Cognitive and neuronal processes involved in sequential generation of general and specific mental images

Mental image generation is a complex process mediated by dynamically interrelated components, e.g. image generation and image enrichment of details. This study investigated the cognitive and neural correlates of sequential image generation. An event-related fMRI experiment was carried out in which general and speciWc images had to be generated sequentially in two diVerent positions. Participants had to generate either a general image Wrst and then a speciWc one or a speciWc image Wrst and then a general one, in response to the same word-stimulus. Generation times showed that speciWc images took shorter to be produced if they had been preceded by the generation of a general image. The fMRI results showed that position of generation and type of image was associated with different patterns of neurofunctional change. When an image was generated as first, areas of activation were found in the parahippocampal, fusiform and occipital regions. These are areas associated with memory retrieval and visual processing. When an image was generated as second, significant activations were found in superior temporal and precuneus areas, brain structures that are involved in the storage of visual memory for object shapes and imagery, respectively. The generation of a general image was supported by frontal areas and by the precuneus. The generation of a specific image involved frontal and thalamic areas (structures associated with visual processing of details) and the posterior cingulate cortex. When shifting from a speciWc image to a general one, a higher level of activity was found in the middle frontal gyrus involved in global visuo-spatial processing, suggesting that the generation of speciWc images required the retrieval of an object’s global shape. Altogether, these data suggest that the sequential generation of diVerent types of image is associated with discrete processes but also shares common cognitive and neural components