The neural bases of visual mental imagery are the object of intense debate; in patients with acquired brain damage, the consensus model predicts a systematic co-occurrence of perceptual and imaginal deficits; however...

Visual mental imagery engages the left fusiform gyrus, but not the early visual cortex: A meta-analysis of neuroimaging evidence. Alfredo Spagna, Dounia Hajhajate, Jianghao Liu, Paolo Bartolomeo. bioRxiv, Feb 7 2020. https://doi.org/10.1101/2020.02.06.937151

Abstract: The neural bases of visual mental imagery (VMI) are the object of intense debate. Their identification is central to define the brain substrates our conscious experience, and can be clinically important to reveal consciousness in non-communicating patients. The dominant model of VMI stipulates a functional and anatomical equivalence between visual mental imagery and visual perception. In patients with acquired brain damage, the model predicts a systematic co-occurrence of perceptual and imaginal deficits. However, patients with lesions restricted to the occipital cortex often experience vivid mental images, even in case of cortical blindness resulting from bilateral V1 damage. Instead, patients with extensive left temporal damage are more likely to have impaired VMI. On the other hand, some neuroimaging and neuromodulatory evidence does suggest an implication of striate cortex in VMI. To address this discrepancy, we conducted an activation-likelihood-estimation-based large-scale meta-analysis of 52 functional magnetic resonance imaging experiments to map the extent of cortical activation associated with three contrasts: (1) all studies combined; (2) VMI versus Control, (3) VMI versus Perception, and (4) Motor Mental Imagery versus Control. Results from the VMI versus Control contrast demonstrated an association between VMI and activation increase in the frontoparietal and cingulo-opercular networks bilaterally, as well as of the left fusiform gyrus. Results from the VMI versus Perception contrast showed the association between VMI and activation increase of areas lateralized to the left hemisphere, including the superior and inferior frontal gyri, as well as the fusiform gyrus. Conjunction analyses between the VMI versus Control and the VMI Mental Imagery versus Perception contrasts showed the activation of the left anterior insular cortex. Results from the Motor Mental Imagery versus Control contrast showed that mental motor imagery increases the activation of the cerebellum bilaterally, of the precentral gyrus bilaterally, of the left supplementary motor area, and of the left fusiform sulcus. Conjunction analyses between the VMI versus Control and the Motor Mental Imagery versus Control contrasts showed the activation of the right superior frontal gyrus. Thus, the results stress the importance for VMI of brain networks associated with attentional control and working memory functions, together with rostral portions of the cortical ventral visual stream. Bayesian analysis confirmed the lack of evidence for an activation of the early visual areas in VMI, consistent with the evidence from brain-damaged patients. Our evidence suggests a revision of the VMI model. A Fusiform Imagery Node in the area FG3 of the left fusiform gyrus might act as a hub retrieving visual information from long-term semantic memory in the anterior temporal lobe, in connection with the medial temporal lobe, important for a vivid VMI episodic experience. Fronto-parietal networks subserving attention and working memory initiate, modulate and maintain activity of the core VMI network in the left temporal lobe. The revised model of VMI reconciles findings from neuroimaging with the reports of patients with brain damage.