Insights on the Connectivity of the Precuneus: Introducing the Retrosplenial Aslant Tract (RAT). Georgios P. Skandalakis; Christos Koutsarnakis MD, MSc; Aristotelis Kalyvas; Dimitris G. Placantonakis MD PhD; John G. Golfinos MD; Constantinos G. Hadjipanayis MD PhD; Kostas N. Fountas MD PhD FAANS; Eftychia Z. Kapsalaki MD; George S. Stranjalis National and Kapodistrian University of Athens Medical School

Introduction the parieto-occipital sulcus, References Trajectory RAT fibers terminating at the The functional connectivity of and passing through the 1. Epstein et al. The cognitive map in temporal pole humans: spatial navigation and the precuneus with regions of parahippocampal place area beyond. Nature neuroscience. (2017) the medial temporal lobe is a (PPA), it curves laterally and 2. Wade-Bohleber et al. Thinking major component of our projects towards the temporal about the past to shape the present: default mode network and horn to finally reach the Neural activation during the recall of relationship episodes. Behavioural underlies high order temporal pole. (Figures 1,3,4) Brain Research (2018). functions.(1-5) Stronger On its way to the temporal 3. Hebscher et al. The precuneus and connectivity of these regions pole this tracts also displays hippocampus contribute to individual differences in the unfolding of spatial is corelated with higher connections with the lingual, Dark blue continuous lines, RAT representations during episodic cognitive performances(7) parahippocampal and fusiform trajectory; highlighted light blue, Left hemisphere infero-medial autobiographical memory. while in neurological and gyri, inferior longitudinal RAT Cortical Projections; CaF, view demonstrating the regional Neuropsychologia. (2018) psychiatric conditions this is fasciculus and hippocampal calcarine fissure; FuG, fusiform fiber tract anatomy after 4. Wen et al., The neural correlates of intelligence comparison. Cerebral found disrupted.(7-9) formation.(Figures 1-3) gyrus; PPA, parahippocampal dissection of the inferior Cortex. (2017) Although a growing body of place area; POS, parieto-occipital longitudinal fasciculus and most 5. Kaboodvand et al., The evidence demonstrates this Conclusions sulcus TePo, temporal pole; Un, of the cingulum fibers. grey, retrosplenial cortex: A memory functional connectivity and its This study demonstrates the uncus retrosplenial aslant tract; yellow, gateway between the cortical default mode network and the medial importance, the underlying direct connectivity of the sledge runner fasciculus; blue, temporal lobe. Hum Brain Mapp. structural circuit remains RAT fibers & ILF precuneus with medial inferior longitudinal fasciculus; (2018) anonymous. During a temporal lobe regions through green, resected cingulum; CAF, 6. Zhang et al. The relationship laboratory investigation of the a distinct fiber tract, which we calcarine fissure; Ci, cingulum; between voxel-based metrics of resting state functional connectivity anatomical connectivity of named the retrosplenial aslant OcPo, occipital pole; POS, and cognitive performance in these regions, we identified a tract (RAT) due to its oblique parieto-occipital sulcus; TePo, cognitively healthy elderly adults. previously unknown fiber trajectory and highest fiber temporal pole Brain Imaging Behav. (2018) tract, thus prompting its density at the retrosplenial 7. Liu et al. The superficial white matter in temporal lobe epilepsy: a further exploration. area. Our results indicate that DTI key link between structural and the RAT is responsible for the functional network disruptions. Brain. Left hemisphere, infero-medial Methods connectivity of high order (2016) view following cortical and U-fiber Nine normal cadaveric areas implicated in memory, 8. Zhu et al.,Reduced functional microdissection. The RAT can be connectivity between bilateral hemispheres were studied attention, consciousness, observed at the anterior bank of precuneus and contralateral through the fiber micro- spatial updating, navigation, parahippocampus in schizotypal the POS highlighted in grey, dissection technique(10) and and visuomotor planning; personality disorder. BMC psychiatry. running between the precuneus, a tailored DTI protocol thus, calling for studies that DTI Representation and (2017) and the ILF. Grey, retrosplenial 9. De Schipper et al. Altered whole- including a two region-of- will enhance our projection over a sagittal MRI aslant tract; yellow, sledge runner image. brain and network-based functional interest (ROI) approach was understanding of its function connectivity in Parkinson's disease. dark; CaF, calcarine fissure; applied in three healthy Frontiers in neurology. (2018). OcPo, occipital pole; POS, adults. 10. Koutsarnakis et al. A laboratory parieto-occipital sulcus manual for stepwise cerebral white Learning Objectives matter fiber dissection. World Results To introduce a previously neurosurgery (2015) A distinct fiber tract is unknown fiber tract which consistently identified at the redefines neuroanatomical depth of the posteromedial knowledge regarding the cortex running between the connectivity of the precuneus precuneus and temporal pole. and temporal lobe. This tract follows the direction