Recording Reconstructions

Two MRI datasets of T1-weighted scans from monkey Q were used to reconstruct recording sites using a frameless stereotaxic technique pre and post ring implantation. The latter included a plastic grid filled with betadine ointment to allow for precise electrode targeting and reconstruction of recordings sites. We used an operator-assisted segmentation tool for volumetric imaging (ITK-SNAP v3.6, www.itksnap.org, last accessed 12 October 2018) to segment in 3D and render the brain structures from the MRI scans (Yushkevich et al. 2006). We aligned the MRI datasets to bony landmarks and brain structures to identify anterior–posterior zero (ear bar zero). All horizontal slices were aligned to the horizontal plane passing through the interaural line and the infraorbital ridge; all coronal slices were aligned parallel to the vertical plane passing through the interaural line (ear-bar zero). Brain structures used for alignment were the anterior and posterior commissure, as well as the genu and splenium of the corpus callosum (Dubowitz and Scadeng 2011; Frey et al. 2011). All of the anatomical landmarks derived from horizontal, coronal, and sagittal sections were then used to index to positions in standard macaque brain atlases (Paxinos et al. 2000; Saleem and Logothetis 2012) and recording sites were then reconstructed using the position on the grid in stereotaxic coordinates.