“…Elegant pharmacology‐based approaches have been classically employed for inferring the putative noradrenergic identity of the recorded units (Aston‐Jones & Bloom, 1981a; Manohar et al, 2017; Sara & Segal, 1991; Shea et al, 2008; Totah et al, 2018). More recent approaches involving high‐density extracellular recordings, in combination with optogenetic tagging, have increased the efficiency of LC sampling and enabled the in vivo characterization of opto‐identified LC units (Breton‐Provencher et al, 2022; Carter et al, 2010; Hickey et al, 2014; Hirschberg et al, 2017; Ito et al, 2020; Martins & Froemke, 2015; McBurney‐Lin et al, 2022; Megemont et al, 2022; Swift et al, 2018; Tortorelli et al, 2022; Uematsu et al, 2017; Xiang et al, 2019; Yamasaki & Takeuchi, 2017). When cell‐type specific properties are very distinct and under low levels of recurrent connectivity, optotagging methods can achieve excellent separation of the extracellularly recorded units (as, e.g., for LC units from the medially located Barrigton's nucleus, Ito et al, 2020); however, if differences are more subtle and neural circuits more intermingled, extracellular optotagging becomes far from trivial and more critically dependent upon the performance of spike‐sorting algorithms.…”