Epstein RA, Higgins JS, Jablonski K, Feiler AM. Visual scene processing in familiar and unfamiliar environments. J Neurophysiol 97: 3670 -3683, 2007. First published March 21, 2007 doi:10.1152/jn.00003.2007. Humans and animals use information obtained from the local visual scene to orient themselves in the wider world. Although neural systems involved in scene perception have been identified, the extent to which processing in these systems is affected by previous experience is unclear. We addressed this issue by scanning subjects with functional magnetic resonance imaging (fMRI) while they viewed photographs of familiar and unfamiliar locations. Scene-selective regions in parahippocampal cortex (the parahippocampal place area, or PPA), retrosplenial cortex (RSC), and the transverse occipital sulcus (TOS) responded more strongly to images of familiar locations than to images of unfamiliar locations with the strongest effects (Ͼ50% increase) in RSC. Examination of fMRI repetition suppression (RS) effects indicated that images of familiar and unfamiliar locations were processed with the same degree of viewpoint specificity; however, increased viewpoint invariance was observed as individual scenes became more familiar over the course of a scan session. Surprisingly, these within-scan-session viewpointinvariant RS effects were only observed when scenes were repeated across different trials but not when scenes were repeated within a trial, suggesting that within-and between-trial RS effects may index different aspects of visual scene processing. The sensitivity to environmental familiarity observed in the PPA, RSC, and TOS supports earlier claims that these regions mediate the extraction of navigationally relevant spatial information from visual scenes. As locations become familiar, the neural representations of these locations become enriched, but the viewpoint invariance of these representations does not change.

A 57-year-old right-handed man complained of difficulty using his hands post-coronary artery bypass graft (figure). Neurologic examination revealed signs of callosal disconnection without hemiparesis. When asked to perform limb gestures such as "brush your teeth" or "wave goodbye," the right hand performed flawlessly whereas the left hand was severely apraxic (video on the Neurology ® Web site at www. neurology.org).Apraxia can be a confusing topic because of overlapping definitions and subtypes. This case illustrates the primary observable manifestation: a previously learned, skilled movement becomes peculiar looking. This occurs because motor memory degrades or becomes inaccessible.1 In this case the right hemisphere, disconnected from motor programs stored on the left, generates exemplary apraxic movement. 2 AUTHOR CONTRIBUTIONSDr. Jablonski: drafting and revising the manuscript. Dr. Antoniello: drafting and revising the manuscript and videos. STUDY FUNDINGNo targeted funding reported. DISCLOSUREThe authors report no disclosures relevant to the manuscript. Go to Neurology.org for full disclosures. Diffusion-weighted images show a high signal intensity lesion in the body and splenium of the corpus callosum, consistent with embolic infarction of the pericallosal artery, a complication of the coronary artery bypass graft (CABG).