Anterior temporobasal sulcal morphology: development of a reliable rating protocol and normative data

The three anterior temporobasal (aTB) sulci, which are the collateral, rhinal, and occipitotemporal sulci, contribute to the morphology of memory-related structures and are important landmarks for neuroimaging. Prevalence of inter-connections among these sulci may distinguish healthy adults and individuals with memory-related disorders (Kim et al. Neurology 70:2159-2165, 2008; Zhan et al. Hum Brain Mapp 30:874-882, 2009). However, methods for quantifying the existence and nature of such connections are vague and varied, and normative frequencies are inconsistent across studies. Therefore, the goals of the current study are twofold: (1) to develop a reliable method of identifying aTB sulci and their interconnections based on surface renderings generated from serial magnetic resonance images (MRIs). This protocol includes training materials and a rating log (see supplementary materials) that can be disseminated and applied by other researchers. (2) To determine the prevalence of interconnections among the three aTB sulci in a large sample of healthy adults (200 undergraduate students), which can be used as normative data for future comparison with clinical samples. Notably, the resulting protocol, called the Sulcal Classification Rating Protocol for anterior Temporobasal sulci, distinguishes "clear" from "ambiguous" connections. When only clear connections are included, our prevalence rates are consistent with post-mortem findings of Ono et al. (Atlas of the Cerebral Sulci. Thieme Medical Publishers, Inc., New York, 1990); when both clear and ambiguous connections are counted as a connection, our results largely replicate MRI-based findings (e.g., Kim et al. Neurology 70:2159-2165, 2008). We propose that systematic variations in rater classification of ambiguous connections could explain discrepancies in the literature.