into picture-like representations. The flow increases in the superior and middle gyri observed during both the CONS and the LIST conditions likely reflect the lexico-semantic treatment required in these two cases (Petersen et al., 1988; Wise et al., 1991; Price et al., 1992; Guaraglia et al., 1993; Mazoyer et al., 1993). The locations and intensities of these activations were remarkably similar in these two conditions. Although it requires the semantic processing of the word, the CONS task did not implicate language areas in a more extensive manner than the LIST did. Rather, an activation of Broca’s area was detected during LIST conditions, congruent with previous PET studies (Mazoyer et al., 1993), with no equivalent during CONS conditions. The lack of Broca’s area activation during the latter task could be related to the nature of the words...

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...his activation cannot be attributed to an increase of oculomotor activity during the CONS task, because the amplitude and the frequency of eye movements did not show any significant differences when compared with both control conditions. The construction of a mental object requires that after transcoding the semantic information into a spatial representation, the relative localization of each cube is upheld on-line so that the object is assembled correctly. The role of the visuospatial sketch pad, one of the working memory components, is to maintain visuospatial information in the short term (Baddeley, 1992). Its involvement in the CONS task could result in the simultaneous activation of the parietal cortex and the premotor lateral cortex. In fact, coupled activations of the parietal and premotor cortices have been described in visuospatial tasks, such as spatial localization (Haxby et al., 1994) or shifting of spatial attention (Corbetta et al., 1993), and in situations explicitly involving the spatial working memory (Jonides et al., 1993; Courtney et al., 1996). They were described recently in a study on the execution of prelearned sequences of eye saccades in total darkness (Petit et al., 1996...