Parietal Lobe Syndromes

Abstract

A convenient time to pick up the parietal lobe evolution is perhaps with Homo erectus ~1.8 mya after the brain size had doubled to about 880 cc from the average of 450 cc in the Australopithecines. The basic stone knapping techniques used by these early hominins presumably promoted the elaboration of the parietal spatial network and shape recognition by temporal lobe ventral pathways. This was due to learning by observation, prolonged practice, and sequences of actions that were eventually incorporated into procedural memory circuits. Much later in our evolution, Homo heidelbergensis artifact evidence points to improved visuospatial sketchpad components of working memory model, exemplified by the finding of the Schoningen spears dated to ~400 kya. This suggested an overall improvement in both their working memory and technical ability when compared to Homo erectus, also supporting the emergence of symbolic thinking and allocentric perception (points of view not pertaining to one’s own viewpoint). With the emergence of Neanderthals around 300–200 kya, with the invention of hafting they are sometimes referred to as the technical experts but are thought to have lacked enhanced working memory, extended theory of mind, and shared attention. In Wynn and Coolidge’s viewpoint they lacked enhanced working memory which is the basis of advanced episodic memory, intelligence, language, and theory of mind and therefore probably also lacked modern, recursive-type language [1, 2]. Finally, a more dramatic parietal lobe enlargement occurred relatively recently with parietal globularization (150–100 kya) with vertical expansion and anterior widening (klinorhynchy), unique to modern humans [3]. This may have facilitated neural intra-connectivity, cortico-cortico hyperconnectivity, further visuospatial integration, multimodal processing, as well as improved social communication.